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The influence of the Loop Current on the diversity, abundance, and distribution of zooplankton in the Gulf of Mexico

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Title:
The influence of the Loop Current on the diversity, abundance, and distribution of zooplankton in the Gulf of Mexico
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Rathmell, Katie
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Copepods
Euphausiids
Vertical migration
Frontal boundary
Sea surface temperature
Dissertations, Academic -- Marine Science -- Masters -- USF   ( lcsh )
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bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

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Abstract:
ABSTRACT: Physical processes in the Gulf of Mexico (GOM) and mesoscale (10-300 km) processes associated with the Loop Current are fairly well known. However, little is known about the physical/ biological interactions of the frontal boundary system of the Loop Current. Zooplankton abundance and distribution was determined at 28 stations in the vicinity of the Loop Current. Species richness was high at all stations. Copepods comprised 60% of the total zooplankton collected. Oithona plumifera, Nannocalanus minor and Euchaeta marina were the most abundant copepods. Chaetognaths and ostracods were also very abundant and made up 11 and 5 % respectively of the zooplankton total. Total zooplankton abundance was higher at the boundary of the LC than it was inside the LC but not significantly different from abundances outside of the LC. Stations in the western Gulf of Mexico and on the western boundary had the highest abundances of zooplankton overall. The chlorophyll concentrations at the chlorophyll maximum were higher at the boundary of the LC than inside the LC. Physical-biological processes associated with the frontal boundary of the LC appear to influence the abundance and distribution of zooplankton in the GOM.
Thesis:
Thesis (M.S.)--University of South Florida, 2007.
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Includes bibliographical references.
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by Katie Rathmell.
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The Influence of the Loop Current on th e Diversity, Abundance and Distribution of Zooplankton in the Gulf of Mexico by Katie Rathmell A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Department of Biological Oceanography College of Marine Science University of South Florida Major Professor: Kendra Daly, Ph.D. Ernst Peebles, Ph.D. Gabriel Vargo, Ph.D. Date of Approval: March 16, 2007 Keywords: copepods, euphausiids, vertical migration, frontal boundary, sea surface temperature Copyright 2006, Katie Rathmell

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Acknowledgements Thanks to Dr. Kendra Daly for her guidance and support throughout this process. Thanks to my committee members Dr. Ernst Peebles and Dr. Gabriel Vargo. Dr. Bruce Comyns, University of Southern Missi ssippi, Gulf Coast Research Lab, for providing zooplankton samples from the Sargassum cruise. Dr. Jo anne Lyczkowski-Shultz for providing access to SEAMAP samples and data. Mark Leiby and Kim Williams for their technical support and friendship. Mindy Stokes for her patience and continued support.

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i Table of Contents List of Tables................................................................................................................. ...ii List of Figures..................................................................................................................iii Abstract....................................................................................................................... .....iv Introduction................................................................................................................... .....1 Methods..............................................................................................................................8 Study area...............................................................................................................8 GCRL data.............................................................................................................8 SEAMAP data........................................................................................................8 Identification methods...........................................................................................9 Statistics...............................................................................................................10 Results........................................................................................................................ ......12 Diversity...............................................................................................................12 Abundance and Distribution................................................................................13 Environmental parameters...................................................................................30 Discussion........................................................................................................................31 Conclusions......................................................................................................................36 References........................................................................................................................37 Appendices.......................................................................................................................41 Appendix A: Zooplankton species collected in the GOM during May 2003.......42 Appendix B: Cruise log, total zooplankton abundance data and environmental parameters..............................................................45 Appendix C: Total number of indi viduals (N) in each split and the abundance of individuals per m 3 (No. m -3 )....................................47

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ii List of Tables Table 1 Total number of copepods in sample splits (N), percent contribution of copepods (% Copepods) and percent contribution of copepods to the total zooplankton in splits (% Total)..................................................................................................12 Table 2 Copepods with the highest abundances (No. m -3 ) from each station.......14 Table 3 Arithmetic mean (Mean) (No m -3 ), geometric mean (GM) (No. m -3 ) and range of means of zooplankton collected from the GOM in May 2003...................................................................................17 Table 4 SIMPER analys is of copepod contribution..............................................27 Table 5 Day and night abundances.......................................................................29 Table 6 Mean chlorophyll a (mg m -3 ) from surface, chlorophyll maximum or midwater depth and 200 m depth at SEAMAP stations.........................30

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iii List of Figures Figure 1. Sea surface temperature image (SST) image taken on May16, 2003 taken by the AVHRR on the NOAA polar orbiting satellite............2 Figure 2. Image of the study area in May 2003.........................................................3 Figure 3. Multidimensional scalin g plot with cluster overlay.................................23 Figure 4. ANOSIM test showing a significant difference (R = 0.212) in zooplankton species and a bundance between regions 1 (inside the LC) and 5 (western outside LC).............................................24 Figure 5. ANOSIM test showing a significant difference (R = 0.125) in zooplankton species and abundance between regions 1 (inside the LC) and 3 (wes tern boundary of the LC)...............................25 Figure 6. ANOSIM test showing a si gnificant difference (R = 0.117) in zooplankton species an d abundance from region 1 (inside the LC) and regions 4 & 5 (stations outside the LC)...................25

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iv The Influence of the Loop Current on th e Diversity, Abundance and Distribution of Zooplankton in the Gulf of Mexico Katie Rathmell ABSTRACT Physical processes in the Gulf of Mexico (GOM) and mesoscale (10-300 km) processes associated with the Loop Current are fairly well known. However, little is known about the physical/ biological interactions of the frontal boundary system of the Loop Current. Zooplankton abundance and distri bution was determined at 28 st ations in the vicinity of the Loop Current. Species richness was high at all stations. Copepods comprised 60% of the total zooplankton collected. Oithona plumifera, Nannocalanus minor and Euchaeta marina were the most abundant copepods. Chaetogna ths and ostracods were also very abundant and made up 11 and 5 % respectiv ely of the zooplankton total. Total zooplankton abundance was higher at the boundary of the LC than it was inside the LC but not significantly different from abundances outside of the LC. Stations in the western Gulf of Mexico and on the western boundary had the highest abunda nces of zooplankton overall. The chlorophyll concen trations at the chlorophyll maximum were higher at the boundary of the LC than inside the LC. Physi cal-biological processes associated with the frontal boundary of the LC appear to in fluence the abundance and distribution of zooplankton in the GOM.

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1 Introduction The Loop Current (LC) in the Gulf of Mexico (GOM) is formed by an intrusion of warm water from the Caribbean, enteri ng through the Yucatan St raits and extending northward to about 26 N (Muller-Karger et al., 2001). Occasionally, the current will extend as far as 29 N (Muller-Karger et al., 2001); however, these events only occur about every three to five years. The eastern boundary of the LC usually is adjacent to and, at times, covers the west Florida shelf (L ohrenz et al., 1999; Mulle r-Karger et al., 2001). Seawater temperature varies, but the LC is characteristically warmer than resident GOM water. Warm LC water extends down into the water column to a depth of 150 to 200 m, detectable by the depth of the 22 C isothe rm (Williams et al., 1977; Muller-Karger et al., 2001). Therefore, the LC is easily identifie d by sea surface temperature (SST) images taken by the Advanced Very High Resoluti on Radiometer (AVHRR) on the NOAA polar orbiting satellite (Fig. 1). In a ddition, salinity is usually higher ( 36) in the LC than in resident GOM water (Bennett and Hopkins 1989). Images taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra and Aqua satellites, also show LC waters entering through the Yucatan straits as dark blue, indicating low chlorophyll levels (Fig. 2).

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2 Fig. 1. Sea surface temperature (SST) image taken on May 16, 2003 by the AVHRR on the NOAA polar orbiting satellite. Warmer water of the LC appears as purple, and resident GOM water as orange, white is no data or clouds. Image from the USF Remote Sensing Lab http://imars.usf.edu/index.html

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3 Fig. 2. Image of the study area in May 2003. SEAMAP and GCRL stations are included. Higher values ofchlorophyll appear as light green to yellow and can be seen along the coast and around the LC edges. GCRL stations with 1700x designation are labeled and denoted by red circles. MODIS image compiled by Carrie Wall (US

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4 Large eddies that form on the norther n boundary of the LC (Williams et al., 1977; Muller-Karger et al., 2001) can bring warm water to shelf areas when they separate from the LC. Warm core rings (WCR) break off fr om the current (Muller-Karger et al., 2001) and often move into the western GOM causi ng the LC to be positioned farther south (Williams et al., 1977). A WCR breaks off from th e LC when the current extends into the northeastern GOM (NEGOM), becomes unstable and eventually separates. The rings can measure 300 km across, generate current veloci ties of 3-4 knots, and persist for up to a year (Sturges et al., 2005). These rings are fo rmed periodically and may play a large role in the ecology of the NEGOM. Mesoscale e ddies of cyclonic and anticyclonic rotation occur throughout the GOM generated by the LC (Muller-Karger et al ., 2001; Sturges et al., 2005). The edges of anticyclones and the cente rs of cyclones appear to be areas of higher productivity (Yoder and Mahood, 1983; Biggs, 1992). When eddies interact with shelf areas they influence flow and pressu re gradients, and may resuspend nutrients (Muller-Karger et al., 2001; St urges et al., 2005). Eddies ar e also a potential transport mechanism for larval fishes and other plan kton (Lee et al., 1994; Lohrenz et al., 1999). The current exits the GOM through the Florida Straits and eventually becomes the Gulf Stream (Muller-Karger et al., 2001). Frontal boundaries between two water masses and fronts associated with the relatively fast moving circular currents of eddies are often areas of relatively high productivity (Daly and Smith, 1993). The LC has a frontal boundary that is identifiable by a change in salinity and temperature, as well as from SST im ages before the GOM

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5 surface becomes isothermal in late spring or early summer (Richards et al, 1993; Sturges et al, 2005). Previous studies have shown higher abundan ces of larval fish associated with the LC frontal boundary (Richards et al., 1993). In addition, studies in fronts located at the Mississippi River plume and the Gulf Stream ha ve indicated that nekton may aggregate at the boundaries due to temperature preferen ce or because of an enhanced feeding environment (Govoni, 1993). Frontal boundaries and eddies induce vertical motion thereby bringing deep water with higher nutrient concentrations into surface waters, which supports the growth of phytoplankton at the base of the ma rine planktonic food web. Upwelling has been observed in associati on with the LC and LC eddies (Lohrenz et al., 1999). In general, the GOM is oligotrophic in areas not associated with coastal waters (Bennett and Hopkins, 1989). Estimated chlo rophyll values for the GOM range from >0.18 mg m -3 in December-February to 0.06 in May-July based on concentrations derived from the Color Zone Coastal Survey (CZC S) pigment fields from November 1978 to November 1985 ( http: www.imars.usf.edu ). Satellite images i ndicate that there are relatively low chlorophyll levels within the LC but elevated levels of chlorophyll at the edge of the current (Fig. 2). Along the eastern boundary of the LC, higher concentrations of chlorophyll were correlated to higher levels of production (Yoder and Mahood, 1983). Previous studies have found that mean leve ls of primary production range from 0.18 to 3.86 g C m -2 d -1 in coastal areas to 0.10 to 0.39 g C m -2 d -1 in areas associated with eddies from the LC (Biggs, 1992). Frontal boundari es associated with the LC may support

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6 higher phytoplankton pr oductivity, resulting in food sources that could sustain higher abundances of zooplankton. In subtropical waters, such as the GO M, biological diversity is generally high, while biomass is usually low to intermedia te (Hopkins and Lancraft, 1984; Daly and Smith, 1993). GOM zooplankton standing st ock averages 1.2 g dry weight m -2 but may be much higher at the boundary of the LC and LC eddies (Lamkin, 1997). Copepods are the dominant taxa both numerically and by weight (Hopkins, 1982). In addition, zooplankton biomass has high diel variability, with the highest biomass being recorded in night tows, suggesting that zooplankton vert ical migration is common in this region (Bennett and Hopkins, 1989). Copepods and eu phausiids vertically migrate to avoid predators and to feed (Hays et al., 1994). The abundant zooplankton species of the GOM and nearby regions have been described. For example, Grice (1960) iden tified 38 species of calanoid and cyclopoid copepods from the Florida Gulf coast and the Florida Keys. Bjornberg (1971) documented plankton from the Caribbean and GOM and Hopkins and Lancraft (1984) identified 148 species of larval fishes and crustaceans from a stat ion in the eastern GOM (27N 86W). In addition, Owre (1962) identif ied 129 species of pelagic copepods found in the Florida Current. Copepods typically obs erved in the Caribbean Sea are also found in the GOM (Owre and Foyo, 1964). Common copepod genera found in the open water regions of the GOM include Euchaeta, Eucalanus, Neocalanus, Calanus, Scolecithrix, Pleuromamma, Clausocalanus, Oithona, Corycaeus, and Aetideus among others

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7 (Hopkins and Lancraft, 1984). Ot her zooplankton taxa includ e chaetognaths, polychaetes, ostracods, scyphozoans, hydrozoans, pteropods decapods, amphipods, and euphausiids. Although zooplankton composition in coastal and shelf habitats is relatively well known, there is little information on zoopla nkton in the central and western oceanic region of the GOM. Also very little is known about the ecology of zooplankton in the LC. In particular, the edge of the LC is of inte rest as it may act as a frontal boundary, having higher nutrient concentrations and food resources that may support higher abundances of zooplankton. The goal of this study was to investigate the diversity, abundance, and distribution of zooplankton in the vicinity of the LC in order to better understand the ecological impact of this boundary system.

