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Zooplankton of the West Florida shelf

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Title:
Zooplankton of the West Florida shelf relationships with karenia brevis blooms
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English
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Lester, Kristen M
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University of South Florida
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Subjects / Keywords:
Red tides
Acartia tonsa
Labidocera aestiva
Paracalanus quasimodo
Temora turbinata
Ammonia excretion
Phosphate excretion
Grazing
Dissertations, Academic -- Marine Science -- Doctoral -- USF   ( lcsh )
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government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

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Summary:
ABSTRACT: Blooms of the toxic dinoflagellate Karenia brevis are common on the West Florida Shelf (WFS), yet little is known of the relationships between zooplankton and K. brevis. A comprehensive analysis was undertaken to examine 1) perturbations in zooplankton community composition within K. brevis blooms 2) the contribution of zooplankton ammonium and phosphate excretion to K. brevis bloom nutrient requirements, and 3) the role of zooplankton grazing in K. brevis bloom termination. Prior to undertaking the first portion of the study, an examination of the perturbations in the normal zooplankton assemblage within K. brevis blooms, it was first necessary to define the normal zooplankton assemblage on the WFS. To this end, a seasonal analysis of abundance, biomass and community composition of zooplankton was undertaken at 6 stations on the WFS. Monthly sampling was conducted for one year at the 5, 25 and 50- m isobaths.Two major groups in community composition were observed at the near shore (5-m and 25-m) and offshore (50-m) stations. Considerable overlap was seen in community composition between the 5-m to 25-m and 25-m to 50-m isobaths, but little overlap in community composition was observed between the 5-m and 50-m isobaths. Of the 95 species identified, only 25 proved to be important (> 90%) contributors to community composition. Near shore, important contributors were Parvocalanus crassirostris, Penilia avirostris, Paracalanus quasimodo, Oithona colcarva, Oikopleura dioica, Centropages velificatus and Pelecypod larvae. As distance offshore increased, important contributors to community composition were Euchonchoichiea chierchiae, Clausocalanus furcatus, Oithona plumifera, Oithona frigida, Oncaea mediteranea, Calaocalanus pavoninius, Oithona similis, and Gastropod larvae.Variations in abundance and biomass between non-bloom and bloom assemblages were evident, including the reduction in abundance of 3 key species within K. brevis blooms. One potential source of nutrients to support K. brevis blooms may be zooplankton regeneration of nutrients. To test this hypothesis, ammonium and phosphate excretion rates of several West Florida Shelf copepods (Labidocera aestiva, Acartia tonsa, Temora turbinata, and Paracalanus quasimodo) were measured and prorated to a 24-hour day. These excretion rates were then extrapolated to other West Florida Shelf zooplankton, combined with available literature excretion rates for some taxa, and applied to zooplankton abundances found for K. brevis blooms on the West Florida Shelf in 1999 and 2001. Ammonium excretion rates were found to be inadequate to support all but 104 cells l-1 of K. brevis, though phosphate excretion rates were adequate to support even 106 cells l-1 of K. brevis.Grazing assessment was conducted for three common zooplankton species that were found within two K. brevis blooms, A. tonsa, P. quasimodo, and L. aestiva, using 14C labeled K. brevis cells. Grazing rates were then applied to the zooplankton community and grazing assessed. Grazing pressure was occasionally heavy, and was capable of reducing K. brevis to background concentrations at stations in the 1999 bloom and at 1 station in the 2001 bloom. Generally, however, grazing pressure proved to be insufficient to reduce K. brevis to background concentrations during the 1999 and 2001 blooms.
Thesis:
Thesis (Ph.D.)--University of South Florida, 2005.
Bibliography:
Includes bibliographical references.
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Mode of access: World Wide Web.
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by Kristen M. Lester.
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Title from PDF of title page.
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Document formatted into pages; contains 216 pages.

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aleph - 001709532
oclc - 68930784
usfldc doi - E14-SFE0001326
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Zooplankton of the West Florida Shelf: Relationships with Karenia brevis blooms by Kristen M. Lester A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy College of Marine Science University of South Florida Co-Major Professor: Gabriel Vargo, Ph.D. Co-Major Professor: John Walsh, Ph.D. Patricia Tester, Ph.D. Joses Torres, Ph. D. Ted Van Vleet, Ph.D. Date of Approval: August 5, 2005 Keywords: Red tides, Acartia tonsa Labidocera aestiva Paracalanus quasimodo Temora turbinata ammonia excretion, phosphate excretion, grazing Copyright 2005, Kristen M. Lester

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ii DEDICATION to my husband, Sean and my children, Joseph and Gabrielle

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iii ACKNOWLEDGMENTS A project of this scope could not be undertaken without the assistance of numerous people. I would first like to tha nk my advisors, Dr. Gabe Vargo and Dr. John Walsh, who provided invaluable assistance in mapping out a difficult data set and in helping me determine what was important. I would also like to thank my committee members, Dr. Pat Tester, Dr. Jose Torres, and Dr. Ted Van Vleet, who were always available and who ensured that I remained on track. Zooplankton sampling assistance was provided under often adverse circumst ances by Dr. Cynthia Heil, Danny Ault, Merrie Beth Neelie, Rachel Merkt, Susa n Murasko, Ryan Pigg, Tom Corbin and Matt Garrett, as well as others on EC OHAB cruises. Thanks are also extended to the Florida Institute of Oceanography and to the crew of the R/V Sunc oaster and R/V Bellows, who were quite patient in assisting with the to ws. Members of the Hopkins and Peebles labs were instrumental in getting together the correct references for zooplankton identification. Members of the Blake lab assi sted with pelecypod larvae identification. There are also others who assisted with this dissertation in less obvious ways. I would especially like to thank Maille Lyons, w ho patiently endured numerous panicked early morning and late night calls throughout the years. Funding for this project was provide d by ECOHAB Florida (NOAA/ECOHAB NA96P00084 and USEPA/ECOH AB CR826792-01-0), Office of Naval Research (N000149615024 and N000149910212), National Sc ience Foundation (NSF OCE 0095970), and the Florida Fish and Wildlif e Conservation Commission (FWCC PO# S7701 623398). Additional funding was provided by th e USF College of Marine Science Murtagh Fellowship.

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iv TABLE OF CONTENTS LIST OF TABLES viii LIST OF FIGURES xi ABSTRACT xv CHAPTER 1: INTRODUCTION 1 Methods 4 Study Design – Evaluation of community composition 4 Collection of Zooplankton 7 Chlorophyll a concentration and K. brevis cell counts 10 Zooplankton abundance and biomass 11 Grazing Pressure Determination 11 Excretion rates 13 Statistical analysis 16 Acknowledgments 21 References 22 CHAPTER 2: ZOOPLANKTON COMMUNITY COMPOSITION OF THE WEST FLORIDA SHELF 28 Abstract 28 Introduction 29 Methods 30 Collection of zooplankton 30

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v Zooplankton abundance and biomass 32 Abiotic and biotic factors 32 Statistical analysis 32 Results 34 Abiotic and biotic factors in the study area 34 Zooplankton abundance and biomass 38 Zooplankton community composition 38 Community associations with abio tic and biotic factors 49 Discussion 56 Abundance 56 Community Composition 59 Conclusions 99 Acknowledgements 101 References 102 CHAPTER 3: ZOOPLANKTON AND KARENIA BREVIS IN THE GULF OF MEXICO 105 Abstract 105 Introduction 106 Methods 108 Collection of Zooplankton 111 Zooplankton abundance and biomass 111 Chlorophyll a concentration and K. brevis counts 112 Statistical analysis 112

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vi Results 114 WFS zooplankton assemblage –1999-2000 114 Zooplankton assemblage – K. brevis blooms 122 Discussion 129 WFS zooplankton taxonomic composition 129 Comparison of bloom and nonbloom community composition 130 Previous associations of K. brevis blooms with zooplankton 131 Conclusions 137 Acknowledgements 135 References 138 CHAPTER 4: ZOOPLANKTON NUTRIENT REGENERATION WITHIN KARENIA BREVIS BLOOMS 143 Abstract 143 Introduction 144 Methods 147 Zooplankton abundance sampling within K. brevis blooms 147 Excretion experiments 149 Ammonium and phosphate sample analysis 150 Nutrient requirement of blooms 150 Results 151 Zooplankton abundance and community composition 151 Excretion rates of WFS zooplankton 153 Discussion 158

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vii Zooplankton nutrient regeneration as a source of nutrients for K. brevis blooms 158 Comparison of excretion rates with other studies 162 Conclusions 165 Acknowledgements 165 References 166 CHAPTER 5: ZOOPLANKTON GRAZING ON KARENIA BREVIS BLOOMS OF THE WEST FLORIDA SHELF 170 Abstract 170 Introduction 171 Methods 172 Zooplankton sampling 172 K. brevis cell counts 174 Grazing assessment 174 Results 177 Grazing experiments 184 Grazing assessment 184 Discussion 188 Conclusions 192 Acknowledgements 192 References 193 CHAPTER 6: CONCLUSIONS 196b

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viii LIST OF TABLES Table 1. Sources of biomass values and length/width re gression equations for WFS zooplankton taxa. 12 Table 2. Taxon and life stage specifi c grazing rates for zooplankton taxa dominant within K. brevis blooms, pro-rated for a 24-hr day. 14 Table 3. Sources of biomass values and length/width re gression equations for WFS zooplankton taxa. 33 Table 4. Results of SIMPER analysis for Subgroup A. 42 Table 5. Results of SIMPER analysis for Subgroup B. 43 Table 6. Results of SIMPER analysis for Subgroup C. 45 Table 7. Results of SIMPER analysis for Subgroup D. 46 Table 8. Results of SIMPER analysis for Subgroup E. 47 Table 9. Environmental and biotic variables for subgroups A-E. 55 Table 10. Results of BIOENV procedure on log transformed data, n=53. 57 Table 11. Comparison of results found w ith this study and those from other studies in Gulf of Mexico and Mediterranean Sea. 58 Table 12. Sources of biomass values a nd length/width regr ession equations for WFS zooplankton taxa. 113 Table 13. Numerical abundance and biom ass for non-red tide 5-m and 25-m isobath stations sampled on the WFS in 1999 and 2000. 115 Table 14. Results of SIMPER analysis showing determinant species for WFS 1. Abundance data s quare root transformed, n=18. 119 Table 15. Results of SIMPER analysis showing determinant species for WFS 2. Abundance data s quare root transformed, n=19. 120 Table 16. Results of SIMPER analys is showing average determinant

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ix dissimilarities between WFS 1 and WFS 2. Abundance data square root transformed, WFS 1, n=18, WFS 2, n=19. 121 Table 17. Zooplankton community co mposition, abundance and biomass at stations sampled within 1999 and 2001 K. brevis blooms. 123 Table 18. Zooplankton community co mposition, abundance and biomass at stations sampled within 1999 and 2001 K. brevis blooms. 124 Table 19. Results of SIMPER analys is showing dissimilarities between K. brevis and WFS stations. 128 Table 20. Top 80% contributor s to zooplankton abundance (m-3) at red-tide stations sampled during 1999 and 2001. 152 Table 21. Ammonium excretion rates us ed in bloom nutrient calculations. 156 Table 22. Phosphate excretion rates used in bloom nutrient calculations. 157 Table 23. Zooplankton community ammonium excretion rates for 1999 and 2001 blooms and K. brevis bloom requirements. 159 Table 24. Zooplankton community phosphate excretion rates for 1999 and 2001 blooms and K. brevis bloom requirements. 160 Table 25. Comparison of ammonium ex cretion rates for various taxa between this study and other studies. 163 Table 26. Taxon and life specific stage sp ecific grazing rate s for zooplankton taxa dominant within K. brevis blooms, prorated for a 24-hr day. 176 Table 27. Zooplankton abundance and community composition sampled in October 1999. 179 Table 28. C. velificatus copepodite abundance at Sta tion 80 in October 1999. 180 Table 29. Zooplankton abundance and community composition sampled in 2001. 185 Table 30. Assessment of grazing pressure in 1999 and 2001 K. brevis blooms on the WFS. 187 Table 31. Comparison of K. brevis grazing activity between this study and Turner and Tester (1989). 189 Table 32. Comparison of carbon ingestion for K. brevis grazing experiments

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x and literature carbon ingestion values. 191

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xi LIST OF FIGURES Figure 1. ECOHAB study area in th e Gulf of Mexico. 5 Figure 2. Sampling matrix for zo oplankton samples taken during the 1999-2000 sampling period on the WFS. 8 Figure 3. Station locati ons for ECOHAB cruises and N SF cruises. 9 Figure 4. ECOHAB study area in th e Gulf of Mexico. 31 Figure 5. Temperature, salinity and chlorophyll a at the 5-meter, 25-meter and 50-meter isobaths. 35 Figure 6. Salinity at st ations 10 and 40 for the 1999 and 2000 sampling period. 37 Figure 7. Abundance and biomass of zooplankton sampled during 1999-2000 sampling period. 39 Figure 8. Cluster derive d dendrogram for 53 stations at the 5, 25 and 50-meter isobaths, using group averaged clustering from Bray-Curtis similarities on square root transformed abundance data. 40 Figure 9. Shade matrix for WFS zooplankton subgroups A-E. 48 Figure 10. Distribution of temperat ure, salinity and chlorophyll a for Subgroup A. 50 Figure 11. Distribution of temperat ure, salinity and chlorophyll a for Subgroup B. 51 Figure 12. Distribution of temperat ure, salinity and chlorophyll a for Subgroup C. 52 Figure 13. Distribution of temperat ure, salinity and chlorophyll a for Subgroup D. 53 Figure 14. Distribution of temperat ure, salinity and chlorophyll a for Subgroup E. 54 Figure 15. Abundance distribut ion of selected WFS zoopl ankton taxa. 60 Figure 16. Distribution of P. avirostris in relation to salinity, temperature and chlorophyll a 62

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xii Figure 17. Distribution of C. americanus in relation to salinity, temperature and chlorophyll a 63 Figure 18. Distribution of O. nana in relation to salinity, temperature and chlorophyll a 65 Figure 19. Distribution of Ci rriped larvae in relation to salinity, temperature and chlorophyll a 66 Figure 20. Distribution of P. crassirostris in relation to salinity, temperature and chlorophyll a 69 Figure 21. Distribution of O. colcarva in relation to salinity, temperature and chlorophyll a 70 Figure 22. Distribution of P. quasimodo in relation to salinity, temperature and chlorophyll a 72 Figure 23. Distribution of E. acutifrons in relation to salinity, temperature and chlorophyll a 73 Figure 24. Abundance distribution of se lected WFS zooplankton taxa. 74 Figure 25. Distribution of Pel ecypod larvae in relation to salinity, temperature and chlorophyll a 76 Figure 26. Distribution of Gast ropod larvae in relation to salinity, temperature and chlorophyll a 77 Figure 27. Distribution of C. amazonicus in relation to salinity, temperature and chlorophyll a 78 Figure 28. Distribution of O. dioica in relation to salin ity, temperature and chlorophyll a 80 Figure 29. Distribution of E. chierchiae in relation to salinity, temperature and chlorophyll a 82 Figure 30. Distribution of C. velificatus in relation to salinity, temperature and chlorophyll a 83 Figure 31. Distribution of O. mediteranea in relation to salinity, temperature and chlorophyll a 85 Figure 32. Distribution of O. plumifera in relation to salinity, temperature and

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xiii chlorophyll a 86 Figure 33. Abundance distribut ion of selected WFS zoopl ankton taxa. 87 Figure 34. Distribution of C. furcatus in relation to salinity, temperature and chlorophyll a 89 Figure 35. Distribution of C. pavo in relation to salinity, temperature and chlorophyll a 90 Figure 36. Distribution of O. frigida in relation to salin ity, temperature and chlorophyll a 92 Figure 37. Distribution of P. pygmaeus in relation to salinity, temperature and chlorophyll a 93 Figure 38. Distribution of P. aculeatus in relation to salinity, temperature and chlorophyll a 94 Figure 39. Distribution of C. limbatus in relation to salinity, temperature and chlorophyll a 96 Figure 40. Distribution of C. pavoninius in relation to salinity, temperature and chlorophyll a 97 Figure 41. Distribution of O. similis in relation to salin ity, temperature and chlorophyll a 98 Figure 42. ECOHAB study area in the Gulf of Mexico. 109 Figure 43. Station locations for ECOHA B cruises and NSF cruises. 110 Figure 44. Zooplankton abundance and bi omass at the 5-meter and 25-meter isobaths. 116 Figure 45. Cluster derived dendrogram for 37 stations at the 5 and 25-meter isobaths, using group averaged clus tering from Bray-Curtis similarities on square root transformed abundance data. 117 Figure 46. Cluster derived dendrogram for 37 stations at the 5 and 25-meter isobaths and 16 stati ons within the 1999 and 2001 K. brevis blooms, using group average clustering from Bray-Curtis similarities on square root transformed abundance data. 127 Figure 47. Abundance of pelecypod larvae on the NWFS averaged over 5 years

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xiv and 5 stations, on the WFS averag ed over 1 year and 4 stations, and within the K. brevis blooms on the WFS. 134 Figure 48. Station locations for ECOHA B cruises and NSF cruises. 148 Figure 49. Ammonium excretion rate s of selected WFS copepods. 154 Figure 50. Phosphate excretion rates of selected WFS copepods. 155 Figure 51. Station locations for ECOHAB and NSF cruises. 173 Figure 52. Surface K. brevis concentrations fo r October 1999. 178 Figure 53. Surface K. brevis concentrations for September 2001. 181 Figure 54. Surface K. brevis concentrations fo r October 2001. 182 Figure 55. Surface K. brevis concentrations for December 2001. 183 Figure 56. Grazing rates of selected WFS copepods on K. brevis 186

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xv Zooplankton of the West Florid a Shelf: Relationships with Karenia brevis blooms Kristen M Lester ABSTRACT Blooms of the toxic dinoflagellate Karenia brevis are common on the West Florida Shelf (WFS), yet little is known of the relationships between zooplankton and K. brevis A comprehensive analysis was undertak en to examine 1) perturbations in zooplankton community composition within K. brevis blooms 2) the contribution of zooplankton ammonium a nd phosphate excretion to K. brevis bloom nutrient requirements, and 3) the role of zooplankton grazing in K. brevis bloom termination. Prior to undertaking the first por tion of the study, an examina tion of the perturbations in the normal zooplankton assemblage within K. brevis blooms, it was first necessary to define the normal zooplankton assemblage on th e WFS. To this end, a seasonal analysis of abundance, biomass and community com position of zooplankton was undertaken at 6 stations on the WFS. Monthly sampling was conducted for one year at the 5, 25 and 50m isobaths. Two major groups in community composition were observed at the near shore (5-m and 25-m) and offshore (50-m) sta tions. Considerable overlap was seen in community composition between the 5-m to 25-m and 25-m to 50-m isobaths, but little overlap in community compositi on was observed between the 5m and 50-m isobaths. Of the 95 species identified, only 25 proved to be important (>90%) contributors to community composition. Near shore, important contributors were Parvocalanus

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xvi crassirostris Penilia avirostris Paracalanus quasimodo, Oithona colcarva Oikopleura dioica, Centropages velificatus and Pelecypod larvae. As distance offshore increased, important contributors to community composition were Euchonchoichiea chierchiae, Clausocalanus furcatus Oithona plumifera Oithona frigida Oncaea mediteranea Calaocalanus pavoninius Oithona similis, and Gastropod larvae. Variations in abundance and biomass between non-bloom and bloom assemblages were evident, including the reduction in abunda nce of 3 key species within K. brevis blooms. One potential source of nutrients to support K. brevis blooms may be zooplankton regeneration of nutrients. To test this hypothesis, ammonium and phosphate excretion rates of several West Florida Shelf copepods ( Labidocera aestiva Acartia tonsa Temora turbinata and Paracalanus quasimodo ) were measured and prorated to a 24-hour day. These excretion rates were th en extrapolated to other We st Florida Shelf zooplankton, combined with available literature excret ion rates for some taxa, and applied to zooplankton abundances found for K. brevis blooms on the West Florida Shelf in 1999 and 2001. Ammonium excretion rates were f ound to be inadequate to support all but 104 cells l-1 of K. brevis though phosphate excretion rates we re adequate to support even 106 cells l-1 of K. brevis Grazing assessment was conducted for three common zooplankton species that were found within two K. brevis blooms, A. tonsa P. quasimodo and L. aestiva using 14C labeled K. brevis cells. Grazing rates were then applied to the zooplankton community and grazing assessed. Grazing pressure was occasionally heavy, and was capable of reducing K. brevis to background concentrati ons at stations in the 1999 bloom and at 1 station in the 2001 bloom Generally, however, grazing pressure

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xvii proved to be insufficient to reduce K. brevis to background concen trations during the 1999 and 2001 blooms.

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1 CHAPTER ONE INTRODUCTION Early Spanish explorers in the Gulf of Me xico described events that suggest fish kills and aerosol production by bloo ms of the toxic dinoflagellate Karenia brevis (previously Gymnodinium breve Davis). Blooms occur most frequently on the West coast of Florida in an area extending from Tarpon Springs so uth to Sanibel, but are also known to occur on the east coast of Florida and as far north as Cape Hatteras (Tester et al., 1991; Tester and Steidinger, 1997; Steidinge r et al., 1998). The economic impact of red tides in the Gulf of Mexico is estimated to range from $250,000 to $120,000,000 per event (Kusek, 1998). K. brevis blooms have been implicated in the mass mortalities of manatees and dolphins (Gunter, 1948; Layne 1965; Geraci, 1989; Bossart et al., 1998, Flewelling et al., 2005), and can cause neur otoxic shellfish pois oning (NSP) in humans (Anderson, 1995). K. brevis is also an important contribut or to the West Florida shelf (WFS) ecosystem. Steidinger (1975) suggested that it may play an important “forest fire” role in regulating the WFS ecosystem, and Va rgo et al. (1987) calculated the total contribution of K. brevis carbon production can range from 10 to 40% of total carbon production for the WFS. How K. brevis manages to out-compete other phytoplankton species and achieve numerical dominance in blooms is still not completely understood. Previous research has identified possible links between K. brevis growth rates and nutr ients, light levels, Trichodesmium spp. blooms, dinoflagellate life cycl es, and hydrography of the Gulf of Mexico (Steidinger, et al., 1998 and references cited therein; Lenes et al., 2001; Walsh

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2 and Steidinger, 2001; Walsh et al., 2002; Lester et al., 2003; Heil et al., 2003; Vargo et al., 2003; Walsh et al., 2003). However, the ability of K. brevis to out-compete other phytoplankton species can only be understood in the c ontext of losses (i.e. grazing rates) as well as growth rates. Selective grazing of zooplankton on microa lgal populations based on cell size, toxicity and nutritional quality is well doc umented, and can result in a dominance shift from edible to inedible species (Huntley, 1982; Lehman, 1984; Sterne r, 1989; Turner and Tester, 1989; Banse, 1995; Kiorboe, 1993; Valie la, 1995). Some studies have suggested that differential mortality leads to the su ccess of toxic phytopla nkton blooms (Fiedler, 1982; Huntley, 1982; Smayda and Villareal, 19 89; Buskey and Stockwell, 1993; Buskey and Hyatt, 1995) while Uye (1986) ascribed the termination of a toxic phytoplankton bloom to grazing. Turner and Anderson (1983) found that grazing was not able to deter initiation of a bloom of the toxic phytoplankter Alexandrium tamarense but an increase in grazing pressure as the bloom progressed ev entually resulted in bloom termination. The impact of grazing on the aforementi oned blooms is not fully understood, but it is clear that the interactions between t oxic phytoplankton and their zooplankton grazers are complex and species specific, and depend on both the characteristics of the phycotoxin and the zooplankton species presen t (Huntley et al., 1986, Turner and Tester, 1989; Turner and Tester, 1997). The only in situ study to date of zooplankton grazing on K. brevis generated intriguing questions about potential interactions between zooplankton and K. brevis Turner and Tester (1989) expos ed 5 dominant species of copepods from North Carolina waters to varying natu ral concentrations of K. brevis All five species ingested the toxic

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3 dinoflagellate, but the rates of ingestion tended to be variable and lo w. The three highest ingestion rates occurred for species that co-occur with K. brevis in the Gulf of Mexico ( Acartia tonsa Oncaea venusta and Labidocera aestiva ), leading to speculation by the authors that K. brevis is most likely to be grazed by c opepods that co-occur with it. Anecdotal field observations made duri ng red tide events, though subjective, indicate that other organism s may be able to ingest K. brevis Woodcock and Anderson (cited in Galstoff, 1948) observed that large numbers of the cladoceran Evadne spp. captured in a red tide bloom had intestines stained deep red, presumably from ingestion of K. brevis Dragovich and Kelly (1964) observed that a K. brevis bloom in Tampa Bay in 1963 coincided with high numbers of tintinnids. A preliminary report on K. brevis blooms by the University of Miami in 1954 (cited in Rounsefell and Nelson, 1966) reported that blooms of K. brevis often contained large numbers of the copepod Acartia spp. Martin et al. (1973) obser ved numerous ciliates within a K. brevis bloom. More recently, C. Heil (pers. comm.) observe d an unidentified tintinnid ingesting K. brevis during a long-lived bloom off the co ast of St. Petersburg, Florida. Besides the question of loss rates of K. brevis there are other enigmas surrounding the blooms and their relationships with zooplankton. Specifically, the source of nutrients available to K. brevis during long term bloom events remains uncertain (Vargo, et. al., in review). Zooplankton excr etion rates, based on measured zooplankton population estimates and excretion rates from the literature, could supply all of the Nitrogen and Phosphorus required to support large populations of K. brevis (Vargo, et. al., review). However, no direct inform ation on WFS zooplankton excretion rates is available.

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4 The potential of zooplankton to ingest K. brevis and the apparent ability of zooplankton to provide all of the nutrients required for a long term K. brevis bloom, generate three critical questions. Firs t, what is the ecological impact of K. brevis blooms on the “normal” West Florida Shelf zooplankt on assemblage? Second, what effect do potential grazers have on the termination of K. brevis blooms? Third, can zooplankton provide the daily turnover of nut rients required by long term K. brevis blooms? METHODS Study Design –Evaluation of community composition This study dovetailed with the ECOHAB : Florida program, the objectives of which include modeling of initiation and transport of K. brevis blooms, description of physical habitat where blooms tend to occur, and determination of K. brevis community regulation processes. The ECOHAB: Florid a study area extends from Tampa Bay to Charlotte Harbor and from shore to the 200-meter isobath (Figure 1). Prior to addressing the relationship between K. brevis blooms and zooplankton assemblages on the WFS, it was first necessa ry to comprehensively define the normal zooplankton assemblage within the study area. This task proved to be difficult with the research at hand. Zooplankton studies previ ously conducted in or near the study area consisted of 1) analyses of total biomass variation with seasonality, 2) quantitative assessments of taxonomic composition at a single station at a single point in time, or 3)

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5 47 48 49 50 70 71 72 73 74 75 76 77 78 79 80 8 1 8 2 83 -84.00-83.50-83.00-82.50-82.00-81.50 26.00 26.50 27.00 27.50 28.00 28.50 1 2 3 4 5 6 7 8 9 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 41 42 43 44 45 46 GULF OF MEXICO 51 40 10 LongitudeL a t i t u d e Tampa Sarasota Ft. Myers 47 48 49 50 70 71 72 73 74 75 76 77 78 79 80 8 1 8 2 83 -84.00-83.50-83.00-82.50-82.00-81.50 26.00 26.50 27.00 27.50 28.00 28.50 1 2 3 4 5 6 7 8 9 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 41 42 43 44 45 46 1 2 3 4 5 6 7 8 9 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 41 42 43 44 45 46 GULF OF MEXICO 51 40 10 LongitudeL a t i t u d e Tampa Sarasota Ft. Myers Figure 1. ECOHAB study area in the Gulf of Mexico. Station locations for ECOHAB cruises are indicated by a ( ). Stations where zoopla nkton tows were conducted are circled and indicated by a number. Tampa Bay Charlotte Harbor

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6 qualitative annual surveys (King, 1950; Bogda nov et al., 1968; Austin and Jones, 1974; Houde and Chitty, 1976; Hopkins, 1982). Sutton et al. (2001) examined spatial changes in taxonomic composition in the northern part of the area, but the study was to genus levels only, and consisted of a single transect. Comprehensive taxonomic seasonal an alyses of estuarine zooplankton assemblages in the Gulf of Mexico ar e more common (Hopkins, 1966; Hopkins, 1977; Weiss, 1978; Squires, 1984), but do not provide insight into composition of shelf communities. Likewise, offshore waters in th e open Gulf of Mexico are relatively well studied (Hopkins et al., 1981; Morris and Hopkins, 1983; H opkins and Lancraft, 1984), but do not include populations typically found shoreward of the 50-m isobath. Minello (1980) studied the neritic zooplankton of the Northwest Florida shelf, but it was unknown whether his findings could be extrapolated to the WFS st udy area, since the shelf is considerably narrower here and Gulf Stream dynamics bring open Gulf of Mexico waters closer to shore (Steid inger et al., 1998). The evaluation of community composition then, had two primary components. The first was to characterize the zooplankt on assemblage in the study area, including seasonal changes in abundance, bioma ss and community composition. The second component was to identify whether K. brevis blooms impacted the normal zooplankton assemblage. Sampling took place in conjunction with monthly ECOHAB cruises on board the R/V Suncoaster and the R/V Bellows in the Gu lf of Mexico (Figure 1). Stations were located approximately every 5 nautical miles. A CTD profile was conducted from bottom to surface at every station. At selected stations (usually every other station, but

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7 occasionally more frequently) water sample s were collected to determine chlorophyll a concentration, and K. brevis cell counts. Zooplankton sampling for the characteriza tion of the normal assemblage began in August of 1999 and continued through July of 2000 (Figure 2). Six stations (1, 5, 10, 40, 46, and 51) at three isobaths (5-, 25and 50-meter) were chosen as representative zooplankton sampling stations. These three se ts of stations were expected to provide three distinct zooplankton populations: a ne ar shore population, a mixed population, and an offshore population, depending on time of ye ar and intrusion of the Loop Current onto the shelf (Austin, 1971; Austin and Jones, 1974; Minello, 1980; Sutton et al., 2001). Additional zooplankton tows were conducted whenever possible at stations where K. brevis concentrations were found to be above background levels. In the fall and winter of 2001, a major K. brevis bloom occurred within and around the study area. In September and December, zooplankton tows were conducted on ECOHAB cruises at stations where K. brevis concentrations were above background levels. In October, zooplankton sa mples were obtained in elevated K. brevis concentrations during a cruise conducted for a companion pr ogram with stations located north of the ECOHAB control volume (Figure 3). Collection of Zooplankton 1999-2000 Zooplankton were collected with a 153 m mesh bongo net, lowered closed through the water column, opened at depth and then towed obliquely from bottom to surface. A calibrated flow meter was used to calculate the volume of water filtered

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8 5-meter Isobath 25-meter Isobath 50-meter Isobath Station 1 Station 51 Station 5 Station 46 Station 10 Station 40 Additional Stations N1 N2 N1N2N1N2N1N2N1N2N1N2 N1 N2 N1 N2N1N2 July x x x x x x x x x x x x 7 7 36 367676 August x x x x x x x x x x x x September x x x x x x x x x x x x October x x x x x x x x x 80 80 November x x x x x x x x x x 1999 December x x x x x x x x x x x x January x x x x x x x x x x x x February 83 83 7070 March x x x x x x x x x x x x 23 23 April x x x x x x x x x x May x x x x x x x x x x x x June x x x x x x x x x x x x 2000 July x x x x x x x x Notes: Bold face type indicates where K. brevis was found above background levels. N1 and N2 refer to Net 1 and Net 2. Numbers in lieu of x's indicate where additional samples were taken. Figure 2. Sampling matrix for zooplankt on samples taken during the 1999-2000 sampling period on the WFS.

