Functional connectivity of coral reef fishes in a tropical seascape assessed by compound-specific stable isotope analyses
AuthorsMcMahon, Kelton W.
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AbstractThe ecological integrity of tropical habitats, including mangroves, seagrass beds and coral reefs, is coming under increasing pressure from human activities. Many coral reef fish species are thought to use mangroves and seagrass beds as juvenile nurseries before migrating to coral reefs as adults. Identifying essential habitats and preserving functional linkages among these habitats is likely necessary to promote ecosystem health and sustainable fisheries on coral reefs. This necessitates quantitative assessment of functional connectivity among essential habitats at the seascape level. This thesis presents the development and first application of a method for tracking fish migration using amino acid (AA) δ13C analysis in otoliths. In a controlled feeding experiment with fish reared on isotopically distinct diets, we showed that essential AAs exhibited minimal trophic fractionation between consumer and diet, providing a δ13C record of the baseline isoscape. We explored the potential for geochemical signatures in otoliths of snapper to act as natural tags of residency in seagrass beds, mangroves and coral reefs in the Red Sea, Caribbean Sea and Eastern Pacific Ocean. The δ13C values of otolith essential AAs varied as a function of habitat type and provided a better tracer of residence in juvenile nursery habitats than conventional bulk stable isotope analyses (SIA). Using our otolith AA SIA approach, we quantified the relative contribution of coastal wetlands and reef habitats to Lutjanus ehrenbergii populations on coastal, shelf and oceanic coral reefs in the Red Sea. L. ehrenbergii made significant ontogenetic migrations, traveling more than 30 km from juvenile nurseries to coral reefs and across deep open water. Coastal wetlands were important nurseries for L. ehrenbergii; however, there was significant plasticity in L. ehrenbergii juvenile habitat requirements. Seascape configuration played an important role in determining the functional connectivity of L. ehrenbergii populations in the Red Sea. The compound-specific SIA approach presented in this thesis will be particularly valuable for tracking the movement of species and life-stages not amenable to conventional tagging techniques. This thesis provides quantitative scientific support for establishing realistic population connectivity models that can be used to design effective marine reserve networks.
CitationMcMahon KW (2011) Functional connectivity of coral reef fishes in a tropical seascape assessed by compound-specific stable isotope analyses. Available: http://dx.doi.org/10.1575/1912/4481.
SponsorsThis thesis would not have been possible were it not for the support of many people. During my time in the MIT-WHOI Joint Program, I have been supported by an Ocean Life Institute Fellowship, a National Science Foundation Graduate Research Fellowship, and the WHOI Academic Programs Office. The research presented in this thesis was supported by an Ocean Life Institute student research grant to K. McMahon, an International Society for Reef Studies-Ocean Conservancy Coral Reef Research Fellowship to K. McMahon, and King Abdullah University of Science and Technology (KAUST) Award Nos. USA 00002 and KSA 00011 to S. Thorrold. Additional support came from the Woods Hole Oceanographic Institution, the Large Pelagics Research Center at the University of New Hampshire, the Carnegie Institution of Washington and the W.M. Keck Foundation.