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8 Methods Study area Plankton tows were collected in the NEGOM during May 2003 between 24N to 29N and 84W to 90W by me mbers of the Gulf Coast Research Lab (GCRL) and National Marine Fisheries Service (NMFS) as part of the SEAMAP program (Fig. 2). The LC boundary was located by SST images for the GCRL study. A subset of samples from these cruises was analyzed as described below. GCRL dataPlankton tows were conducted May 13-16, 2003 aboard the GCRL ship R/V Tommy Munro on cruise 17-031 for the sole purpose of sampling the LC. The LC was located by SST images and a subset of ten sample stations, designated 1700117010 was chosen from inside the current and at current boundaries (Fig. 2). Plankton were collected using 61 cm paired bongo nets having a 333 m mesh, with a flow meter attached to the net frame. The nets were to wed at a 45 oblique angle to 200 m and back to the surface. Samples were initially fixed in 10% buffered formalin, then transferred to a 95% ethyl alcohol solution and transported to GCRL. E ach sample was sorted to remove ichthyoplankton. Zooplankton samples we re processed at the University of South Florida (USF). Surface chlorophyll a values were estimated using MODIS images provided by the Institute for Marine Remote Sensing at USF. MODIS provides an estimate of average pigment concentration. SEAMAP dataGOM zooplankton were collect ed during May 2003 aboard the NOAA ship Oregon II on cruise 04-253 as part of th e spring plankton survey. SEAMAP stations are located along a fixed grid. The s ubset of 18 samples analyzed for this study

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9 was picked according to the location of the st ation relative to the LC (Fig. 2). Plankton tows were conducted at a 45 oblique angle to 200 m and back to the surface using 61 cm paired bongo nets having a 333 m mesh net a nd attached flow meter. All samples were fixed in 10% buffered formalin and then tr ansferred to 95% ethyl alcohol. Sorting and ichthyoplankton identification we re carried out at the Polish Sorting and Identification Center in Szczecin, Poland. One half aliquots of the zooplankton samples were sent from Poland and processed at USF. Three CTD casts were made at each station and water for chlorophyll measurements was collected using ni skin bottles attached to the CTD rosette. Water samples were taken at the surface, mid-water (99.3 m) or at the chlorophyll maximum, and 200 m. An in situ fluorescence sensor determined the depth of the chlorophyll maximum. Identification methods Twenty-eight zooplankton samples were sorted for large specimens, which were removed and stored in 70% ethanol. The remaining sample was split in a Folsom splitter until about 100 indi viduals of the most common taxa were present; typically 5-7 splits were required. Spl its were labeled and stor ed in 70% ethanol. The final split was sorted, counted, and id entified under a dissecting microscope. Copepods were identified to genera and species when possible, other taxa to Order or Family (Appendix A). Adult copepods were measured from the top of the cephalosome, not including rostral filaments or antennae, to the end of the urosome, not including the caudal rami se tae. Copepodites younger than stage IV and unidentified adult copepods were not measured. Euphausiid s were identified and sex determined. The volume of water filtered through th e Bongo nets was calculated by:

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10 Volume filtered (m 3 ) = (flowmeter stop flowmeter start) x 0.007598 (rotor constant) Zooplankton abundance was calculated as: (No. m -3 ) = (# in subsample x sample fraction) / vol. filtered (m 3 ) Cruise log data and environmental paramete rs from both cruises are shown in Appendix B. Samples were categorized as to location re lative to the LC and as day (0700-1900) or night (1900-0700) tows according to SEAMAP pr otocols to evaluate vertical migration. StatisticsSome of the data were not nor mally distributed, therefore, the geometric mean was used as a measure of cen tral trend and non-pa rametric tests were used as described below. PRIMER v.6 was used for several non-parametric data analyses. First, a Bray-Curtis similarity lower triangular resemblance matrix was created as a base analysis using all species and their abundances for each sample. Tests completed in PRIMER were initially perfor med using transformations including square root, fourth root, natural log, and presence-absence. The tr ansformations did not change the data at all, in fact the stress value on the MDS plots increased with the transformations. Therefore, non-transformed data was used to run tests in PRIMER. Non-metric multidimensional scaling (MDS) was performed and plots were created to determine which samples are most similar in abundan ce between stations, using the previously mentioned factors. The MDS routine construc ts a configuration of the samples, which attempts to satisfy all the conditions, imposed by the similarity matrix mentioned above. For instance, if sample 1 is more similar to sample 3 than it is to sample 2 then sample 1 will be placed closer on the map to sample 3 than it is to sample 2 (Clark and Warwick, 2001). Cluster analysis was performed and superimposed on MDS plots.

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11 Then, a global ANOSIM was run and follo wed by pairwise comp arisons. Pairwise tests were completed once for each factor in order to compare differences between day/night, location (i nside LC, outside LC, boundary of LC ) or region, where the stations were further broken down into (1) inside LC (2) eastern boundary of LC, (3) western boundary of LC, (4) eastern GOM outside of LC and (5) western GOM outside of LC. One-way analysis of similarity (ANOSIM) was performed to test the null hypothesis, that there were no differences between samples. U nder the null hypothesis, R is centered near zero in the ANOSIM routine. ANOSIM gives a measure of the level of difference between samples. Similarity was measured using the SIMPER (similarity percentage) routine in which Bray-Curtis similarity is measured, and the percentage contribution of each species is listed in decreasing order of contribution. SIMPER was then used to compare specific samples from different areas to determine differences in species composition. Finally, a one-tailed Mann-Whitney test was performed to determine differences in temperatures from the LC and resident GOM water; a Krus kal-Wallis test was performed to determine differences in chlorophyll concentrations (Z ar, 1974). In addition, a Newman-Keuls test for unequal sample sizes was used to assess di fferences in factors among stations inside the LC, at the boundary of the LC, and outside the LC. These tests were calculated at = 0.05.

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12 Results DiversityA list of all zooplankton taxa and species identified for this study is shown in Appendix A. A total of 47 genera and 101 species of c opepods were identified from 28 samples. Four genera and 11 speci es of euphausiids were identified. Stations 17003 and 17004 inside the LC exhibited the high est diversity of species with 70 and 67 species identified respectively, while Sta. 44 inside the LC had the lowest number of species (41). Oithona plumifera made up 9% of the total number of copepods and about 5% of the total zooplankton (Table 1). Th e top eight most abundant copepods from all stations combined made up about 44% of the copepod total. Table 1. Total number of copepods in sample splits (N), percent contribution of copepods (% Copepods), and percent contribution of copepods to the total zooplankton in splits (% Total). Copepods N % Copepods % Total Oithona plumifera 490 9.01 4.89 Nannocalanus minor 416 7.65 4.15 Euchaeta marina 371 6.82 3.70 Oithona spp. 310 5.70 3.10 Clausocalanus arcuicornis 230 4.23 2.30 Clausocalanus furcatus 226 4.16 2.26 Lucicutia flavicornis 198 3.64 2.00 Scolecithrix danae 197 3.62 1.97

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13 Abundance and distributionWhile Oithona plumifera Nannocalanus minor and Euchaeta marina were consistently among th e most abundant (0.94-13.52 m -3 ) copepods at all stations, there were se veral other species with rela tively high densities at some stations. For instance Scolecithrix danae had the highest abunda nce at stations 17003 and 17009 inside the LC (Table 2). Also several copepod species, such as Clausocalanus arcuicornis Clausocalanus furcatus and Lucicutia flavicornis were relatively abundant in many samples. A couple of species had high de nsities in only one sample. For example, Temora stylifera was abundant at the boundary Sta. 46, and Acartia danae was the dominant copepod at Sta. 20. The top copepod species contributors in daytime samples also were O. plumifera E. marina, and N. minor in decreasing order. The top nighttime contributors in decr easing order were N. minor O. plumifera, and E. marina.

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14 Table 2. Copepods with the highest abundances (No. m -3 ) from each station. Station numbers are shown in bold and designated as Day or Night, regions are labeled Inside, Boundary, and Outside and (N) is total number of individuals in splits. Inside Inside 17001 Day N No. m -3 17010 Day N No. m -3 Oithona setigera 10 1.56 Oithona plumifera 23 13.52 Corycaeus speciosus 9 1.41 Clausocalanus furcatus 13 7.64 Euchaeta marina 9 1.41 Eucalanus monachus 9 5.29 Mesocalanus tenuicornis 7 1.10 Lucicutia flavicornis 7 4.11 Nannocalanus minor 6 0.94 Clausocalanus arcuicornis 7 4.11 17002 Day 22 Night Oithona setigera 31 5.54 Nannocalanus minor 25 5.55 Euchaeta marina 14 2.50 Euchaeta marina 11 2.44 Corycaeus speciosus 7 1.25 Pleuromamma abdominalis 11 2.44 Oithona plumifera 7 1.25 Corycaeus catus 10 2.22 17003 Day 24 Night Scolecithrix danae 30 5.95 Euchaeta marina 19 5.09 Oithona setigera 24 4.76 Oithona plumifera 18 4.82 Oithona plumifera 18 3.57 Nannocalanus minor 12 3.21 Euchaeta marina 17 3.37 36 Night Corycaeus speciosus 13 2.58 Nannocalanus minor 16 3.73 17004 Night Lucicutia flavicornis 11 2.57 Oithona sp. 43 7.19 Oithona plumifera 11 2.57 Oithona plumifera 25 4.18 Euchaeta marina 10 2.33 Euchaeta marina 21 3.51 38 Day Clausocalanus arcuicornis 14 2.34 Pleuromamma abdominalis 16 8.75 17007 Day Oithona plumifera 13 7.11 Nannocalanus minor 24 7.05 Nannocalanus minor 11 6.01 Oithona plumifera 22 6.46 Euchaeta marina 9 4.92 Haloptilus longicornis 11 3.23 42 Day Euchaeta marina 11 3.23 Nannocalanus minor 17 4.40 17008 Night Oithona plumifera 15 3.88 Clausocalanus arcuicornis 12 4.04 Euchaeta marina 11 2.84 Euchaeta marina 8 2.69 Clausocalanus arcuicornis 7 1.81 Nannocalanus minor 7 2.36 44 Night Pleuromamma piseki 7 2.36 Oithona plumifera 22 12.29 17009 Day Pleuromamma abdominalis 11 6.14 Scolecithrix danae 18 12.32 Lucicutia flavicornis 10 5.58 Nannocalanus minor 18 12.32 Nannocalanus minor 9 5.03 Oithona plumifera 14 9.58 Euchaeta marina 10 6.85 Clausocalanus arcuicornis 10 6.85