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9 -84-83.5-83-82.5-82-81.5Longitude 26 26.5 27 27.5 28 28.5L a titude 6 10 16 21 1(NSF Station 5) 5 32 46 51 70 72 73 74 75 80 Figure 3. Station locations for ECOHAB cruises ( ) and NSF cruises (+). Stations where zooplankton tows were conducted are circled an d indicated by a number. NSF Station 5 is in the same location as ECOHAB Station 1. Tampa Sarasota Ft. M y ers

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10 during the oblique tow (Omori and Ikeda, 1992) The time of tow generally varied from 1 to 5 minutes, depending on the water column depth. The sides of each net were washed into the cod end prior to be ing brought on board. The cod ends were filtered through a 2000 m mesh sieve to remove large gelatinous zooplankton. The filtered cod ends were then preserved on board in a 5% buffered fo rmalin solution (Omori and Ikedo, 1992) for later counts of zooplankt on species abundance. 2001 Collection of zooplankton in Septem ber, October, and December of 2001 was accomplished in an identical manner, except that a single 153 m mesh net was used instead of a bongo net. Chlorophyll a concentration and K. brevis cell counts Zooplankton tows were conducted in conj unction with CTD casts, measurements of chlorophyll a and K. brevis cell counts. Water column samples were collected from Niskin bottles mounted on a rosette samp ler. During the October 2001 NSF cruise surface samples at selected stations were take n with a bucket, in addition to samples from Niskin bottles. Duplicate chlorophyll samples we re filtered onto GF/F filters, placed in 10 ml methanol, stored at 4oC in darkness for 3 days, and an alyzed within one week using a Turner design fluorometer (Welschmeyer, 1994). K. brevis was counted live using a dissecting microscope within two hours of collection.

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11 Zooplankton abundance and biomass Zooplankton abundance Subsamples were obtained with a Stempel pipette; such that a typical sample contained ~500-600 an imals (usually 1-5% of initial cod end volume). Zooplankton were then identified and counted using an Olympus dissecting microscope at 10-40x magnification, with critical taxonomic features observed on an Olympus compound microscope. Holoplankt on were identified to species level whenever possible. Meroplankton were identified to major taxonomic group (e.g. pelecypod veligers, cirriped larvae). Copepod nauplii were not identif ied to species level but, when possible, were identified to family level. Zooplankton biomass Dry weight contributions of each major species were either determined mathematically from regression equations or taken directly from available literature (Table 1 and refere nces listed therein). Grazing pressure determination Grazing rates on cultured K. brevis populations were determ ined for three species of zooplankton: Acartia tonsa Paracalanus quasimodo and Labidocera aestiva Zooplankton were collected from th e pier or a small boat with a 202 m mesh net. Cod ends were immediately diluted with natural s ea water and transporte d to the lab. After sorting, 3 replicates each of 2 adult female copepods were added to scintillation vials to which 20 ml filtered seawater was added. 14C labeled K. brevis culture was added to each vial, such that the final K. brevis concentration was 5 X 103, 5 X 104, or 1 X 106 cells per liter. Vials were incubated for 30 minutes. After the incubation period, copepods were

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12 Table 1 Sources of biomass values and length/width regression equations for WFS zooplankton taxa. Taxon Source Comments Undinula Morris and Hopkins, 1983 Eucalanus Morris and Hopkins, 1983 Acrocalanus Weiss, 1978 Derived from Paracalanus Calocalanus “ Paracalanus “ Clausocalanus “ Derived from Centropages Scolothrex Morris and Hopkins, 1983 Euchaeta Morris and Hopkins, 1983 Temora Lester, unpub. Data Centropages Weiss, 1978 Calanopia “ Pseudodiaptomas “ Acartia “ Tortanus “ Labidocera “ Oithona “ Oncaeae Squires, 1984 Corycaeus Weiss, 1978 Farranula “ Euterpina “ Microsetaella “ Euchonchoichiea Hopkins, 1984 Penilia Weiss, 1978 Evadne “ Podon “ E. tergestina value Appendicularians “ Brachiopoda “ Bryozoa “ Cirripedia “ Decapoda “ Echinodermata “ Gastropoda “ Pelecypoda “ Platyhelminthe Squires, 1984 Polychaeta Weiss, 1978

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13 filtered onto 12 m Nuclepore filters, rinsed with f iltered seawater, and dissolved with were Hyamine Hydroxide. After addition of a sc intillation fluor, vials were placed in the dark for two hours. CPM’s were read on a Beta Scout scinti llation counter. Adsorption controls were performed by placi ng 2 copepods each in scintillation vials with K. brevis concentrations reported above. The copepods were not incubated but instead immediately removed, filtered onto 12 m Nuclepore filters, rinsed with filtered seawater, dissolved with Hyamine hydroxide, an d placed in the dark for 2 hours. CPM’s were counted as described above on a Beta Scout scintillation counter. Radioactivity of K. brevis cells was determined by filtering 0.1 ml of the labeled culture onto 1 m Nuclepore filters. Cells were dissolved in Hyamine hydroxide and CPM’s recorded. For remaining dominants within the bloom s, the lowest published grazing rates reported for a variety of species that occur on the WFS were used (Table 2). Grazing rates for Centropages velificatus copepodites and Oithona colcarva and Parvocalanus crassirostris adults were determined using allometric derivations1 based on the biomass of adult C. velificatus, Oithona plumifera and P. quasimodo, respectively (Frost, 1980). Excretion rates Excretion rates were determined for Acartia tonsa Temora turbinata and Labidocera aestiva Zooplankton were collected with a 153 m mesh net. Tows were conducted from a boat, ship, and from the pier. If collected from a boat or ship, engines were cut and the tow collected with the drif t of the boat or ship. Occasionally, it was 1 Based on the allometric equations of Frost, 1980 Y = mb, where b = 0.75.

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14 Table 2 Taxon and life stage specific grazing rate s for zooplankton taxa dominant within K. brevis blooms, pro-rated for a 24-hr day. Taxon Grazing rate Source O. colcarva 1.5 ng chl ind-1 day-1 Dagg 1995, Sutton et al., 1999 Temora turbinata 41.5 ng chl ind-1 day-1 Dagg 1995; Kirboe et al., 1985; Sutton et al., 1999 C. velificatus 16 “ Dagg 1995; Kirboe et al., 1985; Sutton et al., 1999 CV 2.8-6.4 “ Evadne tergestina .432 “ Sutton, 1999 Oikopleura dioica 92.9 “ Dagg 1995; Sutton et al., 1999 1. Cell Counts 2. Gut Fluorescence a. Allometric derivation from O. plumifera (Frost, 1980) b. Allometric derivation from P. quasimodo (Frost, 1980) c. Allometric derivation from adult (Frost, 1980)

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15 necessary to come ahead 1-2 knots to keep current flowing through the net. Typically, tows were conducted at the surface, though o ccasionally oblique tows from bottom to surface were conducted. After being brought on board, cod ends were immediately diluted into a larger volume of natural seawater. The bucket was th en covered with several layers of shade cloth to reduce light. Animals were so rted on an Olympus compound microscope. Animals were rinsed with filtered seawater a nd counted into 200 ml sealed chambers that contained either filtered seawater, natura l seawater, or natural seawater with 104 cell l-1 concentration of K. brevis added. Zooplankton were incubated in the sealed chambers for two hours. Zooplankton were then transferred onto 60 m mesh net, rinsed with filtered seawater, and placed in filtered seawater in 60ml BOD bottles. The BOD bottles were wrapped in aluminum foil, placed in the incuba tor, and allowed to incubate for 8 hours. Controls consisted of BOD bottles filled with filtered sea water and incubated for 8 hours. After the 8 hour incubation period, filte red seawater from the BOD bottles was filtered through a 60 m mesh net into 60ml acid cleaned bottles and frozen. Zooplankton were rinsed onto GF/F filters with filtered seawater and rinsed 3 times with ammonium formate. Zooplankton were then counted on the filter, wrapped in aluminum foil and frozen. At a later date, samples were drie d in a drying oven to constant weight and weighed on a Cahn Electrobalance.

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16 Statistical Analysis After investigation of the data, a variety of statistical analyses were employed to quantify trends suggested by examination of raw data or shade matrices. Analyses consisted of comparing community composition between stations, clus tering stations into observed groups, and relating environmental va riables with community composition. The use of univariate statisti cs was rejected in favor of multivariate statistics due to the nature of the data collected. The te mporal and spatial spread of samples across isobaths resulted in a data set with a larg e number of zeros, even for common species. This made it impossible to reduce counts to the normality required for univariate statistics, and subsequently resulted in a right skewed abundance probability distribution (Clark and Warwick, 1994). Furthermore, univa riate statistics require that the number of species be small in relation to the number of samples, a requirement that could not be met with the data presented here, where the number of species/taxa identified was greater than the number of samples (Clark and Warwick, 199 4). An additional factor in deciding to use multivariate statistics was the nature of the study desi gn. Because sampling location, times and the number of samples obtained we re confined within the parameters of ECOHAB cruises, the data set was essentia lly composed of “convenience samples,” and would not satisfy required a priori assumptions for univariate statisti cs (Motulsky, 1995). Multivariate statistics utilizes comparisons between two samples based on the extent to which these samples share particular species at comparable levels of abundance (Clarke and Warwick, 1994). Though less rigorous than univariate stat istics, the results obtained provided a truer picture of the varia tions in community composition for this data set. Multivariate statistics has become an increasingly common method to analyze

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17 zooplankton community structure (see for ex ample Jerling and Cyrus, 1998; Pakhomov et al., 1999; Hunt et al., 2001; Clark et al., 2001; Poulson and Reusse, 2002; Auel and Hagen, 2002). Three statistical methods of the PRIMER (Plymouth Routines in Multivariate Ecological Research) program were employe d (Clarke and Warwick, 1994). These were 1) hierarchal clustering into groups of samp les, 2) calculation of species contributions (SIMPER) to each group, and 3) correlation between environmental data and community composition (BIOENV). Hierarchal clustering of samples into groups Hierarchal clustering was used to identify groups of samples. The starting poi nt for hierarchal cluster analysis was the calculation of Bray-Curtis (also known as Czekanaowski) similarity coefficients for every pair of samples, and the subsequent developmen t of a triangular similarity matrix. Several methods of data transformation for calculation of similarity coefficients are available to emphasize certain aspects of the data set. At the two extrem es of data transformation are no transformation and total transformation to presence/absence (Clarke and Warwick, 1994). No transformation of the data tends to give a greater emphasis to differences in absolute numerical abundance (Clarke and Wa rwick, 1994), a situation that was less than desirable here due to the decr ease in numerical abundance of zooplankton with increasing distance offshore and the inherent variability of net tows. On the other end of the spectrum is transformation of the data to presence/absence only, which tends to over emphasize the contribution of rare species (Clarke and Warwick, 1994). This was also thought to be undesirable because the primary goa l of the study was to analyze the typical zooplankton assemblage in the study area.

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18 A fine balance was sought between mi nimizing variations in abundance to account for differences in near shore/offshor e numerical abundance gradients and net tow variability without reducing the data to such an extent that rare species dominated the assemblage. Moderate transformation of absolute numerical abundance (square root transformation) was chosen because it redu ced the importance of numerical abundance somewhat while still retaining enough informa tion on the prevalence of a species that the more common species were given more weight then the rare ones (Clarke and Warwick, 1994). Representation of the groups obtained through calculation of similarity coefficients was accomplished through the use of dendrograms, which allow for a visual interpretation of sample groups. In dendrogr ams, percent similarity is shown on the yaxis, with all samples represen ted on the x-axis. Similarity of 100% indicates that the samples are identical, while 0% similarity indicates that the samples are completely dissimilar. When transferred to a dendrogram samples that are most similar to each other are grouped first, and the groups themse lves form clusters at lower levels of similarity. The process ends with a single cluster containing all th e samples (Clarke and Warwick, 1994). Several linkage options, single, complete and group averaged, can be used for clustering samples. In single linkage, dissim ilarity between the groups is shown as the maximum distance apart of the two groups. The pair with the highest similarity value is chosen and then adding the sample or species with the next highest similarity progressively enlarges the group. In practice, single linkage has a tendency to produce chains of linked samples with each successive stage just adding another single sample

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19 onto a large group (Clarke and Warwick, 1994). In the case of the WFS data set the result was one large group that did not tr uly indicate the differences in community structure. Complete linkage tends to pr oduce the opposite effect, with emphasis on small clusters at early stages (Clarke and Warwick, 1994). The result of using complete linkage for the WFS data set was numerous small groups that again did not adequately portray the observed patterns in the groups As with the calcu lation of similarity coefficients, a compromise was sought that would give the maximum number of groups without compromising the overall observed structure. Therefore Group Averaged clustering was used, which is simply the aver age distance apart of the groups (Clarke and Warwick, 1994). SIMPER: Calculation of species contributions to each group The SIMPER routine in PRIMER, which computes the average dissimilarity between all pairs of intergroup samples, was used to identify the primary species accounting for observed assemblage differences and to reduce the data set to those species that were responsible for >90% of the community composition. By looking at the overall percent contribution each species makes to the average dissimilari ty between two groups, it is possible to list species in decreasing order of their importance in discriminating two or more sets of samples. One measure of how consisten tly a species contributes to the average contribution across all pairs is the standard de viation of the average contribution values. If the average contribution is large and the st andard deviation small (resulting is a large ratio of average contribution to the standard deviation) then the species consistently contributes a large amount of the dissimila rity to the group. The final column in SIMPER analysis computes the percent of the total dissimilarity that is contributed by the

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20 species, and cumulates these percentages down the rows of the table (Clarke and Warwick, 1994). It is also possible, using SIMPER, to compute the contribution that each species makes to the average similarity within a group. The more abundant a species is the more it will contribute to the intragroup similarities. If it typifi es the group, then the average contribution to the similarity will be high, and the standard deviation will be low. However, it is important to note that one speci es can typify more than one group, and that considerable overlap between groups can occur. As with hierarchal cluster analysis, seve ral options for transformation of raw data were available. The square root transformati on used in the cluster analysis was retained for the SIMPER analysis, for the reasons described above. However in the SIMPER results tables, average abundance shown is for actual data, not for square root transformed data. Matching of Environmental Variables to Community Composition The BIOENV routine of PRIMER attempts to match biotic variables (sampl es) with environmental data to determine which variable best matches community composition. Three factors were measured simultaneously with net tows: temperature, salinity and chlorophyll a concentration. Before analyzing data with th e BIOENV routine, it was first necessary to ensure all measurements were on the same s cale. This required some transformation since Chlorophyll a values tended to be much lower a nd more variable than temperature or salinity. Transformation of the environmental data was thus obtained by normalizing temperature and salinity (by s ubtracting lowest temperature and salinity values obtained) and then square root transforming all three variables. The transformed environmental

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21 data was then compared to community composition using the BIOENV procedure, where combinations of environmental variables are considered at increasing levels of complexity. The results of the BIOENV procedure do not imply causality, since several causal variables may not have been measured, but the results do imply a correlation between physical and biotic variables and sample community composition. Results of the BIOENV procedure are reported as correlation coefficients. ACKNOWLEDGMENTS Funding was provided by ECOHAB Florida (NOAA/ECOHAB NA96P00084 and USEPA/ECOHAB CR826792-01-0) Office of Naval Research (N000149615024 and N000149910212), National Science Foundation (NSF OCE 0095970), and the Florida Fish and Wildlife Conservati on Commission (FWCC PO# S7701 623398). Additional funding was provided by the USF College of Marine Science Murtagh Fellowship. Thanks are extended to the Florida Institute of Oceanography, and the crew and scientific staff of the R/V Suncoaster and R/V Bellows, and to Cynthia Heil, Danielle Ault, M.B. Neely, Ryan Pigg and Tom Corbin who assisted with the sampling.

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22 REFERENCES Anderson, D. M. (1995). ECOHAB: The Ecology and Oceanography of Harmful Algal Blooms; A National Research Agenda Snow Mountain Ranch Conference Center, CO, Woods Hole Oceanographic Institute. Auel, H. and W. Hagen (2002). "Mesozoopla nkton community structure, abundance and biomass in the central Arctic Ocean." Marine Biology 140 1013-1021. Austin, H. M. and J. I. Jones (1974). "Seasonal variation of physical oceanographic parameters on the Florida Middle Gr ound and their relation to zooplankton biomass on the West Florida Shelf." Florida Scientist 37 16-32. Banse, K. (1995). "Zooplankton: Pivotal ro le in the control of ocean production." ICES Journal of Marine Science 52 265-277. Bogdanov, V., A. Sokolov, et al. (1968). "Reg ions of high biological and commercial productivity in the Gulf of Mexico and Caribbean Sea." Oceanology 8 371-380. Bossart, G. D., D. G. Baden, et al. (1998). "Brevetoxicosi s in manatees ( Trichechuys manatus latirostris ) form the 1996 epizootic: gross, histologic and immunohistochemical features." Toxicologic Pathology 26 276-282. Buskey, E. J. and C. Hyatt (1995). Effects of the Texas "brown tide" alga on planktonic grazers." Marine Ecology Progress Series 126 285-292. Buskey, E. J. (1993). “Effects of a persiste nt "Brown Tide" on zooplankton populations in the Laguna Madre of South Texas.” Toxic Phytoplankton Blooms in the Sea. Proceedings Fifth International Conf. Toxic Marine Phytoplankton. T. J. Smayda and Y. Shimizu. Amsterdam, Elsevier Science Publishers : 659-666. Clark, R. A., C. L. J. Frid, et al. (2001). "A critical comparison of two long-term zooplankton time series from the central-west North Sea." Journal of Plankton Research 23 27-39. Clarke, K. R. and R. M. Warwick (1994). Change in Marine Communities: An approach to statistical analysis and interpretation Plymouth, Bourne Press Ltd. Dragovich, A. and J. A. Kelly (1964). “P reliminary observations on phytoplankton and hydrology in Tampa Bay and the immedi ately adjacent offshore waters.” A collection of data in reference to red tide outbreaks during 1963 St. Petersburg, Florida Board of Conservation Marine Laboratory : 4-22.

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23 Fiedler, P. C. (1982). “Zooplankton avoi dance and reduced grazing response to Gymnodinium splendens (Dinophyceae).” Limnology and Oceanography 27 961965. Flewelling, L.J., J. P. Naar, et al. (2005). “Brevetoxicosis: Red tides and marine mammal mortalities.” Nature 435 755 Frost, B. W. (1980). “The inadequacy of body size as an indicator of niches in zooplankton.” Evolution and Ecology of Zooplankton Communities W. C. Kernot. Hanover, NH, University Press of New England : 742-753. Galstoff, P. S. (1948). Red Tide. Progress repor t on the investigations of the cause of the mortality of fish along the west coast of Florida conducted by the U.S. Fish and wildlife service and cooperating organizations. Wa shington, D.C., United States Fish and Wildlife Service. Geraci, J. R. (1989). Clinical investigation of the 1987-1988 mass mortality of bottlenose dolphins along the US central and Atlantic coast. Washington, D.C., U.S. Marine Mammal Commission. Gunter, G., R. H. Williams, et al. (1948). "C atastrophic mass mortality of marine animals and coincident phytoplankton bloom on the West coast of Florida, November 1946 to August, 1947." Ecological Monographs 18 311-324. Heil, C., G. Vargo, et al. (2003) “Nutrient stoichiometry of a Gymnodinium breve bloom: What limits blooms in oligotrophic environments?” Harmful Algal Blooms 2000 G. M. Hallegraeff, S. I. Blackburn, C. Bo lch and R. J. Lewis, IOC of Unesco. Hopkins, T. L. (1966). "The plankton of the St. Andrew Bay system, Florida." Public Institute of Marine Scien ce, University of Texas 11 12-64. Hopkins, T. L. (1977). "Zooplankton Distri bution in surface waters of Tampa Bay, Florida." Bulletin of Marine Science 27 467478. Hopkins, T. L. (1982). "The ve rtical distribution of zoopla nkton in the eastern Gulf of Mexico." Deep Sea Research 29 1069-1083. Hopkins, T. L. and T. M. Lancraft (1984) "The composition and standing stock of mesopelagic micronekton at 27oN 86oW in the Eastern Gulf of Mexico." Contributions to Marine Science 27 145-158. Hopkins, T. L., D. M. Milliken, et al. ( 1981). "The landward distribution of oceanic plankton and micronekton over the west Flor ida continental shelf as related to their vertical distribution." Journal of Plankton Research 3 645-658.

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24 Houde, E. D. and N. Chitty (1976). S easonal Abundance and Distribution of Zooplankton, Fish Eggs, and Fish Larv ae in the Eastern Gulf of Mexico, 19721974. Seattle, WA, National Oceanic and Atmospheric Administration. Hunt, B. P. V., E. A. Pakhomov, et al. (2001). "Short-term vari ation and long-term changes in the oceanographic environm ent and zooplankton community in the vicinity of a sub-Antarctic archipelago." Marine Biology 138 369-381. Huntley, M. E. (1982). "Yellow water in La Jolla Bay, California, July, 1980." Journal of Experimental Marine Biology and Ecology 63 81-91. Huntley, M. E., P. Sykes, et al. (1986). "Che mically mediated rejection of dinoflagellate prey by the copepods Calanus Pacificus and Paracalanus parvus : Mechanism, occurrence and significance." Marine Ecology Progress Series 28 105-120. Jerling, H. L. and D. P. Cyrus (1998). "The zooplankton communities of an artificially divided subtropical coastal estuarin e-lake system in South Africa." Hydrobiologia 390 25-35. King, J. E. (1950). "A Preliminary Report on th e Plankton of the West Coast of Florida." Journal of Florida Academy of Sciences 12 109-137. Kiorboe, T. (1993). "Turbulence, Phytoplankton cell size, and the st ructure of pelagic food webs." Advances in Marine Biology 29 1-72. Kusek, K. M. (1998). Florida Red Tides from a Scientific and Public Information Perspective. Masters thesis. College of Ma rine Science, St. Petersburg, University of South Florida : 254. Layne, J. N. (1965). "Observations on marine mammals in Florida waters." Bulletin of Florida State Museum 9 131-181. Lehman, J. T. (1984). “Grazing, Nutrient Rele ase, and their impacts on the structure of phytoplankton communities.” Trophic Interactions w ithin Aquatic Systems D. G. Meyers and J. R. Strickler. Boulder, CO, Westview Press : 49-72. Lenes, J., B. Darrow, et al. ( 2001). “Iron fertilization and the Trichodesmium response on the West Florida Shelf.” Limnology and Oceanography 46 12611278. Lester, K., R. Merkt, et al (2003). “Evolution of a Gymnodi nium Breve red tide bloom on the West Florida Shelf.” In: Harmful Algal Blooms 2000 Hallegraeff, G.M., Blackburn, S.I., Bolch, C., and Lewis, R. J. (Eds.), IOC of Unesco, pp. 161-163.

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25 Martin, D. F., M. T. Doig, et al. (1973). "B iocontrol of the Florida red tide organism, Gymnodinium breve through predator organisms." Environmental Letters 4 297301. Minello, T. (1980). Neritic Zooplankton of the Northwestern Gulf of Mexico. Doctoral Dissertation. Texas A&M : 240. Morris, M. J. and T. L. Hopkins (1983). "Biochemical composition of crustacean zooplankton from the eastern Gulf of Mexico." Journal of Experi mental Marine Biology and Ecology 69 1-19. Motulsky, H. (1995). Intuitive Biostatistics New York, Oxford, Oxford University Press. Omori, M. and T. Ikeda (1992). Methods in Marine Zooplankton Ecology Krieger Publishing Company. Pakhomov, E. A., R. Perissinotto, et al (1999). "Predation impact of carnivorous macrozooplankton and micronekton in the Atla ntic sector of th e Southern Ocean." Journal of Marine Systems 19 47-64. Poulsen, L. K. and N. Reuss (2002). "The plankton community on Sukkertop and Fylla Banks off West Greenland during a sp ring bloom and post-bloom period: Hydrography, phytoplankton and protozooplankton." Ophelia 56 69-85. Rounsefell, G. A. and W. R. Nelson (1966) Red-Tide Research Summarized to 1964 Including an Annotated Bi bliography. Washington, D.C, United States Fish and Wildlife Service. Smayda, T. J., and T.A. Villareal. (1989). “An extraordinary, noxious "brown-tide". Narragansett Bay. I. The organism and its dynamics.” Red Tides: Biology, Environmental Science and Toxicology T. Okaichi, D.M. Anderson and T. Nemoto (eds.) : 127-130. Squires, A. P. (1984). The distribution and ecology of zooplankton in Charlotte Harbor, Florida. Master’s Thesis. Department of Marine Science, St. Petersburg, University of South Florida : 60. Steidinger, K. A. (1975). "Implications of dinoflagellate life cycles on initiation of Gymnodinium breve life cycles." Environmental Letters 9 129-139. Steidinger, K. A., G. A. Vargo, et al. (1998). “Bloom Dynamics and Physiology of Gymnodinium breve with Emphasis on the Gulf of Mexico.” Physiological Ecology of Harmful Algal Blooms D. M. Anderson, A. D. Cembella and G. M. Hallegraeff. Berlin-Heide lberg, Springer-Verlag. G 41, 133-153.

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26 Sutton, T. T. Hopkins, et al. (2001). “Multisensor samp ling of pelagic ecosystem variables in a coastal environment to estimate zooplankton grazing impact.” Continental Shelf Research 21 69-87. Tester, P. A. and K. A. Steidinger (1997). Gymnodinium breve red tide blooms: initiation, transport and conseque nces of surface circulation." Limnology and Oceanography 42 1039-1051. Tester, P. A., R. P. Stumpf, et al. (1991) "An expatriate red tide bloom: transport, distribution, and persistence." Limnology and Oceanography 36 1053-1061. Turner, J. T. and P. A. Tester (1989). “Zooplankton feeding ecology: Copepod grazing during an expatriate red tide.” Novel Phytoplankton blooms. Causes and impacts of recurrent brown tides and other unusual blooms E. M. Cosper et. al, Springer : 359-374. Turner, J. T. and P. A. Tester (1997). "T oxic Marine Phytoplankton, zooplankton grazers, and pelagic food webs." Limnology and Oceanography 42 1203-1214. Uye, S. (1986). "Impact of copepod grazing on the red tide flagellate Chatanella antiqua ." Marine Biology 92 35-43. Valiela, I. (1995). Marine Ecological Processes New York, Springer-Verlag. Vargo, G., C. Heil et al. (In Press). “Nutrient availabi lity in support of Karenia brevis blooms on the West Florida Shelf: What keeps Karenia blooming?” Continental Shelf Research Vargo, G., C. Heil, et al. (2003). “Hydrogr aphic regime, nutrient requirements and transport of a Gymnodinium breve DAVIS red tide on the West Florida Shelf.” Harmful Algal Blooms 2000 G. M. Hallegraeff, S. I. Blackburn, C. Bolch and R. J. Lewis, IOC of Unesco : 157-160. Vargo, G. A., K. L. Carder, et al. (1987) "The potential contribution of primary production by red tides to the we st Florida shelf ecosystem." Limnology and Oceanography 32 762-767. Walsh, J. J., K. D. Haddad, et al. (2002). "A numerical analysis of landfall of the 1979 red tide of Karenia brevis along the west coast of Florida." Continental Shelf Research 22 15-38. Walsh, J. J. and K. A. Steidinger (2001). "Saharan dust and Florida red tides: The cyanophyte connection." Journal of Geophysical Research 106 11597-11612

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27 Walsh, J.J. R. H. Weisberg, et al. (2003). “The phytoplankton response to intrusions of slope water on the West Florida Sh elf: models and observations.” Journal of Geophysical Research Oceans 108 1-23 Weiss, W. R. (1978). The zooplankton of the Anclote Estuary, Florida. Master’s Thesis. Department of Marine Science, St. Pe tersburg, University of South Florida : 122. Welschmeyer, N. A. (1994). "Fluorometric analysis of chlorophyll a in the presence of chlorophyll b and phaeopigments." Limnology and Oceanography 39 19851992.

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28 CHAPTER 2 ZOOPLANKTON COMMUNITY COMPOSITION OF THE WEST FLORIDA SHELF Abstract A comprehensive seasonal analysis of abundance, biomass and community composition of zooplankton was undertaken at 6 stations on the WFS. Monthly sampling was conducted for one year at the 5, 25 and 50-m isobaths. Abundance ranged from a low of 127 animals m-3 at the 50-m isobath in April 2000 to 15,179 animals m-3 at the 5m isobath in August 1999. Abundance was always greatest at the 5-m isobath. Biomass ranged from 1.48 mg dry weight m-3 at the 50-m isobath in March 2000 to 40.93 mg m-3 at the 5-m isobath in August 1999. Abundance and biomass were greatest in the late summer and early fall, declin ing through the winter mont hs. Two major groups in community composition were observed at the near shore (5-m and 25-m) and offshore (50-m) stations. Considerable overlap wa s seen in community composition between the 5-m to 25-m and 25-m to 50-m isobaths, but li ttle overlap in comm unity composition was observed between the 5-m and 50-m isobaths. Of the 95 species identified, only 25 proved to be important (>90%) contributors to community composition. Near shore, important contributors were Parvocalanus crassirostris Penilia avirostris Paracalanus quasimodo, Oithona colcarva Oikopleura dioica, Centropages velificatus and Pelecypod larvae. As distance offshore increased, impor tant contributors to community composition were Euchonchoichiea chierchiae, Clausocalanus furcatus Oithona plumifera Oithona frigida Oncaea mediteranea Calaocalanus pavoninius Oithona similis, and Gastropod larvae.

