Population structure and trophodynamics of lanternfish (pisces: myctophidae) larvae of the eastern Gulf of Mexico

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Population structure and trophodynamics of lanternfish (pisces: myctophidae) larvae of the eastern Gulf of Mexico

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Title:
Population structure and trophodynamics of lanternfish (pisces: myctophidae) larvae of the eastern Gulf of Mexico
Creator:
Conley, Walter James
Place of Publication:
Tampa, Florida
Publisher:
University of South Florida
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English
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xiv, 173 leaves : ill. ; 29 cm.

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Subjects / Keywords:
Lanternfishes -- Mexico, Gulf of ( lcsh )
Lanternfishes -- Larvae ( lcsh )
Dissertations, Academic -- Marine Science -- Doctoral -- USF ( FTS )

Notes

General Note:
Thesis (Ph.D.)--University of South Florida, 1993. Includes bibliographical references (leaves 140-156).

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University of South Florida
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Universtity of South Florida
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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
029682513 ( ALEPH )
29961150 ( OCLC )
F51-00029 ( USFLDC DOI )
f51.29 ( USFLDC Handle )

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Graduate Council University of South Florida Tampa, Florida CERTIFICATE OF APPROVAL Ph.D. Dissertation This is to certify that the Ph.D. Dissertation of Walter James Conley with a major in Marine Science has been approved by the examining committee o n 9 July 1993 as satisfactory for the dissertation requirement for the Ph.D. degree. Examining Committee: Major Professor: Thomas L. Hopkins, Ph. D. Member: Kendall L. Carter, Ph.D. Member: Robert G. Muller, Ph.D. Member: Joseph J. Torres, Ph.D. Member: John J. Walsh, Ph.D.

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POPULATION STRUCTURE AND TROPHODYNAMICS OF LANTERNFISH (PISCES: MYCTOPHIDAE) LARVAE OF THE EASTERN GULF OF MEXICO by WALTER JAMES CONLEY A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Marine Science in the University of South Florida August 1993 Major Professor: Thomas L. Hopkins, Ph.D.

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DEDICATION This dissertation is dedicated to my wife, Teresa Ann Hastings, for sharing the road less traveled.

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ACKNOWLEDGEMENTS Any work the magnitude of completed without assistance in a dissertation cannot be various individuals contributed to this research. forms and many I wish to thank my dissertation committee; my major professor Dr. Thomas L. Hopkins, Dr. Kendall L. Carder, Dr. Joseph J. Torres, and Dr. John J. Walsh of the Department of Marine Science of the University of South Florida, and Dr. Robert G. Muller of the Florida Marine Research Institute. I also wish to express my appreciation to Dr. Jefferson T. Turner of the University of Massachusetts for providing a strong foundation to my understanding of plankton dynamics. Many individuals assisted in the collection of zooplankton. My thanks go to Joseph Donnelly, Mark Flock, Dr. John V. Gartner, Jr. Steven Kinsey, Tom Lancraft, Ken Pasarella, Jonathan Rast, and Tracey Sutton who assisted with net collections. A special thank you to Mark Flock who completed the discrete depth series during November 1985 when it became impossible for me to complete the collections. The dive team put in hundreds of hours of training to meet the state safety requirements. These individuals went to great lengths (or depths) to make this aspect of the research a success. I wish to express my sincere gratitude to the dive team; Mark Flock, Dr. John V. Gartner, Jr., Eric Hopkins, Ken

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Pasarella, and Jose Torres. I also wish to express my gratitude to Joseph Donnelly for "walking me through" the analysis of chemical composition and Claire Obordo for her assistance with library searches. My good friend and colleague, Dr. John V. Gartner, Jr., also deserves special gratitude. Jack assisted in the counting of otolith micro increments, shared SEAMAP larval material, provided valuable unpublished information on postmetamorphic lanternfishes, and twice reviewed this manuscript contributing greatly to its final outcome. The cruises were supported by the State of Florida and NSF OCE #841787 grant to Dr. Thomas L. Hopkins. The Houston Underwater Club generously contributed financial support through their Seaspace Scholarship which helped defray the expenses of the dives. Scholarships were also awarded by the John Lake Foundation, Gulf Coast Charitable Trust, St. Petersburg Woman's Book Club, and st. Petersburg Shell Club. Finally, I wish to thank my wife, Teresa. Without her support and continued sacrifices I could never have completed this research.

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TABLE OF CONTENTS LIST OF TABLES. . . . . . . . . . . . . . . . . . . . viii LIST OF FIGURES. . . . . . . . . . . . . . . . . . . x ABSTRACT............................................. xii INTRODUCTION. . . . . . . . . . . . . . . . . . . . 1 THE HYDROGRAPHIC SETTING ............................. 4 MATERIALS AND METHODS Ichthyoplankton Collections (Abundance and Vertical Distribution) .......................... 7 Ichthyoplankton Collections (Diet Analysis) ..... 11 Ichthyoplankton Collections (Energetics) ........ 14 General Zooplankton (Prey) Collections .......... 19 Search Estimates. . . . . . . . . . . . . . . . 22 RESULTS Hydrography. . . . . . . . . . . . . . . . . . . 2 4 Relative Abundance and Vertical Distribution of Ichthyoplankton .............................. 27 Vertical Distribution of Lanternfish Larvae ...... 31 Vertical Abundance of Zooplankton Prey (30-lbottles) .................................. 56 Horizontal Abundances of Zooplankton Prey (Hand-held Containers) ........................... 57 Larval Diet and Feeding Chronology .............. 67 Age and 80 Energetics. . . . . . . . . . . . . . . . . . . 8 8 Search Estimates ................................. 100 Predation Impact . . . . . . . . . . . . . . . . 10 4 DISCUSSION The Eastern Gulf Assemblage ...................... 106 Vertical Distribution of Lanternfish Larvae ...... 111 Larval Diet. . . . . . . . . . . . . . . . . . . 116 Larval Prey Field .............................. 121 Energetics ....................................... 126 Resource Partitioning ........................... 134 Predation Impact ................................. 136 CONCLUSIONS. . . . . . . . . . . . . . . . . . . . . 13 8 vi

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LITERATURE CITED. 14 0 APPEND I X 15 7 vii

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LIST OF TABLES Table 1. Volume of water filtered for collection of ichthyoplankton. 10 Table 2. Comparison of ichthyoplankton vs. other zooplankton abundances. 28 Table 3. Range of zooplankton abundances collected with 30-1 Niskin bottles. 58 Table 4. Median abundance and Fisher Index for hand-collected zooplankton. 64 Table 5. Average dimensions of potential prey items. 66 Table 6. Larval diet composition of five representative species of lanternfishes. 68 Table 7. Larval diet composition of additional species of lanternfishes. 69 Table 8. Chemical composition of the larvae of five representative species of lanternfishes. 89 Table 9. Average daily increase in calories for growth by the larvae of five representa-tive species of lanternfishes. 93 Table 10. Caloric and numerical prey requirements for larvae of Benthosema suborbitale. 94 Table 11. Caloric and numerical prey requirements for larvae of Ceratoscopelus townsendi s.l. 95 Table 12. Caloric requirements for larvae of Hygophum taaningi. 96 Table 13. Caloric and numerical prey requirements for larvae of Myctophum selenops. 97 Table 14. Caloric and numerical prey requirements for larvae of Notolychnus valdiviae. 98 viii

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Table 15. Range of energetic densities available to a 3.8 mm SL Ceratoscopelus townsendi s.l. larva. Table 16. Range of energetic densities available to a 5.3 mm SL Ceratoscopelus townsendi s.l. larva. Table 17. Relative abundance of lanternfish larvae 102 103 compared to other ichthyoplankton. 107 Table 18. Comparison of rank of abundance of eastern Gulf of Mexico premetamorphic and post-metamorphic lanternfishes. 109 Table 19. Comparison of rank abundance of larval lanternfishes throughout the Gulf of Mexico and Caribbean. 112 Table 20. Comparison of the vertical distribution of larval lanternfishes between the eastern Gulf of Mexico and the North Pacific Central Gyre. 114 Table 21. Growth of non-myctophid larvae from the Gulf of Mexico. 129 ix

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LIST OF FIGURES Figure 1. Typical temperature and salinity profiles from standard Station ( 2 I 8 6 W) 2 6 Figure 2. Temporal abundance of fish larvae collected within the upper 200 m of the water column. 30 Figure 3. Vertical distribution of ichthyoplankton at Standard Station from March 1984, June 1984 September 1984, and March 1985. 33 Figure 4. Vertical distribution of ichthyoplankton at Standard Station from June 1985, November 1985, January 1986, and May 1986. 35 Figure 5. Vertical abundance of lanternfish larvae from the subfamilies Myctophinae and Lampanyctinae. 38 Figure 6. Cluster results of vertical distribution patterns of the larval lanternfish assemblage. 40 Figure 7. Relative vertical abundance of Myctophum affine, M asperum, M nitidulum, and M selenops. 42 Figure 8. Relative vertical abundance of Hygophum benoiti,H. hygomii, fi. reinhardtii, and fi. taaningi. 44 Figure 9. Relative vertical abundance of Diogenichthys atlanticus, Lobianchia gemellarii, and Notolychnus valdiviae. 47 Figure 10. Relative vertical abundance of Diaphus type c, Hygophum macrochir, Lampanyctus alatus, and Myctophum obtusirostre. 49 Figure 11. Relative vertical abundance of Benthosema suborbitale, Centrobranchus nigroocellatus, Gonichthys cocco, Notoscopelus resplendens. 51 X

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Figure 12. Relative vertical abundance of Ceratoscopelus townsendi s.l., Lampadena luminosa, and Lepidophanes guentheri. 53 Figure 13. Relative vertical abundance of Diaphus type A and B. 55 Figure 14. Vertical abundance of common protozoan plankton and copepod nauplii at Standard Station during January 1986. 60 Figure 15. Vertical abundance of copepodites at Standard Station during July 1985. 62 Figure 16. Range of caloric values calculated from measured plankton collected along the 5 20 meter (depth) horizontal transects. 70 Figure 17. Range of caloric values calculated from measured plankton collected along the 25 -35 meter (depth) horizontal transects. 73 Figure 18. Cluster results of the diet of 14 species of lanternfish larvae plus the genus Diaphus. 75 Figure 19. Relationship of Standard Length (mm) to width of ingested prey. 79 Figure 20. Feeding chronology of five representative lanternfish species. 82 Figure 21. Age and growth of the larvae of the five representative species of lanternfishes. 85 Figure 22. Relationship between dry weight and standard length. 91 Figure 23. Relative mouth size of larvae. 117 xi

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POPULATION STRUCTURE AND TROPHODYNAMICS OF LANTERNFISH (PISCES: MYCTOPHIDAE) LARVAE OF THE EASTERN GULF OF MEXICO by WALTER J. CONLEY an Abstract Of a dissertation submitted in partial fulfillment of the requirements of the degree of Doctor of Philosophy in the Department of Marine Science in the University of South Florida July 1993 Major Professor: Thomas L. Hopkins, Ph.D. xii

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Larvae of lanternfishes (Pisces: Myctophidae) were collected from the eastern Gulf of Mexico and examined to determine vertical distribution, diet, and potential predation impact through energetic requirements. The abundance distributions of potential prey organisms were also examined over the vertical and micro-to fine-scale horizontal dimensions. Discrete patterns of vertical abundance were detected for the larval lanternfishes. Four clusters were recognized, each cluster was centered around one of the four 25 m depth strata within the upper 100 m of the water column. A significant difference between the vertical distribution patterns of the two subfamilies was detected. Larvae of the subfamily Lampanyctinae were more shallow than larvae of the subfamily Myctophinae. Differences in diet composition of larvae of the two subfamilies was also detected but within each subfamily many species shared a common food resource. larvae preyed upon the various stages Most lampanyctine of calanoid and cyclopoid copepods, whereas myctophinine diets were dominated by ostracods. At least one species within each subfamily revealed a diet dominated by gelatinous zooplankton. overlap of several species in both diet and distribution indicate that resources were not partitioned among species. Larval energetic requirements were estimated from analysis of age and growth, dry weight, chemical composition, respiratory requirements, and estimates of assimilation efficiency. Results suggest that caloric densities of prey of the xiii

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appropriate size and taxa exist over the range of larval foraging. Caloric requirements also indicate that, with the possible exception larvae were too populations. Abstract Approved: of selective predation upon ostracods, diffuse to significantly impact prey Major Professor, Dr. Thomas L. Hopkins Marine Science Department Date of Approval xiv

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1 INTRODUCTION Mesopelagic fishes dominate the pelagic fish fauna in terms of numbers of species and individuals and lanternfishes (Pisces: Myctophidae) are the most abundant of the vertically migrating mesopelagic fish groups (Maynard et al., 1975; Gjosaeter and Kawaguchi, 1980; Hopkins and Lancraft, 1984). Lanternfishes play a primary role in vertical transport of organic matter in the worlds oceans (Hopkins and Baird, 1977; Robison and Bailey, 1981). Along with krill and cephalopods, the lanternfishes are often cited as the most promising unexploited oceanic food resource (Gulland, 1971; Gjosaeter and Kawaguchi, 1980). Limited fisheries for some lanternfishes exist (Newman, 1977), however, the high content of wax esters (Nevenzel et al., 1969) may be an obstacle to human consumption (Kinumaki et al. 1977) Nonetheless, lanternfishes are a dominant biomass group in pelagic ecosystems, providing forage for more readily exploitable populations (Watanabe, 1960; Alverson, 1963; Scott and Tibbo, 1968; Pereyra et al., 1969; Roger and Grandperrin, 1976; Zuez and Nesis, 1971). The importance of early life history events of marine fishes to the adult population size and structure has been a central theme in fisheries biology since Hjort (1914)

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2 suggested a connection with larval survival. This suggestion was based, in part, upon the great number of larvae relative to adults. Lanternfish larvae are at least an order of magnitude greater in abundance than adults in the eastern Gulf of Mexico (Gartner et al., 1987; this study) suggesting that larval mortality is an important factor in determining adult population size and structure. Resource limitation (starvation) and predation have been cited as the two most important factors in the survival of marine fish larvae (May, 1973; Hunter, 1981). This research was population structure designed to gain insight and trophodynamics of into the abundant premetamorphic (larval) lanternfishes in the eastern Gulf of Mexico, with a focus on potential resource limitation. Resource limitation was examined from 1) ability of larvae to meet their caloric concentrations, 2} requirements from feeding incidence, available prey and 3} resource partitioning (or lack thereof). These factors were evaluated from the examination of larval age and growth, chemical composition, diet, plus abundance and distribution of larvae and their prey. Some researchers have suggested that ichthyoplankton, as predators of crustacean zooplankton, have a significant impact upon zooplankton populations in certain environments (Bollens, 19 8 8; Hewett and Stewart, 19 8 9) Others, such as Cushing (1983} argued that marine pelagic fish larvae are far too

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3 diffuse relative to their prey to have a significant impact on their populations. The energetic requirements and dietary habits of lanternfish larvae, combined with abundance information of predator and prey, enabled the estimation of potential predation impact of these larvae upon their zooplankton resource. This work represents only the second report of lanternfish larval densities, vertical distributions, age and growth from any ocean, and is the first from the Atlantic. Data produced from this study provide the first information on larval myctophid feeding chronology, diet composition, chemical composition, and estimates of caloric requirements. This is a companion study to those of Gartner et al. (1987; 1989), Gartner (1991a; 1991b; 1993), and Hopkins and Gartner {1992) who examined the ecology o f postmetamorphic lanternfishes. These results are part of a larger project initiated to provide a detailed analysis of the myctophid assemblage in the eastern Gulf of Mexico. The intent of this research was to combine population size and structure information with diet composition data to determine the predation impact of these fishes on their zooplankton resource as a complement to Hopkins and Gartner's ( 1992) work on postmetamorphic lanternfishes.

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4 THE HYDROGRAPHIC SETTING The major hydrodynamic influence in the eastern Gulf of Mexico is the Loop Current which enters the Gulf through the Yucatan Straits and exits through the Straits of Florida {Hansen and Molinari, 1979; Leipper, 1970; Maul, 1977; Molinari et al., 1978}. The Loop Current exhibits a seasonal signal of spring intrusion and fall spreading (Leipper, 1970; Maul, 1977}, however, the amplitude and timing of the seasonal signal is variable (Behringer et al., 1977; Sturges and Evans, 1983}. Deepest penetration occurs during summer (Molinari et al., 1977}. The boundary of the Loop current is rarely observed farther north than but intrusions as far as have been reported (Huh et al., 1981; cited in Sturges and Evans, 1983}. When the current is strongest in spring and summer, it is also farthest to the west (Maul, 1977}. Minimal intrusion usually occurs in winter, but deep winter intrusions have been recorded (Molinari et al., 1977}. Meanders have been observed at the eastern boundary of the Loop Current. These meanders, which last approximately 23 days, create shoreward intrusions (often beyond the shelf break} of warm water and seaward intrusions of cool water (Vukovich et al., 1978}. In extreme cases, cold tongues have extended 400 km from the southwest Florida Platform (Vukovich

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5 et al., 1979). Cold tongues form on both sides of the Gulf (southwest Florida and Yucatan peninsula) and then meet to form a cold ridge. This merger results in the shedding of large anticyclonic gyres (100-300 km diameter) (Cochrane, 1972; Molinari et al., 1977; Vukovich et al., 1979; Maul, 1985) that advect westward and then dissipate (Elliot, 1982). Vukovich and Crissman (1986) reported that these gyres decrease to 55% of their original size in 150 days, 31% in 300 days, and can extend to depths of 800 m (. When separation occurs, a major change in the position of the northern boundary of the Loop Current occurs (Vukovich and Crissman, 1986) Cold-domed cyclonic eddies (80-120 km diameter and 1000 m deep) are also a feature of the Loop Current (Vukovich and Maul, 1985; Vukovich, 1986). These perturbations form along the northern boundary of the Loop Current and travel south along the boundary of the Loop Current off the West Florida Shelf. These cold features do not travel through the Straits of Florida, rather, they may form a cold tongue, cold ridge, or dissipate (Vukovich and Maul, 1985) Time series from satellite observations suggest that surface-isolated cold centers may be the result of upwelling of subsurface waters rather than a result of horizontal advection and isolation of cooler Gulf Common Water (Vukovich and Maul, 1985). The most common water mass located in the vicinity of sampling 86"W) is residual Gulf water (Austin, 1971).

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6 This water mass can be distinguished from Loop Current water by the depth of the 22C isotherm and salinity. In Loop Current water the isotherm is located between 150 to 200 m and surface salinity is greater than 36.5 ojoo. Gulf residual water has a lower salinity and the shallow (Leipper, 1970; Nowlin, 2 2C isotherm is more 1971; Jones, 1973). Circulation models indicate that Loop Current water should be expected 20-30% of the time in the vicinity of sampling (Science Application International Corporation, 1989) but was only encountered two times during 18 cruises (Hopkins, personal communication) The biological characteristics of the eastern Gulf of Mexico is similar to other low latitude oceanic areas (McGowan, 1974; Longhurst, 1976). Primary production is low (ca 50 gC m-2 year-1 ; El-Sayed, 1972), zooplankton biomass is low (1.2 gDW m-2 in upper 1,000 m; Hopkins, 1982) and faunal diversity is high (Hopkins, 1982; Hopkins and Lancraft, 1984).

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7 MATERIALS AND METHODS Ichthyoplankton Collections (Abundance and Vertical Distribution) All samples were collected within 20 nautical miles of 86"W, a location hereafter referred to as standard Station. Net tows were made during day and night. Only night collections were used to determine abundance and vertical distribution of ichthyoplankton because of problems associated with daytime net avoidance (Bridger, 1956; Richards, 1984). Temperature was determined with expendable bathythermographs (XBT), and salinity was determined from electrical measurement of conductivity with depth (CTD). During the first two cruises (March and June, 1984), ichthyoplankton was collected using collapsible bongo nets. The inner diameter of these 505 mesh nets was ca. 61 em with a 3:1 length-to-mouth ratio. Few fish larvae were collected with this apparatus; thus, for the remaining six cruises, two 505 mesh plankton nets, suspended side by side within a modified Tucker trawl frame (Hopkins et al. 1973), were used. These nets had a mouth opening of 0.56 m2 per net, and a length to mouth ratio of 7:1. Preliminary investigations in the eastern Gulf of Mexico

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9 Moser and Ahlstrom, 1970) were constructed for abundant forms for which no published information was available. When generic assignment was not possible, because of small size or physical damage resulting from collection, individuals were grouped under the category Myctophidae to enable aggregating population estimates at the family level. Over 15,000 larvae were sorted from 177 samples for discrete depth analyses. These samples were collected by filtering approximately 115,000 cubic meters of water during eight cruises (Table 1). In addition, over 5,000 myctophid larvae were examined from 1,055 samples from the SouthEast Area Monitoring and Assessment Program (SEAMAP). The SEAMAP samples represented 456 stations throughout the Gulf of Mexico and were used to complete larval life-history series and to elucidate other taxonomic difficulties (see Appendix). The extent of night-time vertical overlap in abundance of the larval myctophids was compared using a Bray-Curtis (1957) similarity matrix. The vertical distribution of every species pair was contrasted with the equation: PSc = 100 0. 05 E I a-b I where a and b are percentages of species a and b collected within each 25 m stratum of the upper 200 m. Dendrograms were created using average distance linkage to identify groups where values greater than 60% (= 40% dissimilarity) were considered to represent co-occurrence of the two species within the zone of collection (see Hopkins and Gartner, 1992).

