Microspatial Variability Inside Epilithic Algal Communities within Territories of the Damselfish Stegastes nigricans at La Réunion (Indian Ocean)

Abstract

Species composition and spatial variability inside algal turf communities within territories of the damselfish Stegastes nigricans have been studied in a shallow reef flat environment of the Saint Gilles-La Saline reef complex, at La Réunion Island. The sampling of 50 small portions (2 cm long) of staghorn coral Acropora branches and accurate identification and quantification of algal species under a dissecting microscope provided a list of 19 species. Green algae Enteromorpha clathrata and Cladophora socialis and red algae Anotrichium tenue and Gelidiopsis intricata were the most abundant species in the turfs overgrowing Acropora coral branches. A correspondence analysis applied to the samples revealed three major groups of species characterised by (1) Enteromorpha clathrata , (2) Cladophora socialis , and (3) Gelidiopsis intricata . A gradient has been observed from Enteromorpha clathrata turfs usually occurring at the apical parts of the coral branches, to Gelidiopsis intricata turfs present at the basal parts of the branches. The algal composition of the gut contents of Stegastes nigricans was analysed and compared to the algal composition in the field. The feeding selectivity of the fish was established for several algal species. We suggest that Enteromorpha clathrata -dominated turfs correspond to initial aspects of algal colonisation of recently dead corals, while Gelidiopsis intricata -dominated turfs correspond to mature communities; Cladophora socialis -dominated turfs would correspond to the most intensively grazed turfs.