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29 INTRODUCTION Zooplankton are important mediators of energy transfer from primary producers to higher trophic levels, and act as regul ators of phytoplankton abundance, phytoplankton species structure, and seas onal phytoplankton succession (Ban se, 1995; Sterner, 1989). Despite its high productivity and importance to the Gulf of Mexico (Austin and Jones, 1974), there is a paucity of zooplankton assemblage data for the West Florida shelf (WFS). In situ research of this trophic level on th e WFS has generally taken one of two approaches. Those studies that repo rt taxonomic composition of zooplankton assemblages are either 1) primarily descrip tive (King 1950) or 2) are limited spatially and/or temporally (Hopkins et al., 1981; Sutton et al., 2001 Hopkins, 1973; Morris and Hopkins, 1981; Hopkins and Lancraft, 1984) Comprehensive taxonomic seasonal analysis of numerical abundance and biomass ha ve been limited to estuaries of the WFS (Grice, 1956; Hopkins, 1966; Squires, 1974; Hopkins, 1977; Weiss, 1978). Some overlap between estuarine, shelf and offshore zooplankton assemblages is expected due to mechanisms that periodically bring central Gulf water across the Florida shelf (Ortner et al., 1989; Hopkins, 1981), but ac counts published to date indicate that the zooplankton populations on the WFS are diffe rent than those found in estuaries and offshore (Minello, 1980; Hopkins, 1981; Ortner et al., 1989; Sutton et al., 2001). The purpose of this chapter is to provide a comp rehensive taxonomic seasonal analysis of the zooplankton assemblage of the WFS from co astal waters to the 50-meter isobath.

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30 Methods Sampling took place during monthly EC OHAB cruises on board the R/V Suncoaster and the R/V Bellows in the Gulf of Mexico (Figure 4). Stations were located approximately every 5 nautical miles. A CTD profile was conducted at every station. At selected stations (usually every other sta tion, but occasionally more frequently) water samples were collected to determine chlorophyll a concentration and other parameters. Zooplankton sampling began in August 1999 and continued through July 2000. The zooplankton assemblage at the 5-, 25-, a nd 50-meter isobaths were represented by Stations 1 and 51, Stations 5 and 46, and St ations 10 and 40, respect ively (Austin, 1971; Austin and Jones, 1974; Minell o, 1980; Sutton et al., 2001). Collection of Zooplankton 1999-2000 Zooplankton were collected with a 153 m mesh bongo net, lowered closed through the water column, opened at depth and then towed obliquely from bottom to surface. The volume of water filtered wa s calculated from a calibrated flow meter attached at the net mouth (Omori and Ikeda, 1992). After being brought on board, the co d ends were filtered through a 2000 m mesh sieve to remove large gelatinous zooplankton. Each filtered cod end was preserved on board in a 5% buffered formalin solution (O mori and Ikeda, 1992) for later counts of zooplankton species abundance.

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31 47 48 49 50 70 71 72 73 74 75 76 77 78 79 80 8 1 8 2 83 -84.00-83.50-83.00-82.50-82.00-81.50 26.00 26.50 27.00 27.50 28.00 28.50 1 2 3 4 5 6 7 8 9 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 41 42 43 44 45 46 GULF OF MEXICO 51 40 10 LongitudeL a t i t u d e Tampa Sarasota Ft. Myers 47 48 49 50 70 71 72 73 74 75 76 77 78 79 80 8 1 8 2 83 -84.00-83.50-83.00-82.50-82.00-81.50 26.00 26.50 27.00 27.50 28.00 28.50 1 2 3 4 5 6 7 8 9 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 41 42 43 44 45 46 1 2 3 4 5 6 7 8 9 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 41 42 43 44 45 46 GULF OF MEXICO 51 40 10 LongitudeL a t i t u d e Tampa Sarasota Ft. Myers Figure 4. ECOHAB study area in the Gulf of Mexico. Station locations for ECOHAB cruises are indicated by a ( ). Stations where zoopla nkton tows were conducted are circled and indicated b y a number.

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32 Zooplankton abundance and biomass Representative subsamples of 500-600 animals were obtained with a Stempel pipette (usually 1-5% of init ial cod end volume). Zooplankton were then identified and counted using an Olympus di ssecting microscope at 10-40x magnification, with critical taxonomic features observed on an Ol ympus Canon dissecting microscope. Holoplankton were identified to species level whenever possible. Meroplankton were identified to major taxonomic group (e.g. Pe lecypod veligers, Cirriped larvae). Copepod nauplii were not identified to sp ecies level but, when possible, were identified to family level. Replicate samples were averaged for each station. Biomass was determined using published length/width regressi on equations and values (Tab le 3 and references cited therein). Abiotic and biotic factors Zooplankton tows were conducted in conjunction with CTD casts and measurements of chlorophyll a Water column samples were collected from Niskin bottles mounted on a rosette sampler. Dup licate chlorophyll sample s were filtered onto GF/F filters, placed in 10 ml methanol and stored at -20oC in darkness until later analysis with a Turner design fluorometer (Welsc hmeyer, 1994). Salinity, temperature and Chlorophyll a were averaged over the water column. Statistical Analysis Observed community associations were quantified using the multivariate statistical techniques of PRIMER (Plymouth Routines in Multivariate Ecological

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33 Table 3 Sources of biomass values and length/width regression equations for WFS zooplankton taxa. Taxon Source Comments Undinula Morris and Hopkins, 1983 Eucalanus Morris and Hopkins, 1983 Acrocalanus Weiss, 1978 Derived from Paracalanus Calocalanus “ Paracalanus “ Clausocalanus “ Derived from Centropages Scolothrex Morris and Hopkins, 1983 Euchaeta Morris and Hopkins, 1983 Temora Lester, unpub. Data Centropages Weiss, 1978 Calanopia “ Pseudodiaptomas “ Acartia “ Tortanus “ Labidocera “ Oithona “ Oncaeae Squires, 1984 Corycaeus Weiss, 1978 Farranula “ Euterpina “ Microsetaella “ Euchonchoichiea Hopkins, 1984 Penilia Weiss, 1978 Evadne “ Podon “ E. tergestina value Appendicularians “ Brachiopoda “ Bryozoa “ Cirripedia “ Decapoda “ Echinodermata “ Gastropoda “ Pelecypoda “ Platyhelminthe Squires, 1984 Polychaeta Weiss, 1978

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34 Research) software. Hierarchal clustering analysis was used to identify trends in community distribution of the zooplankton asse mblage. Bray-Curtis similarities (Clarke and Warwick, 1994) were calculated and subseque ntly ranked within a similarity matrix. Data were not standardized, since all sta tions were already on the same scale of abundance m-3. However a square root transf ormation was performed to minimize variations in abundance (Clark e and Warwick, 1994). Similari ty percentages within and between groups of zooplankton were determ ined using PRIMER’s SIMPER routine, which calculates the average dissimilarity between inter-group samples and computes dissimilarities between groups (Clark e and Warwick, 1994). PRIMER’S BIOENV procedure was used to determine which m easured variable contributed most to community composition. The BIOENV proce dure matches transformed environmental data (in this case, salinit y, temperature and chlorophyll a concentration) to changes in community composition. Environmental data were normalized and log transformed to ensure that all measurements were on the same scale. RESULTS Abiotic and Biotic Factors in the Study Area Isobath averaged temperature ranged from 18.4 to 31.2 oC, with highest temperatures occurring from June through Se ptember, and lowest temperatures from December through March (Figure 5). Temperat ure fluctuations were most pronounced at the 5-meter isobath, where the highest (31.2 oC) and lowest (18.4 oC) surface temperatures recorded in the study area occurre d. Temperature fluctuations from month

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35 Figure 5. Temperature, Salinity and Chlorophyll a concentrations at the 5-meter ( ), 25-meter( ), and 50-meter (-------) isob aths. Note that no data was collected in February of 2000. Month 0 1 2 3 4 5 6A SONDJMAMJchl a concentration ( g l-1) 33 34 35 36 37 38ASONDJMAMJSalinit y 18 20 22 24 26 28 30 32ASONDJMAMJTemperature (oC)

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36 to month became less pronounced as distance o ffshore increased. Temperature at the 25meter isobath ranged from 19.2 to 30.4 oC, while temperature at the 50-meter isobath ranged from 19.9 to 28.6 oC. At all isobaths, the highest temperature occurred in August. At the 5-meter isobath, the lowest temperat ure occurred in December, while further offshore lowest temperatures occurred in March. Isobath averaged salinity ranged from 34.2 to 37.1 ppt (Figure 5). The greatest range in salinity was found at the 5-meter isoba th. Generally, salinity was lowest at the 5-meter isobath, while salinity at the 50-meter isobath followed the same trend and values as the 25-meter isobath throughout much of the year. Isobath averaged chlorophyll a concentration ranged from less than 0.1 g l-1 at the 50-meter isobath in spring and summer to 2.79 g at-1 l-1 at the 5-meter isobath in October (Figure 5). Chlorophyll a concentration was highly vari able at Stations 1 and 51, with a greater than two fold difference in chlorophyll a concentrations in October 2000 to January 2001. At offshore stations, chlorophyll a concentration was less variable, with the exception of April 2001 at the 50 -meter isobath, where chlorophyll a concentration approached the near shore concentration, most likely due to influx of high chlorophyll Mississippi and Apalachicola rive r water to areas offshore in the Gulf of Mexico (Gilbes et al., 1996; Gilbes et al., 2002) This assertion is supported by the slight drop in salinity in April at Station 40 (Figure 6). Chlorophyll a concentration was usually highest at the 5-meter isobath, and dropped off significantl y as distance offshore increased. Chlorophyll a concentration was usually higher at the 25-meter isobath than at the 50-meter isobath, although there were sampli ng periods where the isobath averaged

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37 33 34 35 36 37 38ASONDJMAMJJSalinit y Figure 6. Salinity at Stations 10 ( ) and 40 ( ) for the 1999-2000 sampling period. No data was collected in February of 2000. Month

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38 chlorophyll concentration at the 50-meter isobath either matched or exceeded the concentration at the 25-meter isoba th. For all isoba ths, chlorophyll a concentration was generally highest in the late summer and fall, declined through the winter, increased in April, and then declined again th rough the summer (Figure 5). Zooplankton Abundance and Biomass Isobath averaged zooplankton abund ance ranged from a low of 127 m-3 animals at the 50-meter isobath in April 2000 to 15,179 m-3 animals at the 5-meter isobath in August 1999 (Figure 7). Abundance was always gr eatest at the 5-meter isobath and was generally higher in the late summer and early fall, declining thr ough the winter months. Isobath averaged zooplankt on biomass ranged from 1.48 mg m-3 at the 50-meter isobath in March 2000 to 40.93 mg m-3 dry weight at the 5-meter isobath in August of 1999 (Figure 7). Biomass was usually greatest at the 5-meter isobath, except for January 2000, when biomass was higher at the 50-meter isobath. Biomass was usually greater at the 50-meter isobath than the 25-meter is obath, except for Apr il, May and June 2000, when biomass was higher at the 25isobath. Zooplankton Community composition Group determination Cluster analysis Two groups of stations separated at the 35% similarity level (Figure 8). All of the 5-meter isobath stations are included in Group I, while all the 50-meter isobath stations are in cluded in Group II. Stations at the 25

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39 0 4,000 8,000 12,000 16,000A SO N D J FM A M J J Numerical Abundance (m-3) 0 25 50ASONDJFMAMJJ Biomass (mg m-3) Figure 7. A. Total zooplankton abundance m-3 for the 5-m (hatched bars), 25-m (solid bars), and 50-m (dotted bars) isoba ths. B. Total zooplankton biomass in dryweight mg-3 for the 5-m (hatched bars), 25-m (solid bars), and 50-m (dotted bars) isobaths. A. B. Month

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40 1 Jul 51 Jun 1 Jan 1 Dec 51 Sep 1 Jun 1 Sep 51 Aug 1 Aug 51 Jan 51 Apr 51 May 1 Mar 51 Nov 51 Dec 1 Apr 51 Mar 1 May 46 May 46 Jun 5 Jun 5 Jul 46 Jan 5 Dec 46 Dec 5 Oct 5 Nov 46 Nov 46 Sep 5 Sep 46 Aug 10 Jul 40 Aug 46 Apr 5 Apr 5 May 10 Mar 5 Jan 5 Mar 46 Mar 10 Oct 10 Sep 40 Sep 10 Jan 40 Jan 40 Mar 10 Dec 40 Dec 10 May 10 Jun 40 May 10 Apr 40 Apr 20406080100 I II (A) (B) (C) (D) (E) Figure 8. Cluster derived dendrogram for 53 stations at the 5, 25 and 50-meter isobaths, using group averaged clustering fr om Bray-Curtis similarities on square root transformed abundance data.

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41 meter isobath are divided between Groups I and II with the majority fa lling into Group I. Groups I and II separated at th e 40% similarity level into 5 sub-groups. Subgroup A is comprised entirely of 5-meter isobath stati ons. Subgroup B is comprised of summer and fall 25-meter isobath stations, with all of th e remaining 25-meter isobath stations falling into subgroup C. Subgroup D is comprised of a mix of winter/spring 25-meter isobath stations and winter/spring 50meter stations. Only late spring/early summer 50-meter isobath stations are included in Subgroup E. Determination of discrimina ting species – SIMPER analysis The SIMPER routine of primer was implemented to dete rmine which zooplankton species were typical of each subgroup (Clarke and Warwick, 1994). T hose species that contributed to 90% of the total abundance were include d in the analysis. 4 species were responsible for 64% of the community composition of Subgroup A (Table 4). The copepods Parvocalanus crassirostris and Oithona colcarva were the primary species defining the group, contributing 26.64 and 19.28%, respectively, to community composition. The cladoceran Penilia avirostris contributed 11.00% to community composition, while the copepod Paracalanus quasimodo contributed 7.23%. Considerable overlap in community composition was seen between Subgroups A and B, with 6 of the 11 species that contri buted to 90% of the community composition of Subgroup A also contributing to 90% of the community composition of Subgroup B (Table 5). Two thirds (64.59%) of the community composition of Subgroup B was defined by 5 taxa: P. quasimodo (25.53%), O. colcarva (15.66%), the larvacean Oikopleura dioica (12.16%), the copepod Centropages velificatus (5.69%), and Pelecypod larvae (5.55%).

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42 Table 4 Results of SIMPER analysis for Subgroup A. Species Av.Abund Sim/SD Contrib%Cum.% P. crassirostris 1655.08 1.55 26.64 26.64 O. colcarva 1224.78 0.87 19.28 45.92 P. avirostris 1105.17 0.47 11.00 56.92 P. quasimodo 343.92 1.11 7.23 64.15 Cirripedia 477.53 0.95 6.91 71.06 E. acutifrons 355.67 0.81 5.44 76.50 Pelecypoda 271.31 0.58 4.26 80.76 Decapoda 201.53 1.02 3.27 84.03 C. americanus 108.06 0.73 2.81 86.84 O. nana 141.5 0.51 2.20 89.04 Gastropoda 106.39 0.93 2.15 91.19

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43 Table 5 Results of SIMPER analysis for Subgroup B. Species Av.AbundSim/SD Contrib%Cum.% P. quasimodo 172.921.5525.5325.53 O. colcarva 121.851.2415.6641.19 O. dioica 72.081.512.1653.35 C. velificatus 114.770.595.6959.04 Pelecypoda 87.920.755.5564.59 Gastropoda 59.50.915.4770.06 P. crassirostris 41.121.075.3175.37 O. mediteranea 71.150.644.2779.64 O. plumifera 24.881.193.8683.5 E. acutifrons 47.581.023.5587.05 E. chierchiae 96.730.22.4689.51 C. amazonicus 28.540.92.1591.66

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44 Only 4 out of 11 species from Subgroup A were respons ible for the top 90% of community composition in Subgroup C, though 8 out of 12 species in Subgroup B proved to be important there (Table 6). Two thir ds (65.07%) of the community composition of Subgroup C were defined by 5 species: the ostracod Euchonchoichiea chierchiae (21.01%), the copepod Clausocalanus furcatus (16.81%), O. dioica (10.86%), C. velificatus (8.45%), and the Oithona Plumifera (7.94%). Seven out of 11 species from Subgroup C were also important contributors to the community composition of Subgroup D (Table 7). Two thirds (64.43%) of th e community composition of Subgroup D was defined by 4 species: E. chierchiae (30.06%), Oithona frigida (13.08%), C. furcatus (11.18%) and Oncaea mediteranea (10.12%). Some overlap between Subgroups D and E was seen, with 6 out of 11 species from subgroup D included in the 9 species contributing to Group E (Table 8). Major contributors (63.47%) to community composition of Subgroup E were C. furcatus (19.06%), Calaocalanus pavoninius (18.13%), Oithona similis (15.17%) and Gastropod larvae (11.11%). Determination of discrimi nating species – Shade Matrix The shade matrix compiled for the 5 subgroups confirms th e considerable overlap in community composition between subgroups (Figure 9). In th is figure, near shore groups trend to the upper left, offshore groups to the lower right. Represented this way, the considerable overlap between groups B, C and D is evident, as is the overlap between subgroups A and B and D and E. However, little overlap is observed between near shore subgroup A and offshore subgroup E.

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45 Table 6 Results of SIMPER analysis for Subgroup C. Species Av.AbundSim/SD Contrib%Cum.% E. chierchiae 65.39 0.75 21.01 21.01 C. furcatus 44.83 1.09 16.81 37.82 O. dioica 24.33 1.50 10.86 48.68 C. velificatus 11.50 2.58 8.45 57.13 O. plumifera 16.67 2.13 7.94 65.07 Gastropoda 17.61 1.34 6.75 71.82 O. colcarva 11.11 0.66 5.63 77.45 O. mediteranea 11.17 0.70 4.25 81.70 P. quasimodo 13.89 0.58 3.96 85.66 Pelecypoda 8.50 0.60 2.75 88.41 C. pavo 10.11 0.41 2.71 91.11

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46 Table 7 Results of SIMPER analysis for Subgroup D. Species Av.Abund Sim/SD Contrib%Cum.% E. chierchiae 316.811.2930.0630.06 O. frigida 101.191.213.0843.13 C. furcatus 114.561.9811.1854.31 O. mediteranea 1001.7610.1264.43 O. dioica 68.751.147.1971.62 Gastropoda 55.311.355.6477.27 O. plumifera 64.251.035.2382.5 C. velificatus 29.51.063.5186.01 P. pygmaeus 43.380.512.0288.03 P. aculeatus 41.630.531.5289.55 C. limbatus 19.690.51.3390.88

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47 Table 8 Results of SIMPER analysis for Subgroup E. Species Av.Abund Sim/SDContrib%Cum.% C. furcatus 18.8 2.35 19.06 19.06 C. pavoninius 19.5 1.57 18.13 37.19 O. similis 15.6 2.93 15.17 52.36 Gastropoda 11.7 1.33 11.11 63.47 E. chierchiae 12.7 1.30 10.12 73.59 O. mediteranea 13.0 0.81 7.69 81.28 O. dioica 5.8 1.20 4.21 85.50 O. plumifera 4.1 1.44 3.28 88.78

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48 Cirripedia Oithona nana Euterpina acutifrons Paracalanus quasimodo Parvocalanus crassirostris Corycaeus americanus Pelecypoda Decapoda Penilia avirostris Oikopleura dioica Oithona colcarva Gastropoda Corycaeus amazonicus Centropages velificatus Calocalanus pavo Oithona plumifera Paracalanus aculeatus Oncaea mediteranea Clausocalanus furcatus Euconchoecinae chierchiae Corycaeus limbatus Oithona frigida Calocalanus pavoninus Paracalanus pygmaeus Oithona similis III E ABCD Figure 9. Shade matrix for WFS zooplankton subgroups A-E. Black squares indicate those months where the species was dominant. Gray squares indicate a species was present. White squares indicate the absence of a species. Near shore species trend to the upper left, offshore species to the lower right. Those species that showed considerable overlap between groups fall into the middle of the matrix.

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49 Community associations with abiotic and biotic factors Temperature All subgroups, with the exception of subgroup E, showed a wide range in temperature (Figures 10-14). Th e greatest range in temperature was observed for subgroups A and B, where highest mean te mperatures were also observed (Figure 11, Table 9). As distance offshore increased, ra nge in temperature and highest temperature observed decreased. Lowest mean temper ature was observed for Subgroup C (Figure 12), while the narrowest range in temperature occurred in subgroup E, where only spring offshore stations are repr esented (Figure 14). Salinity Range in salinity was greatest at subgroup A, with a range of 34.2 to 37.1 ppt (Figure 11). Lowest m ean salinity was also seen for subgroup A (Table 9). A narrower range and higher mean were obs erved for subgroup B, where salinity ranged from 35.9 to 36.7 (Figure 12). The range in salinity narrowed as distance offshore increased, with the narrowest range in salinity, 36.4 to 36.6, observed for subgroup E (Figure 15). Chlorophyll a The greatest range in chlorophyll a concentration was seen in near shore subgroup A, with mean chlorophyll a concentration and range of chlorophyll a concentration decreasing as distance offshore increas ed (Figure 11, Table 9). Chlorophyll a concentration decreased as distance offshore increased (Figures 11-15). The narrowest range in Chlorophyll a concentration occurred in subgroup E, where lowest mean Chlorophyll a concentration was also observed (Figure 15, Table 9). BIOENV The BIOENV procedure of PRIMER was used to determine which of the three measured variables, Temp erature, Salinity or Chlorophyll a correlated best with

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50 Figure 10. Distribution of a) Temperature, b) Salinity and c) Chlorophyll a for Subgroup A.

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51 Figure 11. Distribution of a) Temperature, b) Salinity and c) Chlorophyll a for Subgroup B.

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52 Figure 12. Distribution of a) Temperature, b) Salinity and c) Chlorophyll a for Subgroup C.

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53 Figure 13. Distribution of a) Temperature, b) Salinity and c) Chlorophyll a for Subgroup D.

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54 Figure 14. Distribution of a) Temperature, b) Salinity and c) Chlorophyll a for Subgroup E.

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55 Table 9 Environmental and biotic variables for subgroups A-E. Temperature Salinity Chlorophyll a Subgroup Range Mean St Dev Range Mean St Dev Range Mean St Dev A 18.431.3 24.91 4.59 34.2-37.1 35.700.89 .274.47 1.721.33 B 21.330.4 26.10 3.47 35.9-36.7 36.270.29 .201.34 0.590.42 C 19.228.6 22.89 3.39 36.2-36.5 36.400.10 .130.31 0.210.07 D 21.228.3 24.30 3.09 35.4-36.3 36.040.27 .140.38 0.300.09 E 21.925.4 22.98 1.41 36.4-36.6 36.450.07 .090.15 0.120.03

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56 community composition (Table 10). The singl e variable which correlated best with community composition was Chlorophyll a concentration (corr. of .353). DISCUSSION Abundance Comparison of zooplankton abundance between studies is often difficult due to variations in sampling methods such as mesh size and seasonality, as well as error associated with the patchiness and vari ability of zooplankton population sampling. However, it can be useful to compare overall ab undance with similar studies, if available, to assess the validity of a chosen sampli ng method. The data obtained in this study agrees well with data found in other portions of the Gulf of Mexico (Table 11), with one notable exception. Although th e abundance numbers found in th is study and Ortner et al. (1989) are similar for April, the data diverge significantl y from each other in December at the 5and 25-meter isobaths, where the numerical abundance found in this study is a full order of magnitude greater. This may be due to a combination of the larger mesh size used by Ortner et al. (1989) (333 m vice 153 m) and the prevalence in December of smaller zooplankton forms such as P. crassirostris and O. colcarva which would easily be extruded through the larger mesh net (Calbet, 2001).

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57 Table 10 Results of BIOENV Procedure on log transformed data. n=53 Correlation Variables 0.353 Chl a 0.345 Chl a Salinity 0.275 Chl a Salinity, Temperature 0.255 Chl a Temperature 0.236 Salinity 0.153 Temperature, Salinity 0.103 Temperature

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58 Table 11 Comparison of results found with this study and those from other studies in Gulf of Mexico and Mediterranean Sea. Mesh Size ( m) Location Time of Year Bottom Depth (m) Abundance (# m-3) 5-Meter Isobath comparison This study 153 WFS April 5 2773 Ortner 1989 333 NGOMX 4.5 3124 This study 153 WFS December 5 12227 Ortner, 1989 333 NGOMX 5.3 1298 This study 153 WFS Averaged over year 5 6915 Minello, 1980 200 NWFS 8 3412 25-Meter Isobath comparison This study 153 WFS December 25 2066 Ortner, 1989 333 NWGOMX 30 484 This study 153 WFS April 25 212 Ortner, 1989 333 NGOMX 35 212 Ortner, 1989 333 CGOMX 38 76 This study 153 WFS Averaged over year 25 1289 Calbet et al., 2001 200 Mediterranean 20-25 43865 50-Meter Isobath comparison This study 153 WFS Averaged over year 50 1114 Minello, 1980 200 NWFS 73 1131

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59 Community Composition Of the 95 species and taxa identified in this study, only 25 were found to contribute to the top 90% of community composition. The community composition found here is consistent with that previously repor ted for other areas of the Florida shelf (King 1950; Hopkins, 1966; Hopkins, 1977; Wei ss,1978; Minello, 1980; Squires 1984; Dagg, 1995). Subgroup A Only All stations in subgroup A were at the 5-meter isobath. Four taxa, P. avirostris C. americanus O. nana and Cirriped larvae were significant (top 90%) contributors to community composition in subgroup A, but not B, C, D or E. The cladoceran P. avirostris is circumglobally dist ributed in tropical and subtropical areas, and can demonstrate in termittent abundance and explosive population growth (Paffenhoffer, 1983; Paffenhoffer and Knowles, 1984; Turner and Tester, 1988). On the West Florida Shelf, P. avirostris is present in high concentrations near shore (Minello, 1980; Paffenhoffer 1984), with highest concentrations typically occurring in August and September (Minello, 1980; Paffenhoffer, 1984; Hopkins, 1984) though secondary peaks have been noted in late spring and early summer (Minello, 1980; Squires 1984). The very high populations of P. avirostris found at the 5-meter isobath in this study are a full order of magnitude higher th an reported by Minello (1980) on the NWFS, though Squires (1984) occasionally found populati ons of this cladoceran exceeding 6,000 animals l-1 in Charlotte Harbor. The highest nu mbers reported here were on the same order of magnitude as that found by Squires (1984) (Figure 15).

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60 Figure 15. Abundance distribution of selected WFS zooplankton taxa. 5-m (solid bars), 25-m (hatched bars ), and 50-m (dotted bars). 0 1000 2000 ASONDJFMAMJJ 0 1000 2000 ASONDJFMAMJJ 0 4000 8000 ASONDJFMAMJJ 0 5000 10000 ASONDJFMAMJJ 0 2000 4000 6000 ASONDJFMAMJJ 0 200 400 600 800 ASONDJFMAMJJ 0 200 400 600 800 ASONDJFMAMJJ 0 2000 4000 6000 8000 ASONDJFMAMJJ P. avirostris C. americanus O. nana Cirripid larvae P. crassirostris O. colcarva P. quasimodo E. acutifrons Abundance (m-3)Month Month

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61 Surface temperature appears to be the most important factor in determining P. avirostris distribution. Minello found that above 28oC there appeared to be a correlation with P. avirostris distribution. My study confirms these findings. The maximum P. avirostris populations in this study occurred at temperatures between 30 and 31o C (Figure 16). In most studies performe d to date, the temporal occurrence of P. avirostris is especially related to temperature (Marazzo and Valentin, 2001). C. americanus is more abundant at coastal stations on the NWFS and the WFS than within estuaries (W eiss, 1977; Minello, 1980; Hopkins, 1981; Hopkins, 1984; Squires, 1984). C. americanus was present only intermittently and in low concentration in the St. Andrew’s Bay system and the Ancl ote Estuary, and was not a major contributor to zooplankton assemblages in Tampa Ba y (Hopkins, 1966; Hopkins, 1977; Weiss, 1977). In Charlotte Harbor, C. americanus was present in slightly higher concentrations, but was absent from the assemblage for 6 mont hs out of the year (Squires, 1984). On the NWFS, populations never exceeded 40 animals m-3 (Minello, 1980). Populations in my study were much higher, with a peak concen tration in December and January of over 500 animals m-3 (Figure 15). The primary factor descri bing the distribution of C. americanus was surface temperature, though high concentration of chl a also appeared to be a factor. Minello reported highest numbers betw een temperatures of 10-22 0C. Highest abundances in my study were found between 18 and 24oC (Figure 17).

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62 Figure 16. Distribution of P. avirostris in relation to a) salin ity, b) temperature, and c) chlorophyll a concentration.

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63 Figure 17. Distribution of C. americanus in relation to a) sa linity, b) temperature, and c) chlorophyll a concentration.

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64 O. nana is most abundant in the summer and fall in higher salini ty regions of WFS estuaries (Hopkins, 1966; Weiss, 1977; Hopkins, 1977; Squires, 1984), though Weiss (1977) reported highest numbers in spring and summer. In my study, O. nana was most abundant in summer and fall, and never occurre d at the 25 or 50-meter isobaths (Figure 15). Minello (1980) determined that salinity was the primary variable defining this copepod’s distribution. In my st udy, salinity did not appear to be an important factor in its distribution. O. nana occurred in greatest number s at temperatures exceeding 300C and chlorophyll a concentrations between .5 and 1 g l-1 (Figure 18). Cirriped larvae are common year round in the estuaries of the West Florida coast, with no pattern in seasonal distribution evident (Hopkins, 1966; Weiss, 1977; Hopkins, 1977; Squires, 1984). In this study, Cirriped larvae were never found past the 5-meter isobath (Figure 16), though ther e are reports of Cirriped larv ae occurring further offshore in other studies (King 1950; Minello, 1980). A peak in Cirr iped larvae was observed in December (Figure 15). A strong correlation between Cirriped larvae abundance and temperature were observed in this study (Figure 19). Peak populations occurred between 33 and 38oC. No strong correlation was seen be tween salinity or chlorophyll a concentration and Cirriped concentration. Salinity and chlorophyll a concentration were not significant factors in the distribution of those species represented only in subgroup A. Instead, temperature was the major factor contributing to community distribution. The lack of salinity or

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65 Figure 18. Distribution of O. nana in relation to a) salinit y, b) temperature, and c) chlorophyll a concentration.