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Table 1. Volume of water filtered for the collection of ichthyoplankton discrete depth series. All volumes are expressed in cubic meters. DEPTH MARCH JUNE SEPTEMBER 1984 1984 1984 0-25 1556 429 1113 25-50 1916 593 1229 50-75 938 1202 1653 75-100 1162 200 1477 100-125 1138 383 937 125-150 480 616 904 150-175 646 ----828 175-200 622 672 1232 200-300 1658 ---------TOTAL 10,117 4,095 9,374 MARCH JULY 1985 1985 1241 1282 905 1097 1093 1117 764 695 670 1043 1761 981 1710 11132 778 1188 -----1324 8,923 9,858 NOVEMBER JANUARY 1985 1986 1969 955 4803 2047 3780 1176 4136 1725 4139 1129 5047 2436 4641 3323 4369 2876 8017 ----44,760 15,667 MAY 1986 1206 1128 1215 1157 1189 1218 1304 1592 1858 11,867 1-' 0

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11 Ichthyoplankton Collections (Diet Analysis) Larvae for diet analysis were collected hourly during a 24-hour period in oblique tows of the upper 150 m. The nets were lowered to depth, opened, and raised to the surface where the samples were immediately fixed. Time from net opening to fixation was always less than 10 minutes. Whereas length of tow may affect gut clearance by some fish larvae (Hay, 1981), tow lengths of less than 10 minutes reduce problems associated with gut clearance (Govoni, personal communication). Upon return to the laboratory, all fish larvae were sorted from the entire zooplankton sample and identified to the lowest taxon possible. Lanternfish larvae were measured to the nearest 0.1 mm standard length (SL) The upper jaw was measured from the apex of the premaxilla to the posterior end of the maxilla. The entire gastrointestinal tract, from esophageal sphincter to anus, was removed intact from the abdominal cavity. The dissected alimentary canal was transferred to a few drops of semipermanent mounting medium on a glass microslide and ingested material was teased from the tract and examined at 100-400X magnification. Pre y items were identified to the lowest taxon possible and measured along two dimensions. Biomass of food in each taxonomic category was estimated from volume. Volume estimates of pre y were calculated from the closest geometric form (Beers and Stewart,

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12 1967). Volume was then converted to organic carbon using a standard relation to volume (volume (cm3 ) times 0.08; Beers et al., 1975). Because prey were ingested whole, in most cases crustacean prey could be recognized to genus or family. Urochordates were identified to major class. Ostracods were assigned to genus by the morphology of a pronounced notch in the anterio-dorsal portion of the carapace (Deevy, 1968). Most of the ostracods were members of the genus Conchoecia. The less common genera Halocypris, Halocypria, Euconchoecia, and Archiconchoecia were grouped as Ostracoda. Most cyclopoid copepods were easily recognized from general morphology. Calanoid copepods were identified to genus, when possible, from a combination of mandible m orphology and other distinguishing characteristics (e.g. spination of periopods). For diet-similarity comparisons, calanoid copepods were assigned to two groups, "Calanoid A" consisting of the generalized calanoids such as the families Calanidae, Pseudocalanidae, and Paracalanidae, and the more specialized "Calanoid B" consisting of such families as the Euchaetidae, Metridiidae, Aetideidae, and Heterorhabdidae. Thaliaceans and larvacean house s were o f t e n accompanied by clusters of dinoflagellates, diatoms, and protozoans. These protistans were not considered separately when associated with these structures. Unassocia t e d clusters o f mixed Protista and copepod fecal pellets were also frequently

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13 observed, especially in smaller larvae. This material has variously been referred to as "greenish brown", "olivecolored" and "olive brown" debris of decapod diets (Heffernan and Hopkins, 1981; Flock and Hopkins, 1992; Kinsey, 1992) or chyme of fish larvae (Govoni et al., 1983). These clusters were considered as units and individual cells were not counted and measured. The biomass of food in each taxonomic category was expressed as percent of total diet. were then obtained for the prey Diet similarity indices taxonomic data for all myctophid larval species pair-combinations using the BrayCurtis (1957) index. The similarity indices were clustered and the 40% dissimilarity was used as the criterion for separation of diets. Feeding incidence (average percent gut fullness within a time period) and feeding chronology were determined from information on gut fullness evaluated during a diel cycle. Gut fullness was estimated according to the following criteria: 0 = empty gut; 1 = prey present but gut less than 1/4 full; 2 = gut 1/4 to 1/2 full, 3 = gut 1/2 to 3/4 full; 4 = 3/4 to full gut. In addition, prey size was compared to larval size to determine the range of prey size ingested. Because most prey were swallowed whole and width is considered the critical dimension for prey ingestion (Hunter, 1981), the relationship between maximum prey width to larval SL was examined to determine maximum prey size ingested.

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14 Ichthyoplankton Collections (Energetics) Larvae collected for distribution and feeding analyses were fixed in formalin and could not be used for analysis of chemical composition or extraction of otoliths (Radtke and Waiwood, 1980). Thus, additional samples were collected during four summer cruises from 1988 to 1990 to Standard Station. During this second phase of collection, larvae were sorted immediately from the catch, identified, measured to the nearest 0.1 mm standard length (SL), and frozen in individually sealed nalgene capsules. The larvae were separated into three groups. One group of larvae was used for estimates of age and growth, the second for dry weight measurement, and the third for determination of chemical composition. To estimate the energetic demands ( QJ of lanternf ish larvae, the bioenergetics of five representative species was evaluated. Bioenergetic models have been used to determine the energy budget of adult (Baird and Hopkins, 1981) and larval (Laurence, 1977; Eldridge et al., 1982; Houde and Schekter, 1983; Brightman, 1993) fishes. The following is a slightly modified version of the equation for the bioenergetic model which has been discussed in detail by Winberg (1956) and Warren and Davis (1967): Qc=Qg+Q.+Qm where;

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15 Qc = energy consumed Qg = food energy converted into potential energy through growth Q. = includes energy lost in feces, secretions excretions, and Qm = includes energy consumed in routine metabolism (Qr) and energy consumed in active metabolism (Q.). The calculation of energy converted to potential energy through growth (Qg) requires knowledge of growth rate, increase in biomass, and chemical composition. The sagittal otoliths of five species (= representative species) of lanternfishes (Benthosema suborbitale, Ceratoscopelus townsendi s.l., Hygophum taaningi, Myctophum selenops, and Notolychnus valdiviae) were examined for microincrement analysis. Otoliths were removed from the membranous chondrocranium using insect pins and mounted in Thermoplast. Increment counts were made at 630X magnification. Images were projected to a phase contrast monitor and examined by two independent observers. If increment counts were differing for the two observers, the otolith was reexamined. If individual counts different by more than two microincrements could not be resolved, the otolith was discarded. Protein, lipid, and carbohydrate composition was determined for larvae of the same five species of lanternfishes. Protein content was determined by a slightly modified version (see Donnelly et al., 1990) of the method

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16 developed by Lowrey et al. (1951}. Lipid content was quantified following the methods of Bligh and Dyer (1959} and carbohydrates by the methods of Dubois et al. (1956}. Dry weight was measured by drying formerly frozen larvae at 60C and weighing individuals on a Perkin-Elmer Autobalance AD-2 in a temperature and humidity controlled chamber. Larvae were measured to the nearest 0.1 mm SL and weighed to the nearest 0.001 mg. Daily growth in calories (Qg} was estimated from age and growth information combined with chemical composition (protein, lipid, and carbohydrate} using the following conversions of Brett and Groves (1979}; proteins contain 5.7 calories mg-1 lipids contain 8. 7 calories mg-1 and carbohydrates 4. 2 calories mg-1 Routine respiration was not directly measured for lanternfish larvae but respiration rates for the larvae of a variety of other tropical to subtropical species were in close agreement with one another (Houde and Schekter, 1983; Brightman, 1993}. To approximate the respiratory rates of the five representative lanternfishes, the respiration during routine metabolism for larvae of similar morphology and diet were matched to the measured values of Houde and Schekter ( 1983} Respiration (J-'102 J..'gDW1 hour-1 } was converted to calories using the oxycalorific equivalent of 0.0046 calories J..'l-102 (Brett and Groves, 1979} It was assumed that active (=feeding} metabolism was twice routine metabolism based on Brett and Groove's (1979} estimated mean ratio of active to

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17 routine metabolic rate (1.7 0.4) and Ware's (1975) estimated factor of 2.5 to convert routine to active metabolism for pelagic fishes. Daily cost of metabolism was estimated from the equation of Houde and Schekter (1983): Qm = (2m(t1) + m(t2)]W where; Qm = the 24 hour metabolic cost in calories m = routine metabolic rate (cal p.g-1 h-1 ) W = dry weight of larvae (p.g) t1 = hours in feeding activity t2 = non-feeding hours. Energy lost through feces, excretions, and secretions can be a major source of energy loss for fish larvae (Govoni et al., 1982; Houde and Schekter, 1983). Brett and Groves (1979) reported an average loss through defecation of 27% by young carnivorous fishes. Losses as high as 83% (Houde and Schekter, 1983) and as low as 8% (Brightman, 1993) have been reported for some marine fish larvae. Prey assimilation, or the percentage of food energy used for growth and activity, may be highly variable. Therefore, rather than choose one value, calculations of daily ration included minimum, average, and maximum values for this energy loss. Losses due to metabolic excretions (urine and other metabolic fluids) are reported to be considerably lower, ranging from 1 10% (Brett and Groves, 1979). This potential loss was not separately included in these calculations because of the wide range of

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18 loss calculated for assimilation values. Once caloric values are estimated, knowledge of the type (taxa) and size of prey ingested by larvae, plus caloric content of major prey items, can yield a prediction of larval prey requirements. Caloric value of prey was determined using an average conversion factor from zooplankton dry weight of 0.0059 calories (Cumming and Wuycheck, 1971; Wissing et al., 1973; Laurence, 1977). Dry weights of prey were calculated from dry weight to cephalothorax length relations of copepods collected at Standard Station (Hopkins, unpublished data) Ostracod dry weights were calculated from the relationship of carapace length to dry weight of Conchoecia spp. collected at standard Station (Hopkins, unpublished data) The calculated exponential equations are y = 8 .12e<0 012x) for copepods and y = 8. 7 4e<0 0013x) for ostracods where X = length in and y = Larvae were grouped into three size classes; 3.5 -5 mm SL, 5.1 -7.5 mm SL, and 7.6 10 mm SL for predation impact estimates, which was the same range of larval size examined for diet composition. The average size of dominant prey of each size class was determined. Number of prey items required by larvae for metabolism and growth were then calculated by determining the number of calories of the dominant prey would be necessary to meet the demand. impact on the zooplankton prey Estimates of potential were then determined by examining the minimum, average, and maximum grazing impact of

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19 each species for the cruise in which maximum abundance of lanternfish larvae was detected (March 1985) Extrapolations from the five representative species were accomplished by assuming that larvae of similar diet and size had similar caloric requirements. These results were then compared to the estimated abundance of zooplankton within the upper 200 m during the day. The zooplankton abundance information was obtained from 30-1 bottle casts (see below). General Zooplankton (Prey) Collections Samples were collected from Standard Station during seven cruises from March 1984 to May 1986. Two different collection methods were employed to observe different patterns of distribution (overall vertical and micro-to fine-scale horizontal; em to 900 m). To determine general patterns of abundance over the resident depth of larval lanternfishes, zooplankton (potential prey) was collected with 30-1 Niskin bottles at 25 m intervals from the surface to a depth of 200 m. Water thus collected was filtered through a 30 mesh and the sievings were preserved in 5% v:v buffered formalin. These samples were split and counted as described by Hopkins (1982). Conventional samplers cannot provide reliable distribution and abundance information for potential prey items over a scale appropriate to the diel feeding of an

PAGE 33

20 individual larva (micro-to fine-scale). Filtration samplers can only provide an average abundance for a large volume of water, and fine-mesh nets clog even in oligotrophic waters. Further, wire hung samplers destroy fine scale patterns of abundance through turbulence. Therefore, micro-to fine-scale distributions of zooplankton were estimated from collections by SCUBA divers using handheld containers. These collections were completed within one cruise during July 1985. Each container was constructed from two nalgene screw top jars cut and joined at their base. The containers were, therefore, open at both ends minimizing turbulence during collection. The SCUBA -assisted methods used to collect microzooplankton were adapted from the methods developed by Hamner and colleagues (Hamner, 1975; Hamner et al., 1975) for in situ observation and collection of gelatinous zooplankton at open ocean sites. SCUBA-assisted collections were made at 5 m increments from 5 to 35 m depth. Containers were one liter in volume and 14-20 samples were collected at each depth. divers swam a short distance to "new" For each sample, water. Vertical sampling was along a transect less than the distance the smallest larva could traverse within a short time period (hours). This distance (10-20 m) was approximated from the calculations of swimming speed of anchovy larvae (Rosenthal and Hempel, 1970; Hunter, 1972). Samples were filtered through 30 p.m mesh and the sievings

PAGE 34

21 were preserved in a modified Lugol's solution as recommended for the preservation of soft bodied organisms (Beers, 1976}. Thus, the microzooplankton abundances reported here are of organisms > 30 nominal size. Upon return to the laboratory, the entire sample was filtered into petri dishes and examined under a dissection microscope at SOX magnification. Individuals were identified to major taxa and counted. Wet mounts were made by pipetting small organisms (< 200 onto glass slides for measurement at 100 or 400X magnification. Volume of organisms was estimated from the closest geometric form (Beers and Stewart, 1967}. Calculated volume was converted to dry weight using a standard relation to volume (Beers et al., 1975} for soft bodied (noncrustacean} organisms. Dry weight of copepods was calculated from dry weight to cephalothorax length relations of copepods collected at Standard Station (Hopkins, unpublished data}. Caloric value was determined from an average conversion factor of 0.0059 calories There are three general patterns of abundance for organisms living in a continuum; even, random, and aggregated (=overdispersed} (Pielou, 1984}. These patterns can be identified from samples by an examination of the distribution of the ratio of variance to mean. This ratio is commonly referred to as the coefficient of dispersion or Fisher Index (FI} (Haury, 1976a; 1976b}. If organisms are evenly distributed, FI is generally less than one; if organisms are

PAGE 35

22 randomly distributed, FI is approximately equal to one; if organisms are aggregated, FI is generally greater than one. By itself, the index is a descriptive statistic. However, significant departure from randomness can be detected by testing goodness of fit to a Poisson Distribution. At low densities, this statistical technique is not sensitive and may fail to detect non-randomness where it exists (Cassie, 1961; Fasham et al., 197 4) Unfortunately, the low number of organisms collected by small vessels (as required to examine the microscale) also precludes the use of some of the rigorous statistical techniques available for the examination of macro to fine scale variability (Fasham et al., 1974; Haury, 197Gb; Greenblatt et al. 1982; Haury and Wiebe, 1982) Nonetheless, the data presented herein provide a valuable first-time estimate of prey densities that larval fishes in the wild might expect to encounter daily. Search Estimates The ability of a fish larva to meet its metabolic demand can be assessed if information regarding the availability and concentration of appropriate prey calories are compared to search capabilities (= search area or perceptive field). Only one (Ceratoscopelus townsendi s.l.) of the five representative species of lanternfish larvae meet all of the conditions for this calculation. The distribution of the larvae of this

PAGE 36

23 species was the only one to overlap the zone of sampling for micro-to fine-scale distribution of prey. Knowledge of prey type and size and feeding chronology townsendi s.l., plus published larval swimming speeds and perceptive field calculations for larvae of similar size and morphology, allowed for an examination of the range of ingestible prey. Ceratoscopelus townsendi s.l. larvae are morphologically similar to engrauliform larvae, therefore, a swimming speed (velocity = -0.215 + 1.038SL in cmjs) and area of perceptive field (area = 0. 45SL2 ) from the cinematographic study of larval Engraulis mordax (Hunter, 1972) was applied. It was further assumed that the larvae were active for 15 hours (this study) during a diel cycle and swam 82.6% of that time (Hunter, 1972). Search volume was calculated by multiplying the cross-sectional area of the larval perceptive field by velocity and active feeding time. Larval prey field was compared to available prey concentration as expressed in calories to determine the tractability of a larva encountering adequate concentrations of prey.

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24 RESULTS Hydrography Little change in surface water temperature was observed among cruises. Even within the upper 50 m, where variability was greatest, the lowest temperature (22 C -January 1986) was less than seven degrees cooler than the highest temperature recorded (28. 8C -July 1985). In contrast, vertical temperatures within the upper 200 m routinely varied A shallow mixed layer was generally present in the upper 25-75 m. Temperature rapidly decreased between 75 and 400 m, with little change at greater d epths. Salinity also varied little among cruises. Low (34.8-35.4 ojoo) salinities were recorded in surface waters on three occasions. Maximum salinities were measured at approximately 100 m during all periods sampled. From 100 m to 1000 m, salinities gradually decreased from 36.0 to 34.9 ojoo. Temperature and salinity profiles typical of Standard Station are shown in Figure 1.

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25

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Figure 1. Typical temperature and salinity profiles from Standard Station ( 27"N, 86 W)

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26 0.0 50.0 ) 100.0 150.0 I 200. 0 250.0 , 300.0 350.0 J 400.0 r-.. E 450.0 I 500. 0 I ...c ...... I 0.. 550. 0 Q) 0 600. 0 I 650. 0 I rtJ 700.0 I rtJ 750.0 I rtJ 800.0 I rtJ 850.0 I T Summer 900.0 D Winter 950. 0 I rtJ 1000. 0 0 10 20 30 34 35 36 37 Degrees Centigrade Salinity 0 /00

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Relative Abundance and .Ichthyoplankton Vertical Distribution 27 of Over six thousand (6,158) lanternfish larvae were identified from the 15,384 fish larvae collected in the stratified tows. One hundred and seventy nine (179) fish larvae were in such poor condition from net damage or improper preservation that it was not possible to assign them to any category Two hundred and seven ( 2 o 7 ) of the 6 15 8 fish larvae recognized as myctophids could not be positively assigned to genus. Overall, larval fishes of any taxa were never abundant at standard Station. The difference between the abundance of larval fishes and other zooplankton was several orders of magnitude. For example, during January 1986, the number of fish larvae in the upper 100 m ranged from 0. 06 to 0. 36 m-3 The number of zooplankters collected in 30 liter bottles ranged from 10,643 to 16,127 m-3 similar differences in abundance between ichthyoplankton and other zooplankton were observed during all cruises (Table 2}. Abundance of other (non-myctophid) fish larvae was greatest during July 1985, September 1984, and November 1985 cruises, whereas lanternfish larvae were more abundant during March 1985 and May 1986 cruises (Figure 2}. Few larval fishes of any type were collected during June 1984 or January 1986. Most fish larvae were collected in the upper 150m of the water column, with dramatic reductions in numbers below this depth

PAGE 42

28 Table 2: Range of number of individuals m-3 for all ichthyoplankton collected in the upper 100 m of the water column at Standard Station. Ichthyoplankton was collected with 505 J.tm mesh nets. Other zooplankton were collected in 30 liter bottles and screened through a 30 J.tm mesh net. Date Ichthyoplankton Other Zooplankton March 1984 0.18 0.63 1,870 -11,110 September 1984 0.07 0.15 1,900 14,000 March 1985 0.21 -1. 83 3,870 6,800 July 1985 0.47 0.96 2,230 15,800 November 1985 0.04 0.68 3,070 9,660 January 1986 0.06 0.36 10,600 16,100 May 1986 0.02 0.47 3,480 -13,440

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29

PAGE 44

Figure 2. Temporal abundance of fish larvae collected within the upper 200 m of the water column.

PAGE 45

N E 0 Q) 0 > 250 200 \._ 150 0 _j '+---0 \._ 100 Q) _o E :::J z 50 Temporal Abundance of Fish Larvae ts2SZl .. 01/86 Other Larvae Myctophidae 03/84 03/85 05/86 06/84 07/85 Date of Collection 09/84 30 11/85

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31 (Figures 3 and 4). The lowest densities within a 25 m stratum were observed during June 1984 when larval abundance was generally less than a few hundred individuals per 104 m3 The greatest densities were observed during the September 1984 cruise when larval abundance in the upper water column exceeded 5000 per 104 m3 within a stratum. The relative abundance of lanternfish larvae at Standard Station, compared to other vertebrate plankton, was great. Lanternfishes comprised 40% of the total number of fish larvae collected. Relative abundance varied with depth of capture (Figures 3 and 4) and cruise period (Figure 2}. Myctophid larvae were most abundant between 50-150 m, and at times comprised 85% of the total number of vertebrate larvae collected within a 25 m stratum. Although myctophids were also occasionally abundant in the upper 50 m, (March 1985, July 1985, November 1985, May 1986}, the upper 50 m included the most diverse mixture of fish families (Scombridae, Bothidae, Scorpaenidae, Clupeidae, etc.). At depths greater than 150 m, all larval fishes were less abundant and percentage of myctophids was low (0-25%). Larvae of the families Gonostomatidae and Sternoptychidae were generally well represented below 150 m. Vertical Distribution of Lanternfish Larvae The family Myctophidae includes two subfamilies, the

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32

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Figure 3. Vertical distribution of ichthyoplankton at Standard Station from March 1984, June 1984, September 1984, and March 1985.

