Résumé
In the context of marine environmental management, an important demand exists to develop indicators for increasing threats and actual or potential conflicts of uses. The implementation of the European Water Framework Directive (WFD) offers an example in which a set of indicators need to be defined to classify water bodies with the general aim of reaching a good status by 2015 for all continental and coastal bodies of water in Europe and ultra peripherical regions like La Reunion Island. Little is know on the performance of such indicators in tropical coral reefs ecosystems that are subjected to increasing pressures from anthropogenic activities. Since the 1980s, degradation of La Reunion coral reefs was observed frequently (decrease in coral cover, algae blooms). Both top-down and bottom-up interactions, in terms of grazing by herbivores and nutrient availability, have been shown to be important factors to algae overgrowing. The nutrients in the submarine groundwater discharge (SDG) derived from anthropogenic sources (due to increased population growth and urbanization of the watershed) are pointed in La Reunion Island. In this context, the multi-disciplinary program "EUTROLAG" has been developed with all local research partners to reach various objectives: (a) defined the pressures from the watershed (isotopic and pollutants analysis) (b) characterised eutrophication levels (c) evaluated the impact of the eutrophication on benthic community by focusing on overgrowing algae and (d) defined relevant < health reef> indicators essential for coral reefs management. Different sites (Saint Gilles, Saint Leu, Etang Sale and Saint Pierre) were surveyed during 8 months measuring multiple water quality parameters and monitoring the benthic community (corals, algae, herbivores and filter feeders) using transects, transect-belts and photoquadrats. The results could give powerful tools for tropical coastal management.