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66 Figure 19. Distribution of Cirri pid larvae in relation to a) salinity, b) temperature, and c) chlorophyll a concentration.

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67 chlorophyll a concentration as contributing factors suggests that these organisms are well adapted to the continually changing biotic and abiotic variables in an estuarine environment. Subgroup A and B All stations in subgroup B were at the 25–meter isobath. Six taxa, P. crassirostris O. colcarva P. quasimodo Euterpina acutifrons Pelecypod larvae and Gastropod larvae were primary contribu tors to community composition in subgroups A and B, indicating significant overlap in community composition between the 5 and 25meter isobaths. P. crassirostris was abundant and frequently dominant in all areas of Tampa Bay, Charlotte Harbor, the Anclote Es tuary, and the St. Andrew’s Bay System (Hopkins, 1966; Hopkins, 1977; Weiss, 1977; Squires, 1984). Numerical abundance peaked in late summer, and was generally greate st at the mouths of the estuaries. Minello (1980) reported P. crassirostris abundant at the 8and 14-me ter isobaths, with numerical abundance dropping off sharply with increasi ng distance offshore. Numerical abundance of P. crassirostris in this study (Figure 15) was typi cally an order of magnitude lower than that found in the WFS estuaries, and a fu ll order of magnitude hi gher than that found by Minello (1980) at the 8a nd 14-meter isobaths on the NWFS. This is possibly due to the differences in mesh size used (70 m in estuarine studies, 153 in this study, 200 m in NWFS study) since P. crassirostris is a small (~.5mm) copepod that is easily extruded through larger size nets (Calbet, 2001). Minello (1980) reported a strong co rrelation between both salinity and temperature for this species. In that study, highest concentrations were found at salinities from 29 to 35, with abundance dropping off sharpl y at salinities greater than 35. Greatest

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68 abundances were at lower temperatures of 10 to 20 oC, with a secondary peak at 31oC. In my study, P. crassirostris distribution peaked between salinities of 33.5 to 35.5 and temperatures of 27 to 32 oC (Figure 20). O. colcarva is a primary dominant species in WFS estuaries (Hopkins, 1966 ; Weiss, 1977; Hopkins, 1977; Squires, 1984). This numerically important copepod tends to be least abundant at the mouths of bays where it can still be present in tens of thousands of cells m-3 (Hopkins, 1966 ; Weiss, 1977; Hopki ns, 1977; Squires, 1984). In this study, lowest abundance occurred in the wi nter, with highest popul ations occurring in late summer (Figure 16). Although O. colcarva was found out to the 25-meter isobath, populations there were typically low. Highest populations of O. colcarva were found at salin ities of 35.5 to 36.5, though lowest abundances were also found at these salinities. There was a strong correlation with temper ature and abundance of O. colcarva with highest populations occurring at 20oC (Figure 21). P. quasimodo populations peak at the mouths of WFS estuaries, and the species is usually absent from lower salinity areas at the heads of estuarie s (Hopkins, 1966; Weiss, 1977; Hopkins, 1977; Squires, 1984). P. quasimodo was reported to be less abundant at offshore isobaths by Minello (1980), with highest populations found at the 8-meter isobath in late summer and early fall In this study, peak abundanc es also occurred in late summer and early fall at the 5-meter isobath (Figure 16). Minello (1980) found no relationshi p between the di stribution of P. quasimodo with any of the physical or chemical factor s measured. However, in this study lower

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69 Figure 20. Distribution of P. crassirostris in relation to a) salinity, b) temperature, and c) chlorophyll a concentration.

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70 Figure 21. Distribution of O. colcarva in relation to a) salinity, b) temperature, and c) chlorophyll a concentration.

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71 salinities and higher temperatur es were correlated with P. quasimodo abundance (Figure 22). E. acutifrons was an important contributor to Groups A and B. This harpacticoid copepod is typically present near the mouths of estuaries on the WFS, though highest populations typically occurred in the upper a nd middle portions of the Anclote estuary and Charlotte Harbor (Hopkins, 1966; We iss, 1974; Hopkins, 1977; Squires, 1984). Highest abundances in estuaries occurred in the winter and spring (Hopkins, 1966; Weiss, 1974; Hopkins, 1977; Squires, 1984). King (1950) reported finding E. acutifrons out to the 40meter isobath. In this study, highest populations occurred in winter and in summer at the 5-meter isobath (Figure 15). E. acutifrons occurred only oc casionally at the 25-meter isobath. Salinity and chlorophyll a concentration did not a ffect the distribution of E. acutifrons however there did appear to be some correlation with temperature, with maximum populations occurring at temperatures greater than 24oC (Figure 23). Not surprisingly, Pelecypod larvae and Gastropod larvae contributed to community composition across a range of subgr oups, since each of these taxa represent larval forms of multiple species. Pelec ypod larvae contributed significantly only to subgroups A, B, and C, though it was present at all isobaths for at least one sampling period (Figure 24, Tables 3-5). Gastropod la rvae contributed signi ficantly to abundance and community composition at all subgroups (Figure 24, Tables 37). Minello found that intermediate depths (28to 46-meters) had higher numbers of Gastropod larvae than near shore or offshore depths.

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72 Figure 22 Distribution of P. quasimodo in relation to a) salinity, b) temperature, and c) chlorophyll a concentration.

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73 Figure 23. Distribution of E. acutifrons in relation to a) salin ity, b) temperature, and c) chlorophyll a concentration.

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74 Figure 24. Abundance distribut ion of selected WFS zoopl ankton taxa. 5-m (solid bars), 25-m (hatched bars ), and 50-m (dotted bars). 0 150 300 ASONDJFMAMJJ 0 100 200 300 400 500 ASONDJFMAMJJ 0 200 400 600 800 ASONDJFMAMJJ 0 500 1000 1500 ASONDJFMAMJJ 0 1000 2000 ASONDJFMAMJJ 0 200 400 600 ASONDJFMAMJJ 0 400 800 ASONDJFMAMJJ 0 500 1000 1500 ASONDJFMAMJJ Pelecypod larvae Gastropod larvae C. amazonicus O. dioika E. chierchiae C. velificatus O. mediteranea O. plumifera Abundance (m-3)Month Month

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75 There was no correlation with sali nity, temperature, or chlorophyll a concentration with pelecypod or Gastropod larvae in the Minello (1980) study, nor in this study (Figures 25 and 26). This is most likely do to the fact th at each larval taxa represents many species, all of whom have different exogenou s factors that induce spawning. Subgroup B only One species, Corycaeus amazonicus contributed only to subgroup B but not to subgroups A, C, D or E. C. amazonicus is a common contributor to zooplankton assemblages in higher salinity regions of WFS estuaries in late spring and summer (Hopkins, 1966; Weiss, 1974; Squires, 1984). Minello (1980) reported highest populations in September, with minor peaks in spring. On the WFS, C. amazonicus occurred most often at the 5-meter isobath, with highest numbers occurring in late summer/early fall (Figure 24). Minello ( 1980) found that surface temperature was the most important contributor to C. amazonicus distribution, with peak abundances occurring at temperatures higher than 26oC. In my study, peak abundances occurred at temperatures higher than 28oC (Figure 27). Although Mine llo (1980) did not find a strong correlation betwee n the distribution of C. amazonicus and salinity, there was some evidence from my study that maximum populatio ns occurred at inte rmediate salinities o35 to 36 (Figure 27). Of the above species that contributed to Subgroups A and B, salinity played a greater role in distribution th an it did in those species re presented in Subgroup A alone, indicating that the species in subgroup B become less euryhaline as distance offshore increases. Temperature still proved to be an important contributing factor to distribution. Chlorophyll a concentration was important only in the distribution of P. quasimodo

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76 Figure 25. Distribution of Pel ecypod larvae in relation to a) salinity, b) temperature, and c) chlorophyll a concentration.

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77 Figure 26. Distribution of Gast ropod larvae in relation to a) salinity, b) temperature, and c) chlorophyll a concentration.

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78 Figure 27. Distribution of C. amazonicus in relation to a) sali nity, b) temperature, and c) chlorophyll a concentration.

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79 Subgroups B, C, D and E Six taxa, O. dioica Gastropod larvae, O. mediteranea C. velificatus O. plumifera and E. chierchiae contributed significantly to community composition in subgroups B, C and D. Five of these taxa, O. dioica Gastropod larvae, O. mediteranea O. plumifera and E. chierchiae also contributed to subgroup E. O. dioica, a temperate tropical euryhaline species often reported at the heads and mouths of estuaries, is the most abundant a ppendicularian in coasta l areas and estuaries of the NWFS and WFS, and can reach populations of thousands m-3 (Hopkins 1966; Weiss, 1977; Hopkins, 1977; Minello, 1980; S quires, 1984; Dagg, 1995). In this study O. dioica was found in greatest abunda nce at the 5-meter isobath, but was also frequently present at the 25and 50-meter isobaths (Figure 24). Salinity appeared to be the greatest determining factor in expl aining the distribution of O. dioica in my study, with highest populations occurring at lower salin ities of 34.0 to 35.0 (Figure 28). Sutton et al. (2001) noted that the importance of the pelagic ostracod E. chierchiae to the WFS ecosystem has been overlooked in the past, and ranked it as second in abundance at the 40-meter isobat h, but absent shoreward of the 25-meter isobath. Minello reported populations that were a full order of magnitude lower than that reported here (Figure 24), with peaks in winter and spring. In this study, E. chierchiae never occurred shoreward of the 25-meter isobath, though Hopkins (1966) reported its presence in the high salinity regions of th e St. Andrew’s Bay system. Minello (1980) reported a peak in September in some years, an observation confir med by Sutton et al. (2001), also working in Sept ember. A small peak of E. chierchiae in September was observed in this study at the 50-meter isobath, but highest ab undances occurred in winter months at the 25and 50-m eter isobaths (Figure 24).

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80 Figure 28. Distribution of O. dioica in relation to a) salinit y, b) temperature, and c) chlorophyll a concentration.

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81 Using regression models, Minello (1980) determined that the greatest factor contributing to E. chierchiae distribution was salinity. Th ese findings were confirmed by my study, where maximum abundance of E. chierchiae occurred betwee n salinities of 3536.5 (Figure 29). Low chlorophyll a concentration also appeared to be a factor in E. chierchiae distribution, with peak nu mbers occurring at chlorophyll a concentrations of .50 g l-1 or less. Like P. quasimodo, C. velificatus shows abundance peaks at the mouths of WFS estuaries, and is often absent from lower salinity areas at the heads of estuaries (Squires, 1984; Weiss, 1977; Hopkins, 1977; Hopkins, 1966). C. velificatus was reported to be less abundant at offshore isobaths by Minello (1980) where it was most abundant at the 8-meter isobath. C. velificatus was a frequent contributor at the 5 and 25-meter isobaths in my study, with peak numbers occurring at the 5-meter isobath in early summer and at the 25-meter isobath in October and November (Figure 24). Minello found that abundance of C. velificatus decreased with increasing temperature. In this st udy, maximum populations of C. velificatus occurred between 24 and 28oC (Figure 30). Neither salinity nor chlorophyll a concentration appeared to play a role in the distribution of C. velificatus Ortner (1989) found O. mediteranea and O. plumifera most abundant in transition waters of the Mississippi River ou tflow. Minello (1980) reported O. mediteranea only rarely shoreward of the 14-meter isobath. Sutton et al. (2001) found members of the genus Oncaea (presumably O. mediteranea ) present in high numbers at the 40-meter isobath in September. Minello (1980) reported peaks of O. mediteranea in April and early summer. I n this study, O. mediteranea was found as far offshore as 50-meter

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82 Figure 29. Distribution of E. chierchiae in relation to a) salin ity, b) temperature, and c) chlorophyll a concentration.

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83 Figure 30. Distribution of C. velificatus in relation to a) salin ity, b) temperature, and c) chlorophyll a concentration.

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84 isobath (Figure 24), with peak abundances obs erved at the 50-meter isobath in September and at the 25-meter isobath in winter. A significant correlation w ith salinity was found in my study, with high numbers of O. mediteranea occurring at salinities between 36 and 36.5 (Figure 31). Minello (1980) reported similar findings with peak populations occurring be tween salinities of 35 and 37. No correlation was f ound between the occurrence of O. mediteranea and temperature, though there was some indication that lower chlorophyll a concentrations were correlated with higher populations. O. plumifera was mostly absent at the 5-meter isobath and was most abundant at the 25-meter isobath (Figure 24). High numbers of O. plumifera were occasionally found at the 50-meter isobath. Minello (1980) reported O. plumifera only occasionally shoreward of the 28-meter isobath. Minello (1980) reported that abundance of O. plumifera was highest at salinities higher than 35 and surface temper atures of greater than 21oC. In this study, O. plumifera occurred only between salinities of 35 to 37 (Figure 32). Temperat ures that resulted in the highest numbers ranged from 24 to 30oC, though low populations al so occurred at these temperatures There was also so me indication that low chlorophyll a concentration was correlated with O. plumifera distribution, since highest numbers occurred at concentrations of less than .5 g l-1. Clausocalanus furcatus was found in Subgroups C and E (Figure 33). In the St. Andrews Bay system, this species was present in July and October at higher salinity stations (Hopkins, 1966) Minello (1980) found C. furcatus abundant at th e 28-, 46and 73-meter stations. Mean densit ies in that study were greates t in July at the deepest b

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85 Figure 31. Distribution of O. mediteranea in relation to a) salinity, b) temperature, and c) chlorophyll a concentration.

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86 Figure 32. Distribution of O. plumifera in relation to a) salin ity, b) temperature, and c) chlorophyll a concentration.

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87 Figure 33. Abundance distribut ion of selected WFS zoopl ankton taxa. 5-m (solid bars), 25-m (hatched bars ), and 50-m (dotted bars). 0 50 100 150 ASONDJFMAMJJ 0 250 500 ASONDJFMAMJJ 0 50 100 ASONDJFMAMJJ 0 50 100 ASONDJFMAMJJ 0 150 300 ASONDJFMAMJJ C. furcatus C. pavo O. frigida C. limbatus Abundance (m-3) 0 50 100 150 ASONDJFMAMJJ O. similis C. pavoninius 0 150 300 ASONDJFMAMJJ P. aculeatus 0 150 300 ASONDJFMAMJJ P. pygmaeus Month Month

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88 stations, with C. furcatus only occasionally occurring at the 8and 14-meter isobaths. In my study, C. furcatus was found consistently at the 25and 50meter isobaths, with highest populations occurring in December and January (Figure 33). Minello (1980) reported that a number of f actors contributed to the distribution of C. furcatus with salinity being most im portant. Peak abundances of C. furcatus in the Minello (1980) study occurred at salinities greater than 35 a nd temperatures from 20 to 30oC. Highest populations in my study o ccurred between salinities of 35 and 37, temperatures from 24 to 30oC, and chlorophyll a concentrations of .5 gl-1 or less (Figure 34). Subgroup C Only C. pavo is widely distributed in te mperate and tropical waters where the populations occur mostly in th e upper levels (Owre and Foyo, 1967). Jones (1952) reported it throughout the year but in widely varying abundances. King (1950) reported the presence of C. pavo from 10 to 100 fathoms as well as inshore of the 10 fathom mark. In my study, C. pavo occurred at the 25and 50-meter isobaths, with highest populations occurring in late summer an d fall at the 50-meter isobath (Figure 33). Little correlation was seen between the distribution of C. pavo and salinity, temperature or chlorophyll a concentration. Peak abunda nces tended to occur at intermediate salinities, but the copepod was also present at higher sali nities (Figure 35). This may explain the wide distribution of this species (Owre and Foyo, 1967). Overall, salinity was a greater factor in describing species distribution in subgroups B and C than in A, indicating that these species may not be as euryhaline and are more limited in spatial dist ribution by salinity Chlorophyll a concentration appeared to be a greater factor in Subgroups B and C than in A.

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89 Figure 34. Distribution of C. furcatus in relation to a) salinity, b) temperature, and c) chlorophyll a concentration.

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90 Figure 35. Distribution of C. pavo in relation to a) salinit y, b) temperature, and c) chlorophyll a concentration.

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91 Subgroup D only O. frigida (Figure 33) was found only at the 50-meter isobath from late fall though early spring. Owre and Foyo (1964) reported this species in the Florida Current, but little is known of its distribution in the Gulf of Mexico. Distribution of O. frigida appeared to be correlated with high salinity and low chlorophyll a concentrations (Figure 36). P. pygmaeus (Figure 33) in this study was found at the 50-m eter isobath only, with highest populations occurring in December. Distribution of P. pygmaeus was associated with high salinity and low chlorophyll a concentrations (Figure 37). P. aculeatus was reported by Minello (1980) from June through December at the 28and 46-meter stations. Davis (1950) reporte d it from a sample taken 60 miles west of Anclote light. Grice (1960) found it at stations off Pensaco la and Panama city. This study found P. aculeatus only at the 25and 50-meter isoba ths, with highest populations found at the 50-meter isobath in January (F igure 33). Bowman (1971) reported that P. aculeatus was a common constituent of oceanic a ssociations, but was also tolerant of shelf waters. Both temperature and salinity were important in the distribution of P. aculeatus Minello (1980) found highest numbers at sali nities greater than 30 and temperatures between 20 and 25oC. In my study, P. aculeatus rarely occurred at salinities less than 35.5. Peak abundances were found at salinities ranging from 35.5 to 36.6 and temperatures lower than 24oC (Figure 38). A correlation between P. aculeatus and chlorophyll a concentration was not observed. C. limbatus (Figure 33) was found mostly at the 50-meter isobath in late fall through December. Owre and Foyo (1967) repor ted the presence of this copepod at the

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92 Figure 36. Distribution of O. frigida in relation to a) salinity, b) temperature, and c) chlorophyll a concentration.

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93 Figure 37. Distribution of P pygmaeus in relation to a) salin ity, b) temperature, and c) chlorophyll a concentration.

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94 Figure 38. Distribution of P aculeatus in relation to a) salinit y, b) temperature, and c) chlorophyll a concentration.

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95 40 mile station in the Florida Current. Litt le is known about the distribution of this species elsewhere in the Gulf of Mexico, which may be due to the fact that most taxonomists do not attempt to identify Corycaeus to species level due to difficulty in identification. There appeared to be an association between distribution of C. limbatus and high salinity and low chlorophyll a concentrations (Figure 39), though there appeared to be little association between distribution of C. limbatus and temperature. This association should be interp reted with caution however, due to the low number of samples containing this species. Subgroup E only C. pavoninius (Figure 40) was found in this study at the 50 – meter isobath only. A peak in abundance occurred in December, but minor peaks were observed in spring and early summer. Dist ribution was associated with high (36.0 to 36.5) salinities and temperatures of 22-23oC. O. similis (Figure 33) was found in greatest conc entration in July at the 50-meter isobath. No strong correlation was indicated with salinity, temperature or chlorophyll a concentration. However, the low number of samples of this species make analysis of contributing factors di fficult. (Figure 41). The preference for and tolerance of environmental factors differs between zooplankton species. Organisms can be classi fied by the extent to which they may be widely or narrowly tolerant of such fact ors as salinity, temp erature and chlorophyll a concentration (Omori and Ikeda, 1992). On the WFS, such differences in distribution based on environmental factors is evident. The two major groups seen in community composition (Figure 9) show a clear di sassociation with onshore and offshore environmental factors. Park and Turk (1980) found similar results working on the

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96 Figure 39. Distribution of C. limbatus in relation to a) salinity, b) temperature, and c) chlorophyll a concentration.

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97 Figure 40. Distribution of C. pavoninius in relation to a) salin ity, b) temperature, and c) chlorophyll a concentration.

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98 Figure 41. Distribution of O. similis in relation to a) salinity, b) temperature, and c) chlorophyll a concentration.

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99 NWFS, as did Minello (1980). Bowman ( 1971) reported a marked inshore-offshore zonation working off the west coast of Florid a. Sutton (2001) repor ted that zonation was the most prominent feature of the zooplankton community, and observed a tight correlation with physical oceanographic factor s. In that study, offshore areas were dominated by Oncaea and Ostracods, while inshore areas were dominated by O. dioica Corycaeus Oithona Temora and Paracalanus Upon closer examination of subgroups within these two onshore/offshore groupings, it becomes apparent that across the shelf there is significant overlap between bordering subgroups, but little overlap between near s hore subgroup A and offshore subgroup E. A range of environmental factor s were associated with distribution, with temperature being the most important factor a ssociated with distribut ion near shore. As distance offshore increased, salinity and chlorophyll a concentration became increasingly important factors. CONCLUSIONS Abundance, biomass and community composition of zooplankton on the WFS compares well to other studies performe d on the Florida shelf. The community composition found in this study mirrors that found by Minello (1980) on the NWFS. Since Minello’s (1980) study encompassed 5 ye ars of sampling, the data found here can reasonably be assumed to refl ect the zooplankton assemblage of the WFS for years other than this sampling period.

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100 At the 5-meter isobath, the copepods O. colcarva and P. crassirostris were the most important contributors to abundance and community composition. Other important and intermittent contributors to abundance and community composition at the 5-meter isobath were P. avirostris and P. quasimodo At the 25-meter isobath for much of the year the zooplankton assemblage was dominated by P. quasimodo O. colcarva and the larvacean O. dioica In the winter and spring, E. chierchiae and C. furcatus were dominant. At the 50-meter isobath, fall, winter and early spring as semblages were dominated by E. chierchiae O. frigida C. furcatus and O. mediteranea In the late spring, the assemblage was dominated by C. furcatus C. pavoninius O. similis and Gastropod larvae. The importance of E. chierchiae to the WFS ecosystem is clearly more important than previously realized (Sutton, 2001) The ostracod dominated the zooplankton assemblage at the 25 and 50-meter isobaths fo r much of the year. Little is known about the ecology of E. chierchiae yet it’s prevalence on the WFS suggests that further study is warranted. The 5 subgroups in community composition were tightly coupled with temperature, salinity and chlorophyll a concentration. A range of environmental factors defined distribution, with temperature be ing the most important factor defining distribution near shore. As distance offshore increased, salinity and chlorophyll a concentration became increasingly importa nt as factors defining distribution. The shade matrix developed for the 25 species that contributed to 90% of community composition supports the assertion that many species occu r across a range of

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101 subgroups (Figure 7). Considerable overl ap is observed for subgroups A and B, Subgroups B, C and D, and Subgroups C, D and E. However, no overlap is observed for near shore subgroup A and offshore subgroup E. Range in chlorophyll a concentration, temperature, and salinity decreased as distance offshore increased. Chlorophyll a was found to be the most important in relati on to zooplankton community composition. ACKNOWLEDGEMENTS Funding was provided by ECOHAB Florida (NOAA/ECOHAB NA96P00084 and USEPA/ECOHAB CR826792-01-0) Office of Naval Research (N000149615024 and N000149910212), the National Science Foundation (NSF OCE 0095970), and the Florida Fish and Wildlife Conservation Commissi on. Additional funding was provided by the USF College of Marine Science Murtagh Fell owship. Thanks to Dr. Norm Blake and Noland Elsaesser, who identified the pelecypod larvae found in the October 2001 samples as A. gibbus Thanks is also extended to the Florida Institu te of Oceanography, and the crew and scientific staff of the R/ V Suncoaster and R/V Bellows, and to Cynthia Heil, Danielle Ault, M.B. Neely and Rachel Merkt, who assisted with the sampling.

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102 REFERENCES Austin, H. M. (1971). The characteristics and relationships between the calculated geostrophic current component and selected indicator organisms in the Gulf of Mexico Loop Current System. Doctoral dissertation, Florida State University, Tallahasee, FL, pp. 369. Austin, H. M. and J. I. Jones, (1974). “Seasonal variation of physical oceanographic parameters on the Florida Middle Gr ound and their relation to zooplankton biomass on the West Florida Shelf.” Florida Scientist 37, 16-32. Calbet, A., S. Garrido, et al. (2001). “Annual zooplankton succession in Coastal NW Mediterranean Waters: The importa nce of small size fractions.” Journal of Plankton Research 23 319-331. Clarke, K.R. and R. M. Warwick (1994). Change in Marine Communities: An approach to statistical analysis and interpretation Plymouth, Bourne Press Ltd., pp. 144. Dagg, M. J. (1995). “Copepod grazing and the fa te of phytoplankton in the Northern Gulf of Mexico.” Continental Shelf Research 15 1303-1317. Davis, C.C. (1950). “Observations of plankton taken in marine waters of Florida in 1947 and 1948.” Quarterly Journal of Florida Academic Sciences 12 67-103 Gilbes, F. (2000). “New evidence for the West Florida Shelf plume.” Continental Shelf Research 22 2479-2496. Gilbes, F., C. Tomas, et al. (1996). “An ep isodic chlorophyll plume on the West Florida Shelf.” Continental shelf research 16 1201-1224. Grice, G.D. (1956). “A qualitative and qua ntitative seasonal study of the copepoda of Alligator Harbor.” Studies of Florida University 22 37-76. Grice, G.D. (1960). “Calanoi d and cyclopoid copepods collec ted from the Florida Gulf Coast and Florida Keys in 1954 and 1955.” Bulletin of Marine Science of the Gulf of the Caribbean 10 217-226. Hopkins, T. L. (1966). "The plankton of the St. Andrew Bay system, Florida." Public Institute of Marine Scien ce, University of Texas 11 12-64. Hopkins, T.L. (1977). “Zooplankton distri bution in surface waters of Tampa Bay, Florida.” Bulletin of Marine Science 27 467-478. Hopkins, T.L. (1982). “The vert ical distribution of zooplankt on in the eastern Gulf of Mexico.” Deep Sea Research 29 1069-1083.

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103 Hopkins, T.L. and T. M. Lancraft (1984). “The composition and standing stock of mesopelagic micronekton at 27oN 86oW in the Eastern Gulf of Mexico.” Contributions to Marine Science 27 ,145-158. Hopkins, T.L., D. M. Milliken, et al. ( 1981). “The landward dist ribution of oceanic plankton and micronekton over the west Flor ida continental shelf as related to their vertical distribution.” Journal of Plankton Research 3 645-658. Jones, E.C. (1952). A preliminary survey of the copepods of the Florida Current. Masters Thesis, University of Miami, Coral Gables, FL. 76 pp. Kleppel, G.S., C. A. Burkar t, et al. (1996). “Diets of calanoid copepods on the West Florida continental shelf: relations hips between food concentration, food composition and feeding activity.” Marine Biology 127 209-217. King, J.E. (1950). “A preliminary report on th e plankton of the West coast of Florida.” Journal of Florida Academy of Sciences 12 109-137. Kiorboe, T. (1993). “Turbulence, phytoplankton cell size, and the structure of pelagic food webs.” Advances in Marine Biology 29 1-72. Minello, T. (1980). Neritic zooplankton of the No rthwestern Gulf of Mexico. Doctoral dissertation, Texas A& M, Galveston, pp. 240. Morris, M.J. and T. L. Hopkins (1983). “Biochemical composition of crustacean zooplankton from the eastern Gulf of Mexico.” Journal of Experi mental Marine Biology and Ecology 69 1-19. Ortner, P.B., L. C. Hill, et al. (1989). “Zooplankton community structure and copepod species composition in the nor thern Gulf of Mexico.” Continental Shelf Research 9 387-402. Omori, M. and T. Ikeda (1992). Methods in Marine Zooplankton Ecology, pp. 332: Krieger Publishing Company. Owre, H. B., and M. Foyo (1967). “Copepods of the Florida Current.” Fauna Caribaea I 1-137. Paffenhoffer, G.A., B. T. West er, et al. (1994). “Zooplankt on abundance in relation to state and type of intrusions onto the southeastern United States shelf during summer.” Journal of Marine Research 42 995-1017. Park, E.T. and P. Turk (1980). Zooplankton Project in R.W. Flint N. Rabalais, eds. Environmental Studies, South Texas Oute r Continental Shelf, 1975-1977. Vol III. Study Element Reports. Report Bur. Land. Mgt., Contract AA551-CT-51.

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104 Squires, A.P. (1984). The distribution and eco logy of zooplankton in Charlotte Harbor, Florida. Masters thesis, Department of Marine Science, University of South Florida, St. Petersburg, pp. 60. Sterner, R.E. (1989). The role of grazers in phytoplankton succession. In: Plankton Ecology: Succession in Phytoplankton communities Sommer,U. (Ed.) pp. 107170. Sutton, T., T. Hopkins, et al. (2001). “Mu ltisensor sampling of pelagic ecosystem variables in a coastal environment to estimate zooplankton grazing impact.” Continental Shelf Research 21 69-87. Vargo, G.A., K. L. Carder, et al. (1987) “The potential contribution of primary production by red tides to the we st Florida shelf ecosystem.” Limnology and Oceanography 32 762-767. Weiss, W.R. (1978). The zoopla nkton of the Anclote Estuary, Florida. Masters thesis. Department of Marine Science, Universi ty of South Florida, St. Petersburg, pp. 122. Welschmeyer, N.A. (1994). “Fluorometric analysis of chlorophyll a in the presence of chlorophyll b and phaeopigments.” Limnology and Oceanography 39 1985-1992.

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105 CHAPTER 3 ZOOPLANKTON AND KARENIA BREVI S IN THE GULF OF MEXICO Abstract Blooms of the toxic dinoflagellate K. brevis are common in the Gulf of Mexico, yet no in situ studies of zooplankton and K. brevis interactions have been conducted. Zooplankton abundance, biomass and taxonomic composition of non-bloom and K. brevis bloom stations within the ECOHAB st udy area were thus compared. At nonbloom stations, the most abundant species of zooplankton were Parvocalanus crassirostris Oithona colcarva and Paracalanus quasimodo at the 5-m isobath and P. quasimodo O. colcarva and Oikopleura dioica at the 25-m isobath. There was considerable overlap in dominance of z ooplankton species between the 5 and 25-m isobaths, with 9 species contributing to th e top 90% of abundance at both isobaths. Within K. brevis blooms however, Acartia tonsa Centropages velificatus Temora turbinata Evadne tergestina O. colcarva O. dioica and P. crassirostris were instead dominant. Variations in abundance and biomass between non-bloom and bloom assemblages were evident, including the reduc tion in abundance of 3 key species within K. brevis blooms.

