Résumé
Suspended bivalve culture (e.g. longlines) transfers benthic biomass including bivalves and various epibionts toward the water column, creating strong trophic interactions with the planktonic compartment. Trophic interactions are of central interest for ecologists, yet not well understood in coastal lagoon food webs, especially in tropical areas. Using stable isotope (SI) analyses, this study explored the trophic relationships between marine particulate organic matter (POM), pearl oysters and epibionts, in two contrasted production areas in French Polynesia. Different size classes of POM (0.7-2 mu m, 2-20 mu m, 20-80 mu m, 80-250 mu m and \textgreater250 mu m) were well discriminated both by their delta C-13 and delta N-15 signature and results showed a low dietary overlap between pearl oysters and epibionts, likely due to assimilation of large particles in greater proportion by pearl oysters. Pearl oyster diet may vary in time in relation with variations of the basal trophic resource and selective feeding, such that their isotopic signature is more variable compared with that of epibionts. Pearl oysters and epibionts might alter nutrient cycling in a different way as reflected by their different tissue C:N.