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15 Table 2. Continued Boundary Outside 17005 Day N No. m -3 9 Night N No. m -3 Oithona plumifera 20 2.85 Eucheata marina 22 9.99 Clausocalanus arcuicornis 14 1.99 Nannocalanus minor 17 7.72 Euchaeta marina 16 2.28 Lucicutia flavicornis 10 4.54 Clausocalanus furcatus 13 1.85 Clausocalanus furcatus 9 4.09 Undinula vulgaris 9 1.28 Clausocalanus arcuicornis 8 3.63 17006 Night 19 Night Oithona plumifera 36 6.16 Nannocalanus minor 24 5.02 Euchaeta marina 33 5.65 Euchaeta marina 18 3.76 Clausocalanus arcuicornis 28 4.79 Oithona plumifera 18 3.76 Clausocalanus furcatus 21 3.59 Clausocalanus furactus 12 2.51 Pleuromamma piseki 13 2.23 Lucicutia flavicornis 9 1.88 20 Day 27 Day Acartia danae 21 7.86 Oithona plumifera 26 12.53 Euchaeta marina 19 7.11 Clausocalanus arcuicornis 14 6.75 Lucicutia flavicornis 16 5.99 Oncaea mediterranea 14 6.75 Nannocalanus minor 16 5.99 Clausocalanus furcatus 10 4.82 Oithona plumifera 16 5.99 Acartia danae 9 4.34 29 Night 50 Night Oithona plumifera 24 12.33 Oithona plumifera 18 9.43 Nannocalanus minor 17 8.73 Euchaeta marina 17 8.91 Euchaeta marina 12 6.16 Clausocalanus arcuicornis 15 7.86 40 Day Nannocalanus minor 13 6.81 Nannocalanus minor 21 10.58 52 Day Lucicutia flavicornis 16 8.06 Nannocalanus minor 49 6.34 Oithona plumifera 14 7.06 Oithona plumifera 39 5.05 Neocalanus sp. 11 5.54 Oithona setigera 37 4.79 46 Day Clausocalanus furcatus 33 4.27 Oithona plumifera 32 11.06 Euchaeta marina 29 3.75 Eucalanus monachus 24 8.30 Scolecithrix danae 25 3.24 Temora stylifera 23 7.95 54 Night Clausocalanus furcatus 18 6.22 Nannocalanus minor 21 5.10 Euchaeta marina 18 6.22 Euchaeta marina 13 3.16 Nannocalanus minor 17 5.88 Scolecithrix danae 13 3.16 94 Day Oithona plumifera 7 1.70 Oithona plumifera 23 9.95 56 Night Clausocalanus furcatus 17 7.35 Oncaea mediterranea 18 9.44 Lucicutia flavicornis 17 7.35 Nannocalanus minor 17 8.91 Oncaea mediterranea 13 5.62 Clausocalanus furcatus 16 8.39 Oithona plumifera 13 6.81

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16 A comparison of stations within the LC, at the boundary of the LC, and outside the LC revealed that Oithona plumifera was the most abundant sp ecies of copepod in all regions, with geometric means ranging between 4.03 7.20 m -3 followed by Nannocalanus minor (4.10 5.98 m -3 ) and Euchaeta marina (3.15 4.87 m -3 ) (Table 3). Some species that were found only inside the LC include Acartia tonsa, Acrocalanus gracilis, Aetideopsis carinata, Chiridius grac ilis, Corycaeus furcifer, Farranula carinata, Labidocera nerii, and Paracandacia simplex. The boundary stations had the highest abundances of ostracods (6.05 m -3 ), gastropods (4.91 m -3 ), foraminifera (4.45 m -3 ), salps (2.98 m -3 ), and polychaetes (1.67 m -3 ), as well as high richne ss of copepods, including Corycaeus speciosus, Farranula gracilis, L ubbokia squillimana, Lucicutia flavicornis, Mecynocera clausii, Mesocalanus tenuicornis, and Temora stylifera. Candacia bipinnata and Candacia curta were found only in samples co llected outside the LC. After copepods, chaetognaths were the second highe st contributor to total zooplankton abundance at all stations, with densities ranging from 2.22 to 25.8 m -3 followed by ostracods, which ranged from 1.67 to 15.6 m -3 Euphausiids made up about 5% of the zooplankton collected an d ranged from 0.73 to 13.8 m -3

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17 Table 3. Arithmetic mean (Mean) (No.m -3 ), geometric mean (GM) (No.m -3 ), and range of means of zooplankton collected from the GOM in May 2003 Inside of LC Outside of LC LC Boundary Zooplankton Mean GM Range Mean GM Range Mean GM Range Acartia sp. 0.08 0.27 0-0.34 0.65 0.50 0-1.05 0.02 0-0.17 Acartia danae 0.56 0.50 0-1.37 1.72 1.00 0.24-3.14 2.65 1.41 0-7.86 Acartia tonsa 0.01 0-0.2 0.00 0.00 0.00 0.00 Acrocalanus sp. 0.22 0.62 0-2.35 0.02 0-0.13 0.22 0.51 0-0.51 Acrocalanus gracilis 0.02 0-0.31 0.00 0.00 0.00 0.00 Acrocalanus longicornis 0.35 0.45 0-1.39 0.00 0.00 0.60 0.80 0-2.77 Aetideopsis carinata 0.01 0-0.18 0.00 0.00 0.00 0.00 Aetideus armatus 0.04 0.25 0-0.34 0.15 0-1.05 0.06 0-0.43 Aetideus acutus 0.05 0.33 0-0.20 0.44 0.43 0-0.45 0.27 0.75 0-1.54 Aetideus giesbrechti 0.05 0.22 0-0.34 0.68 0.61 0-0.96 0.87 1.07 0-3.46 Aetideus sp. 0.01 0-0.17 0.00 0.00 0.10 0-0.17 Calanus sp. 0.43 0.72 0-2.94 0.97 0.77 0-1.93 1.31 1.39 0-4.54 Calocalanus pavo 0.78 0.57 0.16-2.79 0.91 0.60 0-2.62 1.67 1.28 0.28-3.46 Calocalanus teniculus 0.01 0-0.20 0.28 0-1.93 0.37 0-2.57 Candacia sp. 0.08 0.22 0-0.36 0.74 0.63 0-1.05 0.38 0.80 0-1.20 Candacia pachydactyla 0.17 0.38 0-1.37 0.07 0-0.52 0.20 0.66 0-0.87 Candacia paenelongimana 0.17 0.67 0-2.23 0.13 0-0.91 0.00 0.00 Candacia catula 0.01 0-0.17 0.02 0-0.13 0.04 0-0.28 Candacia longimana 0.02 0-0.22 0.04 0-0.26 0.05 0-0.35 Candacia bipinnata 0.00 0.00 0.33 0.31 0-0.45 0.00 0.00 Candacia curta 0.00 0.00 0.07 0-0.52 0.00 0.00 Candacia varicans 0.19 0.88 0-0.52 1.55 1.23 0-2.62 0.18 0.57 0-0.87 Canthocalanus pauper 0.03 0.18 0-0.20 0.75 0-5.24 0.25 0-1.73 Centropages violaceus 0.01 0-0.16 0.00 0.00 0.02 0-0.17 Clausocalanus arcuicornis 2.14 1.54 0.29-4.11 3.49 2.00 0.24-7.86 3.44 3.21 1.99-4.86

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18 Table 3. Continued Inside of LC Outside of LC LC Boundary Zooplankton Mean GM Range Mean GM Range Mean GM Range Clausocalanus furcatus 1.99 1.07 0.18-6.85 4.10 3.62 1.46-8.39 3.98 3.55 1.85-7.35 Clausocalanus sp. 0.06 0.22 0-0.29 1.47 1.14 0-2.62 0.58 1.16 0-2.05 Copilia quadrata 0.18 0.34 0-0.54 0.69 0.57 0-1.45 0.25 0.37 0-0.87 Copilia vitrea 0.04 0-0.56 0.00 0.00 0.07 0-0.50 Corycaeus catus 0.89 1.41 0-3.28 0.02 0-0.13 1.05 1.14 0-3.08 Corycaeus flaccus 0.26 0.50 0-0.18 1.64 1.34 0-3.14 0.77 1.19 0-2.02 Corycaeus furcifer 0.07 0-0.31 0.00 0.00 0.00 0.00 Corycaeus latus 0.20 0.41 0-1.98 0.66 0.46 0-1.57 0.44 0.60 0-1.30 Corycaeus lautus 0.09 0.52 0-0.88 0.79 0.55 0-1.68 0.10 0.21 0-0.37 Corycaeus limbatus 0.41 0.62 0-2.35 0.41 0-2.89 0.83 0.69 0.14-1.30 Corycaeus longistylus 0.00 0.00 0.00 0.00 0.07 0-0.51 Corycaeus sp. 0.34 0.66 0-2.34 1.79 1.27 0.21-4.72 0.75 0.83 0-1.54 Corycaeus speciosus 1.24 1.08 0.44-2.58 0.82 0.66 0-1.82 1.52 1.28 0.43-3.46 Corycaeus typicus 0.31 0.53 0-1.18 1.30 1.19 0-1.82 0.39 0.45 0-1.73 Eucalanus attenuatus 0.88 0.74 0-3.42 1.19 0.84 0-2.62 1.65 0.98 0.17-3.02 Eucalanus elongatus 0.14 0.46 0-0.68 0.75 0.54 0-1.57 0.32 0.71 0-1.03 Eucalanus monachus 0.43 1.90 0-5.29 0.65 0.52 0-1.57 1.62 1.16 0-8.30 Eucalanus mucronatus 0.16 0.60 0-1.35 0.00 0.00 0.09 0.20 0-0.35 Eucalanus sp. 0.09 0.63 0-0.68 0.45 0-1.57 0.82 1.62 0-5.24 Euchaeta marina 3.15 2.82 1.18-6.85 4.87 4.12 2.10-9.99 4.54 4.98 0-7.11 Euchaeta media 0.00 0.00 0.50 0.50 0-0.52 0.00 0.00 Euchaeta sp. 0.36 0.64 0-0.88 1.55 0.90 0-5.24 0.77 0.67 0-1.73 Euchirella bitumida 0.00 0.00 0.37 0.33 0-0.52 0.00 0.00 Euchirella curticauda 0.00 0.00 0.07 0-0.52 0.00 0.00 Euchirella sp. 0.08 0.36 0-0.59 0.00 0.00 0.00 0.00 Farranula gracilis 0.40 0.65 0-2.38 1.10 0.80 0-2.10 1.39 1.65 0-3.80 Farranula carinata 0.04 0-0.60 0.00 0.00 0.00 0.00 Farranula sp. 0.01 0-0.20 0.00 0.00 0.00 0.00

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19 Table 3. Continued Inside of LC Outside of LC LC Boundary Zooplankton Mean GM Range Mean GM Range Mean GM Range Gaetanus minor 0.00 0.00 0.07 0-0.52 0.02 0-0.17 Gaetanus pileatus 0.02 0-0.34 0.00 0.00 0.00 0.00 Gaetanus miles 0.00 0.00 0.06 0-0.45 0.00 0.00 Gaetanus latifrons 0.00 0.00 0.07 0-0.52 0.00 0.00 Haloptilus austini 0.11 0.27 0-0.56 0.49 0.48 0-0.52 0.06 0-0.43 Haloptilus longicornis 1.26 0.96 0.17-3.23 1.68 1.32 0-3.67 1.46 0.96 0.35-3.02 Haloptilus mucronatus 0.04 0.00 0-0.59 0.00 0.00 0.07 0-0.50 Haloptilus sp. 0.08 0.32 0-0.31 0.04 0-0.26 0.04 0.15 0-0.17 Heterohabdis papilliger 0.21 0.69 0-2.79 0.44 0.39 0-0.63 0.20 0.67 0-0.87 Heterohabdis sp. 0.00 0.00 0.21 0-1.45 0.07 0-0.51 Labidocera nerii 0.02 0-0.33 0.00 0.00 0.00 0.00 Lubbokia aculeata 0.01 0-0.17 0.00 0.00 0.00 0.00 Lubbokia magna 0.01 0-0.17 0.00 0.00 0.00 0.00 Lubbokia squillimana 0.08 0.25 0-0.56 0.04 0-0.26 0.79 0.88 0-1.38 Lucicutia clausi 0.10 0.32 0-0.59 0.00 0.00 0.00 0.00 Lucicutia flavicornis 2.36 1.64 0.18-6.16 2.38 1.61 0.13-4.54 3.61 2.36 0-8.06 Lucicutia longicornis 0.00 0.00 0.02 0-0.13 0.00 0.00 Lucicutia sp. 0.01 0-0.17 0.36 0.34 0-0.45 0.13 0.47 0-0.51 Macrostella gracilis 0.02 0-0.22 0.00 0.00 0.00 0.00 Mecynocera clausii 0.10 0.67 0-0.68 1.17 0.80 0-1.93 0.48 1.40 0-2.60 Mesocalanus tenuicornis 0.49 0.72 0-1.76 0.71 0.47 0-1.82 1.45 1.08 0-4.15 Metridia sp. 0.01 0-0.17 0.00 0.00 0.07 0-0.50 Microstella sp. 0.00 0.00 0.02 0-0.13 0.10 0-0.69 Nannocalanus minor 4.10 3.10 0.54-12.32 5.98 5.47 1.93-8.91 5.51 4.06 0.57-10.58 Neocalanus gracilis 0.60 0.48 0.16-1.59 0.41 0.40 0.24-0.52 0.21 0.72 0-0.75 Neocalanus robustior 0.07 0-0.70 0.51 0.51 0-0.52 0.13 0.43 0-0.51

