ABSTRACT: Pearl oysters are farmed in oligotrophic tropical atoll lagoons where planktonic communities are dominated by production from cyanobacteria smaller than 2 µm. Paradoxically, the pearl oyster Pinctada margaritifera only retains particles larger than 2 µm. In this study, we assess the relative contribution of hetero/mixotrophic microbiota to the available planktonic resource. In Takapoto Atoll, picocyanobacteria are the dominant biomass (20 µg C l^-1). The carbon biomass of ciliates and dinoflagellates ranges from 1 to 24 and 0.5 to 5 µg C l^-1 respectively, with a mean of 6 µg C l^-1 for ciliates and 2 µg C l^-1 for dinoflagellates. The possible retention by P. margaritifera on a natural protist suspension was investigated. Due to its high clearance rates (ca 20 l h^-1 g^-1) the pearl oyster retained 85 µg C h^-1 g^-1 from ciliates and 65 µg C h^-1 g^-1 from dinoflagellates. Conversely, cyanobacteria were not efficiently retained by the bivalve and did not efficiently contribute to its diet. From our experiments, we concluded that hetero/mixotrophic protists rapidly and efficiently process the picoplanktonic resource towards filter-feeders, particularly pearl oysters.

KEY WORDS: Protists · Atoll lagoon · Pearl oysters · Pinctada margaritifera · Picoplankton · Trophic resource

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Published in AME Vol. 22, No. 3 (2000) on October 26
ISSN: 0948-3055. Copyright © Inter-Research, Oldendorf/Luhe, 2000