Diet of spiny lobsters from Mahé Island reefs, Seychelles inferred by trophic tracers

Spiny lobsters (Panulirus longipes, P. penicillatus and P. versicolor) are an important resource in Seychelles, where they inhabit coastal carbonate and granite reefs that have been impacted by multiple coral bleaching events over the past two decades. Little is known about their biology and ecology in this region. Interspecific competition for food resources was previously suggested, but no quantitative data on the diet of spiny lobsters were available. Using carbon and nitrogen stable isotope compositions and fatty acid profiles of three spiny lobster species and their potential prey, a Bayesian mixing model for diet estimation was applied to compare the diet proportions of spiny lobsters among species and between reef types (carbonate and granite reefs). Model outputs suggested the three lobster species consume mainly crustaceans (Anomoura hermit crabs; half of the diet), then Echinoidea (sea urchins), algae and molluscs. P. versicolor was found to consume slightly more molluscs and algae than the two other studied species, which was consistent with its lower trophic level (2.4 vs 2.8 for the two other species). Trophic level did not increase with carapace length of spiny lobsters, but large individuals had higher carbon isotopic values suggesting that they might feed closer to the coast or more on detritus feeders than their smaller congeners. Diets of spiny lobsters were fairly similar between carbonate and granite reefs, except that lobster inhabiting granite reefs consumed more sea urchins. While our overall findings were consistent with gut contents of Panulirus spp. from other world regions, they should be confirmed, as the discrimination of several prey based on trophic tracers was low, which increased mixing model uncertainty.