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20 Table 3. Continued Inside of LC Outside of LC LC Boundary Zooplankton Mean GM Range Mean GM Range Mean GM Range Neocalanus sp. 0.58 0.61 0-1.76 0.68 0.44 0-1.57 1.25 1.13 0-5.54 Neocalanus tonsus 0.00 0.00 0.07 0-0.48 0.00 0.00 Oithona plumifera 5.11 4.03 0-13.52 6.13 5.14 1.70-12.53 7.91 7.20 2.85-12.33 Oithona robusta 0.14 0.37 0-0.40 0.00 0.00 0.05 0-0.35 Oithona setigera 1.23 0.95 0-5.54 2.09 1.56 0-4.79 0.83 0.81 0-1.54 Oithona sp. 2.48 2.12 0-7.19 4.64 4.03 0-9.16 5.83 3.12 0.35-13.61 Oncaea media 0.11 0.35 0-1.19 3.44 2.19 0-6.81 0.37 0.84 0-1.20 Oncaea mediterranea 0.70 0.64 0-2.05 3.70 2.09 0.24-9.44 2.75 2.35 1-5.62 Oncaea sp. 0.51 0.55 0-2.17 2.28 1.27 0-4.19 0.91 0.83 0-3.53 Oncaea venusta 0.10 0.67 0-0.68 0.00 0.00 0.00 0.00 Pachos tuberosum 0.05 0.32 0-0.59 0.02 0-0.13 0.12 0.42 0-0.51 Paracalanus aculeatus 0.04 0.26 0-0.33 0.00 0.00 0.00 0.00 Paracalanus parvus 0.09 0.63 0-0.79 0.00 0.00 0.04 0-0.28 Paracalanus sp. 0.04 0.27 0-0.36 0.03 0-0.21 0.00 0.00 Paracandacia bispinosa 0.01 0-0.16 0.00 0.00 0.00 0.00 Paracandacia sp. 0.00 0.00 0.00 0.00 0.05 0-0.35 Paracandacia simplex 0.14 0.51 0-1.18 0.00 0.00 0.00 0.00 Phyllops helgae 0.03 0-0.40 0.00 0.00 0.00 0.00 Pleuromamma abdominalis 1.46 1.12 0-6.14 2.85 1.72 0-5.77 0.72 0.76 0-2.57 Pleuromamma gracilis 0.39 1.12 0-2.35 0.45 0-3.15 0.07 0-0.51 Pleuromamma piseki 0.46 1.74 0-2.36 1.82 1.28 0-3.67 0.87 0.90 0-2.42 Pleuromamma quadrungulata 0.45 0.71 0-1.76 1.27 0.80 0-3.63 0.32 0.67 0-1.20 Pleuromamma sp. 0.35 0.50 0-1.17 1.20 0.73 0-4.19 0.51 0.72 0-1.73 Pleuromamma xiphias 0.16 0.46 0-1.01 0.00 0.00 0.00 0.00 Pontellina plumata 0.02 0-0.23 0.00 0.00 0.00 0.00 Pseudocalanus sp. 0.01 0-0.16 0.00 0.00 0.00 0.00

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21 Table 3. Continued Inside of LC Outside of LC LC Boundary Zooplankton Mean GM Range Mean GM Range Mean GM Range Rhincalanus cornutus 0.18 0.48 0-1.35 1.36 1.34 0-1.57 0.49 0.61 0-1.12 Saphirella sp. 0.01 0.09 0-0.16 0.00 0.00 0.00 0.00 Saphirina iris 0.03 0.17 0-0.18 0.00 0.00 0.00 0.00 Saphirina nigromaculata 0.00 0.00 0.15 0-1.05 0.00 0.00 Saphirina opalina 0.02 0-0.27 0.00 0.00 0.00 0.00 Saphirina ovatolanceolatus 0.24 0.64 0-1.12 0.76 0.72 0-0.96 0.20 0.44 0-0.69 Saphirina sp. 0.09 0.44 0-0.67 0.00 0.00 0.00 0.00 Sapphirina stellata 0.00 0.00 0.00 0.00 0.13 0.43 0-0.51 Scolecithrix bradyi 0.05 0.35 0-0.40 0.30 0-2.10 0.11 0.22 0-0.43 Scolecithrix danae 2.34 1.42 0.31-12.32 2.95 2.64 0.84-4.72 1.67 1.28 0.35-3.46 Temora longicornis 0.02 0-0.27 0.00 0.00 0.00 0.00 Temora stylifera 0.37 0.49 0-0.67 1.17 0.76 0-2.89 2.30 1.23 0-7.95 Temora turbinata 0.07 0.49 0-0.68 0.45 0.38 0-0.73 0.28 0.48 0-1.30 Temoropia mayumbaensis 0.08 0.34 0-0.33 0.46 0.45 0-0.52 0.19 0.37 0-0.69 Undeuchaeta plumosa 0.01 0-0.17 0.00 0.00 0.00 0.00 Undinula vulgaris 0.98 0.82 0-4.11 1.05 0.75 0-2.73 1.27 1.10 0-4.15 Unidentified copepods 0.76 1.53 0-3.42 3.75 3.41 0-5.00 1.88 2.23 0-3.80 copepodites 1.50 1.29 0.72-2.79 4.23 3.29 0.97-10.48 5.24 4.43 2.42-10.58 nauplii 0.05 0-0.68 0.00 0.00 0.32 0-2.07 Euphausia sp. 0.29 0-0.47 0.15 0-0.52 0.00 0.00 Nematobrachion flexipes 0.01 0.16 0-0.16 0.00 0.00 0.00 0.00 Nematoscelis tenella 0.02 0.34 0-0.34 0.00 0.00 0.00 0.00 Nematoscelis sp. 0.02 0.34 0-0.34 0.00 0.00 0.00 0.00 Stylocheiron longicorne 0.01 0.16 0-0.16 0.03 0-0.21 0.00 0.00 Stylocheiron sp. 0.40 0.48 0-2.05 0.51 0.42 0-1.05 0.92 0-1.87 Stylocheiron carinatum 0.01 0.18 0-0.18 0.06 0-0.42 0.00 0.00

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22 Table 3. Continued Inside of LC Outside of LC LC Boundary Zooplankton Mean GM Range Mean GM Range Mean GM Range Stylocheiron robustum 0.03 0.18 0-0.20 0.00 0.00 0.00 0.00 Stylocheiron affine 0.09 0.27 0-0.67 0.00 0.00 0.00 0.00 Stylocheiron abbreviatum 0.05 0.67 0-0.67 0.39 0.37 0-0.52 0.00 0.00 Stylocheiron insulare 0.02 0.34 0-0.34 0.00 0.00 0.00 0.00 Stylocheiron elongatum 0.00 0.00 1.35 0.98 0-2.27 0.00 0.00 Thysanopoda micropthalma 0.10 0.73 0-0.79 0.00 0.00 0.00 0.00 Thysanopoda sp. 0.18 1.28 0-1.39 0.00 0.00 0.00 0.00 Thysanopoda acutifrons 0.03 0.18 0-0.20 0.00 0.00 0.00 0.00 Unidentified euphausiids 2.44 2.28 0-5.29 3.80 2.94 0.97-7.86 5.06 3.75 0.75-13.83 Chaetognaths 9.72 7.69 2.89-25.80 14.95 12.59 4.13-25.16 14.62 12.20 2.23-21.77 Ostracods 5.08 4.56 1.07-9.49 5.37 4.71 1.67-10.48 7.33 6.05 2.25-15.57 Gastropods 4.28 2.86 0.36-17.27 2.90 2.13 0.49-6.81 5.85 4.91 1.50-10.02 Forams 3.07 2.33 0-12.88 5.04 3.55 0-9.96 9.48 4.45 0.43-37.80 Amphipods 0.88 0.76 0-3.37 1.75 1.61 0.91-3.37 2.10 1.38 0.17-4.03 Decapods 1.68 1.00 0-8.23 3.44 2.14 0-9.96 2.26 1.63 0.34-4.70 Larvaceans 3.10 2.39 0-6.85 5.60 2.53 0.26-12.58 4.31 3.68 0-10.44 Salps 0.91 0.73 0-2.98 1.42 1.00 0.21-3.14 2.98 2.98 0-6.19 Larval fish 0.22 0.56 0-1.00 0.03 0-0.24 0.06 0-0.28 Cnidarians 2.81 2.53 0.99-5.02 5.42 4.70 1.67-9.96 5.02 4.43 1.88-9.08 Cladocerans 0.75 0.95 0-3.35 0.30 0-2.10 0.84 0.71 0-3.02 Echinoderms 0.90 0.91 0-2.79 1.54 1.11 0-2.98 1.11 0.86 0-2.52 Polychaetes 1.89 1.10 0-7.85 1.22 1.03 0.21-1.91 2.09 1.67 0.51-4.54

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23 Non-metric multidimensional scaling (MDS) plots revealed broad similarity among stations regardless of time of day, location, or region. However, when a cluster analysis overlay is applied, some grouping among stations can be seen (Fig. 3). Species composition and abundances at all stations have a 40% similarity. At the 60% level, stations are grouped into five clusters. The stations with the lowest abundances (Stas 17001 and 17002) are clustered together on the left side of the plot, while stations with higher abundances tend to be located on the right side. No other trends were discernable to explain the observed patterns. The stress value (0.14) indicates that the plot is a reasonable representation of the data. Region 1 2 3 4 5 Similarity 20 40 60 80 17001 17002 17003 17004 17005 17006 1 7007 17008 17009 17010 9 20 19 22 24 27 29 36 38 40 42 44 50 52 46 54 56 94 2D Stress: 0.14 Fig. 3. Multidimensional scaling plot with cluster overlay. Plot shows grouping among samples with similar zooplankton species composition and abundances. Region 1 is inside the LC, region 2 is the eastern LC boundary, region 3 is the western LC boundary, region 4 is outside east of LC, and region 5 is outside west of LC

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24 ANOSIM analyses were used to compare the similarity of zooplankton species and abundances between samples in different regions (Figs 4-6). The first test is the Global analysis, which gives an indication of the similarity between all samples. The Global test revealed an R value of 0.07 and a significance level of 16.2%. The pairwise analyses that followed resulted in significant differences are described below. The largest difference in similarity among all regions occurred between stations inside the LC (region 1) and those stations located to the west outside of the LC (region 5) in resident GOM water (Fig. 4). The next greatest difference occurred between stations located inside the LC (region 1) and those on the western boundary (region 3) (Fig. 5). Finally, a comparison of stations located inside the LC and all stations outside the LC showed the third greatest difference in similarity (Fig. 6). -0.4-0.3-0.2-0.100.10.20.30.40.50.6R 0160Frequency Fig. 4. ANOSIM test showing a significant difference (R = 0.212) in zooplankton species and abundance between regions 1 (inside the LC) and 5 (western outside LC). The significance level equaled 7.4%.