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33 March 1984 June 1984 Depth (meters) De!Xh (meters) 25-50 50-75 50-75 75-100 100-125 100-125 125-150 150-175 175-200 200-300 200-300 3 10 30 100 300 1,000 3,000 10 30 100 300 1,000 3,000 Larvae per 1 OK cubic meters Larvae per 1 OK cubic meters !Other Larvae 111111 Myctophids !Other LarvaeiiiMyctophids September 1984 March 1985 Depth (meters) Dej:th (meters) 25-50 50-75 50-75 75-100 100-125 125-150 150-175 175-200 175-200 200-300 200-300 0 1,000 2,000 3,000 4 000 5,000 6,000 10 30 100 300 1 000 3,000 Larvae per 10K cubic meters Larvae per 1 OK cubic meters Larvaei!IMyctophids LarvaeiiMyctophids

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34

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Figure 4. Vertical distribution of ichthyoplankton at Standard Station from June 1985, November 1985, January 1986, and May 1986.

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35 July 1985 November 1985 Depth (meters) Depth (meters) 25-50 50-75 75-1 ()() 100-125 125-150 150-175 10 30 100 300 1,000 3,000 10 30 100 300 1,000 3,000 Larvae per 1 OK cubic meters Larvae per 1 OK cubic meters !Other Larvae IIIIIIMyctophids Larvae IIIIMyctophids January 1986 May 1986 Depth (meters) Depth (meters) 0-25 0-25 25-50 25-50 50-75 50-75 75-100 75-100 100-125 100-125 125-150 125-150 150-175 150-175 175-200 175-200 200-300 200-300 10 30 100 300 1,000 3 000 10 30 100 300 1 000 3 000 Larvae per 1 OK cubic meters Larvae per 1 OK cubic meters LarvaeiiMyctophids LarvaeiiiiiMyctophids

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36 Lampanyctinae and Myctophinae, which have been separated into five tribes, 36 generic or subgeneric categories, and between 230 and 250 species (Moser et al., 1984). Significant differences (Kolmogorov-Smirnov test; p < 0.01) were detected between the vertical distribution of larvae of the two subfamilies (Figure 5). Lampanyctinae larvae were most abundant in the upper 75 m of the water column. Ninety-one percent (91%) of the larvae in this subfamily were collected between 0-75 m, with most larvae in the upper 25 m of the water column. In contrast, most larvae of the subfamily Myctophinae (62%) were collected between 50-100 m, and were especially abundant between 50-75 m. Species relative abundance within a stratum, expressed as percent of total vertical abundance, exhibited distinctive vertical profiles. Most species exhibited a definite peak in abundance with greater than 40% of the individuals collected within a 25 m stratum. Results from the Bray-Curtis analysis indicated the presence of four clusters (Figure 6). The largest cluster (D1) contained most species within the subfamiliy Myctophinae. This cluster was centered within the 50-75 m stratum. Most species of Myctophum; M affine, M nitidulum, M selenops, and M asperum were concentrated within the 50-75 m zone (55-60% of the population; Figure 7). Hygophum taaningi and fi. reinhardtii displayed similar patterns of abundance (Figure 8). In contrast, fi. hygomii and fi. benoiti inhabited a broader vertical range and were most

PAGE 54

37

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Figure 5. Vertical abundance of lanternfish larvae from the subfamilies Myctophinae and Lampanyctinae.

PAGE 56

E _c -+--' Q_ Q) 0 o-25 +/D 25-50 + Myc\ophinoe 50_ 75 + D Lompanyc\inoe /D /. 7 5-1 o o -1D e 1 00-1 25 -1125-150 +1 50-175 -175-200 -200-300 --1 / / D I / D \ \ D I I 10 I I 100 Number per 1 OK m3 I I 1000 38

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39

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Figure 6. Cluster results of vertical distribution patterns of the larval lanternfish assemblage. Species codes represent the first letter of the genus plus the first three letters of the specific epithet (e.g. Benthosema suborbitale = Bsub).

PAGE 59

Cluster D1 D2 D3 D4 D1 D2 D3 D4 Cluster Characteristics Dominant Subfamily Abundance Peak Myctophinae 50 75 m Mixed 25-50 m Myctophinae 75-100 m Lampanyctinae 0 25 m Maff Nval Mnit Hrei Msel Htaa Dati : Hhyg : Hben : Lgem I --Masp Lala : Mobt I 1 Hmac I DiaC --Gcoc I : Bsub : Cnig I 1 Nres -Llum I : Ctow I 1 Lgue I I DiaA I DiaB 20% 40% 60% Percent Dissimilarity 40

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41

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Figure 7. Relative vertical abundance of Myctophum affine, M asperum, M nitidulum, and M selenops.

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42 0-25 \ \ 50-75 I I 100-125 150-175 E Q) OJ 200-300 M. affine nitidulurn c 0 0 20 40 60 80 100 0 20 40 60 80 100 0::: _C --1-' 0-25 o_ \ Q) 0 50-75 100-125 150-175 200-300 M. selenops M. asperurn 0 20 40 60 80 1 00 0 2 0 40 60 80 1 00 Percent of Total Percent of Total

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43

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Figure 8. Relative vertical abundance of Hygophum benoiti, fi. hygomii, fi. reinhardtii, and fi. taaningi.

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44 150-175 E H benoiti H hygomii 200-300 Q) OJ c 0 2 0 40 60 80 100 0 2 0 40 6 0 80 100 0 cr::: ....c 0 2 5 -+---' Q_ Q) 0 5 0 -75 I 100-125 1 5 0 -175 H. reinhardti 200-300 H taaning i 0 2 0 40 60 80 1 00 0 20 40 60 80 1 00 Percen t of Tot a l Pe rcent of Total

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45 abundant between 50-125 m, Three additional species in this cluster, Notolychnus valdiviae, Diogenichthys atlanticus, and Lobianchia gemellarii, also had rather broad distributional ranges which were centered at 50-75 m (Figure 9) A second cluster (D2) included the species, Lampanyctus alatus, Myctophum obtusirostre, and Hygophum macrochir, plus Diaphus type C. All of these larvae had maximum abundances within the 25-50 m stratum (Figure 10). Of this group, L alatus and Diaphus belong to the Lampanyctinae. Thus, M obtusirostre and fi. macrochir were the most shallow dwelling of the Myctophinae subfamily. Hygophum macrochir was abundant to 125 m, whereas few L alatus and M;. obtusirostre were present below 100 m. The third cluster (D3) was composed of four species that were deep dwelling larvae. Benthosema suborbitale, Centrobranchus nigrocellatus, and Gonichthys cocco were most abundant between 75 and 100 m (Figure 11). Notoscopelus resplendens was the deepest dwelling of all myctophid species with maximum abundance within the 100-125 m stratum (Figure 11) Cluster (D4) consisted of five species primarily collected within the upper 25m (Figures 12 and 13). One species, Lepidophanes guentheri, was largely restricted to the upper 25 m of the water column. Two species, Lampadena

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46

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Figure 9. Relative vertical abundance of Diogenichthys atlanticus, Lobianchia gemellarii, and Notolychnus valdiviae.

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47 0-25 50-75 ? 100-125 / 150-175 Diogenichthys atlanticus 200-300 0 20 40 60 80 100 E 0-25 Q) 50-75 OJ c 0 100-125 0::: _c 150-175 Lobianchia gemellarii -+--' Q_ Q) 200-300 0 0 20 40 60 80 100 0-25 50-75 I 100-125 /. 150-175 N otolychnus valdiviae 200-300 0 20 40 60 80 100 Percent of Total

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48

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Figure 10. Relative vertical abundance of Diaphus type c, Hygophum macrochir, Lampanyctus alatus, and Myctophum obtusirostre.

PAGE 72

0-25 50-75 100-125 150-175 E 2oo-3oo "---.-/ G) OJ c 0 0:::: _c +-' Q_ G) 0 0-25 50-75 100-1 25 150-175 200-300 Diaphus type C Hygophum macrochir 0 20 40 60 80 1 00 0 20 40 60 80 1 00 Lampanyctus alatus Myctophum obtusirostre 0 20 40 60 80 1 00 0 20 40 60 80 1 00 Percent of Toto I 49

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50

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Figure 11. Relative vertical abundance of Benthosema suborbitale, Centrobranchus nigroocellatus, Gonichthys cocco, Notoscopelus resplendens.

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0-25 50-75 100-125 150-175 E '-----"' 200-.300 Q) 01 c: 0 0:::: _c: -+--' 0-25 Q_ Q) 0 50-7 5 100125 150-175 200.300 51 Benthosema suborbitale Gonichthys COCCO 0 20 40 60 80 1 00 0 20 40 60 80 1 00 Centrobranchus nigroocellatus Notoscopelus resplendens \ \ ( ""' / / ; 0 20 40 60 80 1 00 0 20 40 60 80 1 00 P ercent o f Total

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52

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Figure 12. townsendi guentheri. Relative vertical abundance of Ceratoscopelus s. 1. 1 Lampadena 1 uminosa 1 and Lepidophanes

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53 0-2 5 50-75 1 00-125 1501 7 5 200-300 Lepidoph anes guentheri 0 20 40 60 80 100 E 0 -25 '-.__../ Q) 50-75 OJ c 0 100125 0:::: _c 150-175 --1---' Q_ Larnpadena lurninosa Q) 200-300 0 0 2 0 4 0 60 80 10 0 0 -25 5 0-75 100-12 5 1 50-175 200-300 Ceratoscopelus townsendi s l 0 2 0 40 60 8 0 100 P ercen t of T oto!

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54

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Figure 13. Relative vertical abundance of Diaphus type A, and B (see APPENDIX for description of types).

PAGE 81

55 0-25 50-75 100-125 150-175 Diaphus type A E '-...__./ (}) 200-300 01 c 0 0 20 40 60 80 100 0:::: _c --+----' 0-25 o_ (}) 0 /I 50-75 100-125 150-175 Diaphus type B 200-300 20 40 60 80 100 Percent of Total

PAGE 82

56 luminosa and Ceratoscopelus townsendi sensu latu1 exhibited highest abundances in the upper 25 m, but were also abundant in the 25-50 m stratum. More than 70% of the individuals of these three species were collected in the upper 25 m of the water column. Also included in cluster D4 were two of the three distinguishable Diaphus morphological types (Figure 13). Diaphus spp. larvae had significant representation to 75 m depth. All of these shallow dwelling species are members of the subfamily Lampanyctinae. Vertical Abundance of Zooplankton Prey (30-1 Bottles) Microzooplankton collections from the 30-1 Niskin bottles were dominated by protozoans and the naupliar and copepodite stages of copepods. Analysis of protozoans was limited to three rna j or taxa ; foraminiferans, radiolarians (Class Polycystinea) and tintinnids (Order Choreotrichida) All of these organisms have been described as prey of some larval fishes (Rojas de Mendiola, 1974; Arthur, 1976; Govoni et al., 1983). Although there was considerable variability in relative vertical abundances among cruises, protozoans were most abundant in the upper 100m (Figure 14). Densities of 1 ceratoscopelus townsendii s.l. was previously referred to as warmingii. Recent results (Badcock and Araujo, 1988) from the tropical Atlantic suggest that this cosmopolitan fish group displays morphological variation, but the forms are not discrete. The townsendii specific epithet had historical precedent.

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57 protozoans ranged from 0 -3, 334 m-3 (Table 3) Copepod naupliar stages were the most abundant microzooplankton representatives collected during all cruises and at all depths. Naupliar abundances in the upper water column ranged from 2 67 to 10, 899 m-3 (Table 3) During most cruises, maximum abundance was between 0 -75 m (Figure 14). Copepodite taxa were not identified beyond the ordinal level. Cyclopoid copepods were more prevalent than calanoids, although relative abundance varied with depth and cruise. Harpacticoid copepods were always less abundant. Copepodites were usually most abundant between 50-100m (Figure 15). Copepodite abundances in the upper water column ranged from 264 to 5, ooo m-3 (Table 3) Horizontal Abundances of Zooplankton (Hand-Held Containers) The most abundant (>1% of the total identified plankton) forms identified from the SCUBA collections were crustacean zooplankton with naupliar stages of copepods comprising 36% of the total number. copepodites (14%). Nauplii were followed in abundance by Sarcodinians were also abundant with radiolarians (8%) and foraminiferans (1%) well represented. Tintinnids were another fairly abundant (4%) protozoan group. Larvaceans were also common (3%) averaging 1-3 individuals 1-1

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58 Table 3: Range of zooplankton collected with 30 1 Niskin bottles from the upper 200 m at Standard Station. Numbers represent number of individuals per cubic meter. Date Protozoans Nauplii Copepodites Cruise Min. Max. Min. Max. Min. Max. March 134 3167 867 6133 867 2900 1984 Sept. 0 133 267 10899 533 2968 1984 March 0 100 1136 5899 733 3635 1985 July 33 3334 467 8333 466 4132 1985 Nov. 0 1518 528 6468 264 2174 1985 Jan. 152 1356 933 1093 634 5000 1986 May 147 934 1515 8484 767 4501 1986

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59

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Figure 14. Vertical abundance of common protozoan plankton and copepod nauplii at Standard Station during January 1986.

PAGE 87

60 January 1986 Protozoans Nauplii 0 I II 25 0 50 \ ,75 /0 r---(f) 100 L r-Q) / -+--' Q) E 125 / 0 \ ''----"" I ...c -+--' Q_ 150 ... r-0 -Q) 0 /r. Foraminiferans \ 175 '0 I 0 Radiolarians I 200 T -\ 300 0 400 I I 0 200 400 600 800 0 5000 10000 Number per Cubic Meter

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61

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Figure 15. Vertical abundance of copepod i tes at Standard Station during July 1985.

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62 Copepodites -July 1985 0 25 5 0 I 75 I I (f) 100 ..__ Q) -+-' Q) E 1 2 5 ..__.., ..r:: ... -+-' Q_ 150 Q) 0 \ C a l anoid 175 ... Cyclopoid 200 H arpacticoid ... 300 4 0 0 0 500 1000 1500 2000 2500 N umbe r per Cubi c M eter

PAGE 91

63 Early developmental forms included a variety of eggs (5%) and echinoderm larvae (1%). In addition to these heterotrophs, atrophic (= non-feeding) conifer pollen was collected in high numbers (20%). Other forms that were identified but composed less than one percent of the total included; salps, medusae, siphonophores, chaetognaths, pteropods, heteropods, veligers, polychaetes, ostracods, and other (than tintinnid) ciliate protozoans. Horizontal patterns of abundance varied with taxa and depth. Tintinnids ranged from 0. 0 -5. 0 1-1 with median concentrations of 0. 0 to 2. 0 1-1 Maximum density was recorded from samples collected at the 10 m depth horizon but the highest median abundance was at 15 m. Radiolarians ranged from 0. 0 to 8. 0 1-1 with median concentrations from 1. 0 1-1 at 10 m to 3. 5 1-1 at 25 m (Table 4). There was no significant departure from random distribution detected for these protozoans at any sample depth (Table 4). Crustacean zooplankton numerically dominate zooplankton collected on fine (20-70 meshes (Hopkins, 1982; Ortner et al., 1980) and numerically dominated the zooplankton in the present study as well. Copepodites ranged from 0 -12 1-1 with a median concentration from 0. 0 1-1 at 5 m to 7. 0 1-1 at 15 m, with no significant departure from random detected (Table 4). In addition to the common genera reported by Hopkins (1982), the harpacticoid copepods Microsetella, Macrosetella, and

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64 Table 4: Fisher Index and for SCUBA collected zooplankton. Median abundance (number per liter) in parentheses. Radio-Pollen Tin-Copepod Cope-All Depth larian tinnids Nauplii podites Organ (m) s isms 5 0.88 12.41 1.90 1.16 1.19 10.02 ( 3. 00) (27.00} ( 1. 00) (5.00) (0.00} 10 0.90 37.19 2.84 1. 83 0.49 11.21 ( 1. 00) (0.00} (0.00} (10.50} (3.50} 15 1. 08 2.64 0.48 3.07 0.98 2.15 (2.00} (5.00} (2.00} (14.50} (7.00} 20 1. 09 2.49 1.16 3.27 1. 54 2.45 (3.00} (0.500} (1.00} (8.00} (4.00} 25 0.89 0.95 1. 55 2.86 2.07 1. 53 (3.50} ( 1. 00} ( 1. 00) (12.00} (4.00} 30 1. 62 1. 41 0.78 2.75 1. 02 2.88 (3.00} (1.50} ( 1. 00) (9.00} ( 3. 00) 35 0.60 1. 65 0.70 3.44 1. 51 4.18 ( 2. 00) ( 1. 00) (1.00} (7.50} (4.50}

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65 Clytemmestra, and the cyclopoid copepod Oithona were common in these collections. Copepod nauplii, the most abundant microzooplankton group in samples, ranged from 1. o to 28. o 1-1 with a median abundance ranging from 5. o 1-1 at 5 m to 14.5 1-1 at 15m (Table 4). Overall (all depths combined) naupliar distributions revealed a significant departure from random distribution (Table 4; p < 0.05). Significant aggregation was also detected at 35 m (Table 4; p < 0.05). Conifer pollen was also abundant and exhibited highly aggregated patterns at some depths. Densities ranged from 0 to 57 1-1 with median concentrations from 0. 5 to 27. 0 1-1 (Table 4). Significant aggregation was detected at 5 and 10 m with a Fisher Index of 12 and 37, respectively (Table 4). Overall patterns (all items combined) revealed significant overdispersion at 5 and 10 m (Table 4), and random patterns at other depths. The number of items counted ranged from 4. o to 78. o items 1-1 with median concentrations per depth ranging from 22.0 to 41.0 items 1-1 Approximately 4,000 individuals were measured from the one-liter containers and their average dimensions (Table 5) revealed that the majority of the items collected were within the size range of prey detected in the diets of many larval fishes (Rojas de Mendiola, 1974; Arthur, 1976; Laroche, 1982; Govoni et al., 1983) Of these potential prey, aggregated patterns of numerical abundance were detected for pollen and nauplii. conversion of numbers of organisms to potential energy

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66 Table 5: Average dimensions of potential prey items in micrometers. Taxa (Group) Length Width Nauplii 138 62 Copepodites 319 112 Tintinnids 112 91 Radiolarians 158 105 Foraminiferans 87 69

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67 in the form of calories was done to determine the ability of larvae to meet their metabolic requirements. Caloric density (calories 1-1 ) varied by several orders of magnitude, ranging from 0. 008 to 59.20. Variability was high at most depths sampled (Figures 16 and 17). The Fisher Index for caloric content varied from 0.10 to 50.40, thus potential energy of prey was also highly aggregated at certain depths. Larval Diet and Feeding Chronology Over 1, 2 00 larvae were dissected to examine gut contents. A detailed analysis of diet (Table 6) was conducted for five representative species of lanternfishes; Benthosema suborbi tale, Ceratoscopelus townsendi s .1., Hygophum taaningi, Myctophum selenops, and Notolychnus valdiviae. General information on the diet of nine other species and one genus was also obtained (Table 7). Bray-Curtis analysis of diet similarity resulted in six clusters three of which contained a single species (Figure 18) The first cluster (F1) included most of the Myctophinae examined. These larvae were closely associated as a result of their dependence upon ostracod prey. The second cluster (F2) included members of both subfamilies. Calanoid copepods dominated the diet of these larvae. The diet of Hygophum benoiti (Cluster F3) was similar to the larvae in the second cluster with the exception of a relatively high percentage of protistan material. The

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68 Table 6: Composition of diet as determined from gut analysis. All diet categories are mutually exclusive. Values represent the percent of total carbon ingested that could be assigned to that particular category. Species codes represent the first letter of the genus plus the first three letters of the specific epithet (e.g. Benthosema suborbitale = Bsub). Prey Items Trichodesmium Mixed Protista Foraminifera Eggs Cnidaria Heteropoda Pteropoda Nauplii Crustacea Copepoda Cyclopoda corycaeus Oithona Oncaea Sapphirina Harpacticoida Calanoida Calanoid A Clausocalanus Nannocalanus Neocalanus Undinula Rhincalanus Calanoid B Augaptilidae candacia Chirundina Euchaeta Heterorhabdus Metridiidae Pleuromamma Scolecithricidae Scottocalanus Valdiviella Euchirella Euphausiacea Decapod larvae ostracoda Conchoecia Thaliacea Larvacea Bsub n=149 0.02 0.27 0.79 0.08 0.22 0.48 0.7 0.10 4.53 2.8 0.45 1.38 83.75 1.23 4.67 Ctow n=245 1.25 9.99 2.21 6.27 5.41 2. 72 9.87 2.60 0.57 12.88 2.60 2.04 5.89 2.89 0.57 19.56 10.73 Htaa n=82 0.97 5.89 4.52 0.05 7.18 72.62 8.7 Msel n=89 0.17 0.57 0.33 1.35 0.09 3.96 1.06 0.47 0.06 4.76 86.67 0.15 Nval n=139 0.21 0.41 0.06 0.08 0.35 2.87 0.92 0.53 0.53 1.87 1.42 0.39 1.90 2.68 9.90 0.38 0.80 2.23 0.38 0.55 6.70 5.07 1. 21 1.83 12.36 4.10 0.09 14.56 2.13 1.13 1. 51 0.48 0.54 4.09 13.79

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Table 7: Diet of lanternfish larvae expressed as percent of organic carbon ingested in each diet category. Species or Pte Nauplii Crusta Uniden Cal an Cycle Harp Ostr Appe Thal Group N = Proti rop cea tified oid poid acti a cod ndic iace sta ods Copepo coid ular a da ia Dia:Qhus spp. 33 0.2 83.7 0.6 5.6 9.5 Lam:Qanyctus 4.3 11.6 1.4 20.5 12.2 14.4 35.9 0.9 alatus 114 Lobianchia 2.4 29.2 68.2 qemellarii 17 Centrobranchus 96.0 4.0 nigroocellatus 13 Diogenichthys 14.4 2.5 1.0 4.0 61.7 atlanticus 46 Gonichthys 1.5 1.9 96.6 COCCO 19 Hygo:Qhum 23.12 1.0 50.2 7.7 benoiti 30 Hygo:Qhum 57.4 17.0 17.9 hygomii 43 Mycto:Qhum 8.7 2.8 0.7 0.3 84.7 1.5 affine 81 Mycto:Qhum 5.0 2.0 1.6 1.2 89.9 obtusirostre 19

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70

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Figure 16. Range of caloric values calculated from measured plankton collected along the 5 20 meter (depth) horizontal transects with Fisher Index (FI) for each depth series.

