Nova Southeastern University NSUWorks HCNSO Student Theses and Dissertations HCNSO Student Work 5-2-2018 Trophic Ecology and Parasitism of a Mesopelagic Fish Assemblage Matthew oW odstock Nova Southeastern University, [email protected] Follow this and additional works at: https://nsuworks.nova.edu/occ_stuetd Part of the Marine Biology Commons, Oceanography and Atmospheric Sciences and Meteorology Commons, Other Ecology and Evolutionary Biology Commons, and the Zoology Commons Share Feedback About This Item NSUWorks Citation Matthew Woodstock. 2018. Trophic Ecology and Parasitism of a Mesopelagic Fish Assemblage. Master's thesis. Nova Southeastern University. Retrieved from NSUWorks, . (469) https://nsuworks.nova.edu/occ_stuetd/469. This Thesis is brought to you by the HCNSO Student Work at NSUWorks. It has been accepted for inclusion in HCNSO Student Theses and Dissertations by an authorized administrator of NSUWorks. For more information, please contact [email protected]. Thesis of Matthew Woodstock Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science M.S. Marine Biology Nova Southeastern University Halmos College of Natural Sciences and Oceanography May 2018 Approved: Thesis Committee Major Professor: Tracey Sutton Committee Member: Christopher Blanar Committee Member: Tamara Frank This thesis is available at NSUWorks: https://nsuworks.nova.edu/occ_stuetd/469 Woodstock Thesis HALMOS COLLEGE OF NATURAL SCIENCES AND OCEANOGRAPHY Trophic Ecology and Parasitism of a Mesopelagic Fish Assemblage By Matthew S. Woodstock Submitted to the Faculty of Halmos College of Natural Sciences and Oceanography in partial fulfillment of the requirements for the degree of Master of Science with a specialty in: Marine Biology Nova Southeastern University April 23, 2018 i Deep-Pelagic Parasites Table of Contents Abstract ........................................................................................................................................... iv Keywords ........................................................................................................................................ iv Acknowledgements .......................................................................................................................... v List of Tables .................................................................................................................................. vi List of Figures ............................................................................................................................... viii 1. Introduction .................................................................................................................................. 1 1.1. Mesopelagic fishes ................................................................................................................ 1 1.2. Resource partitioning of fishes ............................................................................................. 1 1.3. Parasites ................................................................................................................................ 2 1.4. Food web connectivity .......................................................................................................... 5 1.5. The ecosystem of the oceanic Gulf of Mexico ..................................................................... 6 1.6. Oceanographic characteristics of the Gulf of Mexico .......................................................... 7 2. Project Aims and Significance ..................................................................................................... 7 3. Methods ....................................................................................................................................... 8 3.1. Study location and dates. ...................................................................................................... 8 3.2. Sample acquisition .............................................................................................................. 11 3.3. Specimen processing ........................................................................................................... 12 3.4. Statistical analysis ............................................................................................................... 17 4. Results ........................................................................................................................................ 18 4.1. Fish taxa examined and parasite prevalence. ...................................................................... 18 4.2. Fish feeding ecology ........................................................................................................... 24 4.3. Factors affecting endoparasitism ........................................................................................ 30 4.3.1. Parasite prevalence and abundance as a function of diet ............................................. 30 4.3.2. The differences in parasites of mesopelagic fishes ...................................................... 35 5. Discussion .................................................................................................................................. 38 5.1. Species-specific patterns of parasite infestation in mesopelagic fishes. ............................. 40 5.2. Parasite life histories ........................................................................................................... 50 5.3. Feeding guild descriptions .................................................................................................. 58 5.3.1. Copepod specialists ...................................................................................................... 58 5.3.2. Gelatinivores ................................................................................................................ 58 ii Woodstock Thesis 5.3.3. Upper-trophic level predators ...................................................................................... 59 5.3.4. Copepods and euphausiid predators ............................................................................. 59 5.3.5. Predators of copepods and other zooplankton ............................................................. 60 5.3.6. Generalists.................................................................................................................... 61 5.4. Other life history parameters affecting parasitism .............................................................. 61 5.5. Offshore movement of prey ................................................................................................ 63 6. Conclusions ................................................................................................................................ 63 7. References .................................................................................................................................. 64 Appendices ..................................................................................................................................... 75 iii Deep-Pelagic Parasites Abstract Mesopelagic (open ocean, 200-1000 m depth) fishes are important consumers of zooplankton and are prey of oceanic predators. Some mesopelagic fishes (e.g., myctophids and stomiids) undertake a diel vertical migration where they ascend to the near-surface waters during the night to feed and descend into the depths during the day to avoid predators. Other mesopelagic fishes (e.g., Sternoptyx spp.) do not vertically migrate and remain at deep depths throughout the day. While in the epipelagic zone (surface – 200 m depth), vertically migrating fishes become prey to upper-trophic level predators, such as: tunas and billfishes. Benthic fishes (e.g., macrourids) often vertically migrate as well, ascending into the pelagic zone to feed on pelagic organisms. Fishes of different depths and vertical migration habits likely have a different ecological role in food webs. The relationship between parasites and gut contents provides insights into ecological processes occurring within assemblages, as prey items are often vectors for parasites. This study examined the differences between the prey items present in the gastrointestinal cavity and parasites of 26 mesopelagic fish species in the Gulf of Mexico. Results showed that based on the proportionally dominant prey items per species, six different feeding guilds existed within this assemblage, five based on planktivory: copepodivores, predators of copepods and other zooplankton, predators of copepods and euphausiids, gelatinivores, generalists, crustacean decapodivores, and upper-trophic level predators. Larger fishes preyed on larger prey items and harbored more parasites. Sigmops elongatus exhibited an ontogenetic diet shift at 75 mm standard length, progressing from eating primarily copepods at small sizes to eating primarily euphausiids at large sizes. Compared to similar studies, this study revealed a higher parasitic infestation by trematodes, an endoparasite (parasite within the host) class often restricted to nearshore hosts, in Gulf of Mexico fishes. Helicometrina nimia, the dominant parasite of the gempylid Nealotus tripes, has not previously been recorded in hosts below 200 m depth, suggesting a foodweb pathway that transitions from nearshore to offshore. These data can be used to develop and refine models aimed at understanding ecosystem structure and connectivity. Keywords: Ecosystem connectivity, mesopelagic