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Trophic behaviour of juvenile reef fishes inhabiting interlinked mangrove-seagrass habitats in offshore mangrove islets
Citation:
Vaslet, A., D. Phillips, C. France, I. Feller, AND C. Baldwin. Trophic behaviour of juvenile reef fishes inhabiting interlinked mangrove-seagrass habitats in offshore mangrove islets. JOURNAL OF FISH BIOLOGY. Blackwell Publishing, Malden, MA, 87:256-273, (2015).
Impact/Purpose:
A manuscript by Smithsonian Institution and EPA scientists examines the diets of four offshore fish species in Belize. Gut contents revealed the presence of a number of food resources from both mangrove and seagrass back-reef habitats. Stable isotope analyses were used to determine the relative importance of these two food resource origins and how that changed with growth from small juveniles to adults. Isotopic “mixing models” based on those developed by EPA scientists were used sort out the importance of food sources from the two habitats in the fish diets, calculated from the carbon and nitrogen isotopic composition of the fish and their prey. While one carnivorous species had roughly equal reliance on both habitats, the majority of food resources came from seagrass habitats for the other species. There were shifts to larger prey at higher trophic levels within these habitats as the fish grew. Application of these tools is leading to a better understanding of the importance of highly valued mangrove and seagrass habitats to Caribbean fish food webs.
Description:
Mangroves are essential fish habitats acting as shelters and nurseries, but the relative contribution of mangrove resources to fish diets relies on site-specific context and fish life history stage. Stable isotope (δ13C, δ15N) and gut-content analyses were used to investigate size-related feeding behaviour of four reef fishes (Stegastes leucostictus, Haemulon flavolineatum, Lutjanus apodus, Ocyurus chrysurus) inhabiting an offshore (non-estuarine) mangrove islet off Belize, Central America. Comparisons of isotopic niche space and Schoener diet similarity index suggested a low to moderate degree of niche overlap between fish size groups. The δ13C gradient between mangrove and seagrass prey as well as results of Bayesian mixing models revealed that sampled fishes mostly relied on seagrass-derived organic matter. Only small and large juveniles of the carnivorous species L. apodus derived a part of their diet from mangroves by targeting mangrove-associated Grapsidae crabs and fish prey, respectively. Isotopic niche shifts were particularly obvious for carnivorous fishes that ingested larger prey items (Xanthidae crabs, fishes) during their ontogeny. We conclude that mangrove-derived carbon contributed relatively little to the diets of four fish taxa from an offshore mangrove islet. The utilisation of mangrove food resources is less than expected and depends on the ecology and life history of the fish species considered.