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106 INTRODUCTION Blooms of the toxic dinoflagellate K. brevis (previously Gymnodinium breve Davis) frequently cause massive fish kills on the West Florida Shelf (WFS), with blooms reported by early Spanish explorers as far b ack as the 1500's (Steid inger et al., 1998). Previous research has iden tified possible links between K. brevis growth rates and nutrients, light levels, Trichodesmium spp. blooms, dinoflagellate life cycles, and hydrography of the Gulf of Mexico (Steidinge r et al., 1998 and refere nces cited therein; Lenes et al., 2001; Walsh and Steidinger, 2001; Walsh et al ., 2002; Walsh et al., 2003; Heil et al., 2003; Vargo et al ., 2003; Lester et al., 2003). To date, no studies have examined the qualitative and quantitative relationship between K. brevis and zooplankton in the Gulf of Mexico. Studies of interactions between K. brevis and zooplankters invariably indicate that co-occurrence with and ingestion of K. brevis are associated with so me physiological cost (i.e. reduced grazing, regurgitation, paralysis, twitching, and reduced fecundity), and that zooplankton will avoid ingesting it whenever alternative food sources are present (Huntley et al., 1986; Huntley et al., 1987; Sykes and Huntley, 1987; Turner and Tester, 1989). However, many zooplankton species pr esent in the Gulf of Mexico ingest K. brevis (Galstoff, 1948; Dragovich and Kelly, 1964; Rounsefe ll and Nelson, 1966; Martin et al., 1973; Turner and Tester 1989; Tester et al., 2000). Th ese arguments lead to the question: what effect does the presence of K. brevis have on the subsequent distribution of co-occurring zooplankton?

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107 The first task of this study, comprehensively de fining the non-bloom WFS zooplankton assemblage, proved to be very difficult with the available information. Despite its high productivity and importance to the Gulf of Mexico (Austin and Jones, 1974), there is a paucity of zooplankton assemblage data for the ECOHAB study area. King (1950) described zooplankton species found from January through October 1949, but did not report quantities or seasonal data. Hopkins et al. (1981) examined the landward distribution of crustacean species of zooplankton from the 15 to the 3000 m isobath in the summer only. A more recent study (Sutton et al., 2001) focused on spatial changes in taxonomic composition within th e northern portion of the ECOHAB study area, but was limited to a single transect, with identifications made to genera only. Far more is known about the areas th at border the study area. Taxonomic seasonal analysis of abundance and biom ass have been conducted for Tampa Bay (Hopkins, 1977), the Anclote estuary (Weiss, 1974), Charlotte Harbor (Squires, 1977), Alligator Harbor (Grice, 1956), and the St. Andrew Bay system (Hopkins, 1966). Seasonal changes in taxonomic composition in offshore areas of the WFS are less known due to logistical constraint s, though several studies have been conducted (Hopkins, 1973; Morris and Hopkins, 1981; Hopkins and La ncraft, 1984). Some overlap between estuarine, shelf and offshore zooplankton asse mblages is expected due to intrusions of central Gulf water across th e Florida shelf (Ortner et al ., 1989; Hopkins, 1981), but all data acquired to date indicate that the zoopl ankton populations on the WFS are different than those found in estuaries and offshore (M inello, 1980; Hopkins, 198 1; Ortner et al., 1989; Sutton et al., 2001). Prior to identify ing potential interrelationships between the

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108 zooplankton assemblage and K. brevis blooms, taxonomic characterization of the zooplankton assemblage in the study area was necessary. METHODS Zooplankton sampling took place during m onthly ECOHAB cruises on board the R/V Suncoaster and the R/V Bellows in the Gu lf of Mexico (Figure 42). Stations were located approximately every 5 nautical mile s. A CTD profile was conducted at every station. At selected stations (usually every other station, but occasionally more frequently) water samples were co llected to determine chlorophyll a concentration and K. brevis cell counts. Zooplankton sampling began in August 1999 and continued through July 2000. Stations 1 and 51 were chosen to repres ent the zooplankton assemblage at the 5-m isobath, while Stations 5 and 46 represented the zooplankton assemblage at the 25-m isobath. Although most blooms occur inshore of the 25 m-isobath (Steidinger et al., 1998), the analysis of zooplankton community composition at that isobath was assessed to ensure that advected offshore populations were not responsible for any of observed changes in zooplankton community structure. In addition to the fixe d stations, during the first year of sampling zooplankton tows were also conducted at stations where K. brevis concentrations were found to be above a background concentration of 1,000 cells l-1. During the fall and winter of 2001, a K. brevis bloom occurred in the study area. In September and December 2001, zooplankton tows were conducted on ECOHAB

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109 47 48 49 50 70 71 72 73 74 75 76 77 78 79 80 8 1 8 2 83 -84.00-83.50-83.00-82.50-82.00-81.50 26.00 26.50 27.00 27.50 28.00 28.50 1 2 3 4 5 6 7 8 9 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 41 42 43 44 45 46 GULF OF MEXICO 51 40 10 LongitudeL a t i t u d e Tampa Sarasota Ft. Myers 47 48 49 50 70 71 72 73 74 75 76 77 78 79 80 8 1 8 2 83 -84.00-83.50-83.00-82.50-82.00-81.50 26.00 26.50 27.00 27.50 28.00 28.50 1 2 3 4 5 6 7 8 9 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 41 42 43 44 45 46 1 2 3 4 5 6 7 8 9 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 41 42 43 44 45 46 GULF OF MEXICO 51 40 10 LongitudeL a t i t u d e Tampa Sarasota Ft. Myers Figure 42. ECOHAB study area in the Gulf of Mexico. Station lo cations for ECOHAB cruises are indicated by a ( ). Stations where zoopla nkton tows were conducted are indicated by a circle. 4 40 10

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110 -84-83.5-83-82.5-82-81.5Longitude 26 26.5 27 27.5 28 28.5L a titude 6 10 16 21 1(NSF Station 5) 5 32 46 51 70 72 73 74 75 80 Figure 43. Station locati ons for ECOHAB cruises ( ) and NSF cruises (+). Stations where zooplankton tows were conducted are circled and indicated by a number. NSF Station 5 is in the same loca tion as ECOHAB Station 1. Tampa Sarasota Ft. Myers

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111 cruises at stations within th e bloom, while in October, th e zooplankton tows within the bloom were taken to the north of th e ECOHAB study area (Figure 43). Collection of Zooplankton 1999-2000 Zooplankton were collected with a 153 m mesh bongo net, lowered closed through the water column, opened at depth and then towed obliquely from bottom to surface. The volume of water filtered wa s calculated with a calibrated flow meter attached at the net mouth (Omori and Ikeda, 1992). The cod ends were filtered through a 2000 m mesh sieve to remove macrozooplankton and large gelatinous z ooplankton. Each filt ered cod end was preserved on board in a 5% buffered formalin solution (Omori and Ikeda, 1992) for later counts of zooplankton species abundance. 2001 Collection of zooplankton in 2001 was accomplished in an identical manner, except that a single 153 m mesh net was used instead of a bongo net, because statistical analysis conducted in 1999-2000 had shown th at a single tow could adequately sample the zooplankton population. Zooplankton abundance and biomass Representative subsamples of 500-600 animals were obtained with a Stempel pipette (usually 1-5% of in itial cod end volume). Zoopla nkton were identified and counted using an Olympus di ssecting microscope. Holopl ankton were identified to species level. Meroplankton were identif ied to major taxonomic group (e.g. Pelecypod veligers, Cirriped larvae). Copepod nauplii were not identifie d to species level but, when

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112 possible, were identified to family level. Replicate samples were averaged for each station. Biomass was determined using pub lished length/width data (Table 12). Chlorophyll a concentration and K. brevis cell counts Zooplankton tows were conducted in conjunction with CTD casts, measurements of chlorophyll a and K. brevis cell counts. Water column samples were collected from Niskin bottles of a rosette sampler. Dupli cate chlorophyll samples were filtered on GF/F filters, placed in 10 ml methanol and stored at -20oC in darkness for later analysis with a Turner design fluorometer (Welschmeyer, 1994). K. brevis was counted live using a dissecting microscope within two hours of collection. Typi cally 5 0.2 ml subsamples were counted in duplicate well s lides. Final abundan ce is expressed as the average of all values. Statistical Analysis Observed community associations were quantified using the multivariate statistical techniques of PRIMER (Plymouth Routines in Multivariate Ecological Research) software. Hierarchal clustering analysis was used to identify trends in community distribution of the zooplankton asse mblage. Bray-Curtis similarities (Clarke and Warwick, 1994) were calculated and subseque ntly ranked within a similarity matrix. Data were not standardized, since all sta tions were already on the same scale of abundance m-3. However a square root transf ormation was performed to minimize variations in abundance (C larke and Warwick, 1994).

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113 Table 12 Sources of biomass values and length/width regression equations for WFS zooplankton taxa. Taxon Source Comments Undinula Morris and Hopkins, 1983 Eucalanus Morris and Hopkins, 1983 Acrocalanus Weiss, 1978 Derived from Paracalanus Calocalanus Paracalanus Clausocalanus Derived from Centropages Scolothrex Morris and Hopkins, 1983 Euchaeta Morris and Hopkins, 1983 Temora Lester, unpub. data Centropages Weiss, 1978 Calanopia Pseudodiaptomas Acartia Tortanus Labidocera Oithona Oncaeae Squires, 1984 Corycaeus Weiss, 1978 Farranula Euterpina Microsetaella Euchonchoichiea Hopkins, 1984 Penilia Weiss, 1978 Evadne Podon E. tergestina value Appendicularians Brachiopoda Bryozoa Cirripedia Decapoda Echinodermata Gastropoda Pelecypoda Platyhelminthe Squires, 1984 Polychaeta Weiss, 1978

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114 Similarity percentages within and between groups of zooplankton were determined using PRIMER’s SIMPER routine, which calculates the average dissimilarity between inter-group samples and comput es dissimilarities between groups. RESULTS WFS Zooplankton Assemblage – 1999-2000 Abundance and Biomass Abundance ranged from 185 animals m-3 (at Station 46 in June 2000) to 22 x 103 animals m-3 (at Station 1 in September 1999) (Table 13). Depth-averaged abundance was al ways greatest at the 5-meter isobath, where it peaked in late summer and early fall, increased again in December, and was at its lowest in early spring (Figure 44). At the 25-m isobath, a bundance peaked in October and November, decreased through April, and increased slightly through the summer. Biomass ranged from 0.91 mg m-3 (at Station 46 in June 2000) to 62.12 mg m-3 dry weight (at Station 1 in December) (Table 13). Depth-averaged biomass at the 5-m isobath showed the same trends as abundance, with highest biomass occurring in August, September, and December, decreasing through the spring, and increasing again through the summer (Figure 45). At the 25-m is obath, biomass was highest in November, remained high through January, declined in the spring and increased through the summer and fall. Statistical Analysis and Community Composition Hierarchal cluster analysis showed two major groups of community compos ition at the 30% similarity level. All 5m isobath stations were included in WFS 1, a nd all 25-m isobath sta tions were included

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115 Table 13 Numerical abundance and biomass for non-red tide 5-m and 25-m isobath stations sampled on the WFS in 1999 and 2000. 5-m isobath 25-m isobath Month Station Abund. (m-3) Biomass (mg m-3) Station Abund. (m-3) Biomass (mg m-3) August 1 18995 44.47 5 --1999 51 11469 37.40 46 1105 3.79 September 1 22135 53.81 5 845 5.92 1999 51 10547 26.91 46 1501 8.63 October 1 9020 18.34 5 3013 7.91 1999 51 6613 16.62 46 --November 1 --5 2628 15.31 1999 51 2886 14.04 46 3154 15.93 December 1 20021 62.12 5 1494 10.39 1999 51 4425 10.48 46 2502 14.19 January 1 6312 20.16 5 703 12.07 2000 51 2121 3.59 46 1501 9.67 March 1 2463 6.14 5 503 2.96 2000 51 1311 7.06 46 424 2.24 April 1 1099 12.25 5 224 2.44 2000 51 4446 3.76 46 194 1.42 May 1 1389 4.27 5 301 3.38 2000 51 4499 10.79 46 292 1.57 June 1 10452 45.24 5 1015 7.04 2000 51 6031 20.88 46 185 0.91 July 1 5472 22.95 5 721 3.81 2000

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116 Figure 44. a) Total zooplankton abundance m-3 for the 5-m (hatched bars) and 25-m (solid bars) isobath. b) Total zoopla nkton biomass in dryweight mg–3 for the 5-m (hatched bars) and 25-m (solid bars) isobath. 0 5 10 15 20 25 30 35 40 45ASONDJFMAMJJBiomass (mg m-3) 0 2 4 6 8 10 12 14 16 18ASONDJFMAMJJNumerical Abundance (x 103) m-3

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117 51 JAN 51 APR 51 MAY 1 MAR 51 NOV 51 DEC 1 APR 51 MAR 1 MAY 1 JUL 51 JUN 1 JAN 1 DEC 51 SEP 1 JUN 1 SEP 51 AUG 1 AUG 46 MAY 46 JUN 5 JUN 5 JUL 5 JAN 5 MAR 46 MAR 46 APR 5 APR 5 MAY 46 JAN 5 DEC 46 DEC 5 OCT 5 NOV 46 NOV 46 SEP 5 SEP 46 AUG 20406080100 WFS 2 WFS 1 a b a b Figure 45. Cluster derived dendrogram for 37 stations at the 5 and 25-m isobaths, using group-averaged clustering from Bray-Curtis similarities on square root transformed abundance data.

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118 in WFS 2 (Figure 45). Groups WFS 1 and W FS 2 consisted of two seasonal subgroups each at the 40 and 50% simila rity levels, respectively. At both isobaths, 6 taxa were responsible for 60% of the community structure. At the 5-m isobath, P. crassirostris, O. colcarva, P. quasimodo, Cirriped larvae, Euterpina acutifrons and the cladoceran Penilia avirostris were dominant (Table 14). Less abundant at this isobath were C. velificatus, A. tonsa, Corycaeus americanus, O. dioica, and the larvae of Gastropods, Decapods and Pelecypods. At the 25-m isobath (Table 15), the most abundant zooplankton were P. quasimodo, O. colcarva, O. dioica, C. velificatus, Gastropod larvae and O. plumifera. Lesser contributors were P. crassirostris, Oncaea mediteranea, E. acutifrons, the ostracod Euchonchoichiea chierchiae, and the larvae of Pelecypods and Decapods. Of the 13 taxa that accounted for 90% of the abundance at the 5-m isobath, 9 contributed to 90% of total abundance at the 25-m isobath as well, indicating significant overlap in community structure. Four taxa, Cirriped larvae, A. tonsa, P. avirostris and C. americanus, were dominant at the 5-m isobath but not at the 25-m isobath. Similarly, 5 species, O. plumifera, O. mediteranea, E. chierchiae, C. amazonicus, and C. furcatus, contributed significantly to abunda nce at the 25-m isobath only. Variations in the amount contributed by P. crassirostris, O. colcarva, P. avirostris, E. acutifrons, P. quasimodo, A. tonsa and the larvae of Cirripeds, Pelecypods and Decapods accounted for 60% of the differences in community composition between the two isobaths (Table 16). The 5 species characteristic of 25-m isobath assemblages, O. plumifera, O. mediteranea, E. chierchiae, C. amazonicus, and C. furcatus, accounted for only 7.98% of the difference in commun ity composition between the two groups.

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119 Table 14 Results of SIMPER analysis show ing determinant species for WFS 1. Abundance data square root transformed, n=18. Av. Abund. Contrib. Cum. Taxon (m-3) ( %) ( %) P. crassirostris 1655.08 17.07 17.07 O. colcarva 1224.78 12.35 29.42 P. quasimodo 343.92 8.23 37.65 Cirriped larvae 477.53 7.74 45.39 E. acutifrons 355.67 6.87 52.26 P. avirostris 1105.17 6.77 59.03 Decapod larvae 201.53 5.67 64.70 Pelecypod larvae 271.31 4.97 69.67 C. americanus 108.06 4.35 74.02 C. velificatus 70.14 4.17 78.19 Gastropod larvae 106.39 4.16 82.36 O. dioica 176.31 4.08 86.44 A. tonsa 243.5 3.15 89.59

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120 Table 15 Results of SIMPER analysis show ing determinant species for WFS 2. Abundance data square root transformed, n=19. Av. Abund. Contrib. Cum. Taxon (m-3) ( %) ( %) P. quasimodo 123.05 12.22 12.22 O. colcarva 88.63 11.84 24.07 O. dioica 56.63 11.55 35.62 C. velificatus 82.55 8.20 43.82 Gastropod larvae 46.97 7.81 51.63 O. plumifera 19.87 7.57 59.20 Pelecypod larvae 63.97 6.71 65.91 O. mediteranea 53.24 4.61 70.52 P. crassirostris 29.13 4.60 75.12 E. acutifrons 32.97 3.72 78.84 E. chierchiae 84.55 3.29 82.13 Decapod larvae 7.63 2.81 84.94 C. amazonicus 19.87 2.54 87.48 C. furcatus 26.66 2.47 89.95

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121 Table 16 Results of SIMPER analysis showing aver age determinant dissimilarities between WFS 1 and WFS 2. Abundance data square root transformed, WFS 1 n = 18; WFS n=19. WFS 1 Av. Abund. WFS 2 Av. Abund. Av.Diss Cum. Taxon (m-3) (m-3) (%) P. crassirostris 1655.08 29.13 8.39 12.19 O. colcarva 1224.78 88.63 6.43 21.53 P. avirostris 1105.17 4.95 6.24 30.60 Cirriped larvae 477.53 2.13 4.66 37.36 E. acutifrons 355.67 32.97 3.69 42.72 Pelecypod larvae 271.31 63.97 3.19 47.35 P. quasimodo 343.92 123.05 3.05 51.78 Decapoda 201.53 7.63 2.77 55.80 A. tonsa 243.50 1.61 2.71 59.73 Oithona nana 141.50 0.74 2.52 63.39 C. americanus 108.06 15.26 2.48 66.99 T. turbinata 165.42 36.11 2.20 70.19 O. dioica 176.31 56.63 1.80 72.80 C. amazonicus 90.28 19.87 1.75 75.35 Gastropod larvae 106.39 46.97 1.71 77.83 Polychaete larvae 124.42 13.45 1.59 84.90 E. chierchiae 0.00 84.55 1.64 80.22 C. velificatus 70.14 82.55 1.63 82.58 O. mediteranea 0.00 53.24 1.52 87.11 O. plumifera 0.00 19.87 1.29 88.99 C. furcatus 2.14 26.66 1.05 90.52 Average dissimilarity 68.85

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122 Zooplankton Assemblage K. brevis Blooms Abundance and Biomass Zooplankton abundance and community composition at each station sampled during the 1999 and 2001 K brevis blooms are given in Tables 17 and 18. In October 1999, the highest abunda nce and biomass occurred at Station 80, where K. brevis exceeded 5 X106 cells l-1. In 2001, greatest abundance was found at Station 70 in December, when K. brevis was 1.7 X 105 cells l-1, and at Station 21 in October, with a K. brevis stock of 1 X 106 cells l-1. The lowest abundance in 2001 was 219 animals m-3 at Station 70 in September, at a K. brevis population of only 8 X 103 cells l-1. Maximum zooplankton abundance during the 2001 K. brevis bloom occurred in December at Station 70, when biomass exceeded 355 mg m-3, 5 times greater than the highest biomass at non-bloom stations in 1999-2000. Community Composition In October 1999, K. brevis populations were very low at Stations 1 and 51 where the typical near sh ore assemblage of zooplankton was present and the most important cont ributors to abundance were P. crassirostris and Cirriped larvae. At near shore Station 80, where surface K. brevis exceeded 5 million cells l-1, typical near shore zooplankton sp ecies were either absent or were significantly reduced in importance. A. tonsa, P. quasimodo, P. crassirostris, decapod larvae and pelecypod larvae were >80% less abundant at Station 80 than at Station 51. O. colcarva, O. dioica, and E. acutifrons, all present at Stations 1 and 51, were absent from the assemblage at Station 80.

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123 Table 17 Zooplankton community composition, numerical abundance and biomass at stations sampled within 1999 K. brevis bloom. October-99 K. brevis cells l-1 x 103 7.5 16 5270 Station 51 1 80 A. tonsa 11 245 4 C. amazonicus 39 98 -C. americana 56 --C. americanus 7 --C. velificatus 118 49 4569 E. pileatus --234 E. tergestina ---E. acutifrons 25 405 -E. crassus 57 --L. aestiva --112 L. scotti -25 55 O. nana 52 172 -O. colcarva 102 749 -O .dioica 150 --O. similis ---O. simplex -25 -P. avirostris -37 -P. crassirostris 5553 2884 516 P. quasimodo 206 37 25 T. setacaudatus 18 --T. stylifera ---T. turbinata 70 -2341 Cirriped larvae 4 2037 59 Decapod larvae 43 650 179 Echinoderm larvae 4 --Gastropod larvae 4 12 4 Pelecypod larvae 4 479 31 Polychaete larvae 14 123 -Total Num Abund. m-3 706912993542 Biomass (mg m-3) 24.503.1362.02

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124 Table 18 Zooplankton community composition, numerical abundance and biomass at stations sampled within 2001 K. brevis bloom. K. brevis cells l-1 x 103820050075151268742132010787741668176 Station 70727374756101621570321 A. tonsa 4218512029673--38503372144714516 C. amazonicus 8----212141--22556-----C. americana 734317------0-------C. americanus 12----50------112112481824 C. velificatus 2----4411--225112-----E. pileatus -------------------------E. tergestina 16310--83--11712275151610084462621 E.acutifrons 234--918--2324---------E. crassus -------------------------L.aestiva 41--13123--5056-----L.scotti -------------------------O. nana ----------------------480 O.colcarva 1256281263310813847306121--28924 O.dioka ----26391001471082772421962358 O.similis ----------------826-------O.simplex 19194560--------337-----P. avirostris 83181326----29198-------P. crassirostris --8324156271130681--8261994-----P. quasimodo --271936------752848182 T. setacaudatus 2----------23--75--2---T. stylifera 9-----------------------T. turbinata 2--03729---------------Cirripid larvae687--112342162161216143221721 Decapod larvae--5681--161641205905909618-Echinoderm larvae----------065841197197-----Gastropod larvae--------510117137140140-----Pelecypod larvae------832898366561616851685-----Polychaete larvae2481615121412255055051925410 Total Num Abund. m-321953132563533433881186665022158016480726545623369 Biomass (mg m-3)1.243.952.811.805.770.6417.1810.5938.6431.071.159.77355.40 October-01December-01 September-01

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125 Dominant zooplankton species in October were instead C. velificatus and T. turbinata. C. velificatus was 39 times more abundant at St ation 80 than at Station 51, and 93 times more abundant here than at Station 1. The majority of C. velificatus at Station 80 were Stage III and IV copepodites. T. turbinata was 14 times more abundant at Station 80 than at Station 51 and 98 times more abundant at Station 80 th an at Station 1. No copepodite stages of T. turbinata were observed. E. pileatus, absent at Stations 1 and 51, was a major contributor to biomass at Station 80. During the early stages of the 2001 bl oom in September, the zooplankton assemblage did not appear to diverge from a “normal” coastal assemblage on the WFS, except for lower abundance at most stations. At low K. brevis concentrations, P. crassirostris dominated at Station 75, P. avirostris at Station 72, and A. tonsa and E. acutifrons at Station 70. At Stations 72 and 73, where K. brevis concentrations were 2 X 105 and 5 X 105 cells l-1, respectively, A. tonsa was dominant. Other major contributors at stations 72 and 73 were Decapod larvae, P. crassirostris and O. dioica. As the bloom progressed through October, the zooplankton assemblage changed in both abundance and percent composition. Abundance was high at all stations except Station 6. The greatest departure from zooplankton pop ulations observed in 2001 occurred at stations 16, 10 and 21, when pelecypod larvae dominated the assemblage, in one case exceeding 8,000 larvae l-1 and comprising over 90% of the zooplankton assemblage. At Station 6 most near shore species were present, and Station 5 was characterized by very high concentrations of O. colcarva and Cirriped larvae. By December, a strong estuarine signal characterized the bloom (Vargo et al., in press), with

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126 the estuarine species A. tonsa and the cladoceran Evadne tergestina comprising the majority of the zooplankton assemblage. In October 2001, Pelecypod larvae dominated the assemblage, presumably those of the calico scallop, Argopecten gibbus. Due to the inherent difficulty in identifying early scallop larvae to species this identification should be interpreted with caution. By December, Pelecypod larvae were absent from the assemblage, and meroplankton contributed 3-5% of total abundance. Statistical analysis With the exception of Statio n 1 in October 1999, all of the K. brevis bloom stations fall outsi de the two groups in community composition formed by the non-bloom WFS 19992000 stations (Figure 46). Groups K1, K2 and K3 are different from the rest of the assemblages at the 20, 25 and 30% similarity le vels, respectively. Groups K4 and K5 are more closely associ ated with the WFS 1 assemblage, but are distinct from that assemblage at the 40 and 45% similarity levels, respectively. The results of the SIMPER analysis show ing the average abundance of important (>90%) species and their per cent contribution to community composition for groups K15 and WFS 1 are presented in Table 19. Group K1 was characterized by higher abundances of A. tonsa, E. tergestina and Polychaete larvae and lower abundances of C. americanus and Cirriped larvae. Group K2 consis ted of a single station, Station 80 in October 99. It was separated from the rest of the stations by hi gh concentrations of C. velificatus, T. turbinata and E. pileatus, and by low concentrations of typical coastal zooplankton such as O. colcarva and P. avirostris. K3 was characterized by very low abundances of P. crassirostris, O. colcarva, P. avirostris, Cirriped larvae and E. acutifrons and by the presence of L. aestiva. Group K4 was characterized by higher

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127 Figure 46. Cluster derived dendrogram for 37 stations at the 5 a nd 25-m isobaths and 16 stations within the 1999 and 2001 K. brevis blooms, using group-av erage clustering from Bray Curtissimilaritiesonsquareroottransformeddatan = 53 70 DEC 01 32 DEC 01 1 DEC 01 80 OCT 99 6 OCT O1 70 SEP 01 74 SEP 01 72 SEP 01 73 SEP 01 21 OCT 01 5 OCT 01 10 OCT O1 16 OCT 01 75 SEP O1 51 OCT 99 51 NOV 99 51 DEC 99 1 APR 00 51 MAR 00 1 MAY 00 51 JAN 00 51 APR 00 51 MAY 00 1 MAR 00 1 JUL 00 51 JUN 00 1 JAN 00 1 OCT 99 1 DEC 99 51 SEP 99 51 AUG 99 1 JUN 00 1 AUG 99 1 SEP 99 46 SEP 99 5 SEP 99 46 AUG 99 46 JAN 00 5 DEC 99 46 DEC 99 5 OCT 99 5 NOV 99 46 NOV 99 46 MAY 00 46 JUN 00 5 JUN 00 5 JUL 00 5 JAN 00 5 MAR 00 46 MAR 00 5 APR 00 5 MAY 00 46 APR 00 20406080100 WFS 1 K5 K4 K3 K2 K1 WFS 2

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128 Table 19 Results of SIMPER analysis showing dissimilarities between K. brevis and WFS stations. TaxonAv. %Abund%Av. %Av. %Av. %Av. % A. tonsa 720310.2----7620.9----392.92443.2 C. americana ----34.5----373.7---C. americanus 307.7----------------1084.4 C. velificatus ----456956.2--------805.8704.2 E. acutifrons ----73.0--------223.83566.9 E. tergestina 203046.0----4804.0-----------Labidocera aestiva --------12.7---O. colcarva ----1849.6----299312.01149.2122512.4 O. dioika 1137.7133.0----8375.41259.11764.1 O. simplex ----96.3---------------P. avirostris ----86.2------------11056.8 P. crassirostris 5166.45914.68756.2413230.9165517.1 P. quasimodo ----------------1215.43448.2 T. turbinata ----234128.8--------504.9---Cirriped larvae 23312.044.7----119310.4----4787.7 Decapod larvae ----295.2----3667.3----2025.7 Echinoderm larvae --------2735.3-----------Gastropod larvae ------------1346.2----1064.2 Pelecypod larvae ------------433827.1----2715.0 Polychaeta larvae857.2----1210.53447.9-------K5WFS1 K1K2K3K4

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129 concentrations of pelecypod larvae, O. colcarva and Cirriped larvae and lower abundances of P. crassirostris, P. avirostris, and Decapod larvae. Group K5 was distinguished by very high concentrations of P. crassirostris, and by lower than normal concentrations of O. colcarva, E acutifrons and meroplankton. DISCUSSION WFS Zooplankton Taxonomic Composition The zooplankton community compositions at the 5-m and 25-m isobaths for nonred tide stations are consistent with othe r observations on the Florida shelf (King 1950; Minello, 1980; Ortner et al., 1989; Dagg, 1995, Sutton et al., 2001). Of the 4 taxa that were important at the 5-m isobath only, 3 (A. tonsa, P. avirostris, and Cirriped larvae) are abundant within WFS estuaries (Hopkins, 1966; Hopkins, 1977; Weiss, 1977; Squires, 1984), their concentration decrea sing seaward (King, 1950; Mine llo, 1980; Ortner et al., 1989; Dagg, 1995). The cyclopoid copepod C. americanus was more abundant at coastal stations on the NWFS and the WFS than with in estuaries (Hopkins, 1977; Weiss, 1977; Minello, 1980). Nine taxa contributed to 90% of the community structure at both the 5 and the 25m isobaths. Both P. crassirostris and O. colcarva are dominant in WFS estuaries. P. crassirostris is also present in high salinity areas of the estuaries, and is frequently abundant out to the 14-m isobath (M inello, 1980). The abundance of O. colcarva was lowest at the mouths of bays, where it can st ill amount to tens of t housands of animals m3 (Hopkins, 1966; Weiss, 1977; S quires 1984; Hopkins, 1984). P. crassirostris and O.

