Diversity of trophic niches among herbivorous fishes on a Caribbean reef (Guadeloupe, Lesser Antilles), evidenced by stable isotope and gut content analyses

While herbivorous fishes have been widely studied due to the major ecological role they play on coral reefs, the description of their trophic niche remains challenging. In this study, we asked how 10 species of parrotfishes and surgeonfishes partition trophic resources on a Caribbean reef. The determination of trophic niches was conducted using gut and stomach content and stable isotope analyses (15N:14N and 13C:12C ratios). The contributions of food source to fish diet were calculated with concentration-dependent mixing models. Stomach content analyses distinguished two species of Acanthuridae from other fish species: Acanthurus coeruleus due to its high ingestion of fleshy macroalgae and Acanthurus chirurgus due to its high ingestion of calcified macroalgae. Acanthuridae and Sparisoma aurofrenatum presented similar diets in terms of assimilation of food resources with a high contribution of detritus and invertebrates to their diets. The diets of Sparisoma rubripinne and Sparisoma chrysopterum were more heterogeneous by comparison to the previous species. Scarus iseri, Scarus vetula, Scarus taeniopterus and Sparisoma viride appeared to share a similar trophic niche characterized by the contribution of live coral and fleshy macroalgae to their diet. The resource use among herbivorous fishes was partially related to the nutritional quality of food sources, but also to their physical structure and the capacity of fish to process them efficiently. These results showed that the ten species occupy distinct trophic niches, indicating a high functional diversity among the Caribbean herbivorous fishes.