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71 102 I I I 102 I I I 5 m 10 m 101 1Fl=2.84 -1 01 1Fl=50.44 10 -10 I-1 0 110-1 -L Q) 1 o-2 --.j.---1 -1 o-2 __j II 10-3 -1 o-3 I L Q) 0 5 10 15 20 0 5 10 15 20 Q_ (j) 1 02 I I I 1 02 I I T Q) 15 m 20 m L 101 FI =2.02 1 01 FI = 0 11 0 1I0 1 0 10 u I10-1 10-1 10-2 1 o-2 10-3 10-3 I 0 5 10 15 20 0 5 10 15 20 Sample Number

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72

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Figure 17. Range of caloric values calculated from measured plankton collected along the 25 -35 meter (depth) horizontal transects with Fisher Index (FI) for each depth series.

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73 102 1 02 _I_ I I 25 m 30 m 101 Fl=0.09 101 f-Fl=41.02 10 10 I10-1 1 0 -1 L Q) 10-2 10-2 +--' _j 10-3 10-3 L 0 5 10 15 20 0 5 10 15 20 Q) Q_ (f) 102 I I I Q) 35 m L 101 r-FI=0.66 0 0 10 f-u 10-1 10-2 10-3 I 0 5 10 15 2 0 Sa m p l e Nu mber

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74

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Figure 18. Cluster results of the diet of 14 species of lanternfish larvae plus the genus Diaphus.

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Cluster Characteristics Cluster SubfamiiJ: F1 Myctophinae F2 Mixed F3 Myctophinae F4 Lampanyctinae FS Lampanyctinae F6 Mixed Cluster Species Cnig Gcoc Mobt F1 Msel Matt Bsub Dati Hhyg F2 Nval Diap F3 Hben F4 Lala FS Ctow F6 ,Lgem Htaa Major Prey Ostracoda Calanoida Calanoida/Protista Mixed Crustacean/Larvacean Mixed Crustacean/Gelatinous Thaliacean 20% 40% 60% 80% Percent Dissimilarity 75

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76 diet of Lampanyctus a latus, also a single species cluster (F4), contained a broad mixture of crustacean prey (ostracods, calanoid and cyclopoid copepods) plus appendicularians. The diet of Ceratoscopelus townsendi s.l. (F5) was also crustacean dominated, but included a broad mix of calanoid, cyclopoid, and harpacticoid copepodites plus nauplii and gelatinous material. The last cluster (F6) included two species with a diet dominated by gelatinous organisms. The five lanternf ish species listed in Table 6 were collected in sufficient numbers to enable a detailed analysis of growth (see below), hence the diet of these representative larvae was examined in greater detail. Two of these five species exhibited a high degree of trophic specialization. The diet of Benthosema suborbitale and Myctophum selenops was dominated by ostracods of the genus Conchoecia, with these prey representing between 83 -87% of total carbon ingested (Table 6). Of secondary importance in the diet of suborbitale were calanoid copepods, larvaceans, thaliaceans, and decapod larvae. Of secondary importance in the diet of M selenops were cyclopoid copepods, euphausids, and calanoid copepods. Larvae of Hygophum taaninqi were the only abundant myctophid larvae examined for which crustacean zooplankton was not the dominant diet item. Crustaceans comprised only 7.18% of their ingested carbon. Instead, soft bodied thaliacean (72.62%) and larvacean (8.7%) prey dominated. Other common diet items included mixed protistans, copepod eggs, and

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77 unidentified crustacean remains. Two of the five representative species appeared to be relatively opportunistic predators, with diets dominated by a variety of developmental stages of copepods. Larvae of Ceratoscopelus townsendi s.l. ingested an array of cyclopoid, harpactacoid, and calanoid copepods. This species also exhibited the greatest predation upon naupliar stages. Larvae of Notolychnus valdiviae ingested the greatest variety of prey. Four genera of cyclopoid copepods; Oi thona, Oncaea, Sapphirina and Corycaeus comprised 5.58% of the carbon ingested. Calanoid copepods comprised a greater fraction (67.76%) of the ingested carbon, and many families and genera were recognizable. Dominant among the calanoids were indi victuals of the genera Pleuromamma and Euchaeta. Ostracods of the genus Conchoecia were also present. In addition to crustacean prey, thaliaceans comprised a significant (13.79%) portion of dietary carbon. Of the five species examined in detail, Benthosema suborbitale and Myctophum selenops fed upon the largest prey with respect to standard length (Figure 19). The diet of both species was dominated by Conchoecia, which approached a maximum body width of 1 mm. It was not uncommon to find one large ostracod completely filling or distending the midgut of these fishes. In contrast, Ceratoscopelus townsendi s. 1. ingested the smallest prey items. All prey were under 400 in width and more frequently less than 300 regardless of

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78

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Figure 19. Relationship of standard Length (mm) to width of ingested prey for the larvae of the five representative species of lanternfishes.

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1000 B suborbitale 800 600 400 200 0 M. selenops 0 0 0 0 0 0 79 0 2 4 6 8 10 0 2 4 6 8 10 12 E C. townsendi s.l. =:i 1 000 >, Q) L 0_ 800 600 400 200 OL_________J 0 2 4 6 8 10 1 2 0 0 ,--,.--1--,----1 --,--1 --,--1--,--1---, 0 1 000 1H taaningi -800 1-600 1-400 1-200 1-0 -0 00 r2 0 -0 g o -c:u;lOn O L__.J_I _J__ I _!_ I_J....-I Y-'---------' 0 2 4 6 8 10 1 2 N. valdiviae 0 2 4 6 Standard L ength (mm) 8 10

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fish size. 80 Intermediate in size were the prey of Hygophum taaningi and Notolychnus valdiviae. The soft (gelatinous) nature of the prey ingested by the former results in problematic prey size analysis. The gelatinous organisms were compacted in the gut and size at ingestion was likely greater than indicated here. Although upper limits to prey selection is physically restricted by mouth size, there appears to be a wide range of prey size chosen by individual larva. Increase in larval size increased the size range of prey available (Figure 19) but many small items were also ingested. Unlike adult lanternfishes, larvae are primarily diurnal predators (Figure 20). Four of the f ive species revealed a similar diel pattern; feeding commenced between 06: 00 and 08: 00 hours and terminated between 17: 00 and 21: 00 hours. All five species had some representatives w ith empty guts during the day. Larvae of Ceratoscopelus townsendi s.l. had the greatest percentage of empty guts, hence the lowest feeding incidence. Time of peak feeding incidence varied and there was no consistent pattern among species. Unlike the other representative species, larvae of Myctophum selenops apparently fed at all times, regardless of light availability. Age and Growth Age and growth patterns of larval myctophids were derived

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81

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Figure 20. Feeding chronology of five representative lanternfish species. Zeroes represent empty guts.

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(f) (f) Q) c :::J LL 4 3 2 0 4 3 2 0 4 3 2 0 4 3 2 0 4 3 2 0 1-f.-1-f-1-f.f.-1-f.-I 0 I 1-.3 1-J 0 1 3 1 r--I 1-3 I 0 I 1-J I 0 I 4-6 4-6 0 4-6 1 ;; "" 0 c I 4-6 I 0 I 4-6 I I r--I I 7-9 10-12 7-9 10-12 7-9 10-12 I 1 I I 7 9 10 1 2 I I .----,----I I 7 9 10-12 I ronge I Time of 82 I I I I B. suborbitale n = 149 r--r--ll 0 I I I I 1.31 5 16-16 19-21 22-24 C. townsendi s .l. n = 245 1.3-15 16-16 19-21 22-24 H taaningi n = 82 0 13-15 16-16 19 -21 22-24 1 I I I ,..---M selenops ,----n = 89 r---r-1 I I I I 13 1 5 16 18 19 -21 222 4 I I I I ,--N. valdiviae ,..n = 139 -0 ,---, I I I T 1 3 1 5 16 18 19-21 22-24 range of sunset Collec t ion

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83 from reading microincrements in sagittal otoliths. These data were necessary to enable an examination of the feeding energetics of the five representative species. Of the five species examined, the daily deposition of sagittal otolith microincrements has been validated for two; Benthosema suborbi tale (Gartner, 1991a) and Ceratoscopelus townsendi s .1. (Gartner, unpublished data), and there is strong supportive data for a third, Notolychnus valdiviae (Gartner, personal communication). Microincrements in the sagittae of the other two species are completely analogous in structure and were presumed to be formed on a daily basis as well. A total of sixty-four Benthosema suborbitale otoliths were examined. Larvae of suborbitale exhibited considerable variation in increment number when less than 7 mm SL (Figure 21) Perhaps contributing to this variability was the particular growth pattern of this species. Benthosema suborbitale at less than 4 nun SL is a relatively slender larva. Between 4 and 8 nun SL, the larvae add girth with relatively little increase in body length (Badcock and Merrett, 1976). In addition, information for six transitional (11.0 mm SL) or recently metamorphosed (12.0 mm SL) individuals was provided (Gartner, 1991a). No intermediate forms (7.0 to 11.0 mm SL) were collected during the second phase of research. otoliths were removed from larvae ranging between 3.1 and 6.8 nun SL. Larvae collected during the first phase of this project (APPENDIX) ranged in size from 2.2 to

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84

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Figure 21. Age and growth the larvae of the five representative species of lanternfishes as estimated from the number of microincrements in the sagittal otoliths

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_.--.... E E "----"' _c -l-' 01 c Q) _j -o L 0 -o c 0 -l-' (() 14 12 10 8 6 4 2 0 10 8 6 4 2 0 12 10 8 6 4 2 0 Benthosema suborbitale 85 Ceratoscopelus townsendi s l 12 y = 0.138X + 2.086 10 y = 0 .376X + 0.785 r 2 = 0.92 r 2 = 0 67 8 0 0 6 0 0 4 0 0 2 0 0 1 0 20 30 40 50 60 70 80 0 5 10 15 20 25 Myctophum selenops Hygophum taaningi 10 y = 0 192X + 2.036 8 y = 0 1 79X + 3.27 r 2 = 0 62 OjJ r 2 = 0 .83 OCD 0 0 0 CX) 6 0 0 0 00 4 2 0 0 5 10 15 20 25 30 35 0 5 10 15 2 0 25 30 Notolychnus valdiviae y = 0.150X + 0.637 r 2 = 0.67 0 1 0 20 30 40 50 60 Mic r o in c re m e n t Counts

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86 10.0 mm SL. The smallest juvenile collected in the eastern Gulf of Mexico was 10.0 mm SL and the largest post larval fish collected was 32 mm SL (Gartner et al., 1989). Transformation (metamorphosis) in this species occurred between 10. o and 11. 0 mm SL. Microincrement counts on larvae 3.1-6.8 mm SL ranged from 21-33 days. Using the calculated growth equation (Figure 21), age at metamorphosis is about 57 days. Assuming transformation at 10.5 mm SL and hatching at 2.09 mm SL, the estimated daily increase in SL for this species was 0.14 mm. Thirty-eight Ceratoscopelus townsendi s.l. otoliths were examined. The size range of larvae collected for age and growth estimation was between 4.4 and 9.8 mm SL (Figure 21). Larvae collected during the first phase of this study ranged in size from 2.1 to 14.5 mm SL (APPENDIX). Metamorphosis in these larvae usually occurred between 14.0 to 15.0 mm SL. The smallest juvenile collected was 14 mm SL and the largest adult collected from the eastern Gulf of Mexico was 70 mm SL (Gartner et al., 1989). Using the calculated growth equation (Figure 21), the estimated ages for the size range examined was from 3.5 to 36.5 days. Within the larval stage, daily growth was approximately 0.38 mm SL. Twenty-eight Hygophum taaningi otoliths were analyzed from individuals which ranged in size from 5.4 to 8.8 mm SL. The smallest larvae collected during the first phase of research was 2.2 mm SL and the largest 11.6 mm SL (APPENDIX). Larvae of H. taaningi transformed between 10.0 and 12.0 mm SL.

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87 The smallest juvenile collected from the eastern Gulf of Mexico was 11.0 mm SL and the largest adult collected was 47 mm SL (Gartner et al., 1987). The growth equation calculated from microincrement examination (Figure 21) yielded an age range from less than one to 46.6 days for the larval period. Assuming a transition at approximately 11.0 mm SL, larvae of this species grew an average of 0.18 mm daily. Twenty-two otoliths of Myctophum selenops were examined from larvae that ranged in size from 4.6 to 7.7 mm SL. Larvae of this species were not abundant during the first phase of collections but ranged in size from 2.8 to 8.7 mm SL (APPENDIX) Myctophum selenops metamorphosed between 8. 7 and 10.0 mm SL. The smallest juvenile collected was 10.0 mm SL and the largest adult was 43 mm SL (Gartner et al., 1987). The fewest increments (13) were recorded on the otolith of a 4. 8 mm larva. Extrapolation from the estimated growth equation (Figure 21) resulted in age estimate from 4 to 35 days over the larval period. Assuming a transition at 9.5 mm SL and a hatch at 2.04 mm SL, larvae of this species grew approximately o .19 mm SL daily, with the larval period lasting approximately 39 days. Thirty-six otoliths of Notolychnus valdiviae were examined from larvae that ranged in size from 5.2 to 10.1 mm SL (APPENDIX). Larvae of this species collected during the first phase of this project ranged in size from 2.9 to 10.9 mm SL. Transformation occurred between 9. 0 to 11.0 mm SL.

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88 Notolychnus valdiviae was the smallest of lanternfishes collected in the Gulf of Mexico, not exceeding 22 mm SL as adults (Gartner et al., 1987). Thirty-five increments were observed in the smallest larva. Extrapolation from the estimated growth equation (Figure 21) resulted in a larval period of approximately 67 days with the smallest larvae collected being 15 days old. Assuming metamorphosis at 10.0 mm SL, average daily growth was approximately 0.15 mm SL. Energetics The energetic requirements of the five representative species of lanternfishes were estimated to calculate the number of prey required and thus provide some measure of predation impact. Energetic requirements were estimated from a bioenergetic equation (see MATERIALS AND METHODS). Food energy converted to potential energy through growth (Qg) was estimated using the daily increase in standard length (from otolith microincrement analysis), the relationship of biomass (as dry weight) to length, and the energetic value of tissue from its chemical composition. The increase in dry weight with increase in length for each of the five representative species (Figure 22) was best fit by curvilinear function with r2 values ranging from 0.86 to 0.98. Analysis of chemical composition (Table 8) revealed

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89 Table 8: Chemical composition of representative lanternfish larvae. Species AFDW Protein Lipid Carbohydrate (% OW) (% AFDW) (% AFDW) (%AFDW) Benthosema suborbitale 94.3 55.4 22.8 1.0 CeratoscoJ2elus townsendi s .1. 86.7 48.9 13.6 1.2 Hygo}2hum taaningi 80.5 54.0 14.5 1.0 Mycto}2hum seleno12s 83.9 55.4 13.3 1.3 Notolychnus valdiviae 83.5 58.4 11.7 0.8

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90

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Figure 22. Relationship between dry weight and standard length for the larvae of the five representative species of lanternfishes.

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91 Benthosema suborbitale Ceratoscopelus townsendi s.l. 3.0 3 0 2 5 2.5 Y = 0.95 0 46X + 0.07 x 2 r '= 0.94 2.0 2.0 1 5 1 .5 1.0 1.0 0.5 0.5 0.0 0.0 2 4 6 8 10 12 2 4 6 8 10 12 1 5 Hygophum taaningi Myctophum selenops 2 .5 Y = O.BO 0.056X +0.1 OX 2 01 Y = 0.69 0.40X + 0 06X 2 E r '= 0.66 2.0 r = 0.96 ......___, 0 -+-' 1.0 ....c 1.5 01 0 0 (]) 0 5 0 1 .0 0 .5 0 >.., 0 \...._ 0 .5 0 0.0 0.0 3 4 5 6 7 8 2 3 4 5 6 7 8 2.0 Notolychnus valdiviae Y = -0.45 + 0 09X + 0 1SX2 1 5 r = 0 .92 0 0 1 0 0 0 0 0 5 0. 0 _i_____l_--L-_ 2 3 4 5 6 7 8 9 Standard Length (mm)

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92 that ash-free dry weight (AFDW) as percent of carbon ranged from 80.54% (Hygophum taaningi) to 94.3% (Benthosema suborbitale). Expressed as a percent of AFDW, protein ranged from 48.95% (Ceratoscopelus townsendi s.l.) to 58.41% (Notolychnus valdiviae), lipids ranged from 11.69% (Notolychnus valdiviae) to 22.85% (Benthosema suborbitale), and carbohydrates ranged from o. 83% (Notolychnus valdiviae) to 1.34% (Myctophum selenops). Combining the information on age and growth, dry weight, and chemical composition resulted in an estimate of average daily increase in the caloric content of tissues (Table 9), using the conversion factors of Brett and Groves (1979). Daily increase in the caloric value of fish tissue ranged from 0.142 calories for Notolychnus valdiviae, the slowest growing species represented, to 0. 486 calories for Ceratoscopelus townsendi s.l., the fastest growing species represented. The weight-specific energy cost for activity (Qm) was estimated from the relationship of oxygen consumption to larval dry weight and activity level (see MATERIALS AND METHODS) and ranged from 0.04 to 5.44 calories per day (Tables 10 to 14) Caloric requirements of the larvae (Qc values) were calculated at three l evels according t o the range of published assimilation values where the calculation of QcMin assumes a high assimilation (thus a lower prey requirement) of 92%, Q cAvg assumes an average assimilation o f 73%, and Q c Max

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93 Table 9: Average daily increase in calories for growth (Qg) based on daily increases in standard length and the average increase in dry weight. Species Benthosema suborbitale Protein 0.161 Ceratoscopelus townsendi s.l. 0.337 Hygophum taaningi Myctophum selenops Notolychnus valdiviae 0.114 0.226 0.108 Lipid Carbohydrate Total 0.101 0.002 0.265 0.143 0.006 0.486 0.047 0.002 0.163 0.083 0.004 0.312 0.033 0.001 0.142

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Table 10: Calculation of caloric and numerical prey requirements for larvae of Benthosema suborbitale. Larval respiration is labelled "R" and other column headings refer to the variables of the bioenergetic equation or parts thereof (see MATERIALS AND METHODS). SL w R m X 10-6 Qm Q, Qm & Q, MinQ., AvgQ., MaxQ., AvgPrey Max Prey (mm) J.lgDW J.ll02 cal/ cal/ cal/ cal/ cal/ cal/ cal/ No. /day No.fday /hr J.l9/hr day day day day day day 3.5 80 0.70 40 0.13 0.27 0.39 0.42 o. 54 2.30 6.83 29.33 4.0 130 1.05 37 0.19 0.27 0.45 0.49 0.62 2.67 7.94 34.08 4.5 210 1. 56 35 0.28 0.27 0.55 0.60 0.75 3.22 9.57 41.10 5.0 320 2.23 32 0.40 0.27 0.67 0.73 0.91 3.92 11.66 50.08 5.5 460 3.02 30 0.55 0.27 0.81 0.88 1.11 4.77 8.69 60.81 6.0 630 3.93 29 0. 71 0.27 0.97 1.06 1.34 5.73 10.45 44.87 6.5 830 4.95 28 0.89 0.27 1.16 1.26 1. 59 6.82 12.43 53.36 7.0 1060 6.08 27 1.10 0.27 1.36 1.48 1.87 8.02 14.61 62.73 7.5 1320 7.31 26 1.32 0.27 1. 58 1. 72 2.17 9.32 16.98 72.93 8.0 1610 8.63 25 1. 56 0.27 1.82 1.98 2.50 10.72 18.63 79.98 8.5 1930 10.04 24 1.81 0.27 2.08 2.26 2.85 12.23 21.24 91.20 9.0 2280 11.55 23 2.09 0.27 2.35 2.56 3.22 13.83 24.02 103.12 9.5 2660 13.14 23 2.37 0.27 2.64 2.87 3.61 15.52 26.95 115.74 10.0 3070 14.82 22 2.68 0.27 2.94 3.20 4.03 17.30 30.05 129.04