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130 colcarva were probably under-sampled in this stu dy, due to the large mesh size of the nets. Actual abundance of these two importa nt species may be 4 times those reported here (Calbet et al., 2001). P. quasimodo, C. velificatus, and C. amazonicus are typical of near shore zooplankton assemblages on the Florida shelf (Weiss, 1977; Hopkins, 1977; Squires 1984; Ortner et al., 1989; Minello, 1980; Sutt on et al., 2001). The pelagic harpacticoid copepod Euterpina acutifrons is a major dominant in W FS estuaries (Hopkins, 1966; Weiss, 1977; Hopkins, 1977; Squires, 1984), and has been observed out to the 50-m isobath (King, 1950). O. dioica is the most abundant appendic ularian in coastal areas and estuaries of the NWFS and WFS, reaching populations of thousands m-3 (Hopkins, 1966; Hopkins, 1977; Weiss, 1977; Minello, 1980; Squires, 1984; Dagg, 1995). Five species, E. chierchiae, O. plumifera, O. mediteranea, C. furcatus, and C. amazonicus, were important components of total abundance at the 25-m isobath, but were either absent or infrequent c ontributors at the 5-m isobath. O. plumifera, O. mediteranea and C. furcatus are associated with transition waters on the Florida shelf, where the three species are closely associated (Minello, 1980; Ortner et al ., 1989). The pelagic ostracod E. chierchiae is typically associated with offshor e water masses (Minello, 1980; Sutton et al., 2001), though it has been reported in the higher salinity ar eas of the St. Andrew’s Bay system (Hopkins, 1966). Comparison of bloom and non-bloom community composition Three zooplankton species, C. americanus, P. avirostris and E. acutifrons, had reduced abundance in all K. brevis blooms. Seven species, A. tonsa, C. velificatus, T.

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131 turbinata, E. tergestina, O. colcarva, O. dioica, and P. crassirostris, were important (>4% of total abundance) in two or more of the K. brevis groups. Each of these species were also numerically dominant at leas t one bloom station within the 1999 and 2001 blooms, suggesting that they may be important contributors to K. brevis bloom dynamics on the WFS. Previous associations of K. brevis blooms with zooplankton Far more is known about the interactions of A. tonsa with K. brevis than any other of the species described above. A preliminary report by investigators at the University of Miami in 1954 (cited by Rounsefell and Nels on, 1966) indicated that members of the genus Acartia were usually present within a K. brevis bloom. In situ grazing studies during a novel occurrence of K. brevis in North Carolina waters indicate that A. tonsa will ingest K. brevis if no other food is available (T urner and Tester, 1989), though the ingestion rates were low and variable Subsequently, the ingestion of K. brevis was found to reduce fecundity of A. tonsa (Turner and Tester, 1998). No previous research has indi cated an association between C. velificatus and K. brevis, though two studies have examined the grazing rates of congeners on brevetoxin producing phytoplankton. During the K. brevis bloom off No rth Carolina, Centropages typicus (an ephemeral northern transient in those waters) did not ingest K. brevis, suggesting that co-occurrence with K. brevis in nature may be an indicator of a species’ ability to ingest it (Turner and Tester, 1989). In Japan, Centropages yamadai ingested the brevetoxin producing raphidophyte Chatanella subsalsa (previously C. antiqua) indicating that other copepods of the genus Centropages may have the capacity to ingest

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132 brevetoxins (Uye, 1986). The high numbers of C. velificatus copepodites within the October 1999 bloom imply that the K. brevis red tide provided ample food for reproduction, though carnivory cannot be elimin ated for this species (Kleppel, 1996; Paffenhfer and Knowles, 1980). T. turbinata was not an important compone nt of the non-bloom WFS groups, despite its presence in 39% of the samples. Very high abundances of this copepod have been reported previously on the Florida shelf (Dagg, 1995; Paffenhffer and Knowles, 1980). No in-situ grazing studies of this sp ecies or its congeners on brevetoxin producing phytoplankton have been conducted, but in a toxin vector study T. turbinata ingested an average of 72 K. brevis cells copepod h-1 (Tester et al., 2001). In this study, K. brevis cells were observed trapped in the feeding appendages of T. turbinata specimens at Station 80 in October 1999, where K. brevis concentration exceeded 5 x 106 cells l-1 and abundance of T. turbinata was 2, 341 animals m-3. The cladoceran E. tergestina is a dominant of WFS estuaries (Hopkins, 1966; Weiss, 1977, Hopkins, 1977, Squires, 1984). E. tergestina was not a major contributor to abundance in the non-bloom WFS samples, but was present in 13% of the 5-m isobath stations. Direct evidence of K. brevis ingestion by E. tergestina is not available, though Woodcock and Anderson (cited in Gals toff, 1948) reported large numbers of E. tergestina within a K. brevis bloom had intestines stained deep red, presumably from ingestion of K. brevis. Copepods of the genus Paracalanus will ingest K. brevis (Tester and Turner, 1989), suggesting that Parvocalanus (a subgenus of Paracalanus) may also have the

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133 capability to ingest K. brevis. No congeners of O. colcarva have been examined with respect to grazing on toxic phytoplankton, though the preference of th is genus for motile prey implies that dinoflagellates may comprise a portion of their in-situ diet (see discussion in Paffenhffer, 1993). The high concentration of sca llop larvae found within the 2001 K. brevis bloom is puzzling, since reduced clearance rates, d ecreased size, impaired metamorphosis and increased mortality of bay scallop (A. irradian concentricus) larvae exposed to very low concentrations of K. brevis have been reported (J. Leverone, pers. comm.). The predominant spawn of the calico scallop occu rs in April, and usually involves the majority of the population (Moyer and Blake, 1986). When a fall spawn does occur, it comprises a very small portion of the to tal population (Blake and Moyer, 1991). The highest total Pelecypod larvae concen trations found in the ECOHAB study area prior to this study were 900 larvae m-3 in September of 1999, and on the Northwest Florida Shelf, highest average pelecypod larvae concentrations were 400 larvae m-3 (Figure 47). Minello (1980) found evidence of an April spawn on the NWFS, but did not report a major fall spawn over a five-year sampling period.

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134 Figure 47. Abundance (m-3) of pelecypod larvae a) on th e NWFS averaged over 5 years and 5 stations, b) on the WFS averaged over 1 year and 4 stations and c) within the K. brevis blooms on the WFS in 1999 and 2001. 0 200 400 ASONDJFMAMJJ A 0 250 500 ASONDJFMAMJJ B 0 4,500 9,000EH109951 EH109901 EH1099 80 EH090170 EH090172 EH090173 EH090174 EH090175 DOT-GOM 6 DOTGOM 10 DOTGOM 16 DOT-GOM 21 DOTGOM 5 EH120170 EH120132 EH120101 C NWFS WFS

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135 Aside from age, temperature and food are the most impo rtant exogenous controls for scallop reproduction (Blake and Moyer, 1991). The water temperature range of 24o to 27oC found in October was higher than the ideal spawning range of 19o to 20oC and the 22oC cutoff temperature for spawning (Miller et al, 1981). Given the reduced clearance rates of the congener A. irradians in the presence of K. brevis (Jay Leverone, pers. comm.), it is unlikely that K. brevis is an adequate food sour ce for scallop larvae. In the absence of ideal temperatures and adequate food, the most likely explanation for the magnitude of the fall sp awn may be the stressful conditions of the K. brevis bloom (N. Blake, pers. comm.). Other meroplankton taxa were also abundant in October 2001, most notably Cirriped, Poly chaete and Echinoderm larvae, all of which were more abundant here than in the non-bloom WFS samples. An explanation for this phenomenon is not forthcoming from this analysis, other than the suggestion that increased stress may have been responsible for the increased spawning of benthic forms. CONCLUSIONS The objective of this study was to determine if there were perturbations in the zooplankton community composition associated within K. brevis blooms. Only one K. brevis bloom station was statisti cally indistinguishable from non-bloom WFS stations. The remaining stations differed significantly from non-bloom stati ons in abundance or community composition. No one response by the zooplankton community was evident, but some consistencies between bloom sta tions occurred, including decreased abundance of three important WFS coastal species, C. americanus, P. avirostris and E. acutifrons,

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136 and numerical dominance by A. tonsa, C. velificatus, T. turbinata, E. tergestina, O. colcarva, O. dioica, and P. crassirostris, which were consistently found in high concentrations inside K. brevis blooms. Of these, only T. turbinata and E. tergestina were not major contributors to normal WFS zoopl ankton assemblages at the 5-m isobath. Perturbations in meroplankton contributi on to community structure also were evident. In October 200 1 there were higher than normal abundances of most meroplankton forms, with the most obvious of these being the Pelecypods. The impact of the increased meroplankton abundances are not clear, since the Pelecypod larvae found in October 2001 almost certainly did not survive the bloom (N. Blake, pers. comm.).

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137 ACKNOWLEDGEMENTS Funding was provided by ECOHAB Florida (NOAA/ECOHAB NA96P00084 and USEPA/ECOHAB CR826792-01-0), Office of Naval Research (N000149615024 and N000149910212), the National Science Foundation (NSF OCE 0095970), and the Florida Fish and Wildlife Conserva tion Commission. Additional funding was provided by the USF College of Marine Science Murtagh Fellowship. Thanks to Dr. Norm Blake and Noland Elsaesser, who identified the pe lecypod larvae found in the samples as A. gibbus. Thanks is also extended to the Florida In stitute of Oceanography, and the crew and scientific staff of the R/V Suncoaster.

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138 REFERENCES Austin, H. M. (1971). The characteristics and relationships between the calculated geostrophic current component and selected indicator organisms in the Gulf of Mexico Loop Current System. Doctoral dissertation, Florida State University, Tallahasee, FL, pp. 369. Austin, H. M. and J. I. Jones (1974). “Seasonal variation of physical oceanographic parameters on the Florida Middle Gr ound and their relation to zooplankton biomass on the West Florida Shelf.” Florida Scientist 37, 16-32. Blake, N. J. and M. A. Moyer (1991). The Calico Scallop, Argopecten gibbus, Fishery of Cape Canaveral Florida. In: Shumway, S. E. (Ed.), Scallops: Biology, Ecology and Aquaculture. Elsevier, New York, pp. 899-909. Buskey, E .J. and C. Hyatt (1995). “Effects of the Texas "brown tide" alga on planktonic grazers.” Marine Ecology Progress Series 126, 285-292. Buskey, E. J. and D. A. Stockwell (1993). Effects of a persistent "Brown Tide" on zooplankton populations in the Lagu na Madre of South Texas. In: Toxic Phytoplankton Blooms in the Sea. Proceedings Fifth International Conf. Toxic Marine Phytoplankton. Smayda, T. J., Shim izu, Y. (Eds.), Elsevier, Amsterdam, pp. 659-666. Calbet, A., S. Garrido, et al. (2001). “Annual zooplankton succession in Coastal NW Mediterranean Waters: The importance of small size fractions.” Journal of Plankton Research 23, 319-331. Caron, D. A., E. L. Lim et al. (1989). Trophic interactions between nanomicrozooplankton and the “brown tide,” In: Novel phytoplankton blooms. Causes and impacts of recurrent brown tides and other unusual blooms. E.M. Cosper et. al. (Eds.), Springer, New York, pp. 265-294. Clarke, K. R. and R. M. Warwick (1994). Change in Marine Communities: An approach to statistical analysis and interpretation. Plymouth, Bourne Press Ltd., pp. 144. Dagg, M. J. (1995). “Copepod grazing and the fate of phytoplankton in the Northern Gulf of Mexico.” Continental Shelf Research 15, 1303-1317. Dragovich, A. and J. A. Kelly (1964). Preliminary observations on phytoplankton and hydrology in Tampa Bay and the immediately adjacent offshore waters. In: A collection of data in reference to red tide outbreaks during 1963, Florida Board of Conservation Marine Laborator y, St. Petersburg, pp. 4-22.

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139 Fiedler, P. C. (1982). “Zooplankton a voidance and reduced grazing response to Gymnodinium splendens Dinophyceae.” Limnology and Oceanography 27, 961965. Galstoff, P. S. (1948). Red Tide. Progress repor t on the investigations of the cause of the mortality of fish along the west coast of Florida conducted by the U.S. Fish and wildlife service and cooper ating organizations. United States Fish and Wildlife Service, Washington, D.C. Heil, C., G. Vargo, et al. (2003) Nutrient stoichiometry of a Gymnodinium breve bloom: What limits blooms in oligotrophic environments? In: Harmful Algal Blooms 2000, Hallegraeff, G.M., Blackburn, S.I., Bolc h, C., and Lewis, R.J. (Eds.), IOC of Unesco, pp. 165-168. Hopkins, T. L. (1966). “Zooplankton of the St. Andrews Bay system, Florida.” Contributions in Marine Science 11, 12-64. Hopkins, T. L. (1977). “Zooplankton distri bution in surface waters of Tampa Bay, Florida.” Bulletin of Marine Science 27, 467-478. Hopkins, T. L. (1982). “The ve rtical distribution of zoopla nkton in the eastern Gulf of Mexico.” Deep Sea Research 29, 1069-1083. Hopkins, T. L. and T. M. Lancraft (1984) “The composition and standing stock of mesopelagic micronekton at 27oN 86oW in the Eastern Gulf of Mexico.” Contributions to Marine Science 27,145-158. Hopkins, T. L., D. M. Milliken, et al. (1981). “The landward di stribution of oceanic plankton and micronekton over the west Flor ida continental shelf as related to their vertical distribution.” Journal of Plankton Research 3, 645-658. Huntley, M. E. (1982). “Yellow water in La Jolla Bay, California, July, 1980.” Journal of Experimental Mari ne Biology and Ecology 63, 81-91. Huntley, M. E., P. Sykes, e al. (1986). “Chemically mediated rejection of dinoflagellate prey by the copepods Calanus pacificus and Paracalanus parvus: mechanism, occurrence and significance.” Marine Ecology Progress Series 28, 105-120. Huntley, M. E., P. Sykes, et al. (1987). “Importance of food quality in determining development and survival of Calanus pacificus.” Marine Biology 95, 103-113. Kleppel, G. S., C. A. Burkar t, et al. (1996). “Diets of calanoid copepods on the West Florida continental shelf: relations hips between food concentration, food composition and feeding activity.” Marine Biology 127, 209-217.

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140 King, J. E. (1950). “A preliminary report on th e plankton of the West coast of Florida.” Journal of Florida Academy of Sciences 12, 109-137. Kiorboe, T. (1993). “Turbulence, phytoplankton cell size, and the structure of pelagic food webs.” Advances in Marine Biology 29, 1-72. Lenes, J., B. Darrow, et al. ( 2001). “Iron fertilization and the Trichodesmium response on the West Florida Shelf.” Limnology and Oceanography 46, 12611278. Lester, K., R. Merkt, et al (2003) Evolution of a Gymnodinium Breve red tide bloom on the West Florida Shelf. In: Harmful Algal Blooms 2000, Hallegraeff, G.M., Blackburn, S.I., Bolch, C., and Lewis, R. J. (Eds.), IOC of Unesco, pp. 161-163. Martin, D. F., M. T. Doig, et al. (1973). “B iocontrol of the Florida red tide organism, Gymnodinium breve, through predator organisms.” Environmental Letters 4, 297301. Miller, G. C., D. M. Allen, et al. (1981). “Spawning of the calico scallop Argopecten gibbus in relation to season and temperature.” Journal of Shellfish Research 1, 1721. Minello, T. (1980). Neritic zooplankton of the Northwestern Gulf of Mexico. Doctoral dissertation, Texas A&M, Galveston, pp. 240. Morris, M. J. and T. L. Hopkins (1983) “Biochemical composition of crustacean zooplankton from the eastern Gulf of Mexico.” Journal of Experi mental Marine Biology and Ecology 69, 1-19. Moyer, M. A. (1997). The reproduct ive ecology of the calico scallop, Argopecten gibbus Linnaeus, and mass mortality linked to a prot istan. Doctoral dissertation. Department of Marine Science, University of South Florida, St. Petersburg, pp. 168. Ortner, P. B., L. C. Hill, et al. (1989). “Zooplankton community structure and copepod species composition in the nor thern Gulf of Mexico.” Continental Shelf Research 9, 387-402. Omori, M. and T. Ikeda (1992). Methods in Marine Zooplankton Ecology, pp. 332: Krieger Publishing Company. Rounsefell, G. A. and W. R. Nelson ( 1966). Red-tide research summarized to 1964 including an annotated bibliography. Un ited States Fish and Wildlife Service, Washington, D.C.

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141 Santos, B. A. (1992). “Grazing of Paracalanus parvus (Claus, 1863) upon the red tideproducing dinoflagellates on the Argentine shelf.” Boletin Instituto Espagnol De Oceanografia 8, 255-261. Smayda, T. J. and T. A. Villareal (1 989). The 1985 “brown tide” and the open phytoplankton niche in Narragansett Ba y during summer. In: Novel phytoplankton blooms. In: Causes and impacts of r ecurrent brown tides and other unusual blooms. Cosper, E.M. et al. (Eds), Springer, New York, pp. 159187. Squires, A. P. (1984). The distribution and ecology of zooplankton in Charlotte Harbor, Florida. Masters thesis, Department of Marine Science, University of South Florida, St. Petersburg, pp. 60. Steidinger, K. A. (1975). “Implications of dinoflagellate life cycles on initiation of Gymnodinium breve life cycles.” Environmental Letters 9, 129-139. Steidinger, K. A., G. A. Vargo, et al. (1998). Bloo m dynamics and physiology of Gymnodinium Breve with emphasis on the Gulf of Mexico. In: Physiological Ecology of Harmful Algal Blooms, Anderson, D.M., Cembella, A.D. Hallegraeff, G.M. (Eds.), Springer-Verlag, Be rlin-Heidelberg, pp. 133-153. Sterner, R. E. (1989). The role of grazers in phytoplankton succession. In: Plankton Ecology: Succession in Phytoplankton communities. Sommer,U. (Ed.) pp. 107170. Sutton, T., T. Hopkins, et al. (2001). “Mu ltisensor sampling of pelagic ecosystem variables in a coastal environment to estimate zooplankton grazing impact.” Continental Shelf Research 21, 69-87. Sykes, P. F. and M. E. Huntley (1987 ). “Acute physiol ogical reactions of Calanus Pacificus to selected dinoflagellate s: Direct observations.” Marine Biology 94, 19-24. Tester, P. A., J. T. Turner, et al. (2000) “Vectoral transport of toxins from the dinoflagellates Gymnodinium breve through copepods to fish.” Journal of Plankton Research 22, 47-61. Turner, J. T. and D. M. Anderson (1983) “Zooplankton grazing during dinoflagellate blooms in a Cape Cod embayment; with observations of predation upon tintinnids by marine copepods.” P.S.Z.N.I.Marine Ecology 4, 359-374. Turner, J. T. and P. A. Tester (1989). Zooplankton feeding ecology: Copepod grazing during an expatriate red tide. Novel Phytoplankton blooms. Causes and impacts

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142 of recurrent brown tides and other unusual blooms. E. M. Cosper et al, Springer: 359-374. Turner, J. T. and P. A. Tester (1997). “T oxic Marine Phytoplankton, zooplankton grazers, and pelagic food webs.” Limnology and Oceanography 42, 1203-1214. Turner, J. T. and P. A. Tester (1998). In teractions between toxic marine phytoplankton and metazoan and protistan graze rs: what are the questions? In: Physiological Ecology of Harmful Algal Blooms, Anderson, D.M., Cembella, A.D. Hallegraeff, G.M. (Eds.), Springer-Verlag, Berlin-Heidelber g, pp. 453-474. Uye, S. (1986). “Impact of copepod grazing on the red tide flagellate Chatanella antiqua.” Marine Biology 92, 35-43. Vargo, G. A., K. L. Carder, et al. (19 87). “The potential contribution of primary production by red tides to the we st Florida shelf ecosystem.” Limnology and Oceanography 32, 762-767. Vargo, G. A., C. Heil, et al. (in pres s) Nutrient availabi lity in support of Karenia brevis blooms on the West Florida Shelf: What keeps Karenia blooming? Continental Shelf Research. Vargo, G. A., C. Heil, et al. (2001). The hydrographic regi me, nutrient requirements, and transport of a Gymnodinium breve Davis red tide on the West Florida shelf. In: Harmful Algal Blooms 2000, Hallegraeff, G.M., Blackbur n, S.I., Bolch, C., and Lewis, R.J. (Eds.), IOC of Unesco, pp. 157-160. Walsh, J. J. and K. A. Steidinger (2001). “Saharan dust and Flor ida red tides: the cyanophyte connection.” Journal of Geophysical Research 106, 11597-11612. Walsh, J. J., K. D. Haddad, et al. (2002). “A numerical analysis of landfall for the 1979 red tide of Karenia brevis along the west coast of Florida.” Continental Shelf Research 22:15-38. Walsh, J. J., R. H. Weisberg, et al. (2003). “The phytoplankton response to intrusions of slope water on the West Florida Shel f: models and observations.” Journal of Geophysical Research Oceans 108, 1-23 Weiss, W. R. (1978). The zooplankton of the An clote Estuary, Florida. Masters thesis. Department of Marine Science, University of South Florida, St. Petersburg, pp. 122. Welschmeyer, N.A. (1994). “Fluorometric analysis of chlorophyll a in the presence of chlorophyll b and phaeopigments.” Limnology and Oceanography 39, 1985-1992.

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144 CHAPTER 4 ZOOPLANKTON NUTRIENT REGENERATION WITHIN KARENIA BREVIS BLOOMS Abstract The source of nutrients required to support long lived, high-concentration blooms of the toxic dinoflagellate Karenia brevis on the West Florida Shelf are unknown. One potential source of nutrients to support these blooms may be zooplankton regeneration of nutrients. To test this hypothesis, ammonium and phosphate excretion rates of several West Florida Shelf copepods (Labidocera aestiva, Acartia tonsa, Temora turbinata, and Paracalanus quasimodo) were measured. These excretion rates were then applied to other species of West Florida Shelf zooplankton, combined with available literature excretion rates for some taxa, and used in conjunction with zooplankton populations found for K. brevis blooms on the West Florida Shelf in 1999 and 2001 to estimate Nitrogen and Phosphorus. Ammoni um excretion rates were found to be inadequate to support > 104 cells l-1 of K. brevis, though phosphate excretion rates were adequate to support 106 cells l-1 of K. brevis.

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145 INTRODUCTION The source of nutrients required to s upport long lived, high-concentration blooms of the red tide dinoflagellate K. brevis on the West Florida Shelf are enigmatic. Blooms of this dinoflagellate may reach concentrations of 106 cells l-1 within weeks of bloom initiation when inorganic nutrients are at or below the limits of detection (Steidinger et al., 1998; Vargo et al., in revi ew). The question of which nutrient sources are supporting these blooms remains (Vargo et al., in review). Both inorganic and organic nut rient sources can be used by K. brevis. The major nutrients required by K. brevis for growth and reproduction are nitrogen and phosphorus (Steidinger et al., 1998). Reports of uptake and growth rates for K. brevis as a function of nitrate, nitrite, ammonium and urea availa bility are rare. In a series of preliminary experiments, growth rates were reported to be from 0.16 to 0.2 div day-1 and were independent of ammonia or urea concentration over a range of .5 to 7 M l-1 (Steidinger et al., 1998). Ks values were calculated to be 0.47 for ammonia and 1.07 for urea. Calculated Ks values for nitrate of 0.42 were similar to that of amm onia. Both values are indicative of a species with a high affinity for inorga nic nitrogen and suggest that K. brevis is a species adapted for growth in low-nutrient environments (Ste idinger et al., 1998). Doig (1973) reported use of ammonia as an N source for growth by K. brevis, and Dragovich et al. (1961) suggest that ammonia could be the primary N source for K. brevis. In culture studies, K. brevis has been shown to utilize organic N source s, urea, glycine, leucine, and aspartic acid (Baden and Mende, 1979; Shimizu and Wrensford, 1993; Shimizu et al., 1995).

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146 K. brevis is highly efficient in the acquisi tion and utilizati on of available inorganic phosphate (Steidinger et al., 1998). A Ks of 0.18 M l-1 day-1 suggests that K. brevis is adapted for growth at the low P c oncentrations commonly found in coastal waters (Vargo and Howard-Shamblott, 1990). Vargo (1988) determined that sufficient P was available in the water column to meet the daily requirements of a 1986 bloom off of Tampa Bay, and that K. brevis does not require high nutrien t levels to support normal growth rates and relatively high abundances (Steidinger et al., 1998). However the two stations with the highe st population density (106 cells l-1) would have depleted the water column supply in one day (Vargo et al., in review). Vargo and Shanley (1985) demonstrated production of alkaline phosphatase within a K. brevis bloom in situ, suggesting that DOP sources are also available to blooms. Potential sources of nutrients for K. brevis blooms include aerial deposition, estuarine flux, benthic flux, zooplankton excretion, N2 fixation and subsequent release of organic and inorganic N by Trichodesmium spp., and release of N and P from dead and decaying fish within blooms (Vargo et al., in review). Vargo et al. (in review) determined that atmospheric deposition, benthic flux, and N2 fixation were minor contributors to the flux required to s upport growth of populations >2.6 x 104 cells l-1. Estuarine loadings may not contribute sign ificantly to the growth requirements of K. brevis blooms in coastal waters, but DON levels were high and could not be ruled out as a source of N for coastal blooms (Vargo et al ., in review). However, no near shore source of DON or DOP was de tected during a 1998-1999 bloom, though both were found in higher concentrations near shore at various times over the course of the bloom (Lester et al., 2003). N and P from decaying fish c ould theoretically main tain populations at

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147 moderate concentrations, but there is in sufficient data on flux and mixing rates to determine this decisively (Vargo et al., in review). Inputs of new nitrogen are often insuffici ent to support requirements of primary production (Valiela, 1995). Instead, several pathways by which regenerated nitrogen can be recycled in the water column are of primary importance. One pathway, the regeneration of nitrogen by zooplankt on and its potential contribution to K. brevis bloom nutrient requirements, will be th e focus of this chapter. Zooplankton produce various substances as end products of metabolism. Excretia for most zooplankton include so lid and liquid forms (Ikeda et al., 2000). Liquid forms of nitrogen excreted by zooplankton include free amino acids and ammonia, with urea making up some of the difference (Corner and Newell, 1967). Nitrogen compounds have been measured in terms of total N, ammoni a-N, amino-N and urea N (Ikeda et al., 2000). Ammonia is the major form of dissolved nitr ogen excreted by mari ne zooplankton (Ikeda et al., 2000; Wright, 1995), with urea constitu ting from 0-40% of excreted N (Jawed, 1969; Ikeda and Skjoldal, 1989; Corner and Newell, 1967; Corner et al., 1976). Phosphorus compounds have been measured in terms of total-P, inorganic-P and organic-P. Dissolved phosphorus compounds in zooplankton excretia can be separated into inorganic and organic fractions (Ikeda et al., 2000). Pomeroy et al. (1963) reported that 33-35% of total phos phorus excreted by mixed zooplankton was inorganic. In another study, as much as 75% of phosphor us was excreted as DOP and total DIP excreted by zooplankton exceeded daily alga l requirements (Hargrave and Geen, 1968). Measurements of this source of regenerated nutri ents show that it is potentially capable of

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148 providing substantial amounts of nutrients relative to the amounts assimilated by producers (Ikeda et al., 2000). Zooplankton excretion rates could supply all of the N and P required to support K. brevis populations >106 cells l-1 (Vargo et al., in review). However, the excretion rates used to determine the potential for rege nerated nutrients to support a bloom >106 cells l-1 were from literature values determined for only two species, Acartia tonsa and Centropages velificatus. No other measurements of zooplankton excretion rates are available for the WFS. The purpose of this chapter is to examin e the role of zooplankton regeneration in the nitrogen and phosphorus dynamics of K. brevis blooms by incorporating direct measurements of excretion rates into cal culations of bloom nutrient dynamics. METHODS Zooplankton Abundance Sampling within K. brevis blooms Sampling was conducted in October 1999 a nd September, October, and December 2001 during K. brevis blooms on the WFS. In October 1999 and September and December 2001, zooplankton tows were c onducted on ECOHAB cruises at stations within blooms (Figure 48). In October 2001, zooplankton tows were taken to the north of and within the ECOHAB study area on an NSF research cruise. Zooplankton were collected with a 153 m mesh towed obliquely from bottom to surface. The volume of water filtered was meas ured with a flow mete r attached at the net mouth (Omori and Ikeda, 1992). The cod ends were filtered through a 2000 m mesh

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149 Figure 48. Station locati ons for ECOHAB cruises ( ) and NSF cruises (+). Stations where zooplankton tows were conducted are indi cated by a number. NSF Station 5 is in the same location as ECOHAB Station 1. -84-83.5-83-82.5-82-81.5Longitude 26 26.5 27 27.5 28 28.5Latitu d e 6 10 16 21 1(NSF Station 5) 5 32 46 51 70 72 73 74 75 80 Tampa Sarasota Ft. Myers

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150 sieve to remove macrozooplankton and large gelatinous zooplankton. Each filtered cod end was preserved on board in a 5% buffered formalin solution (Omori and Ikeda, 1992) for later counts of zooplankton species abunda nce. Representative subsamples of 500600 animals were obtained with a Stempel pi pette (usually 1-5% of initial cod end volume). Zooplankton were identified a nd counted using an Olympus dissecting microscope. Holoplankton were id entified to species level. Meroplankton were identified to major taxonomic group (e.g. Pelecypod veligers, Cirriped larvae). Replicate samples were av eraged for each station. Zooplankton tows were conducted in conjunction with K. brevis cell counts. K. brevis was counted live using a dissecting microscope with in two hours of collection. Excretion experiments Underway procedures In 2005, zooplankton were co llected from a ship, boat or from the pier with a 153m mesh net in areas normally impacted by K. brevis blooms. Tows were conducted after sunset with deck lights dimmed. The engines of the ship or boat were cut and the tow collected with th e drift of the ship. Occasionally, it was necessary to come ahead 1-2 knots to keep current flowing through the net. Typically, tows were conducted at the surface, though o ccasionally oblique tows from bottom to surface were conducted. After being brought on board, cod ends were immediately diluted into a larger volume of natural s eawater. The bucket was then covered with several layers of shade cloth to reduce light. Animals were sorted on an Olympus dissecting scope, rinsed with filtered seawater and counted into 200 ml sealed chambe rs that contained either filtered seawater,

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151 natural seawater, or na tural seawater with 104 concentration of K. brevis added. Zooplankton were incubated in the sealed chambers for two hours. Zooplankton were then transferred onto 60m mesh net, rinsed with filtered seawater, and placed in filtered seawater in 60ml BOD bottles. The BOD bottles were wrapped in aluminum foil and allowed to incubate for 8 hours. Controls c onsisted of BOD bottles filled with filtered sea water and incubated for 8 hours. After th e 8 hour incubation period, filtered seawater from the BOD bottles was filtered through a 60m mesh net into 60ml acid cleaned bottles and frozen. Zooplankton were rinsed onto GF/F filters with filtered seawater and rinsed 3 times with ammonium formate. Zooplankton were then counted on the filter, wrapped in aluminum foil and frozen. At a la ter date, samples were dried to a constant weight and weighed on a Cahn Electrobalance. Ammonium and Phosphate Sample Analysis Samples were analyzed for total amm onium and total phosphate on a Technicon Autoanalyzer II continuous flow analyzer using the methods of Grashoff (1976) as modified by Gordon et al. (1993). Nutrient requirements of blooms Bloom nutrient requirements were calculated using an assumed growth rate of 0.2 divisions day-1 and N and P cell content of 1.08 X 10-5 moles and 4.88 X 10-7 moles per cell, respectively (Heil, 1986).