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25 -0.3-0.2-0.100.10.20.30.40.5R 0192Frequency Fig. 5. ANOSIM test showing a significant difference (R = 0.125) in zooplankton species and abundance between regions 1 (inside the LC) and 3 (western boundary of the LC). The significance level equaled 12.4%. -0.25-0.20-0.15-0.10-0.0500.050.100.150.200.250.300.3 5 R 0nc 228 Frequey from region 1 (inside the LC) and regions 4 & 5 (stations outside the LC). The significance level equaled 12.7%. Fig. 6. ANOSIM test showing a significant difference (R = 0.117) in zooplankton species and abundance

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26 When more specific geographic areas are considered, SIMPER analysis of copepods gave somewhat diffe rent results (Table 4). Oithona plumifera Nannocalanus minor and Euchaeta marina were the dominant copepods inside the LC (region 1) and at the eastern boundary (region 2) contributi ng >12 and 11% respectively, to the total and Clausocalanus furcatus each contributing > 7% to the copepod total. C. furcatus also was one of the dominant species (>10%) along with Lucicutia flavicornis (>8%) in the eastern region outside of the LC (region 4) whereas in western outside st ations (region 5), Temora longicornis was a major contributor (> 10%) to the total copepod abundance. copepod abundance. In contrast, stations in the western boundary of the LC (region 3) were dominated by O. plumifera, Clausocalanus arcuicornis,

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27 Table 4. SIMPER analysis of copepod contribution. Mean abundance (No. m -3 ) and percent contribution (%) of copepods from different regions. Region 1 is inside the LC, Region 2 is the eastern boundary, Region 3 is the western boundary, Region 4 is outside east, Region 5 is outside west Region 1 Region 2 Region 3 Region 4 Region 5 Copepods Mean % Mean % Mean % Mean % Mean % Euchaeta marina 3.15 12.97 6.64 11.84 3.70 6.86 5.39 10.47 4.48 9.15 Nannocalanus minor 4.10 12.71 7.36 11.51 4.77 6.23 4.89 11.12 6.79 18.25 Oithona plumifera 5.11 12.68 9.16 11.51 7.42 15.58 6.64 13.16 5.75 10.20 Lucicutia flavicornis 2.36 6.59 4.02 3.94 3.45 2.81 3.26 8.13 1.72 1.95 Oithona sp. 2.48 6.29 6.05 8.88 5.74 5.55 4.87 9.75 3.30 3.34 Clausocalanus arcuicornis 2.14 6.14 3.72 4.94 3.33 7.79 3.88 6.71 3.20 2.31 Temora longicornis 2.34 5.13 2.22 3.59 1.45 2.08 2.13 4.03 3.57 10.30 Corycaeus speciosus 1.24 4.90 1.33 2.15 1.59 2.87 0.00 0.00 0.00 0.00 Haloptilus longicornis 1.26 4.24 0.00 0.00 1.46 1.91 0.00 0.00 1.59 2.33 Eucalanus attenuatus 0.88 2.72 2.46 2.96 1.33 1.38 0.00 0.00 0.97 1.17 Oithona setigera 1.23 2.17 0.00 0.00 1.09 2.38 0.00 0.00 2.37 3.38 Clausocalanus furcatus 1.56 2.04 2.41 4.33 4.61 9.45 3.81 10.47 4.32 7.31 Corycaeus catus 0.89 1.59 2.85 5.04 0.00 0.00 0.00 0.00 0.00 0.00 Oncaea mediterranea 0.70 1.05 1.96 3.59 3.07 5.32 3.37 4.23 3.96 3.29 Mesocalanus tenuicornis 0.49 1.05 0.00 0.00 1.74 1.74 0.91 1.56 0.00 0.00

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28 Total zooplankton abundance va ried across the region by a factor of five (Table 5). Of the 14 stations locate d inside the LC, the lowest zooplankton abundance (43.8 m -3 ) occurred at Sta. 17002 and the highest abundance (175 m -3 ) occurred nearby at Sta. 17009; both samples were collected during the da y. Of the seven stations collected at the boundary of the LC, Sta. 40 collected during the day at the easte rn edge of the LC had the highest abundance (230 m -3 ), whereas Sta.17005 collected during the day on the western edge of the LC had the lowest abundance (107 m -3 ). Outside the LC, the stations with the lowest abundance (Sta. 54: 49.9 m -3 ) and the highest abundance (Sta. 50: 231 m -3 ) were collected at night. Both stati ons are located to the west of the LC. On average, the boundary stations had the highest zooplankt on abundances during both day and night. In addition, when both day and night stations are pooled, boundar y stations had the highest total zooplankton abundance (geometric mean: 157 m -3 ) compared with stations inside the LC (geometric mean: 86.1 m -3 ) or outside the LC (geometric mean: 120 m -3 ). Although zooplankton abundances from the bounda ry were significantly higher than the zooplankton abundances inside the LC, they were not significantly different from abundances collected outsid e the LC (Newman-Keuls te st, following an ANOVA, p< 0.025).

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29 Table 5. Day and night abundances. Total abundance (# m -3 ) of each station, geometric mean (GM) for day and night samples, GM for all inside (ID), outside (OD), and boundary (BD) stations during the day and GM for all inside (IN), outside (ON), and boundary (BN) stations at night Day Night Station No. m -3 Region Station No. m -3 Region 17001 48.66 Inside 17004 108.62 Inside 17002 43.82 Inside 17008 96.64 Inside 17003 117.09 Inside 22 76.17 Inside 17007 86.38 Inside 24 60.01 Inside 17009 174.58 Inside 36 71.42 Inside 17010 123.99 Inside 44 112.81 Inside 38 116.44 Inside 9 135.83 Outside 42 58.96 Inside 19 61.47 Outside 27 179.26 Outside 50 231.14 Outside 52 102.36 Outside 54 49.99 Outside 17005 106.87 Boundary 56 198.67 Outside 20 157.91 Boundary 29 142.88 Boundary 40 230.27 Boundary 17006 108.52 Boundary 46 202.54 Boundary 94 192.88 Boundary GM Day 115.71 GM Night 101.07 GM (ID) 86.30 GM (IN) 85.35 GM (OD) 135.46 GM (ON) 113.90 GM (BD) 172.29 GM (BN) 124.52 GM all inside 86.14 GM all outside 119.68 GM all boundary 157.03

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30 Environmental parametersSea surface temperatures and chlorophyll concentrations (Table 6, Appendix A) were variable between stations. A one-tailed Mann-Whitney test revealed that the temperat ures inside the LC we re significantly higher (p < 0.001) than resident GOM water (Appendix A). A Kruskal-Wallis test indicated that chlorophyll concentrations fr om the chlorophyll maximum inside the LC, at the boundary of the LC, and outside the LC were significantly different (p < 0.001). Table 6. Mean chlorophyll a (mg m -3 ) from the surface, chlorophyll maximum or midwater depth and 200 m depth at SEAMAP stations Stations Surface Mid/Max 200 m Location 9 0.060 0.557 0.005 Outside 19 0.075 0.474 0.007 Outside 20 0.081 0.368 0.009 Boundary 22 0.043 0.356 0.008 Inside 24 0.043 0.346 0.000 Inside 27 0.073 0.521 0.009 Outside 29 0.067 0.500 0.011 Boundary 36 0.049 0.440 0.004 Inside 38 0.076 0.392 0.042 Inside 40 0.104 0.663 0.014 Boundary 42 0.052 0.346 0.011 Inside 44 0.049 0.293 0.034 Inside 46 0.074 0.569 0.086 Boundary 50 0.087 0.579 0.007 Outside 52 0.176 0.539 0.008 Outside 54 0.096 0.872 0.010 Outside 56 0.084 0.461 0.007 Outside 94 0.064 0.584 0.102 Boundary

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31 Discussion The richness of zooplankton species was high across the study area, consistent with previous findings (Owre and Foyo, 1964; Hopkins and Lancraft, 1984). Copepods were the dominant taxa, comprising ~ 60% of the total number. Hopkins (1982) found that copepods contributed 80% to the tota l zooplankton collected in his study of the eastern GOM, near the west Florida shelf. C opepods are an important prey item for larval fishes and other zooplankton (Hunter, 1981; H opkins and Lancraft, 1984). The species of copepods identified were similar to the lists of species compiled by other researchers (Owre and Foyo, 1964; Hopkins et al., 1981; H opkins and Lancraft, 1984). Most samples contained high abundances of the genera Oithona, Nannocalanus and Euchaeta (Table 2), which have been reported to be ve ry common throughout the upper 200 m in the GOM (Bjornberg, 1971; Hopkins et al., 1981). In my study, species of Oithona were prominent in daytime samples, whereas Nannocalanus minor was more abundant in nighttime samples. Abundances of these dominant species ( Oithona and Nannocalanus) are similar to reported abundances in other studies (Owre and Foyo, 1964; Hopkins et al., 1981; Hopkins and Lancraft, 1984). Chaetognaths and ostracods also had relatively high abundances at all stations (Appendix B). Chaet ognaths are voracious predators of many zooplankters and larval fish (Hunter, 1981). Ostracods play a large role in the ecology of the GOM as well, as prey for decapods, euphaus iids and species of larval fish, such as

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32 Cyclothone (Boltovskoy, 1999). Some small species such as Oithona plumifera may be underestimated due to the relatively la rge mesh size of the plankton nets. The MDS plot indicates a relatively good representation of the dissimilarity among samples. While species composition is 40% similar across all samples, there is dissimilarity in abundance. ANOSIM test s gave a Global R value of 0.07 and a significance level of 16.2%. T ypically, the low Global R value would indicate that no further comparisons were warranted, however a significant difference was noted between the inside stations and the out side stations. To further el ucidate possible patterns, the samples were tested in smaller groups pairwi se comparisons. Pairwise tests resulted in significant differences; the R value for test one between regions 1 and 5 is 0.212, (Fig. 4), which is on the low end of the continuum and the significance level is 7.4%, meaning the probability of an R value > 0.5 (the largest possible outcome) occurred 74 out of 1000 times. The two following ANOSIM tests (Figs 5 & 6) had relatively low R values and significance levels > 12%. Again, the differe nces while significant were on the low end. The similarity of the geometric mean total zooplankton abundance between day (116 m -3 ) and night (101 m -3 ) samples was surprising given that vertical migration by zooplankton usually results in higher night densitie s (Hopkins, 1982). One possible reason for the relatively low ni ght abundances of zooplankton in this study is that samples were not collected on a specific time schedule. Rather, the samples were collected when the ship reached the next station without regard to time. Of the 13 samples collected between 1900-0700, five were collected approximately one hour after apparent sunset (1930); two were collected around midnight, and the remaining five were

PAGE 39

33 collected between 0300 and 0530. The samples collected between the hours of 0350 and 0400 had the highest abundan ces with 231 and 199 m -3 respectively. Apparent sunrise was approximately 0600. The sample with the lowest abundance was collected at sunset (1926), and the next lowest we re collected near midnight. Ty pically, copepod species of Pleuromamma, Eucalanus, Euchaeta, Rhincalanus, Neocalanus, Oncaea and species of euphausiids inhabit waters be low 200 m during the day and mi grate toward the surface at night to feed (Shuert and Hopkins, 1987). Euchaeta marina has been reported to have a narrow migration range stayi ng at 50 m during the day and migrating to about 20 m at night (Shuert and Hopkins, 1987) which would not have been detected by my net collection methods. However, the previously mentioned species did not exhibit an increase in abundance at night in my study. Total zooplankton abundance was relatively low inside the LC compared to the LC boundary and resident GOM waters. Low nutrient (Biggs and Ressler, 2001) concentrations are typical of the Caribbean S ea, which is the source water for the LC. In addition, immature stages of copepods are common in the Caribbean Sea, which is thought to be a source area for zooplankton th at are transported to the GOM by the LC (Owre and Foyo, 1964). Thus, low chlorophyll concentrations and zooplankton abundance inside the LC in the GOM are expected. Relatively high total zooplankton abundance at the boundary of the LC supports the hypothesis that this boundary system may play an important role in the ecology of the GOM. Indeed, Lamkin (1997) found that high abundances of the bigeye cigarfish, Cubiceps pauciradiatus and bluefin tuna Thunnus thynnus were positively correlated to the frontal boundary of the LC.