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Table 11: Calculation of caloric and numerical prey requirements for larvae of Ceratoscopelus townsendi s.l. Larval respiration is labelled "R" and other column headings refer to the variables of the bioenergetic equation or parts thereof (see MATERIALS AND METHODS). SL w R rn X 10-6 Qm (rnrn) J,JgDW J,Jl02/ cal/ cal/ hr J.lg/hr day 3.5 172 1.18 32 0.21 3.8 196 1.33 32 0.24 4.0 213 1.45 32 0.26 4.5 264 1. 79 31 0.32 5.0 326 2.20 31 0.40 5.3 371 2.49 31 0.45 5.5 404 2. 71 31 0.49 6.0 500 3.34 31 0.60 6.5 618 4.11 31 0.74 7.0 765 5 .06 31 0.91 7.5 947 6.23 30 1.12 8.0 1172 7 .67 30 1.39 8.5 1450 9 .45 30 1. 71 9.0 1795 11.63 30 2.10 9.5 2221 14.32 30 2.59 10.0 2749 17.64 30 3.19 Q, Qm&Q, MinQ., AvgQ., cal/ cal/ cal/ cal/ day day day day 0.49 0.70 0.76 0.96 0.49 0.73 0.79 1.00 0.49 0.75 0.81 1.02 0.49 0.81 0.88 1.11 0 .49 0.88 0.96 1.21 0.49 0.94 1.02 1.28 0.49 0.98 1.06 1. 34 0.49 1.09 1.18 1.49 0.49 1.23 1. 33 1. 68 0.49 1.40 1. 52 1.92 0.49 1.61 1. 75 2.21 0.49 1.87 2.03 2.56 0.49 2.19 2.38 3.00 0.49 2.59 2.81 3.54 0.49 3.07 3.34 4.21 0.49 3.67 3.99 5.03 MaxQ., AvgPrey cal/ No. /day day 4.11 14.07 4.28 14.64 4.40 15.06 4.76 16.28 5.20 19.60 5.51 20.77 5.74 21.64 6.40 24.15 7.22 27.24 8.23 31.05 9.47 35.74 11.01 40.35 12.89 47.26 15.21 55.77 18.07 66.25 21.60 79.16 MaxPrey No.jday 60.40 62.85 64.66 69.90 84.16 89.19 92.92 103.71 116.99 133.35 153.49 173.25 202.93 239.48 284.50 339.93 1.0 (J1

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Table 12: Calculation of caloric and numerical prey requirements for larvae of Hygophum taaningi. Larval respiration is labelled "R" and other column headings refer to the variables of the bioenergetic equation or parts thereof (see MATERIALS AND METHODS). SL w R m X 10-6 Qm Qg Qm&Qg MinQc AvgQc MaxQc (mm) p.gDW p.l02/ cal/ calf calf calf cal/ cal/ cal/ hr p.gjhr day day day day day day 3.5 100 1. 09 51 0.20 0.16 0.36 0.39 0.49 2.12 4.0 160 1. 70 49 0.31 0.16 0.47 0.51 0.64 2.77 4.5 240 2.49 48 0.45 0.16 0.61 0.67 0.84 3.61 5.0 340 3.46 47 0.62 0.16 0.79 0.86 1. 08 4.63 5.5 460 4.60 46 0.83 0.16 0.99 1. 08 1. 36 5.84 6.0 600 5.91 46 1. 07 0.16 1.23 1. 34 1. 68 7.23 6.5 760 7.38 45 1. 33 0.16 1. 50 1. 63 2.05 8.80 7.0 MwO 9.01 44 1. 63 0.16 1. 79 1.95 2.45 10.53 7.5 1140 10.81 44 1.95 0.16 2.11 2.30 2.90 12.44 8.0 1360 12.76 43 2.30 0.16 2.47 2.68 3.38 14.51 8.5 1600 14.87 43 2.69 0.1 6 2.85 3.10 3.90 16.75 9.0 1860 17.14 43 3 .09 0.16 3.26 3.54 4.46 19.16 9.5 2140 19.55 42 3 .53 0.16 3.69 4.02 5.06 21.73 10.0 2440 22.13 42 4.00 0.16 4.16 4.52 5.70 24.46

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Table 13: Calculation of caloric and numerical prey requirements for larvae of Myctophum selenops. Larval respiration is labelled "R" and other column headings refer to the variables of the bioenergetic equation or parts thereof (see MATERIALS AND METHODS). SL w R m X 10-6 Qm Q, Qm&Q, MinQ., AvgQ., MaxQ., AvgPrey Max Prey (mm) J.lgDW J.1l02/ cal/ cal/ cal/ cal/ cal/ cal/ cal/ No. /day No. /day hr J.Jg/hr day day day day day day 3.5 152.50 1.20 36 0.27 0.31 0.58 0.63 0.79 3.40 7.26 31.19 4.0 300.00 2.11 33 0.47 0.31 0.78 0.85 1.07 4.59 9.81 42.14 4.5 492.50 3.20 30 0.71 0.31 1.02 1.11 1.40 6.01 12.85 55.17 5.0 730.00 4.45 28 0.99 0.31 1.30 1.41 1. 78 7.65 10.72 46.01 5.5 1012.50 5.85 27 1. 30 0.31 1.61 1. 75 2.21 9.48 13.28 57.05 6.0 1340.00 7.40 26 1.64 0.31 1.96 2.13 2.68 11.51 16.12 69.23 6.5 1712.50 9.09 25 2.02 0.31 2.33 2.53 3.19 13.71 19.21 82.51 7.0 2130.00 10.91 24 2.42 0.31 2.74 2.97 3.75 16.10 22.55 96.85 7.5 2592.50 12.86 23 2.86 0.31 3.17 3.45 4.34 18.65 26.13 112.21 8.0 3100.00 14.94 22 3.32 0.31 3.63 3.95 4.98 21.37 29.32 125.92 8.5 3652.50 17.14 22 3.81 0.31 4.12 4.48 5.65 24.25 33.27 142.88 9.0 4250.00 19.47 21 4.33 0.31 4.64 5.04 6.35 27.28 37.44 160.76 9.5 4892.50 21.90 21 4.87 0.31 5.18 5.63 7.10 30.47 41.81 179.54 10.0 5580.00 24.46 20 5.44 0.31 5.75 6.25 7.87 33.81 46.39 199.20

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Table 14: Calculation of caloric and numerical prey requirements for larvae of Notolychnus valdi viae o Larval respiration is labelled "R" and other column headings refer to the variables of the bioenergetic equation or parts thereof (see MATERIALS AND METHODS) o SL w R m X 10-6 Qm Q, Qm&Q, MinQ, AvgQ, MaxQ, AvgPrey Max Prey (mm) 1Jl02/ cal/ cal/ cal/ cal/ cal/ cal/ cal/ No. /day No./day hr 1J9/hr day day day day day day 3.50 20o00 0.22 so 0.04 0.14 0.18 0.20 0.25 1.07 4.50 19.34 4.00 90.00 0.77 40 0.14 0.14 0.28 0.31 0.38 1.65 6.98 29.95 4.50 170.00 1.31 36 0.24 0.14 0.38 0.41 0.52 2.23 9.40 40.38 5.00 260.00 1.87 33 0.34 0.14 0.48 0.52 0.66 2.82 9.63 41.33 5.50 360.00 2.46 32 0.44 0.14 0.59 0.64 0.80 3.45 11.75 50.46 6.00 470.00 3.07 30 0.56 0.14 0.70 0.76 0.95 4.10 13.98 60.03 6.50 590.00 3.72 29 0.67 0.14 0.81 0.88 1.11 4.79 16.32 70.07 7.00 720.00 4.40 28 0.79 0.14 0.94 1.02 1.28 5.50 18.76 80.58 7.50 860.00 5.10 27 0.92 0.14 1.06 1.16 1.46 6.25 21.32 91.55 8.00 1010.00 5.84 27 1.05 0.14 1.20 1.30 1.64 7.04 21.19 91.01 8.50 1170.00 6.60 26 1.19 0.14 1. 33 1.45 1.83 7.85 23.64 101.53 9.00 1340.00 7.40 26 1.34 0.14 1.48 1.61 2.02 8.69 26.19 112.45 9.50 1520.00 8.22 25 1.48 0 1 4 1.63 1. 77 2.23 9.57 28.83 123.78 10.00 1710.00 9.08 25 1.64 0.14 1. 78 1.94 2.44 10.48 31.56 135.50

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99 assumes a low assimilation of 18%. Caloric requirements of larvae (Qc) ranged from less than 0. 5 to over 33 calories day-1 (Tables 10 to 14). Results were restricted to the size groups for which diet was determined, and also to those species which preyed upon crustacean zooplankton because of the difficulty of determining daily caloric value of gelatinous plankton. Greater differences were obvious from changes in size of the larvae and assimilation efficiency (choice of Q5 ) than among species. The greatest caloric requirement was for M selenops larvae, which may be in part due to the nocturnal foraging by larvae of this species in addition to its day-time feeding. The lowest caloric requirement was for larvae of N valdiviae, which was largely the result of the slow growth of these larvae. The number of individual zooplankters required daily was calculated from the caloric value of known preferred prey items and the size of prey ingested by each size class of larvae. The number of prey ingested also varied more according to size and assimilation efficiency within a species than among species. The average number of prey required daily for larvae less than 5.0 mm SL ranged from 4.5 -16.28. The maximum number of prey required daily for larvae less than 5. 0 mm SL ranged from 19.34 -64.66. For larvae in the second t (5o 7 5 mm SL), average daily prey s1ze ca egory requirements ranged from 9. 63 to 35.74 and maximum prey requirements ranged from 41.33 -153.49. The average number

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100 of prey required daily for species greater than 7. 5 mm SL ranged from 16.98 -79.16. The maximum number of prey required daily for species greater than 7.5 mm SL ranged from 79.98 -339.93. Search Estimates The ability of a lanternfish larva to meet its metabolic needs can be estimated from a comparison of larval search volume and caloric content of the prey field. The median length of larvae within the upper 25 m of the water column was 3.8 mm. Using the swimming speed values of Hunter (1972), a 3.8 mm larva could travel 79.45 m during a feeding day. Thus the range of calories calculated over the micro-to fine-scale would be appropriate for the foraging capacity of a larva this size. The search volume of a 3. 8 mm SL larva would be approximately 520 ml and its caloric requirement would range from o. 79 -4. 28 calories day-1 (Qc values of Table 11) Using only those items which are known prey for the larvae of Ceratoscopelus townsendi s.l., the maximum number of calories per liter calculated over the micro-to fine-scale was 59.20. This concentration would be more than adequate for the nutritional requirements of the larvae. However, the largest prey ingested by a larva of this size was 140 in width. Exclusion of larger (by width) prey resulted in a range of calories from 0.001 to 2.236 1-1 (Table 15). If these larvae

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101 had a high (92%) assimilation efficiency, then any concentration greater than 1. 52 calories 1-1 could meet the energetic requirements of a larva of this size. At an average assimilation efficiency of 73%, caloric densities of 1.92 1 -1 or higher could meet the energetic requirements of a larva of this size. Concentrations of this magnitude were detected (Table 15) but were not common. Survival would thus require the detection of the highest caloric concentrations by the larva. At low assimilation efficiencies, caloric density of 8. 23 1-1 or higher would be required. Values this high were not detected. The median length of larvae within the 25-50 m stratum was 5. 3 mm SL. A larva of this size could travel 148.4 m day-1 and require only slightly greater number o f calories per day (1.025.51; Table 11). A 5.3 mm SL larva i s size restricted to prey with a maximum body width of 290 J.tm. The search volume of a 5. 3 mm SL larva would be approximately 1. 9 1. This larva could encounter ingestible prey densities ranging from o. 001 to 2. 336 calories 1-1 (Table 16). Thus, assuming a high prey assimilation efficiency (92%), concentrations of 0. 54 calories 1 -1 could m eet the caloric requirements of a larva of this size. At average a ssimilation efficiency (73%), caloric densities of o. 67 r1 or higher could meet their caloric requirements. Larvae o f this size could, therefore, meet their caloric r equire m ents w ithin the range detecte d ove r the micro-to fine-scale. Many prey densities were below even

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102 Table 15: Range of prey energetic densities available to a 3.8 mm SL Ceratoscopelus townsendi s.l. larva in the upper 35 m. All concentrations are expressed as calories per liter and are based on replicate samples collected at each depth horizon. 5m 10m 15m 20m 25m 30m 35m 0.276 0.233 1. 718 0.556 0.666 0.691 0.824 0.369 0.747 1.173 0.896 1.010 0.427 0.178 0.001 0.640 0.917 0.636 0.949 0.393 1.282 0.111 0.898 0.732 0.920 0.907 0.971 0.495 0.214 1.157 1. 752 0.558 0.614 0.614 0.620 0.169 1.201 1.168 0.592 0.676 0.875 0.563 0.412 0.838 1.185 0.588 1.341 0. 511 0.290 0.287 0.234 1.447 0.889 0. 718 0.658 1.076 0.150 0.529 0.407 0.967 0.067 0.424 0.847 0.384 0.966 0.974 0.829 1.112 0.449 0.944 0.402 0.817 2.236 1.423 1. 551 0.884 0.805 0.334 0.736 1.099 0.837 1.478 0.938 0.370 0.214 0.889 0.670 0.220 0.231 0.917 0.959 0.353 0.858 0.884 0.520 0.902 0.443 0.198 1.138 0.825 0.91 0.518 0.813 1.377 0.665 0.300 1.090 1. 542 0.790 0.576 0.988 0.702 0.629 0.843 o. 720 0.85 1.238 0.622

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103 Table 16: Range of prey energetic densities avalable to a 5.3 mm SL Ceratoscopelus townsendi s.l. larva in the upper 35 m. All concentrations are expressed as calories per liter and are based on replicate samples collected at each depth horizon. 5m lOrn 15m 20m 25m 30m 35m 0.276 0.233 1.873 0.863 0.666 0.795 1.005 0.506 0.751 1.234 0.896 1.134 0.617 0.300 0.001 0.640 0.917 0.644 0.949 0.419 1.427 0.111 0.902 0.732 0.920 1.180 0.971 0.497 0.215 1.236 1. 759 o. 725 0.614 0.617 0.908 0.169 1.201 1.323 0.605 0.685 0.962 0.639 0.504 0.530 1.336 0.592 1. 341 0.588 0.389 0.306 1.006 1. 561 1.01 0.718 0.678 1.144 0.163 0.239 0.605 0.976 0. 771 0.688 0.879 0.394 1.048 1.051 0.857 1.119 0.433 1.261 0.402 1.008 2.333 1.455 1. 629 0.536 0.840 0.501 0.750 1.103 1.002 1. 513 0.886 0.469 0.241 0.924 0.767 0.227 0.261 0.940 1.067 0.364 1.001 1.003 0.608 1.026 0.456 0.392 1.138 0.853 1.066 0.520 1.155 1.474 0.910 0.305 1.463 1. 641 0.747 0.597 1.081 0.877 0.847 0.845 0. 720 1.245 1.330

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104 the requirements of this larger larva. This would, therefore, also require a non-random search behavior with which the individual could detect and stay within high prey concentrations. At low assimilation efficiencies, caloric density of 2. 29 1-1 or higher would be required. one concentration greater than 2.29 was detected (Table 16). Predation Impact Lanternfish larvae were most abundant during the March 1985 cruise when density within the upper 200 m was about 215 per 10 m2 Three taxa dominated the abundance; Ceratoscopelus townsendi s.l. (27.59%), Benthosema suborbitale (20.44%) and Diaphus spp. (19.46). Estimates of daily ingestion was based on the entire assemblage (see MATERIAL AND METHODS). Estimates of the daily removal of metazoan zooplankton ranged from approximately 2,760 (average) to 12,100 (maximum) individuals per 10 m2 in the upper 200 m. The number of metazoan zooplankton in the upper 200 m during March 1985 was The potential impact of the larval assemblage on their zooplankton resource was small, ranging from 0.02% (average) to 0.11% (maximum) of the standing stock per day. However, larvae of the subfamily Myctophinae prey primarily upon ostracods. The estimated daily removal of ostracods by the larval assembla g e o f March 1985 was between 1,080 (average) to 4,370 (maximum) ostracods within 10 m2 of

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105 the upper 200 m. Daytime ostracod density during March 1985 was approximately 92,000 per 10 m2 of the upper 200 m. Thus, although overall impact of lanternfish larvae on the overall zooplankton population is small, specialized feeding by some members of the group resulted in a daily removal of 1 -5% of the ostracod component.

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106 DISCUSSION The Eastern Gulf Assemblage Myctophid larvae dominate all oceanic ichthyoplankton collections and are especially abundant in oligotrophic areas where relative abundance varies from about 30 to over 70% of the ichthyoplankton (Table 17) In the eastern Gulf of Mexico lanternfish larvae comprised 40% of the total ichthyoplankton and their concentration was usually more than 100 individuals per 10 m-2 They were, therefore, at least an order of magnitude more abundant than postmetamorphic individuals (Gartner et al., 1979). Although little is known regarding the distribution and types of larval lanternfishes in the Atlantic ocean, the distribution of postmetamorphic lanternfishes within this ocean has been well studied (Badcock and Merrett, 1976; Backus et al., 1977; Nafpaktitis et al., 1977; Hulley and Krefft, 1985). The family was used to separate the Atlantic Ocean into nine zoogeographic zones (Backus et al., 1977). The myctophid fauna of the Gulf of Mexico contains representatives from five of the nine faunal zones but was considered a "special" region by these authors because it was physically and faunally distinct. The abundance of postmetamorphic lanternfishes resident in the eastern Gulf of Mexico was determined from more than

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107 Table 17: relation to upper 200 m Relative abundance of lanternfish larvae in total ichthyoplankton abundance collected in the of the world's ocean. Location Eastern tropical and subtropical Pacific Eastern tropical and subtropical Pacific Subtropic to subarctic Pacific North Pacific Central Gyre (NPCG) Gulf of Tonkin Northern Indian ocean Arabian sea North Indian Ocean Indian Antarctic sargasso Sea Percent Reference 47.2% Ahlstrom, 1972 37.9-Ahlstrom, 1972 57.1% 46.7% Moser and Ahlstrom, 1970 42.0% 73.0% 43.2% 30.7% 47.6 % 46.9% 29.8 % Loeb, 1979a; 1980 Belyanina, 1987 Nellen, 1973 Tsokur, 1981 Ahlstrom, 1968 PertesevaOstroumova, 1974 Rasonanariuo and Aboussouan, 1983 John, 1984 Eastern Gulf of Mexico 40.0% This study Comments EASTROPAC I EASTROPAC II NORPAC cruise series Oceanic reg ions Included many nearshore stations Coastal area of southeastern Arabia Maximum Number Limited sampling

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108 two decades of active sampling (Gartner et al., 1987; 1989; Gartner, 1990). Within the resolution of identification, the larval assemblage closely aligned with the adult assemblage in composition and relative abundance (Tabl 18) e This assemblage was dominated by tropical-subtropical species (Backus et al., 1977). Of the 49 species of postmetamorphic lanternfishes known to occur in the eastern Gulf of Mexico, over half (25) were also identified in the larval assemblage. The majority (16) of the unidentified larval forms were members of the genus Diaphus. Diaphus larvae are a morphologically homogeneous group, making larvae of this genus particularly difficult to separate from one another. Moser et al. (1984) concluded that "Myctophid species have distinct melanophore patterns, with the exception of the large genus Diaphus, for which only a few specific patterns have been identified." The few discrepancies that exist between relative abundance of adults and larvae may be the result of sampling strategy in relation to their vertical distribution or temporal variations associated with reproduction or hydrography. For example, Lepidophanes guentheri was the third most abundant postmetamorphic species collected but only the 14th most abundant larval form (Table 18). The larvae of this species had the most restricted vertical distribution observed, being confined largely to the upper 25 m of the water column (Figure 12). It is likely that these larvae are

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109 Table 18: Comparison of rank of abundance for lanternfish larvae (= premetamorphics) vs. juveniles and adults (= postmetamorphics) from Gartner et al. (1987)) collected at Standard Station. Species or Group No. of Premeta-Post-Larvae morphics meta-morphics CeratoscoJ2elus townsendi s.l. 1185 1 1 Dia]2hUS type B 810 2 NA Benthosema suborbitale 651 3 6 Notolychnus valdiviae 479 4 2 Mycto)2hum affine 444 5 7 Dia]2hUS type A 243 6 NA HygoJ2hum taaningi 240 7 10 HygoJ2hum benoiti 226 8 8 LamJ2anyctus a latus 209 9 4 Diogenichthys atlanticus 174 10 15 HygoJ2hum hygomii 118 11 42 HygoJ2hum reinhardtii 101 12 19 Mycto12hum nitidulum 79 13 36 DiaJ2hus J2ers)2icillatus 71 14 28 LeJ2idoJ2hanes guentheri 71 14 3 Lobianchia gemellarii 63 15 20 Centrobranchus nigroocellatus 57 16 17 NotoscoJ2elus resJ2lendens 43 17 22 LamJ2adena luminosa 42 18 18 Mycto12hum obtusirostre 38 19 31 Mycto12hum selenoJ2S 37 20 35 Gonichthys COCCO 34 21 30 (tie) Hygo)2hum macrochir 24 22 30 (tie) Bolinichthys spp. 13 23 NA Mycto]2hum asJ2erum 9 24 32 S:ymboloJ2horus rufinus 7 25 43

