Influence of reef to ocean distance on coral reef fish assemblages in New Caledonia

Coral reef fish are bound to the pelagic environment throughout their larva l stage, although they spend most of their adult life on reefs. Thus, the m orphology of a lagoon and the location of a reef within the lagoon may infl uence the nature of its fish assemblage. Because of its asymetrical shape, the SW lagoon of New Caledonia allows us to test such a hypothesis. Several fringing reefs located 4-34 km from the open ocean were compared with one another. No influence of the reef-ocean distance could be found on the glob al values of diversity, density or biomass. However, presence-absence data of the 343 taxa encountered are related to this distance. Similarly, ecolog ical structures based on diet, size and mobility of fish present strong cor relations with reef-ocean distance. Thus, the major effects of an increase in reef-ocean distance concern both taxinomical and ecological structures. Suggested explicative hypotheses are linked to the fish feeding habits clos ely related to the environment but also to their utilisation of space. Terr itorial behaviour seems indeed to be important in structuring reef fish ass emblage. ((C) Academie des sciences / Elsevier, Paris.)