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152 RESULTS Zooplankton Abundance and Community Composition Zooplankton abundance and community composition sampled on ECOHAB and NSF cruises for the 1999 and 2001 K brevis blooms are given in Table 20. In October 1999, the highest zooplankton abundan ce occurred at Station 80, where K. brevis concentrations exceeded 5 X 106 cells l-1. The zooplankton assemblage here deviated from a normal WFS assemblage and consisted almost entirely of Centropages velificatus copepodites and Temora turbinata adults. At Stations 51 a nd 1, in the northern and southern portions of the study area, the K. brevis concentration was low, and the normal WFS zooplankton assemblage was present. The K. brevis concentration was low at most stations in September 2001, with greatest concentration (105 cells l-1) occurring at stations 72 and 73. Zooplankton abundances were relatively low, except at Station 75, where the common, small copepod Parvocalanus crassirostris was dominant. All zooplankton assemblages in September were normal WFS zooplankton assemblages. In October 2001 K. brevis was present in conc entrations exceeding 106 cells l-1 at most zooplankton stations sampled. The zooplankton assemblages sampled deviated from those normally found on the WFS in Oct ober. The most radical departure from a normal WFS zooplankton assemblage (see Chapter 2) occurred at Stations 10, 16 and 5, when pelecypod larvae dominated the assemblage s and were present in concentrations of 103 larvae m-3. Other important components of the zooplankton assemblage in October

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153 Table 20 Top 80% of contributors to zooplankton abundance (m-3) at red tide stations sampled during 1999 and 2001. K. brevis cells l-1 x 1037.5165270820050075151268742132010787741668176 Station 5118070727374756101621570321 A. tonsa --245--4218512029673------3372144714516 C. americana ------7-----------------------C. americanus -------------------------------C. velificatus 118--4569--------41--------112-----E. tergestina ------------------------1516--4462621 E.acutifrons --405--23-----------------------E. crassus 57-----------------------------O.colcarva --749------------331081--47306121-----O.dioka ----------2639100------2772-------O.similis ----------------------826-------P. avirostris -------------------------------P. crassirostris 55532884----------2711--------1994-----P. quasimodo 206--------71936---------------T. turbinata 70--23412----3729---------------Decapod larvae--650------81----------590590-----Pelecypod larvae----------------28983665616--1685-----October-99September-01October-01December-01

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154 were the common copepods Oithona colcarva and P. crassirostris and the larvacean Oikopleura dioica, which is normally present in WFS zooplankton assemblages. By December an estuarine signature char acterized the bloom (Vargo et al., in press). The copepod Acartia tonsa and the cladoceran Evadne tergestina, both associated with estuaries on the WFS (Hopkins, 1977; We iss, 1978; Squires, 1984) were the main contributors to the zooplankton assemblage in December. Excretion rates of WFS zooplankton Ammonium and phosphate excretion rate s were determined for 4 WFS copepods, A. tonsa, P. quasimodo, L. aestiva, and T. turbinata (Figure 49). Highest ammonium excretion rates were obser ved for the large copepod L. aestiva, while lowest excretion rates were observed for the relatively small copepod T. turbinata. Phosphate excretion rates followed the same trend, with L. aestiva demonstrating the highest phosphate excretion rate, and T. turbinata demonstrating the lowest phos phate excretion rate (Figure 50). No correlation was observed between the presence of K. brevis and ammonium excretion rates. With phosphate excretion rate s, there did appear to be a trend to lower excretion rates in the presence of K. brevis, but this was never significant. Generally, excretion rates for starved copepods were lo wer than excretion ra tes for fed copepods. The excretion rates found here were prorated to a 24-hour day using the results of Checkley et al, (1992) who found that excreti on rates were approximately 2 times greater during the day than at night. These prorated excretion rates were extrapolated to other WFS zooplankton found within the 1999 and 2001 K. brevis blooms (Tables 21 and 22),

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155 T. turbinata 0.0000 0.0005 0.0010 0.0015 0.0020 0.0025 0.0030Jan L. aestiva 0.00 0.05 0.10 0.15 0.20Jan P q uasimodo 0.000 0.002 0.004 0.006 0.008 0.010 0.0121 A. tonsa -0.01 0.00 0.01 0.02 0.03 0.04 0.05Jan Figure 49. Ammonium excretion rates of selected WFS copepods. NSW NSW with K. brevis added FSW Ammonium excretion rate copepod-1 hr-1 ( M l-1)

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156 T. turbinata 0.000 0.010 0.020 0.030 0.040 0.050Jan L. aestiva 0 2 4 6 8 10Jan P. quasimodo 0.0 0.5 1.0 1.5 2.0Jan A. tonsa -0.10 0.00 0.10 0.20 0.30 0.40Jan Figure 50. Phosphate excretion rates of selected WFS copepods. NSW NSW with K. brevis added FSW Phosphate excretion rate copepod-1 hr-1 (mM l-1)

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157 Table 21 Ammonium excretion rates used in bloom nutrient calculations. Taxa Excretion rate (M animal-1 day-1) Based on Source Acartia tonsa 0.318 Actual Present study Calanopia americana 1.963 L. aestiva Present study Centropages velificatus 0.039 Actual Checkley et al, 1992 Corycaeus americanus 0.115 T. turbinata Present study Eucalanus crassus 1.963 L. aestiva Present study Euterpina acutifrons 0.115 T. turbinata Present study Evadne tergestina 0.048 Daphnia Martin ez and Gulati, 1999 Labidocera aestiva 1.963 Actual Present study Oikopleura dioica 0.026 Mnemiopsis ledyii Nemazie et al., 1993 Oithona colcarva 0.115 T. turbinata Present study Oithona similis 0.318 A. tonsa Present study Penilia avirostris 0.048 Daphnia spp. Martinez and Gulati, 1999 Parvocalanus crassirostris 0.059 1/2 P. quasimodo Present study Paracalanus quasimodo 0.118 Actual Present study Temora turbinata 0.115 Actual Present study Decapod larvae 0.003 Actual Schmitt and Santos, 1998 Pelecypod larvae 0.010 Actual Yantian et al, 1999

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158 Table 22 Phosphate excretion rates used in bloom nutrient calculations. Excretion rate Taxa (M animal-1 day-1 x 10-3) Based on Source Acartia tonsa 1.82685 Actual Present study Calanopia americana 71.80433 L. aestiva Present study Centropages velificatus 1.82685 L. aestiva Present study Corycaeus americanus 3.59312 T. turbinata Present study Eucalanus crassus 71.80433 L. aestiva Present study Euterpina acutifrons 3.59312 T. turbinata Present study Evadne tergestina 0.20000 Daphnia spp. Martinez and Gulati, 1999 Labidocera aestiva 71.80433 Actual Present study Oikopleura dioica 1.82685 .5 A. tonsa Present study Oithona colcarva 3.59312 T. turbinata Present study Oithona similis 1.82685 A. tonsa Present study Penilia avirostris 0.20000 Daphnia spp. Martinez and Gulati, 1999 Parvocalanus crassirostris 5.42666 P. quasimodo Present study Paracalanus quasimodo 10.85332 Actual Present study Temora turbinata 3.59312 Actual Present study Decapod larvae 0.03593 T. turbinata Present study Pelecypod larvae 0.03593 .01 T. turbinata Present study

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159 applied to zooplankton abundan ce numbers obtained within the blooms, and compared to bloom nutrient requirements (Tables 23 and 24). Highest prorated ammonium and phospha te excretion rates were observed for larger copepods such as L. aestiva. Lowest prorated ammonium and phosphate excretion rates were found for Decapod and Pel ecypod larvae. Zooplankton community ammonium excretion rates for the 1999 a nd 2001 blooms ranged from a low of 0.0076 M l-1 day-1 at Station 6 in October 2001 to a high of 6.8192 M l-1 day-1 at Station 70 in December 2001. Zooplankton community phosph ate excretion rates ranged from a low of 0.0059 mM l-1 day-1 at Sta tion 6 in October 2001 to a hi gh of 0.5144 mM l-1 day-1 at Station 80 in October 1999. DISCUSSION Zooplankton nutrient regeneration as a source of nutrients for K. brevis blooms Generally, zooplankton ammonium excreti on rates were adequate to support the nutrient requirements of blooms that were 104 cells l-1. However, ammonium excretion rates proved to be an inadequate nutrient source for the booms with a 105 or 106 cells l-1 concentration. There were several stations where ammoni um excretion proved to be inadequate in providing enough nut rients to support even a 104 cells l-1 bloom. At Station 74 in September 2001 the presence of high concentrations of O. dioica, an animal with a relatively low ammonium excr etion rate compared to WFS copepods, resulted in a low total ammonium excretion rate for the zooplankton community and subsequently there

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160 Table 23 Zooplankton community ammonium excretion rates for 1999 and 2001 blooms and K. brevis bloom requirements K. brevis Concentration (cells L-1 X 10-3) Ammonium Excretion Rate ( M liter-1 day-1) Bloom Requirements ( M liter-1 day-1) % of Bloom Nitrogen Requirements Provided By Zooplankton October 1999 517.50.36440.1620224.93% 1160.38320.03461108.85% 8052700.445411.38323.91% September 2001 7080.36150.01732092.24% 722000.12930.432029.93% 735000.01401.08001.30% 74750.04000.162024.71% 75150.25840.0324797.45% October 2001 612680.00762.73890.28% 107420.20791.602712.97% 1613200.05622.85121.97% 2110780.88002.328537.79% 57441.02431.671861.27% December 2001 1160.03490.38029.18% 32680.26030.1469177.21% 701766.81920.034619731.61%

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161 Table 24 Zooplankton community phosphate excretion rates for 1999 and 2001 blooms and K. brevis bloom requirements K. brevis Concentration (cells L-1 X 10-3) Zooplankton Excretion Rate ( M liter-1 day-1) Bloom Requirements ( M liter-1 day-1) % of Bloom Phosphate Requirements Provided by Zooplankton October 1999 517.50.49770.007320006799.67% 1160.63600.0015616040727.46% 8052700.67620.51435200131.47% September 2001 7080.01560.000780801995.85% 722000.02660.01952000136.48% 735000.02980.0488000061.01% 74750.00740.00732000101.35% 75150.35550.0014640024284.85% October 2001 612680.00590.123756804.74% 107420.17480.07241920241.32% 1613200.01570.1288320012.21% 2110780.87930.10521280835.70% 57441.15280.075542401526.01% December 2001 1160.02430.01717760141.36% 32680.21770.006636803280.56% 701763.08840.00156160197769.47%

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162 was not enough ammonium present to support the K. brevis population at this station. At Station 1 in December 2001 the zooplankt on abundance was very low. The major zooplankton taxa present was the cladoceran Evadne tergestina, which like O. dioica has a relatively low ammonium excretion rate. Th ese two factors combined resulted in a low total zooplankton ammonium rate. The percentage of ammonium supplied by zooplankton at this station was only 28%. At Station 70 in December 2001, a very high concentration of the copepod A. tonsa resulted in enough ammonium to support a 105 concentration bloom. This was the only situation during the 1999 or 2001 blooms where zooplankton excretion provide d enough ammonium to support a bloom of greater than 104 cells l-1. Unlike ammonium excretion rates, phospha te excretion rates generally proved to be adequate to support blooms of even 106 concentrations. There were however a few exceptions. At Station 73 in September 2001 hi gh concentrations of Decapod larvae with their low phosphate excretion rates resulted in low excret ion rates for the zooplankton community at that station and subsequently there was not enough phos phate to support a 105 concentration of K. brevis. Similarly, at Stations 6 and 16 in October 2001 the zooplankton community was dominated by sm all pelecypod larvae with a low phosphate excretion rate. This resulted in a low tota l phosphate excretion rate for the zooplankton community and an inadequate amount of phosphate to support the 106 concentration of K. brevis located at those stations.

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163 Comparison of excretion rates with other studies The ammonium excretion rates found he re were normalized to mg body weight and compared to other studies examining excretion rates of copepods and general zooplankton populations (Table 25). The numbers obtained here are on the high end of those found in the literature, and compare well to those found by Martin (1968) working with the total zooplankton community in Narraga nsett Bay. It is in teresting to note that despite the high excretion rate s found here, ammonium excr etion rates were still not adequate to provide nutrients for a 105 or 106 cells l-1 bloom. This is probably due to the fact that, when calculating the ammonium excretion load of the zooplankton community as a whole, literature values were used for several important z ooplankton taxa, including pelecypod larvae, O. dioica and E. tergestina. The excretion rates for these three taxa tended to be low and kept the total zoopla nkton community excretion rate low. The range of ammonium excretion for the entire zooplankton community was generally on the same order of magnitude as that found in Narragansett Bay (Vargo, 1976; Vargo, 1979) where ammonium excretion for the zoopla nkton community ranged from 0.56 to 1.66 g mg dry wt-1 day-1. The situation for phosphate excretion ra tes was quite different. Phosphate excretion rates were generally high enough to provide enough phosphate for the bloom, even at 106 l-1 concentrations. Compared with Narragansett Bay, where phosphate excretion rates for the zooplankton community ranged from 0.03 to 0.19 M phosphate mg dry wt-1 day-1, the phosphate excreti on rates for the zoopla nkton community on the

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164 Table 25 Comparison of ammonium excretion rates for various taxa between this study and other studies Study Taxa Average Ammonium Excretion Rate (M mg body weight)Range Temperature Present study Temora turbina 1.5960.314-5.16622oC Present study Labidocera aestiva 4.4882.365-5.78322oC Present study Paracalanus quasimodo 0.4010.224-2.33522oC Present study Acartia tonsa 1.0770.006-5.03522oC Checkley et al, 1992 Acartia tonsa 0.1200.05-0.2125oC Miller and Glibert, 1998 Acartia tonsa 0.0010.00-0.002Not available Kirboe et al., 1985 Acartia tonsa 0.1500.06-0.2518oC Checkley et al, 1992 Centropages velificatus 0.1270.09-0.2222-30oC Martin, 1968Total zooplankton community 1.1230.25-2.42Not available Isla et al., 2004Small size fraction of zooplankton community1,20.1000.04-0.16Not available 1. Those zooplankton that passed through a 200 mesh net 2. Assuming a carbon content of 44.7% (Mauchline, 1998)

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165 WFS during K. brevis blooms had a wider range, w ith values ranging from 0.0059 to 3.0884 M l-1 day-1 (Vargo, 1976). Phosphate excretion rates for pelecypod larvae and O. dioica were not available from the literature, and therefore phosphate excretion rates for these taxa were extrapolated from WFS cope pod excretion rates. For pe lecypod larvae, this was accomplished by multiplying the T. turbinata excretion rate by 10-3, the same ratio observed for ammonium excretion rates. The three stations where pelecypod larvae were important contributors to the zooplankton community were stations 6 and 16 in October 2001 where phosphate excretion by zooplankton contributed 5 and 12%, respectively, of the phosphate required by the K. brevis bloom. These low numb ers indicate that the phosphate excretion rates of pelecypod larvae were like ly not overestimated. For O. dioica, phosphate excretion rate s were the value of A. tonsa, due to the size ratio between the two species. This ma y have resulted in an overestimation of O. dioica phosphate excretion rates. The station wh ere this overestimation would have been a factor was Station 21 in October 2001, when the O. dioica population was quite high. The phosphate excretion rates for the total zooplankton comm unity resulted in 836% of the required phosphate for the bloom being pr ovided by zooplankton. However, 75% of the zooplankton excretion rate at that station was provi ded by the small cyclopoid copepod Oithona colcarva, with only 0.02% of the to tal phosphate excretion rate supplied by O. dioica, indicating that the larvacean was not an important contributor to the phosphate requirements of the bloom.

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166 CONCLUSIONS The values calculated here for ammoni um and phosphate excretion for the total zooplankton community indicate that K. brevis blooms could be obtaining their phosphate from zooplankton excretion, though a mmonium excretion rates proved to be too low to support all but a 104 cells l-1 concentration of K. brevis. ACKNOWLEDGEMENTS Funding was provided by ECOHAB Florida (NOAA/ECOHAB NA96P00084 and USEPA/ECOHAB CR826792-01-0) Office of Naval Research (N000149615024 and N000149910212), National Science Foundation (NSF OCE 0095970), and the Florida Fish and Wildlife Conservation Commission (FWCC PO# S7701 623398). Additional funding was provided by the USF College of Marine Science Mu rtagh Fellowship. Thanks is extended to the Florida Institute of Oceanography, and the crew and scientific staff of the R/V Suncoaster and R/V Bellows, and to Cynthia Heil, Danielle Ault, M.B. Neely, Ryan Pigg, Tom Corbin and Matt Ga rrett, who assisted with the sampling.

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167 REFERENCES Baden, D. G. and T. J. Mende (1979). "Amino acid utilization by Gymnodinium breve." Phytochemistry 18, 247-251. Checkley, J. R., D. M. Dagg, et al. (1992) "Feeding, excretion, and egg production by individual and populatio ns of the marine planktonic copepods, Acartia spp. and Centropages furcatus." Journal of Plankton Research 14, 71-96. Corner, E. D. S., R. N. Head, et al. (1976). "On the nutrition and metabolism of zooplankton. X. Quantitative aspects of Calanus helgolandis feeding as a carnivore." Journal of the Marine Biologica l Association of the United Kingdom 56, 345-358. Corner, E. D. S. and B. S. Newell (1 967). "On the nutriti on and metabolism of zooplankton. IV. The forms of nitrogen excreted by Calanus." Journal of the Marine Biological Association of the United Kingdom 47, 113-120. Doig, M. T. (1973). The growth and toxi city of the Florida red tide organism, Gymnodinium breve. Master’s thesis. Tampa, University of South Florida: 80. Dragovich, A., J. H. Finucane, et al. (1961). Counts of red tide organisms, Gymnodinium breve and associated oceanographic data from Florida west coast, 1957-1959., U.S. Fish and Wildlife Service: 40. Frost, B. W. (1980). The inadequacy of body size as an indicator of niches in zooplankton. Evolution and Ecology of Zooplankton Communities. W. C. Kerfoot. Hanover, NH, University Press of New England: 742-753. Gordon, L. I., J. C. J. Jennings, et al. ( 1993). A suggested Protocol For Continuous Flow Automated Analysis of Seawater Nutrients. WOCE Operations Manual : 1-52. Grasshoff, K. (1976). Methods of Seawater Analysis. Weinheim, Germany, and New York, NY, Verlag Chemie. Hargrave, B. T. and G. H. Geen (1968). "Phosphorus excretion by zooplankton." Limnology and Oceanography 13, 332-342. Heil, C. A. (1986). Vertical Migration of the Florida Red Tide Dinoflagellate Ptychodiscus brevis. Master’s thesis. Departme nt of Marine Science. St. Petersburg, University of South Florida: 118. Hopkins, T. L. (1977). "Zooplankton Distri bution in surface waters of Tampa Bay, Florida." Bulletin of Marine Science 27, 467478.

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168 Ikeda, T. and H. R. Skioldal (1989). "Metabolism and elemental composition of zooplankton from the Barents s ea during early Arctic summer." Marine Biology 100, 173-183. Ikeda, T., J. Torres, et al. (2000). Metabolism. ICES Zooplankton Methodology Manual. R. P. Harris, P. H. Weibe, J. Lenz, H. R. Skioldal and M. E. Huntley. London, Academic Press. Isla, J. A., M. Llope, et al. (2004). "S ize-fractionated mesozooplankton biomass, metabolism and grazing along a 50oN-30oS transect of the Atlantic Ocean." Journal of Plankton Research 26, 1301-1313. Jawed, M. (1973). "Ammonia excretion by z ooplankton and its significance to primary productivity during summer." Marine Biology 23, 115-120. Kirboe, T., F. Mohlenburg, et al. (1985). "Bioenergetics of the planktonic copepod Acartia tonsa: relation between feeding, egg production and respiration, and composition of specific dynamic action." Marine Ecology Progress Series. 26, 85-97. Lester, K., R. Merkt, et al (2003) Evolution of a Gymnodi nium Breve red tide bloom on the West Florida Shelf. In: Harmful Algal Blooms 2000, Hallegraeff, G.M., Blackburn, S.I., Bolch, C., and Lewis, R. J. (Eds.), IOC of Unesco, pp. 161-163. Lu, Y.T., N. J. Blake, et al. (1999). "Oxygen consumpti on and ammonia excretion of larvae and juveniles of the bay scallop, Argopecten irradians concentricus (Say)." Journal of Shellfish Research 18, 419-423. Martin, J. H. (1968). "Phytoplankton-zooplankton relationships in Narragansett Bay. III. Seasonal changes in zooplankton excret ion rates in relation to phytoplankton abundance." Limnology and Oceanography 13, 63-71. Miller, C. A. and P. M. Glibert (1998). "Nitrogen excretion by the calanoid copepod Acartia tonsa: Results of mesocosm experiments." Journal of Plankton Research 20, 1767-1780. Nemazie, D. A., J. E. Purcell, et al (1993). "Ammonium excretion by gelatinous zooplankton and their contribution to the ammonium requirements of microplankton in Chesapeake Bay." Marine Biology 114, 451. Omori, M. and T. Ikeda (1992). Methods in Marine Zooplankton Ecology, Krieger Publishing Company. Perez-Martinez, C. and R. D. Gulati (1999). "Species specific N and P release rates in Daphnia." Hydrobiologica 391, 147-155.

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169 Pomeroy, L. R., H. M. Mathews, et al (1963). "Excretion of phosphate and soluble organic phosphorus compounds by zooplankton." Limnology and Oceanography 8, 50-55. Shimizu, Y., N. Watanabe, et al. (1995). Biosynthesis of brevet oxis and heterotrophic metabolism in Gymnodinium breve. Harmful Marine Algal Blooms. P. Lassus, G. Azrul, E. Erard-Le Denn, P. Gentien a nd C. Marcaillou-Le Ba ut. Paris, Lavoisier: 351-357. Shimizu, Y. and G. Wrensford (1993). Peculiar ities in the biosynthesis of brevetoxins and metabolism of Gymnodinium breve. Developments in Marine Biology. T. J. Smayda, Shimitzu, Yuzuru. Amsterdam, Elsevier Science Publishers. Toxic Phytoplankton Blooms in the Sea: 919-923. Squires, A. P. (1984). The distribution and ecology of zooplankton in Charlotte Harbor, Florida. Master’s thesis. Department of Marine Science. St. Petersburg, University of South Florida: 60. Steidinger, K. A., G. A. Vargo, et al. (1998). Bloom Dynamics and Physiology of Gymnodinium breve with Emphasis on the Gulf of Mexico. Physiological Ecology of Harmful Algal Blooms. D. M. Anderson, A. D. Cembella and G. M. Hallegraeff. Berlin-Heidelberg, Springer-Verlag. G 41, 133-153. Sutton, T., T. Hopkins, et al. (2001). Mu ltisensor sampling of pelagic ecosystem variables in a coastal environment to estimate zooplankton grazing impact. Continental Shelf Research 21, 69-87. Turner, J. T. and P. A. Tester (1989). Z ooplankton feeding ecology: Copepod grazing during an expatriate red tide. Novel Phytoplankton blooms. Causes and impacts of recurrent brown tides and other unusual blooms. E. M. Cosper et. al, Springer: 359-374. Valiela, I. (1995). Marine Ecological Processes. New York, Springer-Verlag. Vargo, G., C. Heil, et al. (In Press). Four Karenia brevis blooms: a comparative analysis. Proceedings of the Xth Internat ional Conference on Harmful Algae. K. Steidinger, J. H. Landsberg, C. Thomas and G. Vargo, Florida Fish and Wildlife Conservation Commission, Florid a Institute of Oceanography and Intergovernmental Oceanographic Commission of UNESCO, Paris. Vargo, G.A., C. Heil, et al. (In Press) Nutrient availability in support of Karenia brevis blooms on the West Florida Shelf: What keeps Karenia blooming? Continental Shelf Research.

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170 Vargo, G. and D. Howard-Shamblott (1990). Phosphorus dynamics in Ptychodiscus brevis: cell phosphorus, uptake and growth requirements. Toxic Marine Phytoplankton. E. Graneli, B. Sundstrom, L. Edler and D. M. Anderson. New York, NY, Elsevier Science Publishing, Inc.: 324-329. Vargo, G. A. and E. Shanley (1985). "Alka line phosphatase activity in the red tide dinoflagellate Ptychodiscus brevis." PSZNI Marine Ecology 6, 251-262. Weiss, W. R. (1978). The zooplankton of the An clote Estuary, Florida. Master’s thesis. College of Marine Science. St. Pete rsburg, University of South Florida: 122. Wright, P. A. (1995). "Nitrogen excreti on: Three end produc ts, many physiological roles." The Journal of Ex perimental Biology 198, 273-281.

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171 CHAPTER 5 ZOOPLANKTON GRAZING ON KARENIA BREVIS BLOOMS OF THE WEST FLORIDA SHELF Abstract Blooms of the toxic dinoflagellate K. brevis are common in the Gulf of Mexico. An in situ study of two of these blooms that occurred during 1999 and 2001 was conducted to determine whether zooplankton gr azing could prove sufficient to terminate K. brevis blooms. Sampling was conducted to determine zooplankton abundance and community composition during bloom periods A grazing assessment was conducted for three common zooplankton species that were found within the blooms, A. tonsa, P. quasimodo, and L. aestiva, using 14C labeled K. brevis. Grazing rates were then applied to the zooplankton community and grazing asse ssed. Grazing pressure was capable of reducing K. brevis to background concentrations at only one station, Station 1 in December 2001. Generally, however, grazing pressure proved to be insufficient to reduce K. brevis to background concentrations du ring the 1999 and 2001 blooms.

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172 INTRODUCTION Blooms of the toxic dinoflagellate K. brevis are common in the Gulf of Mexico, where populations can reach concentrations in the millions of cells pe r liter within weeks of detection. Prior to my study, no in situ studies of zooplankton and K. brevis have been conducted in the Gulf of Mexico. Previous research has examin ed numerous factors affecting growth rates (Steidinger et al., 1998 an d references cited ther ein; Lenes et al., 2001; Walsh and Steidinger, 2001; Walsh et al., 2002; Lester et al., 2003; Heil et al., 2003; Vargo et al., 2003; Walsh et al., 2003), yet the ability of K. brevis to out-compete other phytoplankton species can only be understood in the cont ext of losses as well as growth rates. Differential mortality can lead to th e success (Fiedler, 1982 ; Huntley, 1982; Smayda and Villareal, 1989; Buskey and Stockwell, 1993; Buskey and Hyatt, 1995) or failure of toxic phytoplankton bl ooms (Uye, 1986). In the only in situ study to date of zooplankton grazing on K. brevis, 5 species of zooplankt on ingested the toxic dinoflagellate, but the rates of ingestion tende d to be variable and low (Turner and Tester, 1989). Anecdotal field obs ervations indicate that cladocer ans, tintinnids, and ciliates may also have the ability to ingest K. brevis. (Woodcock and Anderson (cited in Galstoff, 1948); Dragovich and Kelly, 1964; Rounsefell and Nelson, 1966; Martin et al., 1973; C. Heil, pers. comm.). Lester et al. (in review) calculated K. brevis grazing rates based on literature values and reported that gr azing had little effect on K. brevis blooms. However, the grazing rates used for the calculations were derived from zooplankton feeding on natural

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173 non-toxic populations, or from No rth Carolina copepods feeding on K. brevis, and were difficult to extrapolate to Gulf of Mexico K. brevis blooms. Experimentally derived ingestion rates of naturally occurring zooplankton in the Gulf of Mexico on K. brevis populations are needed to determine the impact of zooplankton grazing rates on K. brevis bloom termination. METHODS Zooplankton Sampling Sampling was conducted as a component of the ECOHAB:Florida program in October 1999 and September, October, and December of 2001 during K. brevis blooms on the WFS. In October 1999 and September and December 2001, zooplankton tows were conducted on ECOHAB cruises at stations within blooms (Fi gure 51). In October 2001, zooplankton tows were taken to the nor th of and within the ECOHAB study area on an NSF research cruise. Zooplankton were collected with a 153 m mesh towed obliquely from bottom to surface. The volume of water filtered was meas ured with a flow meter attached at the net mouth (Omori and Ikeda, 1992). The cod ends were filtered through a 2000 m mesh sieve to remove macrozooplankton and large gelatinous zooplankton. Each filtered cod end was preserved on board in a 5% buffere d formalin solution (Omori and Ikeda, 1992) for later counts of zooplankton species abundance. Representative subsamples of 500-600 animals were obtained with a Stempel pipette (usually 1-5% of in itial cod end volume). Zoopla nkton were identified and

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174 Figure 51. Station locati ons for ECOHAB cruises ( ) and NSF cruises (+). Stations where zooplankton tows were conducted are indi cated by a number. NSF Station 5 is in the same location as ECOHAB Station 1. -84-83.5-83-82.5-82-81.5Longitude 26 26.5 27 27.5 28 28.5Latitu d e 6 10 16 21 1(NSF Station 5) 5 32 46 51 70 72 73 74 75 80 Tampa Sarasota Ft. Myers

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175 counted using an Olympus dissecting micros cope. Holoplankton were identified to species level. Meroplankton were identi fied to major taxonomic group (e.g. Pelecypod veligers, Cirriped larvae). Replicate sa mples were averaged for each station. K. brevis cell counts Zooplankton tows were conducted in conjunction with CTD casts and K. brevis cell counts. Water column samples were co llected from Niskin bottles mounted on a rosette sampler. During the October 2001 NSF cr uise surface samples at selected stations were taken with a bucket, in addition to samples from Niskin bottles. K. brevis was counted live using a dissecting microsc ope within two hours of collection. Grazing assessment Grazing studies were conducte d in 2005 using cultured K. brevis and the copepods Acartia tonsa, Labidocera aestiva, and Paracalanus quasimodo. Zooplankton were collected from the pier or a small boat with a 202 m mesh net. Cod ends were immediately diluted with natural sea water, covered with shade cloth and transported to the lab. After sorting, 2 adult female copepods were added to scinti llation vials to which 20 ml filtered seawater was added. 14C labeled K. brevis culture was added to each vial, such that the final K. brevis concentration was 5 X 103, 5 X 104, or 1 X 106 cells per liter. Vials were incubated for 30 minut es. After the incubation period, copepods were filtered onto 12m Nuclepore filters, rinsed with filtered seawater, and dissolved with Hyamine Hydroxide. After addition of a scintillation fluor, vials were placed in the dark for two hours. CPM’s were read on a Beta Scout scintillation counter.