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34 Furthermore, Lee et al. (1994) observed that a cyclonic eddy genera ted from the LC near the Dry Tortugas provided an enhanced food supply and transport for locally spawned snapper and grouper. Mississippi River water can become entrained in LC eddies, such as an anticyclonic-cyclonic pair, pulling chlor ophyll-rich river/shelf water into deeper oceanic water (Biggs et al., 2004). Sperm whales were observed in conjunction with rotating pairs of eddies that were pulling Mississippi River water off of the shelf during three consecutive summers (Biggs et al., 2004). The mean surface chlorophyll a levels inside the LC, at the boundary of the LC, and outside the LC (Table 6), were 0.06, 0.07, and 0.08 mg m -3 respectively, indicative of an oligotrophic enviro nment. Mean chlorophyll a levels recorded at the chlorophyll maximum, however, were an order of magnitude higher, ranging from 0.35 mg m -3 inside the LC to 0.87 mg m -3 outside the LC (Table 8). Ch lorophyll concentrations were elevated at boundary stations in comparison to concentrations insi de the LC (range: 0.370.66 mg m -3 ; Table 7). The LC may influence nutrient concentr ations and primary productivity in the GOM in several ways. As the LC passes thr ough the Yucatan Straits, the current velocity is sufficient at 1 2 m sec -1 to create a frontal boundary (Badan et al., 2005). In the GOM, the LC moves in an anticyclonic fashion with velocities >1 m sec -1 (Oey et al., 2005), occasionally shedding anticyclonic warm core eddies (Walker et al., 2003). The boundary of the LC was measured using a shipboard mounted ADCP (75 and 300 kHz) to be ~55.5 km across with a 9 km core of high velocity water moving at 3.54 knots (personal observation, 2006). Cyclonic (col d core) frontal eddies are common along the

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35 periphery of the LC and could be the source of nutrient injection into near surface waters. Anticyclonic (clockwise) circulation of th e LC and eddies cause downwelling at the center, but upward tilting of nutrient isopleths near their perimeters (Paluskiewicz et al., 1983; Walsh et al., 1989). Nutrient injection into lighted surface waters can lead to enhanced phytoplankton productivity in these ar eas. In addition, filaments of the LC may transport chlorophyll-rich water from the productive northern shelf into the GOM (Chassignet et al., 2005). Enhanced productivity has been measured and correlated with higher chlorophyll concentrations associated with LC eddi es and meanders (Yoder and Mahood, 1983). Conditions at the boundary of th e LC may support high er abundances of zooplankton, either by advection of nutrients from zones of upwelling and river water entrainment, or by supporting new production through the physical pr ocesses occurring at the boundary. The high zooplankton abundances collected at the boundary of the LC suggests that this frontal system may si gnificantly influence the ecology of the GOM.

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36 Conclusions The LC is a complex and dynamic environment that may strongly influence the ecology of the GOM. The LC has a frontal boundary, with elevated chlorophyll and zooplankton abundances. Physical processes a ssociated with this frontal boundary and LC eddies may replenish nutrients in de pleted surface areas of the GOM, thereby supporting enhanced primary and secondary production. Because the position of the LC in the GOM varies, its effects on the ecosyst em may differ both spatially and seasonally. The role of the LC on the GOM ecology requires further study.

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37 References Badan, A., Candela, J., Sheinbaum, J., and Ochoa, J. 2005. Upper-layer circulation in the approaches to the Yucatan Channel. In: Circulation in the Gulf of Mexico: Observations and Models. W. Sturge s and A. Lugo-Fernandez, (eds.), Geophysical Monograph Series 161, Am erican Geophysical Union. 57-69. Bennet, J. L. and Hopkins, T. L. 1989. Aspects of the ecology of the Calanoid copepod genus Pleuromamma in the eastern Gulf of Mexico. Contrib. Mar. Sci ., 31:119-136. Biggs, D. C. 1992. Nutrients, plankton and productivity in a wa rm-core ring in the western Gulf of Mexico. J. Geophys. Res. 97:2143-2154. Biggs, D. C. and Ressler, P. H. 2001. Distribution and abundance of phytoplankton, zooplankton, ichthyoplankton, and micronekton in the deepwater Gulf of Mexico. Gulf Mex. Sci. 19(1):7-29. Biggs, D. C., Jochens, A. E., Howard, M. K ., DiMarco, S.F., Mullin, K. D., Leben, R. R., Muller-Karger, F. E., and Hu, C. 2004. Eddy forced variations in on and offmargin summertime circulation along th e 1000-m isobath of the northern Gulf of Mexico, 2000-2003, and links with sperm whale distri butions along the middle slope. In: Circulation in the Gulf of Mexi co: Observations and Models. W. Sturges and A. Lugo-Fernandez, (eds.), Geophysical Monograph Series 161, American Geophysical Union. 71-85. Bjornberg, T.K.S. 1971. Distri bution of plankton relative to the general circulation system in the area of the Caribbean Sea and adjacent regions. In : Proceedings of the symposium on investigations and resources of the Caribbean Sea and adjacent regions, Willemstad, Curacao, Netherlands Antilles, 18-26 November 1968, United Nations Educational, Scientific and Cultural Orga nization (UNESCO), Paris, France. 343-356 Boltovskoy, D. 1999. South Atlan tic Zooplankton, Vols. 1 & 2. Backhuys Publishers, Leiden, The Netherlands.

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38 Chassignet, E. P., Hurlburt, H. E., Smedstedt, O. M., Barron, C. N., Ko, D. S., Rhodes, R. C., Shriver, J. F., WalLCraft, A. J., and Arone, R. A. 2005. Assessment of data assimilative ocean models in the Gulf of Mexico using ocean color. In: Circulation in the Gulf of Mexico: Obse rvations and Models. W. Sturges and A. Lugo-Fernandez, (eds.), Geophysical Monograph Series 161, American Geophysical Union. 87-100. Clarke, K. R and Warwick, R. M. 2001. Change in Marine Communities: An approach to statistical analysis and interpretation, 2 nd edition. PRIMER-E: Plymouth Daly, K. L. and Smith, W.O. 1993. Physical-B iological interaction influencing marine plankton production. Annu. Rev. Ecol. Syst ., 24:555-585. Grice, G. D. 1960. Calanoid and Cyclopoid c opepods collected from the Florida Gulf Coast and Florida Keys in 1954 and 1955. Bull. Mar. Sci. Gulf and Carib., 10(2):217-226. Govoni, J. J. 1993. Flux of larval fishes acr oss frontal boundaries: examples from the Mississippi River plume front and the we stern Gulf Stream front in winter. Bull. Mar. Sci. 53(2):538-566. Hays, G. C., Proctor, C. A., John, A. W. G. and Warner, A. J. 1994. Interspecific differences in the diel vertical migrati on of marine copepods: The implications of size, color, and morphology. Limnol. Oceanogr., 39(7):1621-1629. Hopkins, T. L., Milliken, D. M., Bell, L. M ., McMichael, E .J., Heffernan, J. J. and Cano, R.V. 1981. The landward distribution of oceanic plankton and micronekton over the west Florida continental shelf as related to their vertical distribution J. Plank. Res., 3(4):645-658. Hopkins, T. L. 1982. The vertical distribution of zooplankton in the eastern Gulf of Mexico. Deep Sea Res., 29(9):1069-1083. Hopkins, T. and Lancraft, T. 1984 The com position and standing stock of mesopelagic micronekton at 27N 86W in the eastern Gulf of Mexico. Cont. Mar. Sci., 27:143-158. Hunter, J. R. 1981. Feeding ecology and predation of marine fish larvae. In: Marine fish larvae:Morphology, ecology and relation to fisheries. R. Lasker, (ed.), Washington Sea Grant Program, University of Washington Press, Seattle and London.

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39 Lamkin, J. 1997. The LC and the abundance of Cubiceps pauciradiatus (Pisces: Nomeidae) in the Gulf of Mexico: evidence for physical and biological interaction. Fish. Bull. 95:250-266. Lee, T. N., Clarke, M. E., Williams, E., Szmant, A. F., and Berger, T. 1994. Evolution of the Tortugas Gyre and its inluence on recruitment in the Florida Keys. Bull. Mar. Sci. 54:621-646. Lohrenz, S. E., Wiesenburg, D. A., Arnone, R. A., and Chen, X. 1999. What controls primary production in th e Gulf of Mexico? In: The Gulf of Mexico large marine ecosystem: Assessment, sustainability and management. H. Kumpf, K. Steidinger, and K. Sherman (eds.) Blackwell Science, Malden Massachusetts. 151-170. Muller-Karger, F. E., Vukovich, F., Leben, R., Nababan, B., Hu, C., Myre, D. 2001. Surface circulation and transport of the LC into the Northeastern Gulf of Mexico: Final Report. OCS Study MMS 2001-102, U.S. Dept. of the Interior, Minerals Management Service, Gulf of Mexi co OCS Region, New Orleans, La. 39 pp. Oey, L. Y., Ezer, T., and Lee, H. C. 2005. Lo op Current rings and related circulation in the Gulf of Mexico:A re view of numerical models and future challenges. In: Circulation in the Gulf of Mexico: Observ ations and Models. W. Sturges and A. Lugo-Fernandez, (eds.), Geophysical Monograph Series 161, American Geophysical Union. 31-56. Omori, M. and Ikeda, T. 1984. Methods in Marine Zooplankton Ecology. Krieger Pub. Co., Malabar, Fl. Owre, H. B. 1962. Plankton of the Florida cu rrent part VIII. A list of the copepoda. Bull. Mar. Sci. Gulf and Carib., 12(3):488-495. Owre, H. B. and Foyo, M. 1964. Report on a co llection of copepoda from the Caribbean Sea. Bull. Mar. Sci. Gulf and Carib ., 14(2):359-372. Paluskiewicz, T., Atkinson, L. P., Posmentier, E. S., and McClain, C. R. 1983. Observations of a LC frontal eddy intr usion onto the West Florida continental shelf. J. Geophys. Res. 88:9639-9651. Richards, W .J., McGowan, M. F., Leming, T., Lamkin, J. T., and Kelley, S. 1993. Larval fish assemblages at the Loop Current boundary in the Gulf of Mexico. Bull. Mar. Sci. 53(2):475-537. Shuert, P.G. and Hopkins, T.L. 1987. The vert ical distribution and feeding ecology of Euchaeta marina in the eastern Gulf of Mexico. Cont. Mar. Sci. 30:49

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40 Sturges, W., Lugo-Fernandez, A. and Sharge l, M. D. 2005. Introduction to circulation of the Gulf of Mexico. In : Circulation in the Gulf of Mexico: Observations and Models. W. Sturges and A. Lugo-Fern andez, (eds.), Geophysical Monograph Series 161, American Geophysical Union. 1-10. Walker, N., Myint, S., Babin, A. and Haag, A. 2003. Advances in satellite radiometry for the surveillance of surface temperatures, ocean eddies, and upwelling processes in the Gulf of Mexico usin g GOES-8 measurements dur ing summer. Geophysical Research Letters 30, No. 16, 1854, doi:10.1029/2003GLO17555,2003. Walsh, J. J., Dieterle, D. A., Meyers, M. B., and Muller-Karger, F. E. 1989. Nitrogen exchange at the continental margin: A numerical study of the Gulf of Mexico. Prog. Oceanog. 23:245-301. Williams, J., Grey, W. F., Murphy, E. B. and Cr ane, J. J. 1977. Memoirs of the Hourglass Cruises: Drift bottle analyses eastern Gulf of Mexico surface circulation. Mar. Res. Lab. FDNR., 4(3). Yoder, J.A. and Mahood, A. 1983. Primary production in LC upwelling. In: Southwest Florida ecosystems study. H. Kumpf, K. St eidinger, and K. Sherman (eds.) Year 2, Hydrography and primary productivity: fi nal report. Georgia, Woodward-Clyde Consultants, Skidaway Institute of Oceanography. 219-278. Zar, J. H. 1974. Biostatistical Analysis. Prentis Hall, Englewood Cliffs, N.J.

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41 Appendices

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42 Appendix A. Zooplankton spec ies collected in the GOM during May 2003 Protozoa Candacia paenelongimana Foraminifera Candacia catula Globigerina Candacia longimana Cnidaria Candacia bipinnata Hydrozoa Candacia curta Siphonophora Candacia varicans Scyphozoa Canthocalanus pauper Semaeostomeae Centropages violaceus Mollusca Chiridius gracilis Opisthobranchia Clausocalanus arcuicornis Thecosomata Clausocalanus furcatus Cavolina spp. Clausocalanus spp. Gymnosomata Eucalanus attenuatus Clione spp. Eucalanus elongatus Annelida Eucalanus monachus Polychaeta Eucalanus mucronatus Tomopteris spp. Eucalanus spp. Crustacea Euchaeta marina Cladocera Euchaeta media Ostracoda Euchaeta spp. Myodocopida Euchirella bitumida Copepoda Euchirella curticauda Calanoida Euchirella spp. Acartia spp. Gaetanus minor Acartia danae Gaetanus pileatus Acartia negligens Gaetanus miles Acartia tonsa Gaetanus latifrons Acrocalanus spp. Haloptilus austini Acrocalanus gracilis Haloptilus longicornis Acrocalanus longicornis Haloptilus mucronatus Aetideopsis carinata Haloptilus spp. Aetideus armatus Heterohabdis papilliger Aetideus acutus Heterohabdis spp. Aetideus giesbrechti Labidocera nerii Aetideus spp. Lucicutia clausi Calanus spp. Lucicutia flavicornis Calocalanus pavo Lucicutia longicornis Calocalanus teniculus Lucicutia spp. Calocalanus spp. Mecynocera clausii Candacia spp. Mesocalanus tenuicornis Candacia pachydactyla Metridia spp.