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109 Table 18: Comparison of rank of abundance for lanternfish larvae (= premetamorphics) vs. juveniles and adults (= postmetamorphics) from Gartner et al. (1987)) collected at Standard Station. Species or Group No. of Premeta-Post-Larvae morphics meta-morphics Ceratoscogelus townsendi s.l. 1185 1 1 Diaghus type B 810 2 NA Benthosema suborbitale 651 3 6 Notolychnus valdiviae 479 4 2 Myctoghum affine 444 5 7 Diaghus type A 243 6 NA Hygoghum taaningi 240 7 10 Hygoghum benoiti 226 8 8 Lamganyctus alatus 209 9 4 Diogenichthys atlanticus 174 10 15 Hygoghum hygomii 118 11 42 Hygoghum reinhardtii 101 12 19 Myctoghum nitidulum 79 13 36 Diaghus gersgicillatus 71 14 28 Legidoghanes guentheri 71 14 3 Lobianchia gemellarii 63 15 20 Centrobranchus nigroocellatus 57 16 17 Notoscogelus resglendens 43 17 22 Lamgadena luminosa 42 18 18 Myctoghum obtusirostre 38 19 31 Myctoghum selenogs 37 20 35 Gonichthys COCCO 34 21 30 (tie) Hygoghum macrochir 24 22 30 (tie) Bolinichthys spp. 13 23 NA Myctoghum asgerum 9 24 32 SYIDbologhorus rufinus 7 25 43

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110 neustonic, as suggested for larvae of other lanternfishes that have been rarely collected (Moser and Ahlstrom, 1974). The neuston was poorly represented by our sampling strategy. Temporal influences from reproductive patterns of adults or local hydrography may have affected the abundance of fish larvae. Lanternf ishes spawn throughout the year, but seasonal peaks in reproductive effort have been detected (Clarke 1973 , Karnella, 1987; Gartner, 1990; 1993). Further, some larvae were likely transported from outside the Gulf of Mexico. The Loop Current has a strong influence on circulation in the eastern Gulf of Mexico (Maul, 1977; Molinari et al., 1977). Among the 26 species listed by Gartner et al. (1987) as uncommon eastern Gulf residents, 15 were represented only by newly metamorphosed to juvenile individuals. Some of the adults of these species may reside at great depth, but it is also likely that some larvae were transported from spawning events in the caribbean or tropical Atlantic. The postmetamorphic forms of Myctophum selenops were considered uncommon in the eastern Gulf by Gartner et al. (1987), but were the second most abundant lanternfish larvae collected in the Caribbean (Richards, 1984). Houde et al. (1979) reported that this species was absent from the Gulf north of 28. N and west of 86 W during August and most abundant during spring and summer. Myctophum selenops larvae were not abundant in the stratified tows at standard Station. However, during later collections for material for age and

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111 growth and chemical composition (1987-1990}, larvae of M selenops were so abundant that it was the only Myctophum species for which enough material could be collected. This species was among the five most common premetamorphic lanternfishes occurring at that time. It is likely that the adults of this species spawn in the Caribbean basin during the summer, and the larvae are carried from that area to the eastern Gulf of Mexico by the Loop Current. Other larvae (e.g. Diogenichthys atlanticus) may also have Loop Current affinities (Houde et al., 1979). Results from four separate ichthyoplankton surveys in the Gulf of Mexico and Caribbean allowed for direct comparison with results from Standard Station. Three of these investigations reported similar species composition (Table 19) with minor discrepancies that could be explained by temporal and spatial differences in collection or lack of taxonomic resolution (see APPENDIX). The fourth investigation (Romero and del Castillo, 1984} contained many obvious identification errors. Vertical Distribution of Lanternfish Larvae Knowledge of the vertical distribution of ichthyoplankton is requisite to understanding their general ecology and all species of lanternfish larvae exhibited defined patterns of vertical distribution. Nonetheless, most surveys for larval

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112 Table 19: Comparison of abundance of myctophid larvae collected at Standard Station with larvae collected in the Caribbean (Richards, 1984), Eastern Gulf of Mexico (Houde et al., 1979), and Southern Gulf of Mexico (Flores-Coto and Ordonez-Lopez, 1991). Rank and (Absolute Number) Genus Ceratoscopelus Diaphus Hygophum Benthosema Myctophum Notolychnus Lampanyctus Diogenichthys Lepidophanes Lobianchia Centrobranchus Notoscopelus Lampadena Gonichthys Bolinichthys Symbolophorus Lowe ina Grouped as Lepidophanes. Standard Station 1 (1185) 2 (1124) 3 (709) 4 ( 651) 5 (607) 6 ( 479) 7 (475) 8 ( 174) 9 (71) 10 ( 63) 11 (57) 12 (43) 13 (42) 14 ( 34) 15 ( 13) 16 (7) Caribbean 1 (1233) 4 (178) 13 (4) 3 (190) 7 (44) 5 ( 82) 10 (8) 2 12 ( 5) 13 ( 7) 9 ( 12) 6 ( 46) 8 (24) 13 ( 4) 14 ( 1) Eastern GO MEX 7 (151) 1 (3646) 2 ( 1090) 4 ( 345) 3 ( 704) 4 ( 267) 8 ( 124) 5 ( 183) 6 (169) 11 (38) 9 (56) 10 ( 42) 14 (4) 13 (5) 12 ( 9) Southern GO MEX 11 ( 1) 1 (923) 3 (248) 2 (384) 4 ( 212) 5 ( 199) 6 ( 140) 7 ( 95) 9 ( 21) 10(15) 8 ( 36) a complex including the genera Ceratoscopelus and

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113 abundance have obliquely sampled the upper 200 m of the water column (Houde et al., 1979; Richards, 1984). The upper 200m of the water column is not a homogeneous water mass. Many physical (temperature, light levels, dissolved oxygen, salinity) and biological (food and competitor abundance, predator abundance) parameters change dramatically with depth. Variability in these parameters, combined with larval morphology, may be responsible for many of the observed patterns of abundance. In the eastern Gulf of Mexico, lanternfish larvae were most abundant in the upper 100 m, with larvae of the subfamily Lampanyctinae concentrated between 0-50 m, and larvae of the subfamily Myctophinae most abundant between 50-100 m (Figure 5). Similar patterns of vertical distribution were reported for lanternfish larvae in the North Pacific Ocean. Loeb (1979a; 1979b; 1980), working in the North Pacific Central Gyre (NPCG) found 98% of the lanternfish larvae residing above 100 m, with a maximum abundance between 25-50 m. Several taxa were common between the eastern Gulf of Mexico and the NPCG, and similarities in vertical distributions are apparent (Table 20). Comparative larval morphology is salient in understanding the observed patterns of vertical distribution. Practically every larval teleost body form is represented among myctophid

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114 Table 20: Comparison of vertical distribution among species and generic groups from Standard Station and the North Pacific Central Gyre (Loeb, 1979a, 1979b, 1980) Species or Group Standard North Pacific station Central Gyre LAMPANYCTINAE Bolinichthys spp. 0-50 ( 85%). longi2es 0-25 {79%) 0-50 {100%) CeratoscoJ2elus townsendi 0-25 (75%) 25-50 {78%) 0-50 {92%) 25-75 {94%) DiaJ2hUS type A 0-50 ( 86%) Q. anderseni 0-25 ( 96%) D. brachyceJ2halus 25-50 {73%) DiaJ2hUS type B 0-75 Q. elucens 25-50 {71%) D. rolfbolini 25-50 {73%) LamJ2adena luminosa 0-25 (67%). 0-2 5 ( 48%). 0-50 (98%). 0 -50 ( 96%). LamJ2anyctus alatus 25-50 ( 49%) L. steinbecki 25-50 {89%) Lobianchia gemellarii 50-75 ( 37%) 50-75 (50%) Notolychnus valdiviae 50-75 (53%) 75-100 {88%) MYCTOPHINAE Benthosema suborbitale 75-100 ( 40%) 75-100 (83%) Diogenichthys atlanticus 50-75 {31%) 75-100 (67%) 50-100 (71%) 50-125 (88%) HygoJ2hum reinhardtii 50-75 (60%) 50-75 {69%) Mycto2hum nitidulum 50-75 (54%) 75-100 (86%) 5 0 100 (6 7%) Few larvae collected.

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115 genera (Moser, 1981) The most notable difference in morphology within the family is the difference in eye shape between the two subfamilies. Larvae of the Lampanyctinae, which are mainly shallow dwelling species, possess round, sessile eyes (Moser and Ahlstrom, 1974); whereas larvae of the subfamily Myctophinae, primarily deeper dwelling species, possess narrow elliptical eyes that are often borne on stalks (Moser and Ahlstrom, 1970). The narrowing of the eyes, with an increased rotational ability along the long axis, could increase the visual field ten fold (Weihs and Moser, 1981). Extensions of the eyes on stalks could increase the visual field an additional ten fold (Weihs and Moser, 1981). Selective pressure toward the latter morphology must be great as similar trends can be observed among larvae of other mesopelagic fish groups (e.g. Idiacanthidae and Evermannellidae; Moser, 1981). The larval stage of fishes is particularly susceptible to high mortality and survival during the first few months of life has an important impact on adult population size (Hjort, 1914; May, 1974). Starvation (or poor growth) and predation are among the factors frequently considered in larval teleost mortality. The increase in visual field conveys potential ecological advantages in both areas. Greater visual range allows larvae to feed deeper where larger (copepodite) prey are in greater abundance (Figure 15). In addition, greater visual range may enable better avoidance from predators.

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116 Larval Diet Differences in diet were noted between larvae of the two subfamilies, but most species within each subfamily shared a common food resource. Most of the larvae within the subfamily Lampanyctinae preyed upon a variety of copepod developmental stages. Two larval species {Ceratoscopelus townsendi s .1. and Notolychnus valdiviae) within this subfamily appeared to be opportunistic, feeding for the most part upon the crustacean zooplankters that were common to the study area (see Hopkins, 1982) These lanternfishes also exhibited the highest diversity of prey type {Table 6}. The diet of these two species appears to reflect the overlap in distribution of predator and prey, with size restrictions set by mouth size. For example, Ceratoscopelus townsendi s.l. had the largest percentage of nauplii prey ingested (Table 6}. The vertical distribution of this species overlaps, to a large degree, the maximum abundance of nauplii (Figure 14). In addition, townsendi s.l. larvae had the smallest mouth size of all the species examined {Figure 23} and this was reflected in the small size of prey ingested (Figure 19} The diet i terns ingested by N valdiviae were generally larger (Figure 19}, consisting for the most part of copepodites. This general pattern continues in the postmetamorphic stages (see Hopkins and Gartner, 1992) The distribution of N valdi viae overlaps the zones of maximum abundance of copepodites (Figure 15). In

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117

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Figure 23. Relative mouth size of lanternfish larvae as determined from the measurement of the upper jaw. Standard length vs. upper jaw length is plotted for five species; (a} Myctophum selenops, (b) Notolychnus valdiviae, (c) Benthosema suborbitale, (d) Hygophum taaningi, and (e) Ceratoscopelus townsendi s.l.

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1 1 8 2.5 0 /b E E 2.0 '---"' d e ...c -+-' Ol c QJ 1 5 _j 5: 0 '-QJ 1.0 Q_ Q_ =:l 0 .5 0.0 0 2 4 6 8 10 12 14 Standard Length (m m)

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119 addition, the mouth size of N. valdiviae is larger (Figure 23) relative to standard length than that of .Q. t d' ownsen 1 s.l., allowing for a greater range of prey size. With the exception of the genus Hygophum, the diets of all members of the Myctophinae were dominated by ostracods (Tables 6 and 7). These crustaceans were greatly outnumbered by copepods at Standard station. Ostracods were broadly distributed throughout the upper 300 m during the day (Hopkins, 1982) and similar distributional patterns have been detected elsewhere (Angel, 1969). Thus, ostracod prey were unlikely to overlap the distributions of these larvae more than other crustacean zooplankters. Ostracods appear to be more visible than most copepods. The body of a typical ostracod is thick and opaque as opposed to the usually semi transparent bodies of copepods. The unique morphology of these larvae may relate to this prey choice. Most of these larvae are short and stout with large heads and mouths, allowing for the ingestion of larger prey at a younger stage. In addition, the elliptical eyes of these larvae likely provide better vision at depth than round eyes typical of Lampanyctinae (Weihs and Moser, 1981) Both Benthosema suborbitale and Myctophum selenops preyed heavily upon ostracods. The diet of lampanyctine larvae, which was dominated by various stages of marine copepods, is similar to the diets of most other marine fish larvae (Arthur, 1976; Hunter, 1981).

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120 Whereas many fish larvae are believed to be size selective feeders (Blaxter, 1965; Arthur, 1976), prey pellucidity, color and pigment pattern (Zaret, 1972; Govoni et al., 1986), and swimming behavior {Peterson and Ausubel, 1984) also are believed to be important factors in prey selection. Some marine larvae are less selective during their earliest growth stages, feeding upon such diverse items as phytoplankton, tintinnids, trochophores, veligers, and nauplii, becoming more selective with growth (Arthur, 1976, Govoni et al. 1983; 1986; Stoecker and Govoni, 1984). Qualitative comparisons of zooplankton composition and vertical abundance suggest that three species of lanternf ishes display remarkable selectivity of prey type. Larvae of Hygophum taaningi fed, for the most part, upon gelatinous zooplankton. other fish larvae have displayed similar diet preferences {Shelbourne, 1962), and adult lanternfishes are also known to feed on gelatinous material (e.g. Ceratoscopelus townsendi s.l.; Hopkins and Gartner, 1993). Gelatinous organisms are abundant in oligotrophic environments (Hamner et al., 1975; Hopkins and Lancraft, 1984). Little is known regarding the biology of the larvae of fi. taaninqi that would relate to this type of selectivity. It is not known if the distributions of predator and gelatinous prey overlap to a large degree. Hygophum taaningi larvae have an unusual gut morphology that may be related to their prey choice. This species has extensive gut diverticulae that may relate to the

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121 difficulty in digesting tunics of thaliaceans which are composed of a tough cellulose-like material. Examination of digestive tracts of bathylagids, midwater fishes which specialize on gelatinous prey, revealed that tunics are only partially digested and still recognizable in their hind guts near the anus (Hopkins, unpublished data). The bathylagids have proportionally larger digestive tract compared to myctophids. Both Benthosema suborbitale and Myctophum selenops, members of the Myctophinae subfamily, preyed heavily upon ostracods. As previously mentioned, the abundance of ostracods in the diets was in sharp contrast to their abundance in the water column and may be related to prey body morphology or visibility. The unique morphology of these larvae may also relate to this prey choice. All of these larvae are short and stout with large heads and mouths, allowing for the ingestion of larger prey at a younger stage. Larval Prey Field Full understanding of larval trophic patterns also requires knowledge of prey concentrations. Feeding experiments with marine fish larvae revealed that unusually high concentrations of prey were required for larval survival in the laboratory (Detwyler and Houde, 1970; Houde, 1977; 197B; Houde and schekter, 1981). High larval mortality was

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122 recorded in the first few days following yolk sac absorption in the laboratory (Lasker et al., 1970; Hunter, 1972} and the field (Incze et al., 1989}, a time often referred to as the critical period (May, 1973}. Field data revealed that average abundances of microzooplankton in the marine environment were lower than experimental concentrations required to sustain laboratory-reared larvae through their early stages of feeding (Wyatt, 1972; Houde, 1978; Laurence, 1974}. Evaluation of these data resulted in the invocation of the hypothesis that prey are concentrated in micro-to fine-scale aggregations, and the location of these aggregations may determine the survival of an individual larva (Lasker, 1975; Lasker and Zweifel, 1978; Vlymen, 1977; Houde and Schekter, 1978; Hunter, 1981}. It is almost a platitude that abundance in the oceans varies over a wide range of spatial and temporal scales. Because standard methods of zooplankton collection provide average abundances for a large volume of water, little is known regarding the micro-to fine-scale patterns of zooplankton abundance. Most studies of marine micro-zooplankton have focused on vertical (Bottger, 1982; Hopkins, 1982; owen, 1981; 1989}, latitudinal (Zeitschel, 1982}, or seasonal (Beers et al., 1982; Sanders, 1987} distributions. h 1 g1' st is the range of abundance Of interest to the trop 1c eco o variability on a macro-to mega-scale (1,000's of km; ocean fronts} and micro-to fine-scale (em to 900 m; range of

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123 zooplankton feeding; Haury et al., 1978) Macro-scale to fine-scale variability has been relatively well studied (Pingree et al., 1974; Weibe, 1970; Ortner et al., 1980) This range of variability means little to the individual fish larva which can only travel tens to hundreds of meters and search milliliters to liters of water per day. Fish larvae search for food on the micro-to fine-scale, and variability within this scale has rarely been investigated (Cassie, 1959; Owens, 1981; 1989) Hunter (1972) stated "It would be of interest ... to determine the size, density, and distribution of food patches in the natural environment on a scale appropriate to fish larvae." Because zooplankton vertical and micro-to fine-scale concentrations determine the prey available to lanternfish larvae, zooplankton concentrations were examined over the range appropriate to foraging by the larval assemblage. Lanternf ish larvae fed upon a variety of zooplankton prey types. Results from the examination of prey concentrations of the micro-to fine-scale suggest that adequate concentrations of their prey do exist over the range of daily foraging for lanternfishes. However, the concentrations of prey necessary for early growth are not evenly distributed. Meeting caloric needs would thus require the location and exploitation of higher than average prey concentrations. Vlymen (1977) reached the same conclusion using a mathematical model to simulate the prey field of larval anchovy (Engraulis mordax)

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124 From his calculations, Vlymen concluded that prey concentrations with a Fisher Index of 6 -14 would be required for growth and survival. Indices within this range were detected in the eastern Gulf of Mexico (Table 4). Fishes are visual predators (Confer et al., 1978) and conclusions regarding their ability to meet caloric requirements rests upon the determination of larval search volume and prey concentrations. Few detailed laboratory examinations of the behavioral aspects of marine larval feeding have been conducted (Blaxter, 1966; Rosenthal and Hempel, 1970; Blaxter and Staines, 1971; Hunter, 1975). These investigations have determined that although the shape and size of the perceptive field was different for different species of larvae, the volume of water searched is relatively constant with respect to larval standard length (Hunter, 1981) The results of Hunter (1972) were chosen to approximate the search volume of Ceratoscopelus larvae because it was the only study to employ natural prey of various size and taxa, and a species mordax) which is similar in general morphology of Ceratoscopelus larvae. Although the visual ambit of larvae is small (Rosenthal and Hempel, 1970; Blaxter and Staines, 1971; Hunter, 1975), once prey are detected in abundance, some larvae are able to remain within a prey patch (Hunter and Thompson, 1974). A combination of "search and stay" within a patchy environment offers far more trophic opportunities to a larva than random searching through

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125 an environment in which the prey items are randomly or evenly distributed. Because adequate prey concentrations were able to be detected even with limited sampling, and larval behavioral observations indicate that some larvae have the ability to detect and exploit prey patches (Hunter and Thompson, 1974), it is likely that the pelagic environment provides adequate prey for lanternfish larvae within the size range (3.5-10.0 mm SL) investigated. A likely scenario for these larvae would include periods of search during which no feeding occurred and the commencement of feeding upon the location of high concentrations of prey. Further evidence that larvae fed sporadically comes from feeding incidence results. All species examined had some empty guts during the day. This suggests that feeding is not continuous, but occurs in spurts as prey concentrations are detected and exploited. In addition, the high feeding incidence (based on gut fullness) observed during the day for these lanternfishes indicates an adequate food supply (Figure 20). Of the five species examined here, only one, Ceratoscopelus townsendi s.l., did not display a high level of feeding incidence. The larvae of this species are similar in morphology to engrauliform fishes with a long but straight gut. Long straight guts have been associated with evacuation during capture (Arthur, 1976; Hay, 1981), therefore the lower feeding incidence detected for this species may merely be a

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126 consequence of capture. Energetics The amount of energy required for daily growth (Qc) by the five representative species of lanternfishes was estimated from a bioenergetic equation. Variations in each of the three major parameters used to calculate Qc would affect the final determination of energy requirements. The estimate of prey energy converted into potential energy through growth (Qg) was evaluated from analysis of age and growth, plus measurement of dry weight and chemical composition. Growth was determined from microincrement analysis of sagittal otoliths. Although validation of microincrements as daily is important to establish for each species examined (Beamish and McFarlane, 1983), common techniques for the assessment of daily growth in nearshore fishes were not applicable to these midwater fishes. Lanternfishes are extremely sensitive to the stress of capture and are rarely collected live. Attempts at maintaining fishes for more than brief periods have been largely unsuccessful (Robison, 1973) In almost a decade of sampling in the eastern Gulf, lanternfish larvae were never collected alive. Nonetheless, the assumption of microincrements as indicators of age in days is reasonable for lanternfish larvae because of the following: 1) daily deposition of microincrements has been confirmed for all postmetamorphic lanternfishes that have been

