Stable isotope analysis reveals community-level variation in fish trophodynamics across a fringing coral reef
In contrast to trophodynamic variations, the marked zonation in physical and biological processes across coral reefs and the concomitant changes in habitat and community structure are well documented. In this study, we demonstrate consistent spatial changes in the community-level trophodynamics of 46 species of fish across the fringing Ningaloo Reef, Western Australia, using tissue stable isotope and fatty acid analyses. Increasing nitrogen (δ15N) and decreasing carbon (δ13C) isotope ratios in the tissues of herbivores, planktivores and carnivores with increasing proximity to the ocean were indicative of increased reliance on oceanic productivity. In contrast, detritivores and corallivores displayed no spatial change in δ15N or δ13C, indicative of the dependence on reef-derived material across the reef. Higher δ13C, as well as increased benthic- and bacterial-specific fatty acids, suggested reliance on reef-derived production increased in back-reef habitats. Genus-level analyses supported community- and trophic group-level trends, with isotope modelling of species from five genera (Abudefduf sexfasciatus, Chromis viridis, Dascyllus spp., Pomacentrus spp. and Stegastes spp.), demonstrating declining access to oceanic zooplankton and, in the case of Pomacentrus spp. and Stegastes spp., a switch to herbivory in the back-reef. The spatial changes in fish trophodynamics suggest that the relative roles of oceanic and reef-derived nutrients warrant more detailed consideration in reef-level community ecology.
KeywordsCarbon Ningaloo Reef Nitrogen Particulate organic matter Recycling Stable isotope analysis
F. McGregor and K. Brooks provided valuable sampling assistance. Sample grinding facilities were generously made available by P. Grierson, West Australian Biogeochemistry Centre. Isotope analysis was performed by J. Tranter, Natural Isotopes/Edith Cowan University. Fatty acid analysis was performed by S. Wang, ChemCentre, Perth. Funding was provided by a Natural Environment Research Council Advanced Fellowship (NE/B500690/1) and a grant from the British Ecological Society to SH; grants from The University of Western Australia, the Faculty of Engineering, Computing and Mathematical Sciences and the Western Australian Marine Science Institution (Node 3) to AMW; an Australian Research Council (ARC) Discovery Grant #DP0663670 to AMW et al.; an Australian Coral Reef Society Fellowship to ASJW; and CSIRO Wealth from Oceans funding to AMW and to ASJW. The authors would like to acknowledge the support provided by the Australian-American Fulbright Commission during manuscript preparation in the form of a Fulbright Western Australia Scholarship to ASJW. The manuscript was improved by comments from P. Munday and four anonymous reviewers.
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