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43 Appendix A. (Continued) Nannocalanus minor Corycaeus catus Neocalanus gracilis Corycaeus flaccus Neocalanus robustior Corycaeus furcifer Neocalanus spp. Corycaeus latus Neocalanus tonsus Corycaeus lautus Paracalanus aculeatus Corycaeus limbatus Paracalanus parvus Corycaeus longistylus Paracalanus spp. Corycaeus spp. Paracandacia bispinosa Corycaeus speciosus Paracandacia spp. Corycaeus typicus Paracandacia simplex Farranula gracilis Phyllops helgae Farranula carinata Pleuromamma abdominalis Farranula spp. Pleuromamma gracilis Lubbokia aculeata Pleuromamma piseki Lubbokia magna Pleuromamma quadrungulata Lubbokia squillimana Pleuromamma spp. Oncaea media Pleuromamma xiphias Oncaea mediterranea Pontellina plumata Oncaea spp. Pseudocalanus spp. Oncaea venusta Rhincalanus cornutus Pachos tuberosum Scolecithrix bradyi Saphirella spp. Scolecithrix danae Saphirina iris Temora longicornis Saphirina nigromaculata Temora stylifera Saphirina opalina Temora turbinata Saphirina ovatolanceolatus Temoropia mayumbaensis Saphirina spp. Undeuchaeta plumosa Sapphirina stellata Undinula vulgaris Unidentified copepods Cyclopoida copepodites Oithona frigida nauplii Oithona plumifera Amphipoda Oithona robusta Phronima gracilis Oithona setigera Streetsia steenstrupi Oithona spp. Euphausiacea Harpacticoida Euphausia spp. Macrostella gracilis Nematobrachion flexipes Microstella spp. Nematoscelis tenella Poecilostomatoida Stylocheiron longicorne Copilia quadrata Stylocheiron spp. Copilia vitrea Stylocheiron carinatum

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44 Appendix A. (Continued) Stylocheiron robustum Stylocheiron affine Stylocheiron abbreviatum Stylocheiron insulare Stylocheiron elongatum Thysanopoda micropthalma Thysanopoda spp. Thysanopoda acutifrons Unidentified euphausiids Decapoda Lucifer faxoni Chaetognatha Sagitta enflata Saggita setosa Eukrohnia fowleri Echinodermata Appendicularia Oikopleura spp. Salpida Teleostei

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45 Appendix B. Cruise log, total zooplankton a bundance data and environmental parameters Cruise Station Lat.N Lon.W Date Time Loc. D/N Split Count Vol. F # m -3 17-031 17001 26.016 87.949 5/13 1035 IN D 5 300 204.52 48.66 17-031 17002 25.945 88.062 5/13 1334 IN D 5 245 178.90 43.82 17-031 17003 25.965 88.422 5/13 1632 IN D 5 372 161.25 117.09 17-031 17004 25.806 88.698 5/13 2011 IN N 5 650 191.49 108.62 17-031 17005 25.858 88.940 5/14 0850 BN D 5 564 224.58 106.87 17-031 17006 25.878 88.909 5/14 2041 BN N 5 541 186.96 108.52 17-031 17007 25.904 88.704 5/15 0840 IN D 6 294 217.83 86.38 17-031 17008 25.888 88.672 5/15 2140 IN N 6 287 190.07 96.64 17-031 17009 25.906 88.636 5/16 1050 IN D 7 307 186.96 174.58 17-031 17010 26.007 87.997 5/16 1757 IN D 7 211 217.83 123.99 04-253 9 26.005 84.991 5/15 0532 OT N 7 299 281.76 135.82 04-253 19 25.003 84.493 5/17 0020 OT N 6 282 306.12 61.45 04-253 20 24.987 84.983 5/18 1240 BN D 7 422 342.06 157.52 04-253 22 24.700 85.496 5/18 2046 IN N 6 343 288.19 75.05 04-253 24 24.974 85.989 5/19 2335 IN N 6 226 238.90 60.52 04-253 27 26.000 85.995 5/19 1232 OT D 7 372 265.63 167.68 04-253 29 26.992 85.980 5/20 2048 BN N 7 279 249.21 143.30 04-253 36 27.991 87.002 5/21 0250 IN N 6 306 274.21 71.42 04-253 38 26.979 87.003 5/21 0929 IN D 7 212 234.17 115.88 04-253 40 26.284 86.999 5/21 1417 BN D 7 457 254.00 230.30 04-253 42 26.005 88.016 5/21 1722 IN D 6 228 247.47 58.96 04-253 44 27.000 88.017 5/22 0327 IN N 7 202 229.19 112.81 04-253 46 26.996 88.996 5/22 1045 BN D 6 572 185.17 202.54 04-253 50 26.007 89.994 5/23 0354 OT N 7 441 244.21 231.15 04-253 52 27.006 89.994 5/23 1144 OT D 5 771 247.29 102.36 04-253 54 27.006 90.979 5/23 1926 OT N 6 203 263.69 49.27 04-253 56 26.000 90.989 5/24 0405 OT N 7 379 244.17 198.68 04-253 94 28.011 87.999 5/30 1444 BN D 7 445 295.95 188.14 Time = time tow began, Loc. = Location of tow, insi de (IN), outside (OT), and boundary (BN) of LC, D/N = day (D) or night (N), Split = # times sample was split, Count = total # of individuals in split, Vol. F = volume of water filtered through net, No. m -3 = zooplankton abundance, ND = no data, Temp = sea surface temperature, S = salinity, DO = dissolved oxygen, S. ch l = surface chlorophyll

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46 Appendix B. (Continued) Cruise Station Temp C S DO mg L -1 S. chl mg m -3 17-031 17001 28.6 37 8.3 0.08 17-031 17002 29.7 36 8.4 0.07 17-031 17003 29.5 36 8.6 0.07 17-031 17004 28.2 36 8.8 0.08 17-031 17005 26.9 36 8.8 0.12 17-031 17006 27.6 36 8.8 0.12 17-031 17007 28.9 36 8.8 0.08 17-031 17008 27.3 36 8.6 0.09 17-031 17009 28.6 36 8.7 0.08 17-031 17010 28.3 36 8.4 0.10 04-253 9 28.1 36 6.3 0.09 04-253 19 27.9 36 6.4 0.13 04-253 20 27.7 36 6.4 0.09 04-253 22 28.6 36 6.3 0.03 04-253 24 28.6 36 6.3 0.05 04-253 27 28.9 36 6.5 0.03 04-253 29 27.7 37 6.4 0.03 04-253 36 28.6 36 6.3 0.05 04-253 38 28.4 36 6.3 0.03 04-253 40 28.2 36 6.3 0.03 04-253 42 29.1 ND ND ND 04-253 44 28.8 36 6.2 0.03 04-253 46 28.6 36 6.3 0.07 04-253 50 27.2 37 6.4 0.07 04-253 52 26.8 36 6.3 0.17 04-253 54 27.0 36 6.5 0.01 04-253 56 27.1 36 6.4 0.09 04-253 94 27.9 36 6.3 0.01

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47 Appendix C. Total number of individuals (N) in each split and the abundance of individuals per m 3 (No. m -3 ). Time = time tow began, Region =location in reference to LC, Samp. frct. = fraction of sample analyzed, Vol. filt. = volume filtered through Bongo nets Station Time Region Station Time Region 17001 1035 Inside the LC 17002 1334 Inside the LC Samp. frct. 1/32 Vol. filt. 204.52 Samp. frct. 1/32 Vol. filt. 178.90 Taxa N No. m -3 Taxa N No. m -3 Copepods 194 30.35 Copepods 123 22.00 Euphausiids 14 2.19 Euphausiids 8 1.43 Decapods 4 0.62 Decapods 5 0.89 Chaetognaths 28 4.38 Chaetognaths 30 5.37 Amphipods 1 0.16 Amphipods 5 0.89 Echinoderms 4 0.62 Echinoderms 8 1.43 Cnidarians 10 1.56 Cnidarians 11 1.97 Cladocerans 2 0.31 Ostracods 6 1.07 Ostracods 16 2.50 Gastropods 2 0.36 Gastropods 8 1.25 Foraminifera 14 2.50 Foraminifera 4 0.62 Polychaetes 1 0.18 Polychaetes 2 0.31 Larvaceans 27 4.83 Larvaceans 21 3.28 Salps 3 0.54 Salps 3 0.47 Fish 2 0.36 Total 311 48.66 Total 245 43.82 Station Time Region Station Time Region 17003 1632 Inside the LC 17004 2011 Inside the LC Samp. frct. 1/32 Vol. filt. 161.25 Samp. frct. 1/32 Vol. filt. 191.49 Taxa N No. m -3 Taxa N No. m -3 Copepods 273 54.18 Copepods 348 58.15 Euphausiids 35 6.94 Euphausiids 22 3.67 Decapods 4 0.79 Decapods 3 0.50 Chaetognaths 130 25.80 Chaetognaths 125 20.89 Amphipods 4 0.79 Amphipods 10 1.67 Cnidarians 5 0.99 Cnidarians 19 3.17 Cladocerans 5 0.99 Ostracods 28 4.68 Ostracods 35 6.94 Gastropods 49 8.19 Gastropods 19 3.77 Polychaetes 47 7.85 Foraminifera 22 4.36 Larvaceans 13 2.17 Polychaetes 4 0.79 Salps 2 0.33 Larvaceans 37 7.34 Fish 6 1.00 Salps 15 2.98 Total 672 108.62 Fish 2 0.40 Total 590 117.09

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48 Appendix C. (Continued) Station Time Region Station Time Region 17007 1603 Inside the LC 17008 2140 Inside the LC Samp. frct. 1/64 Vol. filt. 217.83 Samp. frct. 1/64 Vol. filt. 190.07 Taxa N No. m -3 Taxa N No. m -3 Copepods 180 52.88 Copepods 199 67.01 Euphausiids 20 5.88 Euphausiids 7 2.36 Decapods 1 0.29 Decapods 15 5.05 Chaetognaths 23 6.76 Chaetognaths 22 7.41 Echinoderms 1 0.29 Amphipods 10 3.37 Ostracods 17 4.99 Ostracods 17 5.72 Polychaetes 3 0.88 Polychaetes 7 2.35 Larvaceans 14 4.11 Larvaceans 11 3.70 Salps 1 0.29 Salps 3 1.01 Cnidarians 4 1.17 Cnidarians 7 2.35 Foraminifera 12 3.52 Foraminifera 2 0.67 Gastropods 18 5.29 Gastropods 7 2.35 Total 294 86.38 Fish 2 0.67 Total 309 96.64 Station Time Region 17009 1050 Inside the LC Station Time Region Samp. frct. 1/128 Vol. filt. 186.96 17010 1757 Inside the LC Taxa N No. m -3 Samp. frct. 1/128 Vol. filt. 217.83 Copepods 165 112.96 Taxa N No. m -3 Euphausiids 7 4.79 Copepods 126 74.04 Decapods 3 2.05 Euphausiids 3 1.76 Chaetognaths 26 17.8 Decapods 14 8.23 Amphipods 3 2.05 Chaetognaths 15 8.81 Ostracods 10 6.85 Cladocerans 5 2.94 Polychaetes 6 4.11 Ostracods 8 4.70 Larvaceans 10 6.85 Polychaetes 8 4.70 Cnidarians 7 4.79 Larvaceans 9 5.29 Foraminifera 7 4.79 Salps 2 1.17 Gastropods 8 5.48 Cnidarians 4 2.35 nauplii 1 0.68 Foraminifera 5 2.94 Total 253 174.58 Gastropods 7 4.11 Fish 1 0.59 Total 207 123.99