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127 examined thus far from the Gulf of Mexico including two of the species examined in this study (Gartner, 1990; 1991a; unpublished data); 2) there is circumstantial evidence for daily deposition of microincrements for lanternfishes from the Mediterranean (Gjosaeter, 1987) and Tasmania (Young et al., 1988); 3) microincrements exhibit a strong one-to-one relationship to age in days for almost all teleost larvae that are not growth 1 imi ted (see Jones, 1985) ; 4) the microincrements exhibited by the larvae examined in this study displayed clearly defined, easily distinguished microincrements that were regularly spaced, and; 5) back-calculation from estimated growth equations resulted in ages for the smallest larvae collected to within a few days of hatch. In addition, ageing techniques generall y work well when fishes are growing rapidly as in early life, becoming less reliable as growth slows during maturity (Beamish and McFarlane, 1983). As one would expect, larval growth rates were different among different lanternfish species. Larvae of Ceratoscopelus townsendi s .1. exhibited the fastest growth of all the lanternfishes examined. This finding agrees with unpublished results for the postmetamorphic stages which indicate that this species also exhibits rapid growth throughout the juvenile stage and reaches maturity in approximately six months (Gartner, personal communication). I n contrast, larvae Of Vald1v1ae exhibited the slowest growth. Notolychnus

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128 Notolychnus valdi viae is an abundant yet diminutive species of lanternfish (Gartner et al., 1989). This species continues to grow slowly throughout the postmetamorphic stages as well (Gartner, unpublished data). Although lanternfish larvae of different species exhibited variability in growth rate and size at transformation, estimated growth was within the range of growth of the larvae of other Gulf of Mexico teleosts (Table 21} Of the few non-myctophid species for which information is available, larvae transformed between 65 to 100 days at lengths ranging from 17 to 22 mm (Table 21}. Average daily growth rates of these species ranged from 0.189 mm SL to 0. 405 nun SL day1 Lanternfishes had comparable growth rates but their size and age at transformation was lower. A linear growth model was chosen to represent the growth of lanternfishes throughout the larval period. Linear growth models were used to estimate larval growth in other Gulf of Mexico species (Cowan, 1988; Peebles and Tolley, 1988). Some commercial species which have been examined in great numbers as part of large scale fisheries investigation exhibit curvilinear growth curves (Warlen, 1988}. The curves take a variety of forms depending on species. Clupeoid fishes exhibited curvilinear growth best approximated by the Gompertz growth model (Warlen, 1988). such expressions are concave down and larvae exhibiting this type of growth experienced relatively rapid growth in the first weeks of life but growth

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129 Table 21: Growth of representative non-myctophid larvae from the Gulf of Mexico. Age in days at Species Growth Equation Trans-Reference forma-tion Deegan and Brevoortia Loge = 0.005(t) + 2.7 90 -Thompson Qatronus 100 (1987) Brevoortia L(t) = 2 3 5 5e2.212(I-e-0.0608t> 65 War len Qatronus {1988) Peebles Cynoscion L = 0.405{t) + 0.116 and Tolley -nebulosus {1988) MicroQogonias L = 0.189{t) + 0.634 > 80 Cowan undulatus (1988)

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130 rate gradually deceased as larvae approached metamorphosis. Other larval groups, like Atlantic gadoid fishes, also exhibited exponential growth but the resulting growth curves were concave up (Campana and Hurley, 1989). Larvae of these fishes exhibited a pattern of growth that is represented by the first part of a sigmoidal or logistic growth pattern. These larvae grew relatively slowly in the first week or two of life but growth rate accelerated as larvae approached metamorphosis. The only other examination of otoliths removed from larval lanternfishes was an examination of growth patterns of the Pacific lampfish, Stenobrachius leucopsarus (Methot, 1988). The larvae of this species exhibited a growth pattern similar to that of Atlantic gadoid fishes, with a concave up growth curve. Larval growth accelerated from 0.11 mm SL d-1 at 5 mm SL to o. 28 mm d-1 at 15 mm SL (Methot, 1988). If growth of lanternfish larvae is better expressed as a curvilinear function, it would result in a larger size estimate of o-age larvae and lower energy requirements for small larvae. The linear functions used with the present data set appear to estimate age o size quite well, however, because estimates of o-age fish closely match the size of the smallest larvae collected for all species examined. The chemical composition of lanternfish larvae (Table 8), with proteins and lipids being predominant over carbohydrates, is similar to that exhibited by the larvae of other fish

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131 species (Cetta and Cauzzo, 1982; Brightman, 1993) In addition, results for these larvae fall within the range reported for postmetamorphic lanternfishes from the eastern Gulf of Mexico (Stickney and Torres, 1989). The unusually high lipid level in adult Notolychnus valdiviae was not found in the larvae of this species, which had the lowest percent lipid content of all species examined. The amount of energy consumed by daily activity (Qm) was estimated from field and laboratory results. Time spent in active (= feeding) metabolism was determined from the analysis of feeding chronology for each of the representative species. Most lanternfish larvae were actively feeding for 15 hours a day except larvae of Myctophum selenops which fed continuously. Minor feeding has been detected during the night for some larvae (Last, 1978; Govoni et al., 1983), but this high nocturnal feeding incidence is unique among marine larvae. Most marine larvae lack the rods and retinomotor pigment migration necessary for nocturnal feeding (Blaxter, 1968; O'Connell, 1981). There is general agreement that marine fish larvae exhibit their lowest feeding incidence prior to dawn, and feeding intensity during the day exhibits one or more peaks. The time of greatest feeding intensity is quite variable however, and perhaps species specific (Ryland, 1964; Bainbridge and McKay, 1968; Last, 1978; Govoni et al., 1983) t d r1 ng routine metabolism was estimated from Energy spen u

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132 the only examination of respiration by the larvae of a variety of tropical-subtropical species (Houde and schekter, 1983). These authors concluded that oxygen uptake (R) related strongly to biomass (dry weight) and did not differ significantly among species. Further, recent analysis of respiration by larval redfish (Sciaenops ocellatus) was similar to the respiratory requirements of other tropical-subtropical species (Brightman, 1993). It is likely, therefore, that the equations generated by Houde and Schekter (1983) are applicable for approximating the metabolic caloric requirements of lanternfish larvae. Whereas the values for energy funneled into growth (Q1 ) and burned for activity (Qm) were either measured or derived from corroborated values in the literature, the amount of energy lost through non-assimilation is contentious. The ability to capture and measure the amount of prey energy lost in feces (unassimilated food) is difficult, thus it is often measured indirectly (Houde and Schekter, 1983; Theilacker, 1987). Even when direct measurement of prey assimilation was attempted (Govoni et al., 1982) assimilation levels were shown to be highly variable within a species and were not significantly related to age, standard length, or dry weight. Results of assimilation calculations range from 17 -92% in marine larvae, with an average value of 73%. Because of the high degree of variability associated with this parameter, Qc was determined for the lowest, average, and highest levels for

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133 assimilation reported for marine fish larvae. Larval fishes probably have lower assimilation levels than adults because of the lack of development of gut tissues and digestive organs (Govoni, 1981), but the values are probably not as low as indicated by some experimental results. Among the factors contributing to the variability of measured assimilation levels are prey availability and type. The maintenance of larvae in the laboratory requires prey densities much higher than those available in situ (Houde, 1978). Under such conditions larvae pack their guts, forcing prey items through more quickly than would probably occur naturally (Theilacker, 1987). Lack of retention within the gut would result in lower assimilation efficiencies. Houde and Schekter (1983) suggested that the poor assimilation of prey by bay anchovy (Anchoa mitchilli) was related to a residence time in the gut of only a few minutes duration. Even though high prey concentrations are likely encountered by marine larvae (Cassie, 1959; Owen, 1981; 1989; this study), these do not match the high levels of prey consistently provided to laboratory-reared larvae (Houde, 1978). It is likely, therefore, that the minimum and average prey requirements calculated herein are closer to the natural feeding requirements of larvae, which assumes a relatively high assimilation rate. The digestibility of prey also affects assimilation efficiencies. Brightman (1993) attributed the high

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134 assimilation of rotifers by redfish larvae to the relative ease at which these prey can be digested. It may be more difficult to extract energy from other prey items, such as phytoplankton and crustacean prey. Most marine larvae feed upon a variety of prey, especially during the early part of larval development (Arthur, 1976, Govoni et al. 1983; 1986; Stoecker and Govoni, 1984). The average assimilation rate (73%) of Brett and Groves (1979) is likely the best estimate for assimilation of prey for larvae over a range of sizes. Resource Partitioning Comparison of clustering results for diet and distribution (Figures 6 and 18) revealed that many of the 14 species examined for both parameters overlap. Although the water column was broadly subdivided by major morphological type (subfamily), within each stratum there were several closely related species sharing a common zooplankton resource. The greatest overlap was between closely related species (same subfamily and congeners). With the exception of the genus Hygophum, all of the Myctophina e larvae examined overlapped with at least one other species in diet and vertical distribution. The highest degree of overlap was among larvae within the 50-75 m stratum, the zone of maximum larval lanternfish abundance. Thus, cluster analysis of vertical distribution plus diet information suggests resource

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135 partitioning among larval lanternfishes is not at the between-species level but at the subfamily level. Similar patterns were detected among the copepod assemblage of the North Pacific where groups broadly subdivided the water column but exhibited a high degree of within group similarity of diet and vertical distribution (McGowan and Walker, 1979). In fact, the closer the taxonomic relationship, the greater the similarity (see also Hopkins, 1985). In the absence of resource partitioning, the authors argued that the population was more regulated by predation than by food limitation. Heavy predation may enable coexistence by reducing populations to levels where there is little competition among survivors. The same argument can apply to the myctophid larval assemblage. Although separation of major morphological forms was evident, within the subfamilies overlap of spatial and diet niche parameters were clear, thereby suggesting an adequate food supply. In contrast, the diet and spatial distribution of postmetamorphic lanternfishes suggested resource partitioning among the dominant species occurring in the eastern Gulf of Mexico (Hopkins and Gartner, 1992). Other forms of micronekton also appear to partition their resources (e.g. 1 s) The lack of niche sergestids; Hopkins et a J.n pres concordance among the micronekton suggests a different set of biological pressures on these individuals. The micronekton th t h h r trophic level to lanternf ish larvae and occupy e nex J.g e

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136 other macrozooplankton taxa (e.g. copepods), and it is theoretically impossible for successive trophic levels to be predator controlled (Hayward and McGowan, 1979). Predation Impact The results presented herein suggest that lanternfish larvae are too dilute to affect the density of their zooplankton prey. The estimate of predation impact was based upon lanternfish larval densities at their highest detected during eight cruises to Standard Station and also upon a maximum, and perhaps unrealisticall y high, estimate of prey ingestion (MaxQc). Further, the estimate o f predation impact was based upon the prey concentrations measured i n the upper 200 m during the day when feeding by these larvae was most intense. Many crustacean zooplankton taxa undergo diel vertical migrations (Miller, 1970), and the crustacean biomass in the upper 200 m is considerably lower during the day at Standard station (Hopkins, 1982). Therefore, the predation impact by these larvae on the entire zooplankton community could be even lower than estimated using daytime abundances. Cushing (1983) also concluded that marine pelagic ichthyoplankton (larval clupeoids and gadoids) would have no significant impact on their zooplankton resource. In environments where ichthyoplankton abundances are higher, their impact on their zooplankton resource may be greater.

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137 Cushings' exploratory model of predation by larval Pacific herring (Clupea harengus) and Pacific whiting (Merluccius product us) concluded that when larval densities reach 1. o m-3 they could remove approximately 1% of the adult copepod assemblage each day. In fresh water environments, estimates as high as 2 0% daily removal of zooplankton have been reported (Hewett and Stewart, 1989). Both of these estimates assume maximum larval abundances, which are short lived, and highly selective feeding, which is unrealistic.

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138 CONCLUSIONS An understanding of animal populations requires knowledge of the entire life history of the organisms. Lanternfishes are a dominant life form in the largest ecosystem of the planet (ocean pelagial), yet little is known of their early life history. Survival during early life may determine adult population size and structure (see May, 1974, Hunter, 1981, and Lasker, 1981 for reviews). Results from larval prey requirements, prey distribution and caloric value, feeding incidence, and absence of resource partitioning suggest that lanternfish larvae of the size range examined ( 3 5 10.0 mm SL} are not resource limited. These results do not, however, contradict the critical period hypothesis of Hjort (1914}. This hypothesis of larval survival is based upon the successful feeding of larvae within the first few days of yolk sac absorption (May, 1973). Lanternfishes unlike most other marine larvae, release their I eggs at great depths (Efremenko, 1976; Yefremenko, 1976; Robertson, 1977} and their eggs develop and hatch as they ascend (Marshall, 1979; Gjosaeter and Tilseth, 1988}. Yolksac and other small larvae were rarely collected and were not included in these analyses. If resources are limiting during the first few days of feeding by these smallest of larvae,

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139 they appear not to be for lanternfish larvae 3.5 mm SL and larger. Thus predation or some as yet unknown factor may control population abundance of these larvae.

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140 LITERATURE CITED E. 1965. Kinds and abundance of fishes in the Cal1forn1a Current region based on egg and larval surveys. Calif. Mar. Res. Conun., CalCOFI Rept. 10:31-52. Ahlstrom, E. H. 1968. Appraisal of the IIOE larval fish collection of IOBC, Cochin, India. UNESCO/NS/IOC/INF 137:1-10. Ahlstrom, E. H. 1972. Kinds and abundance of fish larvae in the eastern tropical Pacific on the second multivessel EASTROPAC survey, and observations on the annual cycle of larval abundance. Fish. Bull. 70:1153-1242. Ahlstrom, E. H. 1976. Maintenance of quality in fish eggs and larvae collected during plankton hauls. In H. F. Steedman (ed.) Zooplankton fixation and preservation. The Unesco Press. Paris Pp. 313-318. Alverson, F.G. 1963. The food of yellowfin and skipjack tunas in the eastern tropical Pacific Oc ean. Bull. IATTC 7:293-396. Angel, M.V. 1969. Planktonic ostracods from the Canary Island region; Their depth distributions, diurnal migrations, and community organization. J. Mar. Biol. Ass. U.K. 49:515-553. Arthur, D. K. 1976. Food and feeding of larvae of three fishes occurring in the Ca lifornia current, Sardinops saqax, Engraulis mordax, and Trachurus symmetricus. Fish. Bull. 74:517-530. Austin, H.M. 1971. The characteristics and relationships between the calculated geostrophic current component and selected indicator organisms in the Gulf o f Mexico Loop current syste m. Ph.D. Di.ssert.ation, Dept. of Oceanography, Florida State Un1vers1ty, 369 PP Backus, R.H., J.E. Craddock, R.L. and B H. 1977. Atlantic mesopelag1 c zoogeography. In. R:H Gibbs, Jr. (ed.) Fishes of the North Atlant1c. sears Found. Mar Res. Yale Univers1ty, N e w Haven, CT. Mem.l, Pt.7:266-287

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153 Paxton, J. R., E.H. Ahlstrom, and H.G. Moser. 1984. Myctophidae: systematics of 244. Relationships. In: Ontogeny and fishes. H.G. Moser, ASIH Spec. Pub. 1:239-Peebles, E.B., S.G. Tolley. 1988. Distribution, growth and mortal1ty of larval spotted seatrout, Cynoscion nebulosus: a comparison between two adjacent estuarine areas of southwest Florida. Bull. Mar. Sci. 42:397-410. Pereyra, T., W. G. Pearcy and F. E. Carvey, Jr. 1969. Feed1ng on mesopelagic fauna, with consideration of the ecological implications. J. Fish. Res. Bd. canada 26:2211-2215. Perteseva-Ostroumova, T.A. 1964. Some morphological characteristics of the myctophid larvae (Myctophidae, Pisces). In: Fishes of the Pacific and Indian Oceans, Biology and Distribution. T.S. Rass, ed. Akad. Nauk S.S.S.R., Inst. Okeanologii, Trudy, 73:79-97. Perteseva-Ostroumova, T.A. 1972. The larvae of lanternfish (Myctophidae) collected by Australian expeditions on the H.M.A.S. Gascoyne and H.M.A.S. Diamantia. J. Ichthyol. 12:634-648. Perteseva-Ostroumova, T.A. 1974. New data on lanternfish larvae (Myctophidae, Pisces) with oval eyes from the Indian and Pacific Oceans. Tr. Inst. Okeanol, SSSR, 96:77-142. Peterson, w. T. and s. J. Ausubel. 1984. Diets and feeding by larvae of Atlantic mackerel Scomber scombrus on zooplankton. Mar. Ecol. Prog. Ser. 17:65-75. Pingree, R.D., G.R. Forster, and G.K. Morrison. 1974. Turbulent convergent tidal fronts. J. Mar. Biol. Ass. U.K. 54:469-479. 1 1984 The interpretation of ecological data. P1e ou, E.C. J. Wiley and Sons, New York. 263 PP R dtk R L and K.G. Waiwood. 1980. Otolith formation and a e' 1 1 d ( G dus body shrinkage due to f1xat1on 1n c'?.. =a== morhua). can. Tech. Rep. Fish. Aquat. Sc1. 929:111 +lOp. b an 1983. Larves de Rasonanariuo, R. and A. A oussou 1878) (Teleostei, Electrona antarctica (Gunther, Myctophidae) recoltees durant campagne FIBEX-MD/25 dans le sud-ouest de L'Ocean Ind1en. Cybium 7:75-86.

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154 Richards, W. J. 1984. Kinds and abundance of fish larvae in the Caribbean Sea and adjacent areas. NOAA Tech. R NMFS SSRF-776. 54 pp. ep., Robison, B. H. 1984. Herbivory by the myctophid fish Ceratoscopelus warmingii. Mar. Biol. 84:119-123. B. and T: G. Bailey. 1981. Sinking rates and d1ssolut1on of m1dwater fish fecal matter. Mar. Biol. 65:135-142. Roger, C. and R. Grandperrin. 1976. Pelagic food webs in the tropical Pacific. Limnol. Oceanogr. 21:731-735. Rojas de Mendiola, B. 1974. Food of the larval anchoveta Enqraulis ringens J. In J.H.S. Blaxter (ed.) The early life history of fish. Springer-Verlag, New York. Pp. 277-285. Romero, M. and J. Del Castillo. 1984. Distribucion y abundancia de larvas y juveniles de peces mictofidos en el Mar Caribe. Rep. Invest. Inst. Oceano!. 26:1-16. Rosenthal, H. and G. Hempel. 1970. Experimental studies in feeding and food requirements of herring larvae (Clupea harengus L.) 344-364. Ryland, J.S. 1964. The feeding of plaice and sand-eel larvae in the southern North Sea. J. Mar. Biol. Ass. U.K. 44:343-364. sanders, R.W. 1987. Tintinnids and other microzooplanktonseasonal distributions and relationships to resources and hydrography in a Main estuary. J. Plank. Res. 9:65-77. Sanzo, L. 1931. Uova e primi stadi di gemellari Cocco (=Scopelus gemellar1 C. e V.) Att1 Accad. Naz. Lincei 14:515-519. Science Applications International Corporation .. 1989. Gulf of Mexico physical oceanography program, f1nal report: year 5. volume II: Technical report. MMS Contract No. 14-12-0001-29158, ocs Report/MMS 89-0068. 333 pp. S tt W B and S N Tibbo. 1968. Food and feeding habits co th t N th of swordfish, Xiphias glad1us, 1n e wes ern or Atlantic. J. Fish. Res. Bd. Canada. 25:903-919 Sh. T A 1974 Postembryonic development of Hygophum 1ganova, . . benoiti. Vopr. Ikht1ol. 14.1-88.

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155 Shiganova, T.A. 1977. The larvae d f' an 1ngerl1ngs of lanternfishes (Myctophidae, Pisces) of the Atlantic Ocean. Trudy Inst. Okeanol. 109:42-112. Stickney, D.G., and J.J. Torres. 1989. Proximate composition and energy content of mesopelagic fishes from the eastern Gulf of Mexico. Mar Biol. 103:13-24. Stoecker, D. K. and J. J. Govoni. 1984. Food selection by young larval gulf menhaden (Brevoortia patronus). Mar. Biol. 80:299-306. Sturges, W.A. and J.C. Evans. 1983. on the variability of the Loop Current in the Gulf of Mexico. J. Mar. Res. 41:639-653. Taning, A.V. 1918. Mediterranean Scopelidae (Saurus, Alopus, Chlorophthalmus and Myctophum) Per. Danish Oceanogr. Medit. 1908-1910. Vol. II(A7), 154 Pp. Theilacker, G.H. 1987. Feeding ecology and growth energetics of larval northern anchovy, Enqraulis mordax. Fish. Bull. 85:213-228. Tsokur, A. G. 19 81. The larvae of Benthosema pterota (Alocock, 1891) Myctophidae, from the Arabian Sea. J. Ichthyol. XX:38-53. Vlymen, W.J. 1977. A mathematical model of t h e relationship between larval anchovy (Enqraulis mordax) growth, prey microdistribution, and larval behavior. Env. Biol. Fish. 2:211-233. Vokovich, F.M. and B.W. Crissman. 1986. Aspects of warm rings in the Gulf of Mexico. J. Geophys. Res. 91:26452660. Vokovich F.M. and G.A. Maul. eastern Gulf of Mexico. 1985. Cyclonic eddies in the J Phys. Oceanogr. 15:105-117 Vokovich, F.M., B.W. Crissman, M. Bushnell, and King. 1978. sea-surface variability analysis potent1al OTEC sites utilizing satellite data. Res. Tr1. Inst. 153 pp. V k h F M B w Crissman M. Bushnell, and W.J. King. 0 OV1C I I I lf f 1979. some aspects of the of the Gu o Mexico using satellite and 1n s1tu data. J. Geophys. Res. 84:7749-7768. w D M 1975 Bioenergetics of pelagic fish: Theoretical are, h. 1.mm1 ng speed and motion with body size. J. c ange 1n sw Fish. Res. Bd. Canada 35:33-41.

