Abstract

Herbivorous fishes control the algal dynamic on coral reefs and are widely exploited by Caribbean fisheries. Among this guild, acanthurids are routinely seen in multi-specific foraging groups and are globally considered as a homogenous functional group. In fact, the different species can display various dietary patterns. In this study, we stated the hypothesis that the formation of such multi-specific groups can be explained by a difference of trophic niche among the acanthurid species. To investigate this fact, a study was conducted on three species of Acanthuridae (Acanthurus coeruleus, A. chirurgus and A. bahianus), common on the reefs of Guadeloupe. Stomach content analyses were coupled with stable isotope analyses (13C/12C and 15N/14N ratios) to determine their trophic niches. Contributions of sources in fish diet were estimated using a mixing model. Among the three species, A. coeruleus showed the most diversified diet and was the only species to ingest benthic invertebrates. Food items were assimilated proportional-ly to the quantity ingested. A. chirurgus ingested an important amount of calcareous macroalgae that was not assimilated proportion-ally to the quantity ingested. Finally, A. bahianus presented an important amount of unidentified matter in its stomach contents and assimilated a high proportion of fleshy macroalgae. These three acanthurids could then coexist in the same foraging group because they ingest and assimilate the food items in different proportions, avoiding competitive interactions for food resources.

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