DYNAMICS OF FISH COMMUNITIES ON REUNION FRINGING REEFS, INDIAN-OCEAN .1. PATTERNS OF SPATIAL-DISTRIBUTION

This work describes the distribution of fish communitites, including s pecies richness, abundance of individuals and trophic structures on th e four main fringing reefs of Reunion Island. Patterns are quantified on several spatial scales: an intra-reef scale and an inter-reefs scal e which includes within-reefs, between-reefs, and between-reefs and zo nes scales. The total ichthyofauna (217 species) is structured into th ree main communities - back-reef, inner reef flat and outer reef flat communities - which are influenced by the wave exposure and topographi c relief. These communities are organized in a spatial continuum rathe r than into three totally separate communities; Herbivorous (mainly ac anthurids) and omnivorous fishes (mainly pomacentrids) are the most nu merous on the inner and outer reef flats. Diurnal carnivorous (mainly mullids) and herbivorous fishes (mainly schooling juveniles) are the d ominant fishes in the back-reef zones. The low abundance of carnivorou s fishes on the reef flat, irrespective of diet, is most likely due to alterations of benthic communities (e.g. coral damage, increase in al gae populations) as a result of anthropogenic activities. The ichthyof auna of each of the four reefs is organized into the same three fish c ommunities. There is a north-south gradient of decreasing distribution of species and abundance of individuals in these communities. However , fish communities are more clearly separated on the northern reefs co mpared with those of the southern reefs. This pattern is probably due to differences in coral vitality, habitat complexity and width of the reefs. Hydrodynamic conditions, more pronounced in the south of the is land, might also lead to a higher flux of recruitment of fish larvae o n the northern reefs.