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156 Warlen, S.M .. 1988. Age and growth of larval gulf menhaden Brevoort1a Patronus, in the northern Gulf of Mexico. Fish. Bull. 86:77-90. Warren, C.E. and G.E. Davis. 1967. Laboratory studies on the feeding, bioenergetics and growth of fish. In: Gerking, S.D. (ed.) The biological basis of fresh-water fish production. Wiley, New York. Pp. 175-214. Weihs, D. H.G. Moser. 1981. Stalked eyes as an adaptat1on toward more efficient foraging in marine fish larvae. Bull. Mar. Sci. 31:31-36. Wiebe, P.H. 1970. Small-scale spatial distribution in oceanic zooplankton. Limnol. Oceanogr. 15:205-217. Winberg, G.G. 1956. The relation of the metabolic rate of fish to temperature. In: Role of metabolism and food requirements of fishes. J. Fish. Res. Bd. Canada Trans!. Ser. 194:21-38. Wissing, T.E., R.M. Darnell, M.A. Ibrahim, and L. Berner Jr. 1973. Caloric values of marine animals from the Gulf of Mexico. Contrib. Mar. Sci. 17:1-7. Wyatt, T. 1972. Some effects of food density on the growth and behaviour of plaice larvae. Mar. Biol. 14:210-216. Yefremenko, V.N. 1976. Vertical distribution of myctophid eggs in the South Atlantic. Oceano!. 16:404-405. Young, J.W., C.M. Bulman, 1988. Age and growth hectoris (Myctophidae) Mar. Biol. 99:569-576. S.J.M. Blaber, and S.E. Wayte. of the lanternfish Lampanyctodes from eastern Tasmania, Australia. Zaret, T.M. 1972. Predators, invisible prey, and the nature of polymorphism in the Cladocera (class Crustacea) Limnol. oceanogr. 17:171-184. Zeitzchel, B. 1982. Zoogeography of pelagic marine protozoa. Ann. Inst. oceanogr. 58:91-116. Zuez, G. V. and K. N. food chains of Voodzinskiy, N. and fisheries. Nesis. 1971. The role of squids in the the ocean. In B. N. El 'kina, B. V. I. Matyushina (eds.) Squids -Biology Fishing Industry Press, Moscow.

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157 APPENDIX Identification of Larvae of the Family Myctophidae The family Myctophidae includes two subfamilies, the Lampanyctinae and Myctophinae, which have been separated into five tribes, 36 generic or subgeneric categories, and between 230-250 species (Moser et al., 1984}. Species can be distinguished by a variety of adult morphological features (Paxton, 1972; Paxton et al. 1984} with photophore patterns and number of gill rakers being important specific characteristics (Nafpaktitis et al., 19 77}. Morphological differences between the larvae of the two subfamilies are best exhibited by eye shape (Moser and Ahlstrom, 1 9 70}. Members of the subfamily Lampanyctinae possess round eyes. Members of the subfamily Myctophinae possess narrow eyes, which may be borne on stalks (Moser and Ahlstrom, 1970; 197 4; Moser et al., 1984}. The species Notolychnus valdiviae is an intermediate form, but is usually placed with the Lampanyctinae. Published identification characters along with new characters determined during the course of this study, are listed in the following species accounts. Species accounts are arranged in alphabetical order w ithin subfa milies and include size range s and number of individuals examined from the discrete depth

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158 series of collections. Subfamily Lampanyctinae Bolinichthys spp. (3.1-9.5 mm SL; n=13) This genus is represented by juveniles and adults of two species in the eastern Gulf of Mexico, photothorax and supralateralis (Gartner et al., 1987) Larvae of one species, supralateralis, has been described (Moser and Ahlstrom 1974). Although the larvae in this collection matched published accounts, it was not possible to eliminate photothorax from consideration without knowing its larval morphology. Ceratoscopelus townsendi s.l. (2.1-14.5 mm SL ; n 1185) The status of the species in this genus is uncertain. Nominally, the genus contains three cosmopolitan species; maderensis, a berea-temperate North Atlantic species, townsendi, formerly restricted to the eastern Pacific, warmingii, a cosmopolitan low latitude species. Recently, the specific distinction between the latter two has been questioned. These two species, as adults, are distinguished by the presence or absence of supraorbital luminous patches. Badcock and Araujo (1988) examined adults and larvae collected

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from many locations. 159 The authors concluded that only one species, townsendi, exists but with a number of distinct and geographically separated populations. A single larval illustration of townsendi s.l. was published by Moser and Ahlstrom (1974). A single illustration (Miller et al., 1979), two larval illustrations (Badcock and Araujo, 1988) and a complete life-history series (Shiganova, 1977) have also been published for larvae identified as warmingii. Five distinct larval morphs of this genus were collected from the eastern Gulf of Mexico. Ceratoscopelus type A This morph displayed a series of melanophores along the dorsal and ventral midlines from the med i a n f i n s to caudal peduncle. The number of dorsal "patches" ranged f rom zero to three. The number of ventral "patches" ranged from one to ten. All permutations of these numbers were observed. In addition, both dorsal and ventral "patches" of p igment occasionally occurred as a single streak. There is a trend toward the reduction in the number of melanophores increasing larval size (Miller et al., 1979). Ceratoscopelus type B with This larval morph is similar to A but with a single,

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160 persistent melanophore sagittally located just above the hindbrain. Ceratoscopelus type c This larval morph is also similar to A but with a single, persistent melanophore posterior to the pectoral fin base that is obscured by the fin. Larvae of maderensis are similarly marked. However, adults of maderensis, a boreo-temperate species (Nafpaktitis et al., 1977), have never been collected from the Gulf or Caribbean although Richards (1984) reported maderensis larvae from the Caribbean. Specimens of larval maderensis were borrowed from the Museum of Comparative Zoology in Cambridge, Massachusetts for comparison with larvae collected from the eastern Gulf of Mexico. These larvae were distinct from any of the forms collected in the eastern Gulf. Ceratoscopelus type D This larval form contains all of the pigment patterns described above. Ceratoscopelus type E This morph was completely lacking in pigmentation.

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161 Variations in larval form support the observation of Badcock and Araujo (1988} that larvae of this species are plastic in their display of pigment. Although the distribution of body pigment and eye shape are the most common characteristics used to identify the different species of larval lanternfishes, in most species the distribution of melanin is conservative. Larval forms in this group differ in presence, absence, or location of melanophores. Rather than discrete larval morphs, the larvae display a continuum from no pigment to a variety of possible permutations of pigmentation. Because of the continuum of pattern thus displayed, all forms will be considered as a single townsendii s.l., as suggested by Badcock and Araujo (1988). Diaphus spp. (n = 1,124} Diaphus rafinesguii is the only species recorded from the eastern Gulf of Mexico for which larvae have been described (Taning, 1918). Published illustrations and descriptions of this species match many of the larval Diaphus spp. collected. The larvae of Ih mollis, a common Gulf of Mexico species (Gartner et al., 1987}, were described by Shiganova (1977). Loeb ( 1 979a} considered mollis a complex including both major larval morphologies, therefore the validity of these published descriptions is in question. Thus, no individuals uld be identified with certainty. of this spec1es co

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162 Diaphus larvae are a morphologically homogeneous group. Larvae display melanophores on caudal fin rays, one to several melanophores on the ventral caudal peduncle, and a pigment patch anterior to digestive diverticula. Larvae of this genus were particularly difficult to separate from one another. Moser et al. ( 1984) concluded that "Myctophid species have distinct melanophore patterns, with the exception of the large genus Diaphus, for which only a few specific patterns have been identified." Identification of the individuals collected at Standard Station led to the construction of one possible life history series (Diaphus dumerilii) and the discovery of a third major group(= type C). Diaphus type A (2.5-8.1; n = 243) Diaphus type A have a slender body, small head, and several melanophores on the ventral surface from the anus to the caudal fin base (Moser and Ahlstrom; 1974). Type A larvae correspond to adults without a suborbital photophore. In the eastern Gulf of Mexico this includes: .Q. dumerilii (abundant); _g. lucidus, _g. problematicus, and .Q. splendidus (commom); .Q. effulgens, _g. fragilis, .Q. garmani, .Q. luetkeni, .Q. perspicillatus, _g. taaningi, .Q. termophilus (uncommon) ; and .Q. bertelseni, .Q. metopoclampus (rare). Diaphus B (2.0-12.3 mm SL; n = 810 )

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163 Diaphus type B has a deeper body and a bulbous snout, a single persistent ventral tail melanophore or none (Moser and Ahlstrom, 1974) The adults of this form possess a suborbital photophore. In the eastern Gulf of Mexico this includes: Q. mollis (common); and Q. brachycephalus, Q. rafinesguii, Q. subtilis (uncommon). Diaphus type c (2.9-11.0 mm SL; n = 71) Larvae of this type are uncharacteristically pigmented for members of the genus. There are many melanophores scattered over the anterior abdomen, immediately posterior to the cleithrum. This pattern is clear in even the smallest (2.9 mm) forms examined. A complete series from larvae to adult was constructed (Conley and Gartner, in prep) for Q. perspicillatus. These larvae are similar to the larvae of Q. luetkeni described by Pertseva-Ostroumova (1972; Figure 6) from the waters off Australia, thus these two species are part of this morphological type. Lampadena luminosa (1.6-11.4 mm SL; n = 42) Moser and Ahlstrom (1974) included one illustration of a relatively large (12.4 mm SL) Lampadena luminosa and Miller et al. (1979) illustrated a 4.8 mm specimen. Individuals examined prior to fixation exhibited a series of erythrophores

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164 on the operculum. A complete life-history series was constructed (Conley and Gartner, in prep) to facilitate the identification of all larval 1 luminosa. Lampanyctus spp. (2.0-13.0 mm SL; n = 264) Six species of this genus occur in the eastern Gulf of Mexico (Gartner et al., 1987). Larvae are distinctive in appearance but relatively few life-history series have been constructed. Transitional stages are rare, probably residing at great depth (> 500 m). Of Gulf of Mexico species, only one illustration for a 3.6 mm 1 nobilis (Miller et al., 1979) has been published. Richards (1984) provided additional information regarding larval morphology of 1. nobilis. In addition, a description of larvae of 1 cuprarius was related by Richards (1984) from unpublished work of Ahlstrom. Lampanyctus alatus (2.2-10.4 mm SL; n = 209) The larvae of this species were previously not described even though the species is the most abundant member of the genus occurring in the eastern Gulf (Gartner et al., 1987). Pigmentation is distinct and resembles the pattern described by Taning (1918) for 1 pusillus (originally described as 1 alatus, but later recognized as a distinct species.) Larvae are stout with a large head and rounded snout. Sagittal

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165 pigmentation includes a dorsal melanophore anterior to the forebrain and midbrain, as well as posterior to the midbrain. There is pigmentation at the tip of the premaxilla and mandible, above the swim bladder, and in the gular region. Also, a distinct series of spots is displayed along the pectoral fin rays and melanin may be located between the myomeres dorsal to the midgut. Lampanyctus cuprarius The larvae of this species were verbally described by Richards ( 1984) from the unpublished figures of Ahlstrom. This species was not observed in the stratified tows but was identified from the samples collected for diet analyses, age and growth, and chemical composition. Lampanyctus nobilis (6.1-6.5 mm SL; n = 2} Richards ( 1984) provided a verbal description of the larvae of this species. Lepidophanes guentheri (2.2-13.6 mm SL; n = 71} Larvae of this species are similar in morphology to Ceratoscopelus and, to a lesser extent, members of the genus Diaphus type A. Identification is particularly difficult with

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166 small (< 4.0 mm) larvae as they have the same elongate body and similar caudal pigmentation to Ceratoscopelus. As the larvae of Lepidophanes mature, a distinct patch of pigment appears anterioventral to the digestive diverticuli. Also, the eye is smaller relative to body size than in Ceratoscopelus. A single specimen was illustrated by Moser and Ahlstrom ( 1972) and a complete life-history series by Shiganova (1977). Lobianchia gemellarii (2.6-10.0 mm SL; n = 63) Taning (1918) described the larvae of this species under the name Diaphus Gemellarii (sic). To date, the information provided by Taning (1918) remains the only life-history series for this distinctive larva, although additional figures of single larva have been published (Sanso, 1931; Pertseva-Ostroumova, 1964, Moser and Ahlstrom, 1974). Notoscopelus caudispinosus Larvae of this genus were first identified by Belyanina (1982) who included an illustration of a single specimen (12.8 mm). In addition, Richards (1984) provided a morphological description of the larvae, including features useful for distinguishing N caudispinosus from its congener Notoscopelus resplendens.

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167 Notoscopelus resplendens (3.0-12.4 mm SL; n = 43) The larvae of Notoscopelus resplendens were originally described by Moser and Ahlstrom (1970) who also provided illustrations of a 11.2 mm larvae and a 21.0 mm transitional stage. The authors also included a detailed account of meristics, sequence of photophore and fin ray development, plus other features. Fully illustrated life-history series were published by Badcock and Merrett (1976) and Shiganova (1977). Notolychnus valdiviae (2.9-10.9 mm SL; n = 479) This species is unusual in many respects. Notolychnus valdiviae is the smallest of the lanternfishes (maximum SL 25 mm) and it is also unusual in its adult morphology (Nafpaktitis et al., 1977). N valdiviae has been considered a monotypic tribe which can not be placed with certainty in either subfamily (Moser et al., 1984). A complete description of the larvae, under the name Myctophum Valdiviae (sic), was provided by Taning (1918). Additional illustrations and descriptive information have been published (PertsevaOstroumova, 1964; Moser and Ahlstrom, 1974; Fahay, 1983). Subfamily Myctophinae

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167 Notoscopelus resplendens (3.0-12.4 mm SL; n = 43) The larvae of Notoscopelus resplendens were originally described by Moser and Ahlstrom ( 1970) who also provided illustrations of a 11.2 mm larvae and a 21.0 mm transitional stage. The authors also included a detailed account of meristics, sequence of photophore and fin ray development, plus other features. Fully illustrated life-history series were published by Badcock and Merrett (1976) and Shiganova (1977). Notolychnus valdiviae (2.9-10.9 mm SL; n = 479) This species is unusual in many respects. Notolychnus valdiviae is the smallest of the lanternfishes (maximum SL 25 mm) and it is also unusual in its adult morphology (Nafpaktitis et al., 1977). N valdiviae has been considered a monotypic tribe which can not be placed with certainty in either subfamily (Moser et al. 1984) A complete description of the larvae, under the name Myctophum Valdiviae (sic), was provided by Taning (1918). Additional illustrations and descriptive information have been published (PertsevaOstroumova, 1964; Moser and Ahlstrom, 1974; Fahay, 1983). Subfamily Myctophinae

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168 Benthosema suborbitale (2.2-10.0 mm SL; n = 651) Illustrations of complete developmental series and detailed descriptions have been published by many authors (Pertseva-Ostroumova, 1974; Badcock and Merrett, 1976; Shiganova, 1977). Illustrations of single specimens are also available (Pertseva-Ostroumova, 1964; Moser and Ahlstrom, 1974). Centrobranchus nigroocellatus (3.4-11.3 mm SL, n = 57) An illustration of a single larva of Centrobranchus nigroocellatus was included in the work of Pertseva-Ostroumova (1974). In addition, Richards (1984) suggested that the larvae of this species are identical to choerocephalus larvae described from the Pacific by Moser and Ahlstrom (1970; 1974). A complete life-history series was constructed for the larvae of this species from Standard Station collections (Conley and Gartner, in prep.). Diogenichthys atlanticus (2.9-10.6 mm SL; n = 174) This larvae was first described by Taning (1918) as Myctophum lanternatum, which was later changed to Diogenichthys atlanticus (Fraser-Brunner, 1949). Additional larval illustrations were published by Pertseva-Ostroumova

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169 (1964) and Ahlstrom (1965). Moser and Ahlstrom (1970) provided a detailed account of larval morphology including; meristic information, size at fin an photophore development, and complete illustrations of larval development. Larval morphology was later summarized by Fahay (1983) and Moser et al. (1984). This species has the most distinctive larval form of any myctophid, possessing a heavily pigmented symphyseal barbel. Gonichthys COCCO (2.8-14.6 mm SL; n = 34) Several complete life-history series of illustrations and detailed descriptions have been published for this distinctive larva (Taning, 1918; Dekhnik and Sinyukova, 1966; Shiganova, 1977) Hygophum benoiti (3.1-12.2 mm SL; n = 226) Larvae of this species were first described by Taning (1918) as Myctophum Benoiti (sic). Shiganova (1974), recognizing some of the vagaries within published larval descriptions of membe r s of the g enus, provided a detailed morphological account of Hygophum benoiti larvae. morphology was summarized by Fahay (1983). Hygophum hygomii (2.7-13.4 mm SL; n = 118) Larval

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170 These larvae were originally described by Taning (1918) under the name Myctophum Hygomi (sic). Additional illustrations of larval growth series have been published (Pertseva-Ostroumova, 1974, Shiganova, 1977). Ahlstrom (1974) illustrated a single specimen. Hygophum macrochir (3.2-7.0 mm SL; n = 24) Moser and Larvae of fi. macrochir first appeared in the literature as an illustration of a single 8.5 mm larva (Zhadova, 1969) followed by an illustration of a single 7.3 mm larva (Moser and Ahlstrom, 1974). The first complete life-history series was published by Shiganova (1975) with a detailed description of morphology. Hygophum reinhardtii (2.6-16.5 mm SL; n = 101) The first published larval figure for this species (Pertseva-Ostroumova, 1964) was erroneous, according to Moser and Ahlstrom (1970). Details on larval morphology; including meristic information, size at fin and photophore development, and complete life-history illustrations were published by Moser and Ahlstrom (1970; 1974). Summary information is also available (Fahay, 1983; Moser et al., 1984). Hygophum taaningi (2.2-11.6 mm SL; n = 240)

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171 The larvae of Hygophum taaningi were first described by Moser and Ahlstrom (1974). The description included detailed information regarding the differences between these larvae and morphologically similar fi. macrochir but only a single specimen (6.8 mm) was illustrated. Myctophum affine (2.6-10.9 mm SL; n = 444) Myctophum affine was previously not described and its similarity to the less common M nitidulum has resulted in its apparent inclusion with this species by many authors. FloresCoto and Ordonez-Lopes ( 1991) reported their pooled abundances. Although general appearance is similar, the following features separate this species from M nitidulum. The body is stouter than M nitidulum. Both species possess a pair of dorsal melanophores in the nasal region but M affine also exhibits a pair of melanophores on the anterior lobes of the forebrain. Pigmentation of the gut and jaw is also unique. Myctophum ni tidulum larvae larger than 5. 0 mm SL display a double row of melanophores along the ventral surface, from the gular region to the abdomen. Myctophum affine larvae display a single row of melanophores in this region. Myctophum nitidulum display a row of melanophores from the mandibular midline to the articular region, and from the articular region toward the operculum. In M affine, few melanophores extend beyond the articular region. Myctophum

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172 nitidulum usually displays a dorsal spot sagittally, near the base of the hindbrain. Myctophum affine usually has two markings dorsal to the hypural elements. Myctophum asperum (3.3-10.4 mm SL; n = 9) Illustrations of complete developmental series have been published by two researchers (Imai, 1958; Pertseva-Ostroumova, 1974), as have illustrations of single specimens (PertsevaOstroumova, 1964; Moser and Ahlstrom, 1974). Myctophum nitidulum (2.8-12.2 mm SL; n = 79) Larvae of this species were originally described by Moser and Ahlstrom (1970) and summary information has subsequently been published (Fahay, 1983; Moser et al., 1984). Myctophum obtusirostre (3.1-9.7 mm SL; n = 38) A single specimen was illustrated by Moser and Ahlstrom ( 197 4) A complete life-history series was developed for this study (Conley and Gartner, in prep). Myctophum selenops (2.8-8.7 mm SL; n = 37) A single specimen was illustrated by Moser and Ahlstrom

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173 ( 197 4) A complete life-history series was developed for this study (Conley and Gartner, in prep). Syrnbolophorus rufinus (4.9-12.4; n = 7) Larvae of this species have not been described. Only one species of Syrnbolophorus resides in the Gulf and Caribbean as adults (Nafpaktitis et al., 1977; Gartner et al., 1987). Because there were too few larvae collected to complete a life-history series, I assumed these to be the larvae of Symbolophorus rufinus. The genus is similar in general morphology to Myctophum larvae but the pectoral fins are aliform, whereas the pectoral fins of Myctophum larvae are not ventrally attenuated.


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