SPATIAL PATTERNS IN BIODIVERSITY OF A FRINGING-REEF COMMUNITY ALONG OPUNOHU BAY, MOOREA, FRENCH-POLYNESIA

Opunohu Bay, located on the North coast of Moorea Island (Society Arch ipelago), is approximately 3 km long and partially edged by a small fr inging reef no wider than 100 m. The main objective of this first quan titative survey concerning bays in French Polynesia, was to examine th e spatial pattern of diversity of the macro-benthic fringing reef comm unity between the land-end and the ocean-end of the bay. This study co nsidered the conspicuous benthic organisms (Cnidaria, Echinodermata, M ollusca, Porifera and seaweeds) more than 1 cm long and attached to th e substratum. A strong gradient in percent cover and species richness was found for corals and echinoderms, between the land-end where the t wo taxa are almost absent and the ocean-end where they are dominant. S pecies richness of macroalgae, molluscs and sponges, and macroalgal co verage are high in the middle part of the bay. At the ocean-end, domin ance (in terms of coverage) of the coral genus Porites is responsible for the decrease in diversity (H'c) and evenness (J'c). Factorial corr espondance analysis and ascending hierarchical clustering of species c omposition correspond to the land-end, the middle part and the ocean-e nd. The absence of corals and echinoderms at the land-end, where only a few tolerant macro-benthic species occur, can be explained by low sa linity and high turbidity which occur after heavy rains during the wet season.