PAGE 55

49 Appendix C. (Continued) Station Time Region Station Time Region 36 0250 Inside the LC 38 0929 Inside the LC Samp. frct. 1/64 Vol. filt. 274.21 Samp. frct. 1/128 Vol. filt. 234.17 Taxa N No. m -3 Taxa N No. m -3 Copepods 143 33.38 Copepods 145 79.26 Euphausiids 11 2.57 Euphausiids 6 3.28 Decapods 1 0.23 Chaetognaths 29 15.85 Chaetognaths 22 5.13 Amphipods 1 0.55 Amphipods 2 0.47 Echinoderms 1 0.55 Echinoderms 2 0.47 Cnidarians 8 4.37 Cnidarians 10 2.33 Cladocerans 1 0.55 Cladocerans 2 0.47 Ostracods 9 4.92 Ostracods 27 6.30 Gastropods 4 2.19 Gastropods 74 17.27 Foraminifera 3 1.64 Foraminifera 6 1.40 Polychaetes 2 1.09 Polychaetes 1 0.23 Larvaceans 1 0.55 Larvaceans 3 0.70 Salps 3 1.64 Salps 2 0.47 Total 213 116.44 Total 306 71.42 Station Time Region St ation Time Region 42 1722 Inside the LC 44 0327 Inside the LC Samp. frct. 1/64 Vol. filt. 247.47 Samp. frct. 1/128 Vol. filt. 229.19 Taxa N No. m -3 Taxa N No. m -3 Copepods 135 34.91 Copepods 124 69.25 Euphausiids 9 2.33 Euphausiids 7 3.91 Decapods 2 0.52 Decapods 3 1.67 Chaetognaths 26 6.72 Chaetognaths 9 5.03 Amphipods 2 0.52 Amphipods 1 0.56 Cladocerans 3 0.77 Echinoderms 5 2.79 Ostracods 12 3.10 Cnidarians 9 5.03 Echinoderms 4 1.03 Cladocerans 6 3.35 Larvaceans 5 1.29 Ostracods 17 9.49 Salps 8 2.07 Gastropods 2 1.12 Cnidarians 12 3.10 Foraminifera 5 2.79 Foraminifera 3 0.77 Polychaetes 5 2.79 Gastropods 7 1.81 Larvaceans 5 2.79 Total 228 58.96 Salps 3 1.67 Total 201 112.24

PAGE 56

50 Appendix C. (Continued) Station Time Region Station Time Region 22 2046 Inside the LC 24 2335 Inside the LC Samp. frct. 1/64 Vol. filt. 288.19 Samp. frct. 1/64 Vol. filt. 238.90 Taxa N No. m -3 Taxa N No. m -3 Copepods 174 38.64 Copepods 139 37.24 Euphausiids 18 4.00 Euphausiids 13 3.48 Chaetognaths 13 2.89 Decapods 3 0.80 Amphipods 2 0.44 Chaetognaths 12 3.21 Echinoderms 5 1.11 Amphipods 3 0.80 Cnidarians 12 2.66 Echinoderms 2 0.53 Ostracods 26 5.77 Cnidarians 13 3.48 Gastropods 23 5.11 Ostracods 15 4.02 Foraminifera 58 12.88 Gastropods 6 1.61 Polychaetes 3 0.67 Foraminifera 15 4.02 Larvaceans 2 0.44 Polychaetes 2 0.53 Salps 1 0.22 Salps 3 0.80 crab megalopa 1 0.22 Total 226 60.52 Total 338 75.05

PAGE 57

51 Appendix C. (Continued) Station Time Region Stati on Time Region 9 0532 Outside the LC 19 0020 Outside the LC Samp. frct. 1/128 Vol. filt. 281.76 Samp. frct. 1/64 Vol. filt. 306.12 Taxa N No. m -3 Taxa N No. m -3 Copepods 205 93.13 Copepods 204 42.65 Euphausiids 18 8.18 Euphausiids 6 1.25 Decapods 2 0.91 Decapods 1 0.21 Chaetognaths 19 8.63 Chaetognaths 27 5.64 Amphipods 2 0.91 Amphipods 5 1.04 Echinoderms 4 1.82 Echinoderms 5 1.04 Cnidarians 8 3.63 Cnidarians 9 1.88 Ostracods 14 6.36 Ostracods 8 1.67 Gastropods 13 5.90 Gastropods 14 2.93 Foraminifera 3 1.36 Foraminifera 8 1.67 Polychaetes 3 1.36 Polychaetes 1 0.21 Larvaceans 6 2.72 Larvaceans 4 0.84 Salps 2 0.91 Salps 1 0.21 Total 299 135.82 Pycnogonid 1 0.21 Total 294 61.45 Station Time Region Station Time Region 27 1232 Outside the LC 50 0354 Outside the LC Samp. frct. 1/128 Vol. filt. 265.63 Samp. frct. 1/128 Vol. filt. 244.21 Taxa N No. m-3 Taxa N No. m-3 Copepods 237 114.21 Copepods 261 136.80 Euphausiids 3 1.44 Euphausiids 19 9.96 Chaetognaths 46 22.17 Chaetognaths 48 25.16 Amphipods 7 3.37 Amphipods 4 2.10 Cnidarians 11 5.30 Echinoderms 5 2.62 Ostracods 13 6.26 Cnidarians 19 9.96 Gastropods 3 Cladocerans 4 2.10 Foraminifera 20 9.64 Ostracods 20 10.48 Polychaetes 2 0.96 Gastropods 13 6.81 Salps 6 2.89 Foraminifera 19 9.96 Total 348 167.68 Polychaetes 3 1.57 1.44 Larvaceans 20 10.48 Salps 6 3.14 Total 441 231.14

PAGE 58

52 Appendix C. (Continued) Station Time Regi on Station Time Region 52 1144 Outside the LC 56 0405 Outside the LC Samp. frct. 1/32 Vol. filt. 247.29 Samp. frct. 1/128 Vol. filt. 244.17 Taxa N No. m-3 Taxa N No. m-3 Copepods 413 53.44 Copepods 253 132.63 Euphausiids 21 2.72 Euphausiids 18 9.44 Chaetognaths 163 21.09 Chaetognaths 34 17.82 Decapods 31 4.01 Amphipods 3 1.57 Amphipods 12 1.55 Echinoderms 1 0.52 Mysids 1 0.13 Cnidarians 26 13.63 Echinoderms 23 2.98 Ostracods 12 6.29 Cnidarians 43 5.56 Gastropods 2 1.05 Ostracods 30 3.88 Polychaetes 3 1.57 Gastropods 13 1.68 Larvaceans 24 12.58 Foraminifera 20 2.59 Salps 3 1.57 Polychaetes 15 1.94 Total 379 198.67 Larvaceans 2 0.26 Salps 4 0.52 Total 791 102.36 Station Time Region 54 1926 Outside the LC Samp. frct. 1/64 Vol. filt. 263.69 Taxa N No. m-3 Copepods 134 32.52 Euphausiids 3 0.73 Decapods 4 0.97 Chaetognaths 17 4.13 Amphipods 7 1.70 Echinoderms 1 0.24 Cnidarians 14 3.40 Ostracods 11 2.67 Gastropods 2 0.48 Polychaetes 4 0.97 Larvaceans 3 0.73 Salps 3 0.73 Fish 1 0.24 crab megalopa 1 0.24 Pycnogonid 1 0.24 Total 206 49.99

PAGE 59

53 Appendix C. (Continued) Station Time Region Station Time Region 17005 0850 Boundary 17006 1113 Boundary Samp. frct. 1/32 Vol. filt. 224.58 Samp. frct. 1/32 Vol. filt. 186.96 Taxa N No. m-3 Taxa N No. m-3 Copepods 311 44.31 Copepods 356 60.93 Euphausiids 7 1.00 Euphausiids 21 3.59 Decapods 33 4.70 Decapods 2 0.34 Chaetognaths 52 10.69 Chaetognaths 13 2.22 Amphipods 4 0.57 Amphipods 1 0.17 Echinoderms 2 0.28 Echinoderms 3 0.51 Cnidarians 28 3.99 Cnidarians 11 1.88 Ostracods 22 3.13 Cladocerans 3 0.51 Gastropods 27 3.85 Ostracods 27 4.62 Polychaetes 13 1.85 Polychaetes 6 1.03 Larvaceans 8 1.14 Larvaceans 61 10.44 Salps 15 2.14 Salps 6 1.03 Foraminifera 3 0.43 Foraminifera 10 1.71 Fish 2 0.28 Gastropods 17 2.91 Total 527 106.87 Fish 1 0.17 Cephalapod 1 0.17 Total 539 108.52 Station Time Region Station Time Region 20 1240 Boundary 29 2048 Boundary Samp. frct. 1/128 Vol. filt. 342.06 Samp. frct. 1/128 Vol. filt. 249.21 Taxa N No. m-3 Taxa N No. m-3 Copepods 298 111.51 Copepods 167 85.77 Euphausiids 8 2.99 Euphausiids 16 8.22 Chaetognaths 58 21.70 Decapods 1 0.51 Amphipods 3 1.12 Chaetognaths 31 15.92 Echinoderms 1 0.37 Amphipods 7 3.59 Cnidarians 14 5.24 Echinoderms 2 1.03 Ostracods 6 2.24 Cnidarians 10 5.14 Gastropods 4 1.50 Ostracods 13 6.78 Foraminifera 11 4.12 Gastropods 12 6.16 Polychaetes 8 2.99 Foraminifera 8 4.11 Larvaceans 3 1.12 Polychaetes 1 0.51 Salps 7 2.62 Larvaceans 10 5.14 Total 421 157.52 Total 278 142.88

PAGE 60

54 Appendix C. (Continued) Station Time Region St ation Time Region 40 1417 Boundary 46 1045 Boundary Samp. frct. 1/128 Vol. filt. 254.00 Samp. frct. 1/64 Vol. filt. 185.17 Taxa N No. m-3 Taxa N No. m-3 Copepods 240 120.94 Copepods 315 108.87 Euphausiids 14 7.05 Euphausiids 40 13.82 Decapods 3 1.51 Decapods 8 2.76 Chaetognaths 27 13.61 Chaetognaths 63 21.77 Amphipods 8 4.03 Amphipods 10 3.46 Echinoderms 5 2.52 Cnidarians 22 7.60 Cnidarians 5 2.52 Cladocerans 3 1.04 Cladocerans 6 3.02 Ostracods 23 7.95 Ostracods 22 11.09 Gastropods 29 10.02 Gastropods 19 9.57 Foraminifera 35 12.10 Foraminifera 75 37.79 Polychaetes 2 0.69 Polychaetes 9 4.53 Salps 20 6.19 Larvaceans 15 7.56 nauplii 7 0.34 Salps 9 4.53 Total 577 202.54 Total 457 230.27 Station Time Region 94 1444 Boundary Samp. frct. 1/128 Vol. filt. 295.95 Taxa N No. m-3 Copepods 263 113.75 Euphausiids 10 4.32 Chaetognaths 38 16.43 Decapods 7 3.03 Amphipods 4 1.73 Echinoderms 7 3.03 Cnidarians 21 9.08 Cladocerans 1 0.43 Ostracods 36 15.57 Gastropods 16 6.92 Foraminifera 14 6.05 Polychaetes 7 3.03 Larvaceans 11 4.76 Salps 10 4.32 Nemertea 1 0.43 Total 446 192.88


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Rathmell, Katie.
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The influence of the Loop Current on the diversity, abundance, and distribution of zooplankton in the Gulf of Mexico
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by Katie Rathmell.
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[Tampa, Fla] :
b University of South Florida,
2007.
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ABSTRACT: Physical processes in the Gulf of Mexico (GOM) and mesoscale (10-300 km) processes associated with the Loop Current are fairly well known. However, little is known about the physical/ biological interactions of the frontal boundary system of the Loop Current. Zooplankton abundance and distribution was determined at 28 stations in the vicinity of the Loop Current. Species richness was high at all stations. Copepods comprised 60% of the total zooplankton collected. Oithona plumifera, Nannocalanus minor and Euchaeta marina were the most abundant copepods. Chaetognaths and ostracods were also very abundant and made up 11 and 5 % respectively of the zooplankton total. Total zooplankton abundance was higher at the boundary of the LC than it was inside the LC but not significantly different from abundances outside of the LC. Stations in the western Gulf of Mexico and on the western boundary had the highest abundances of zooplankton overall. The chlorophyll concentrations at the chlorophyll maximum were higher at the boundary of the LC than inside the LC. Physical-biological processes associated with the frontal boundary of the LC appear to influence the abundance and distribution of zooplankton in the GOM.
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Thesis (M.S.)--University of South Florida, 2007.
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Text (Electronic thesis) in PDF format.
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Adviser: Kendra Daly, Ph.D.
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Copepods.
Euphausiids.
Vertical migration.
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Sea surface temperature.
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Dissertations, Academic
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x Marine Science
Masters.
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t USF Electronic Theses and Dissertations.
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