Influence of environmental factors on the structure of coastal fish communities of Reunion Island (South-western Indian Ocean)

This work, conducted on both reef and non-reef habitats of Reunion island, represents the first study on the coastal ichthyofauna structure at the scale of the whole island. It aims at (1) describing and analyzing the dominant characteristics of fish communities, (2) identifying the main spatial patterns in the fish distribution, and then (3) interpreting the interactions between fish communities and environmental variables. Sampling was implemented using Underwater Visual Censuses (UVC) on twenty sectors distributed all along the island. coastline. Sixty-four families and 406 species were recorded. For each species identified, diet, demographic strategy, geographical distribution and associated reef or non-reef habitats were attributed. Four ichthyological clusters, characterized by their environmental variables (substrate rugosity, energy of swell, current velocity, turbidity), were identified according to their geographical location. The northern cluster was rich in planktivorous and non-reef habitat species, with a circumtropical distribution and relatively low fecundity, focusing their reproductive strategy on juvenile survival. The southern one was rich in herbivorous fish and browsers of sessile,invertehrates, coral reef habitat species with high fecundity and low juvenile survival. The eastern cluster was' composed of high proportion of south-western Indian Ocean species whereas the western one presented no ichthyological characteristic linked to any of the analysed environment variables. The comparison between reef and non-reef fish communities showed that there was a high affinity between coral reef dependent species and environmental variables such as high rugosity and coral cover, also found outside the reef areas. Although this study was limited to the outer slopes of fringing reefs, the distinction between reef and non-reef communities could be mitigated by the small area, fragmentation and degradation of coral health in Reunion Island, which promote the development of opportunistic and ubiquitous species at the expense of the characteristic species of coral reefs.