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176 Adsorption controls were performed by pl acing 2 copepods each in scintillation vials with K. brevis concentrations reporte d above. The copepods were not incubated but were instead immediately re moved, filtered onto 12m Nuclepore filters, rinsed with filtered seawater, dissolved with Hyamine hydr oxide, and placed in the dark for 2 hours. CPM’s were counted as described above on a Beta Scout scintillation counter. Radioactivity of K. brevis cells was determined by filtering 0.1 ml of the labeled culture onto 1m Nuclepore filters. Cells were dissolved in Hyamine hydroxide and CPM’s recorded. Clearance rate (F in ml animal-1 h-1) was calculated as: F=(dpmanimal x v)/(dpmalgae x t) where dpmanimal is the radioactivity of one animal, dpmalgae is the radioactivity of v ml of the phytoplankton suspension, and t is the incubation time in hours (Bamstedt et al., 2000). Ingestion rate (in cells ingested per hour) was calculated by multiplying the clearance rate by the phytopl ankton concentration during in cubation (Bamstedt et al., 2000). For remaining dominants within the bl ooms, grazing pressure was calculated using published grazing rates (T able 26). Grazing rates of Centropages velificatus copepodites and Oithona colcarva and Parvocalanus crassirostris adults were determined using allometric derivations2 based on the biomass of adult C. velificatus, Oithona plumifera, and P. quasimodo, respectively (Frost, 1980). Several assumptions were made to a ssess the impact of grazing pressure on K. brevis blooms. First, if other phytopla nkton species were present, grazing on K. brevis 2 Based on the allometric e quations of Frost, 1980 Y = mb, where b = 0.75.

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177 Table 26 Taxon and life stage specific grazing rate s for zooplankton ta xa dominant within K. brevis blooms, pro-rated for a 24-hr day. Taxon Grazing rate Source Comments O. colcarva 1.5 ng chl ind-1 day-1 Dagg 1995, Sutton et al., 1999 2,a P. crassirostris .05 x 103 cells ind-1 day-1 Turner and Tester, 1989 1,b Temora turbinata 41.5 ng chl ind-1 day-1 Dagg 1995; Kirboe et al., 1985; Sutton et al., 19992 C. velificatus 16 Dagg 1995; Kirboe et al., 1985; Sutton et al., 19992 CV 2.8-6.4 2,c Evadne tergestina .432 Sutton, 1999 2 Oikopleura dioica 92.9 Dagg 1995; Sutton et al., 1999 2 1. Cell Counts 2. Gut Fluorescence a. Allometric derivation from O. plumifera (Frost, 1981) b. Allometric derivation from P. quasimodo(Frost, 1981) c. Allometric derivation fro m adult (Frost, 1981)

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178 was assumed to be negligible si nce copepods will avoid ingesting K. brevis if alternate food is available (Turner and Tester, 1989). Second, carnivory and diel variation in feeding rates were not consid ered, resulting in a probable overestimation of the grazing pressure. In addition to the numerically dominant species, 2 additional species, L. aestiva and P. quasimodo, were incorporated into the grazing analysis because they have been shown to ingest K. brevis (Turner and Tester; 1989, this study). Pel ecypod larvae were not included in the analysis, due to the appa rent inability of scallop larvae to ingest K. brevis (J. Leverone, pers. comm.). RESULTS Two separate K. brevis blooms were sampled during the course of the ECOHAB:Florida program. The first bl oom occurred in October of 1999 and was relatively short lived (Figure 52). Near shore stations 1 and 51 both had low K. brevis concentrations and were dominated by typi cal near shore WFS zooplankton assemblages (Table 27). Station 80, also n ear shore, and with a very high K. brevis concentration of over 5 million cells l-1, had a zooplankton assemblage dominated by Centropages velificatus and Temora turbinata, with much of the assemblage consisting of C. velificatus copepodites (Table 28). The second bloom spanned a four mont h sampling period from September to December, 2001 (Figures 53-55). In Septem ber the bloom was present in very low concentrations, and the typical WFS zooplankton assemblage wa s present (Table 29). As the bloom progressed through October, the bl oom was present at several stations at

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179 Figure 52. Surface K. brevis concentrations for October 1999. -83.5-83-82.5-82-81.5 Longitude 26 26.5 27 27.5 28 28.5Latitude 80 51 0 500,000 1,000,000 1,500,000 2,000,000 2,500,000 3,000,000 3,500,000 4,000,000 4,500,000 5,000,000Tampa Cells l-1

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180 Table 27 Zooplankton abundance and community composition sampled in October 1999 October-99 K. brevis cells l-1 x 103 7.5 16 5270 Station 51 1 80 A. tonsa 11 245 4 C. amazonicus 39 98 -C. americana 56 --C. americanus 7 --C. velificatus 118 49 4569 E. pileatus --234 E. acutifrons 25 405 -E. crassus 57 --L. aestiva --112 L. scotti -25 55 O. nana 52 172 -O. colcarva 102 749 -O. dioica 150 --O. simplex -25 -P. avirostris -37 -P. crassirostris 5553 2884 516 P. quasimodo 206 37 25 T. setacaudatus 18 --T. turbinata 70 -2341 Cirriped larvae 4 2037 59 Decapod larvae 43 650 179 Echinoderm larvae 4 --Gastropod larvae 4 12 4 Pelecypod larvae 4 479 31 Polychaete larvae 14 123 -Total Num Abund. m-3 706912993542

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181 Table 28 C. velificatus copepodite abundance at Station 80 in October 99 Stage Abund. (m-3) I 92 II 506 III 2177 IV 2667 V 410 Adult 355

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182 Figure 53. Surface K. brevis concentrations for September 2001. -83-82.5-82-81.5 Longitude 26 26.5 27 27.5 28 28.5La t i t u d e 70 72 73 74 75 0 40,000 80,000 120,000 160,000 200,000 240,000 280,000 320,000 360,000Tampa Cells l-1

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183 Figure 54. Surface K. brevis concentrations for October 2001. -83.5-83-82.5-82-81.5 Longitude 26 26.5 27 27.5 28 28.5Latitude 5 6 10 16 21 0 1,000,000 2,000,000 3,000,000 4,000,000 5,000,000 6,000,000 7,000,000 8,000,000 9,000,000 10,000,000Tampa Cells l-1

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184 Figure 55. Surface K. brevis concentrations for December 2001. -84-83.5-83-82.5-82-81.5 Longitude 26 26.5 27 27.5 28 28.5Latitude 1 32 70 0 20,000 40,000 60,000 80,000 100,000 120,000 140,000 160,000 180,000 200,000 220,000Tampa Cells l-1

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185 concentrations of over 1 million cells liter (Figure 55). The zooplankton assemblage in October changed in both abundance and percen t composition (Table 29). The greatest departure from normal WFS zoopl ankton populations occurred at stations 16, 10 and 5, when pelecypod larvae dominated the assemblage. By December, an estuarine signature characterized the bloom (Vargo et al., in press). The copepod A. tonsa and the cladoceran E. tergestina dominated the assemblage. Grazing experiments All three experimental animals, A. tonsa, P. quasimodo, and L. aestiva, ingested K. brevis (Figure 56). For all three species, highes t ingestion rates were observed when K. brevis concentrations were at 106 cells liter, though variability was high. Lowest ingestion rates were found at lowest K. brevis cell concentrations. P. quasimodo ingested the lowest number of K. brevis. One of the species examined, L. aestiva, ingested negligible quantities of K. brevis at 104 concentrations. Grazing assessment The results of the grazing assessment indicate that heavy grazing pressure occurred at one station in the 1999 and 2001 blooms. At Station 1 in December 2001, grazing pressure was 34.52% of the K. brevis population. Taking into account an assumed growth rate of 0.2 divisions day-1, the zooplankton assemblage at Station 1 in December 2001 could have reduced the K. brevis concentration to ba ckground levels in 7 days. For the remainder of the stations, gr azing pressure was negl igible, and was never above 2%.

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186 Table 29 Zooplankton abundance and community composition at stations sampled within the 2001 K. brevis bloom K. brevis cells l-1 x 103820050075151268742132010787741668176 Station 70727374756101621570321 A. tonsa 4218512029673--38503372144714516 C. amazonicus 8----212141--22556-----C. americana 734317------0-------C. americanus 12----50------112112481824 C. velificatus 2----4411--225112-----E. tergestina 16310--83--11712275151610084462621 E.acutifrons 234--918--2324---------L.aestiva 41--13123--5056-----O. nana ----------------------480 O.colcarva 1256281263310813847306121--28924 O.dioka ----26391001471082772421962358 O.similis ----------------826-------O.simplex 19194560--------337-----P. avirostris 83181326----29198-------P. crassirostris --8324156271130681--8261994-----P. quasimodo --271936------752848182 T. setacaudatus 2----------23--75--2---T. stylifera 9-----------------------T. turbinata 2--03729---------------Cirripid larvae687--112342162161216143221721 Decapod larvae--5681--161641205905909618-Echinoderm larvae----------065841197197-----Gastropod larvae--------510117137140140-----Pelecypod larvae------832898366561616851685-----Polychaete larvae2481615121412255055051925410 Total Num Abund. m-321953132563533433881186665021551716368233695456726 September-01October-01December-01

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187 P. quasimodo 0 5 10 15 20 25K. brevis concentration L. aestiva -100 0 100 200 300 400Jan A. tonsa -500 0 500 1000 1500 20001 Figure 56. Grazing rates of selected WFS copepods on K. brevis 10 4 concentration K brevis 10 5 concentration K. brevis 10 6 concentration K brevisIngestion Rate Cells copepod-1 h-1

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188 Table 30 Assessment of grazing pressure on 1999 and 2001 K. brevis blooms on the WFS. Month Phytoplankton assmblage Dominant grazer(s) Oct-99517.5Monospecific P. quasimodo 1.64 116Monospecific A. tonsa P. quasimodo 0.37 805270Monospecific T. turbinata, C. velificatus 0.82 Sep-01708Monospecific A. tonsa 0.12 72200Diatoms-73500 Microflagellates, Bellerochea -7475Monospecific A. tonsa 0.17 7515Dinoflagellates-Oct-0161268Diatoms -10742 Microflagellates, Bellerochea -161320Monospecific O. dioica 0.15 211078Dinoflagellates-5774Monospecific O. dioica 0.51 Dec-017016 Dinoflagellates, Thalassiosira spp. -3268Small dinoflagellates, flagellates -1176Monospecific O. dioica, A. tonsa 34.52 Station K. brevis cells l-1 (x 10-3)Grazing pressure (% of K. brevis population)

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189 DISCUSSION The ingestion numbers obtained here for WFS copepods grazing on cultured K. brevis are lower than those found by Turner a nd Tester (1989) (Tab le 31). There are three potential reasons for this. The firs t is the difference in methodology between the two studies. The Turner and Tester (1989) study used cell co unts to determine ingestion rates of naturally occurring K. brevis, and it is possible that th e difference in methodology between that study and this one resulted in th e discrepancies in graz ing rate. Secondly, the very high concentrations of K. brevis used by Turner and Test er (1989) in their study (as high as 20 million cells l-1) could explain the discrepanc ies between our studies, since ingestion rate for all species examined appears to increase with increasing concentrations of K. brevis. A third explanation is the potential resistance to brevetoxins developed by copepods that have been exposed to brevetoxins for some time. The K. brevis bloom studied by Turner and Tester (1989) was an expatriate red tide, new to North Carolina waters, but had reportedly been in the area for at least a month (Turne r and Tester, 1989). It is possible then, that the North Carolina copepods studied by Turn er and Tester (1989) had developed resistance to brevetoxins, resul ting in a higher grazing rate. Most of the animals examined in my study were taken from waters that were free of brevetoxins. The P. quasimodo specimens were taken from waters with high K. brevis concentrations (>100,000 cells l-1), but this bloom had been in the area for less than one month. Resistance to algal toxins in copepods has b een demonstrated for other species of toxic algae (Colin and Dam, 2 005), while rejection of K. brevis as a food source has been

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190 Table 31 Comparison of K. brevis grazing activity between this st udy and Turner and Tester (1989) This Study Turner and Tester K. brevis concentration K. brevis concentration 10X103 10X104 10X105 10X103 10X104 10X105 Ingestion Rate Ingestion Rate A. tonsa 220 210780 9298,129 80,129P. quasimodo 1 613 --1,000L. aestiva 1 53203 1,01510,285 102,985

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191 shown by copepods that do not normally co-occur with K. brevis in nature (Huntley et al., 1986). The grazing numbers found here represent ca rbon ingestion rates that are lower than the typical carbon ingestion ranges f ound for these species (T able 32), indicating that there are factors presen t that reduce copepod grazing on K. brevis. Carbon ingestion values were at least one orde r of magnitude lower than the lowest carbon ingestion rates reported. Sutton et al. (2001) found th at an average of 7.9% of phytoplankton standing stock was grazed by the zooplankton a ssemblage on the WFS sampled during a September 1999 cruise, with occasional hea vy concentration of grazing depending on zooplankton taxa present. Dagg (1995), worki ng in the Northern Gulf of Mexico during September, found that ingestion rem oved 14-62% of phytoplankton biomass in Mississippi river plume waters. My rates are much lower, suggesting that grazing rates on K. brevis blooms by the mesozooplankton community are lower than grazing rates for non-bloom phytoplankton assemblages. Teegarden (2001) and Turner and Tester (1997) suggested th at the effect of grazing on toxic algae blooms coul d be species specific, with the impact of grazing on the bloom dependent on species present. In this study, highest inges tion rates for copepods feeding on cultured K. brevis were found for A. tonsa, yet the dominance of the zooplankton assemblage by A. tonsa appeared to less important than the total number of zooplankton present and the concentration of K. brevis.

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192 Table 32 Comparison of carbon ingestion for K. brevis grazing experiments and litera ture carbon ingestion values1 Carbon ingested (g day-1) at varying K. brevis concentrations Typical non red-tide ingestion values (g day carbon ingestion) 10X103 10X104 10X105 min max mean A. tonsa 0.0046 0.0044 0.0163 0.01 0.09 0.05 2,3 P. quasimodo 0.0000 0.0001 0.0003 --0.05 4 L. aestiva 0.0000 0.0011 0.0042 0.4 1.2 0.8 5,6 1. Based on Carbon concentration of K. brevis of 7.25 x 10-5 M cell (Heil, 1986) 2. Irigoien et al., 1993 3. Roman, 1977 4. Based on the values for Paracalanus parvus from Checkley, 1980 5. Conley and Turner, 1985 6. Based on assumed carbon value of 44% (Bamstedt, 1986)

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193 CONCLUSIONS The results of the grazing assessment s uggest that grazing pressure from the mesozooplankton community during the 1999 and 2001 blooms was not sufficient for K. brevis bloom termination. However, other components of the zooplankton community that may have contributed to total grazing pre ssure, such as tintinnids and ciliates, were not assessed in this analysis. These com ponents may prove to be important grazers of K. brevis, since tintinnids were observed to ingest K. brevis during the 2001 bloom (C. Heil, pers. comm.). ACKNOWLEDGMENTS Funding was provided by ECOHAB Florida (NOAA/ECOHAB NA96P00084 and USEPA/ECOHAB CR826792-01-0) Office of Naval Research (N000149615024 and N000149910212), National Science Foundation (NSF OCE 0095970), and the Florida Fish and Wildlife Conservation Commission (FWCC PO# S7701 623398). Additional funding was provided by the USF College of Marine Science Mu rtagh Fellowship. Thanks is also extended to the Florida In stitute of Oceanography, and the crew and scientific staff of the R/V Suncoaster and R/V Bellows, and to C ynthia Heil, Danielle Ault, M.B. Neely, Ryan Pigg and Tom Co rbin who assisted with the sampling.

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194 REFERENCES Bamstedt, U., D. J. Gifford, et al. (2000). Feeding. Zooplankton Methodology Manual. R. P. Harris, P. H. Weibe, J. Lenz, H. R. Skioldal and M. E. Huntley. London, Academic Press. Buskey, E. J. a. D. A. S. (1993). Effects of a persistent "Brown Tide" on zooplankton populations in the Laguna Madre of South Texas. Toxic Phytoplankton Blooms in the Sea. Proceedings Fifth Internatio nal Conf. Toxic Marine Phytoplankton. T. J. Smayda and Y. Shimizu. Amsterdam, Elsevier Science Publishers, 659-666. Checkley, D. M. (1980). "The egg production of a marine planktonic copepod in relation to its food supply." Limnology and Oceanography 25, 430-446. Colin, S. P. and H. G. Dam (2004). "Testing fo r resistance of pelagic marine copepods to a toxic dinoflagellate." Evolutionary Ecology 18, 355-377. Dagg, M. J. (1995). “Copepod grazing and the fate of phytoplankton in the Northern Gulf of Mexico.” Continental Shelf Research 15, 1303-1317. Dragovich, A. and J. A. Kelly (1964). Preliminary observations on phytoplankton and hydrology in Tampa Bay and the imme diately adjacent offshore waters. .A collection of data in reference to red tide outbreaks during 1963. St. Petersburg, Florida Board of Conservation Marine Laboratory, 4-22. Fiedler, P. C. (1982). "Zooplankton avoi dance and reduced grazing response to Gymnodinium splendens (Dinophyceae)." Limnology and Oceanography 27, 961965. Galstoff, P. S. (1948). Red Tide Progress report on the investig ations of the cause of the mortality of fish along the west coast of Florida conducted by the U.S. Fish and wildlife service and cooper ating organizations. Washi ngton, D.C., United States Fish and Wildlife Service. Heil, C. A. (1986). Vertical Migration of the Florida Red Tide Dinoflagellate Ptychodiscus brevis. Master’s thesis, Department of Marine Science, St. Petersburg, University of South Florida, 112. Heil, C., G. Vargo, et al. (2003) Nutrient stoichiometry of a Gymnodinium breve bloom: what limits blooms in oligotrophic environments? Harmful Algal Blooms 2000. G. M. Hallegraeff, S. I. Blackburn, C. Bo lch and R. J. Lewis, IOC of Unesco.

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195 Huntley, M. E. (1982). "Yellow water in La Jolla Bay, California, July, 1980." Journal of Experimental Marine Biology and Ecology 63, 81-91. Irigoien, X., J. Castel, et al (1993). "In situ grazing activity of planktonic copepods in the Gironde estuary." Cahiers de Biologie Marine 34, 225-237. Lenes, J., B. Darrow, et al. ( 2001). “Iron fertilization and the Trichodesmium response on the West Florida Shelf.” Limnology and Oceanography 46, 12611278. Lester, K., R. Merkt, et al (2003). Evolution of a Gymnodi nium Breve red tide bloom on the West Florida Shelf. In: Harmfu l Algal Blooms 2000, Hallegraeff, G.M., Blackburn, S.I., Bolch, C., and Lewis, R. J. (Eds.), IOC of Unesco, pp. 161-163. Martin, D. F., M. T. Doig, et al. (1973). "B iocontrol of the Florida red tide organism, Gymnodinium breve, through predator organisms." Environmental Letters 4, 297301. Omori, M. and T. Ikeda (1992). Methods in Marine Zooplankton Ecology, Krieger Publishing Company. Roman, M. R. (1977). "Feeding of the cope pod Acartia tonsa on th e diatom Nitzschia closterium and brown algae (F ucus vesiculosus) detritus." Marine Biology 42, 149-155. Rounsefell, G. A. and W. R. Nelson (1966) Red-Tide Research Summarized to 1964 Including an Annotated Bib liography. Washington, D.C, United States Fish and Wildlife Service. Smayda, T. J., and T.A. Villareal. (1989). An extraordinary, noxious "brown-tide". Narragansett Bay. I. The organism and its dynamics. Red Tides: Biology, Environmental Science and Toxicology. T. Okaichi, D.M. Anderson and T. Nemoto (eds.): 127-130. Steidinger, K. A., G. A. Vargo, et al. (1998). Bloom Dynamics and Physiology of Gymnodinium Breve with Emphasis on the Gulf of Mexico. Physiological Ecology of Harmful Algal Blooms. D. M. Anderson, A. D. Cembella and G. M. Hallegraeff. Berlin-Heidelberg, Springer-Verlag. G 41, 133-153. Sutton, T., T. Hopkins, et al. (2001). Mu ltisensor sampling of pelagic ecosystem variables in a coastal environment to estimate zooplankton grazing impact. Continental Shelf Research 21, 69-87. Sykes, P. F. (1991). Physiological-e cology and chemical-ecology of copepoddinoflagellate interactions. Do ctoral dissertation. Univ ersity of California, San Diego.

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196 Teegarden, G. J., R. G. Campbell, et al (2001). "Zooplankton f eeding behavior and particle selection in natural plankton assemblages containing Alexandrium spp." Mar. Ecol. Prog. Ser. 218, 213-226. Turner, J. T. and P. A. Tester (1989). Z ooplankton feeding ecology: Copepod grazing during an expatriate red tide. Novel Phytoplankton blooms. Causes and impacts of recurrent brown tides and other unusual blooms. E. M. Cosper et. al, Springer: 359-374. Uye, S. (1986). "Impact of c opepod grazing on the red tide flag ellate Chatanella antiqua." Marine Biology 92, 35-43. Vargo, G., C. Heil, et al. (2003). Hydrogr aphic regime, nutrient requirements and transport of a Gymnodinium breve DAVIS red tide on the West Florida Shelf. Harmful Algal Blooms 2000. G. M. Hallegraeff, S. I. Blackburn, C. Bolch and R. J. Lewis, IOC of Unesco: 157-160. Vargo, G., C. Heil, et al. (In Press). Four Karenia brevis blooms: a comparative analysis. Proceedings of the Xth Internat ional Conference on Harmful Algae. K. Steidinger, J. H. Landsberg, C. Thomas and G. Vargo, Florida Fish and Wildlife Conservation Commission, Florid a Institute of Oceanography and Intergovernmental Oceanographic Commission of UNESCO, Paris. Walsh, J. J., K. D. Haddad, et al. (2002). “A numerical analysis of landfall for the 1979 red tide of Karenia brevis along the west coast of Florida.” Continental Shelf Research 22:15-38. Walsh, J. J. and K. A. Steidinger (2001) "Saharan dust and Fl orida red tides; the cyanophyte connection." Journal of Geophysical Research 106: 11597-11612. Walsh, J.J. R. H. Weisberg, et al. (2003). The phytoplankton respons e to intrusions of slope water on the West Florida Sh elf: models and observations. Journal of Geophysical Research Oceans 108, 1-23

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197 CHAPTER 6 CONCLUSIONS The purpose of this study was to exam ine the relationships between zooplankton and K. brevis blooms on the West Florida Shelf. To this end, a sampling program was undertaken to assess the normal zooplankton assemblage of the WFS on a seasonal and taxonomically distinct basis. The results of this assessment were compared to the zooplankton assemblage sampled during redtide events on the WFS. The abundance and community composition found during K. brevis blooms on the WFS during 1999 and 2001 were used to assess the effects of z ooplankton nutrient regene ration and grazing on K. brevis blooms. The community composition found here agr ees well with other studies conducted in the Gulf of Mexico. At the 5-meter isobath, the copepods O. colcarva and P. crassirostris were the most important contributors to abundance and community composition. Despite their high ab undances in this study, both P. crassirostris and O. colcarva are probably present in even greater amounts, but were underrepresented due to the relatively large mesh size used. Other important and intermittent contributors to abundance and community composition at the 5-meter isobath were P. avirostris and P. quasimodo. At the 25-meter isobath for much of the year the zooplankton assemblage was dominated by P. quasimodo, O. colcarva and the larvacean O. dioica. In the winter and spring, E. chierchiae and C. furcatus were dominant.

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198 At the 50-meter isobath, fall, winter and early spring assemblages were dominated by E. chierchiae, O. frigida, C. furcatus and O. mediteranea. In the late spring, the assemblage was dominated by C. furcatus, C. pavoninius, O. similis and Gastropod larvae. The importance of E. chierchiae to the WFS ecosystem needs to be explored further. The ostracod dominated the zoopl ankton assemblage at the 25 and 50-meter isobaths for much of the year. Little is known about the ecology of E. chierchiae, yet it’s prevalence on the WFS suggests that further study is warranted. The 5 subgroups (A-E) in community co mposition were tightly coupled with temperature, salinity and chlorophyll a concentration. A range of environmental factors defined distribution, with temperature be ing the most important factor defining distribution near shore. As distance offshore increased salinity and chlorophyll a concentration became increasingly important as factors defining distribution. Considerable overlap in community com position was observed for subgroups A and B, Subgroups B, C and D, and Subgroups C, D and E. However, virtually no overlap was observed for near shore subgroup A and offshore subgroup E. Range in chlorophyll a concentration, temperature, and salinity decreased as distance offshore increased. Chlorophyll a was found to be the most important contributing factor to zoopla nkton community composition. Statistical analysis of K. brevis bloom stations and non-bl oom near shore stations showed that most K. brevis bloom stations differed signifi cantly from non-bloom stations in abundance or community composition. Some of the consistent differences observed between bloom and non-bloom stations were decreased abundance of three important

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199 WFS coastal species, C. americanus, P. avirostris and E. acutifrons, and numerical dominance by A. tonsa, C. velificatus, T. turbinata, E. tergestina, O. colcarva, O. dioica, and P. crassirostris, which were consistently found in high concentrations inside K. brevis blooms. Of the 7 species fo und in high concentration inside K. brevis blooms, only T. turbinata and E. tergestina were not major contributors to normal WFS zooplankton assemblages at the 5-m isobath. Perturbations in me roplankton contribution to community structure also were evident. In October 2001 there were higher than normal abundances of most meroplankton forms, with the most obvious of these being the Pelecypods. The values calculated here for ammonium and phosphate excretion for the total zooplankton community indicate that K. brevis blooms could be obtaining their phosphate from zooplankton excretion, though a mmonium excretion rates proved to be too low to support all but a 104 cells l-1 concentration of K. brevis. The results of the grazing assessment s uggest that grazing pressure from the mesozooplankton community during the 1999 and 2001 blooms was not sufficient for K. brevis bloom termination. There was only one station where grazing pressure exceeded the assumed growth rate of 0.2 divisions day-1, however grazing pressure was not consistently heavy across stati ons. At most stations, grazing pressure was 1.64% or less of the K. brevis population. It is important to note that other components of the zooplankton community that may have contri buted to total grazing pressure, such as tintinnids and ciliates may prove to be important grazers of K. brevis.


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ABSTRACT: Blooms of the toxic dinoflagellate Karenia brevis are common on the West Florida Shelf (WFS), yet little is known of the relationships between zooplankton and K. brevis. A comprehensive analysis was undertaken to examine 1) perturbations in zooplankton community composition within K. brevis blooms 2) the contribution of zooplankton ammonium and phosphate excretion to K. brevis bloom nutrient requirements, and 3) the role of zooplankton grazing in K. brevis bloom termination. Prior to undertaking the first portion of the study, an examination of the perturbations in the normal zooplankton assemblage within K. brevis blooms, it was first necessary to define the normal zooplankton assemblage on the WFS. To this end, a seasonal analysis of abundance, biomass and community composition of zooplankton was undertaken at 6 stations on the WFS. Monthly sampling was conducted for one year at the 5, 25 and 50- m isobaths.Two major groups in community composition were observed at the near shore (5-m and 25-m) and offshore (50-m) stations. Considerable overlap was seen in community composition between the 5-m to 25-m and 25-m to 50-m isobaths, but little overlap in community composition was observed between the 5-m and 50-m isobaths. Of the 95 species identified, only 25 proved to be important (> 90%) contributors to community composition. Near shore, important contributors were Parvocalanus crassirostris, Penilia avirostris, Paracalanus quasimodo, Oithona colcarva, Oikopleura dioica, Centropages velificatus and Pelecypod larvae. As distance offshore increased, important contributors to community composition were Euchonchoichiea chierchiae, Clausocalanus furcatus, Oithona plumifera, Oithona frigida, Oncaea mediteranea, Calaocalanus pavoninius, Oithona similis, and Gastropod larvae.Variations in abundance and biomass between non-bloom and bloom assemblages were evident, including the reduction in abundance of 3 key species within K. brevis blooms. One potential source of nutrients to support K. brevis blooms may be zooplankton regeneration of nutrients. To test this hypothesis, ammonium and phosphate excretion rates of several West Florida Shelf copepods (Labidocera aestiva, Acartia tonsa, Temora turbinata, and Paracalanus quasimodo) were measured and prorated to a 24-hour day. These excretion rates were then extrapolated to other West Florida Shelf zooplankton, combined with available literature excretion rates for some taxa, and applied to zooplankton abundances found for K. brevis blooms on the West Florida Shelf in 1999 and 2001. Ammonium excretion rates were found to be inadequate to support all but 104 cells l-1 of K. brevis, though phosphate excretion rates were adequate to support even 106 cells l-1 of K. brevis.Grazing assessment was conducted for three common zooplankton species that were found within two K. brevis blooms, A. tonsa, P. quasimodo, and L. aestiva, using 14C labeled K. brevis cells. Grazing rates were then applied to the zooplankton community and grazing assessed. Grazing pressure was occasionally heavy, and was capable of reducing K. brevis to background concentrations at stations in the 1999 bloom and at 1 station in the 2001 bloom. Generally, however, grazing pressure proved to be insufficient to reduce K. brevis to background concentrations during the 1999 and 2001 blooms.
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