Impact of the oyster Crassostrea gigas on a microbial community in Atlantic coastal ponds near La Rochelle

• Published in: Aquatic Microbial Ecology
• Main Authors: Dupuy, Christine, Pastoureaud, Annie, Ryckaert, Mireille, Sauriau, Pierre-Guy, Montanié, Hélène
• Other Authors: LIttoral ENvironnement et Sociétés - UMRi 7266 (LIENSs), Université de La Rochelle (ULR)-Centre National de la Recherche Scientifique (CNRS), Centre de Recherche sur les Ecosystèmes Marins et Aquacoles (CREMA), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Centre National de la Recherche Scientifique (CNRS), LER/LR, Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Laboratoire de Biologie et Environnement Marin (LBEM), Université de La Rochelle (ULR)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2000
• Subjects: microbial food web; bacteria; Bivalve; oysters; food source; coastal pond; trophic link; protists; [SDV.MP]Life Sciences [q-bio]/Microbiology and Parasitology; [SDV.EE]Life Sciences [q-bio]/Ecology; environment; [SDE.BE]Environmental Sciences/Biodiversity and Ecology; Crassostrea gigas
• Online Access: https://hal.archives-ouvertes.fr/hal-01248027; https://hal.archives-ouvertes.fr/hal-01248027/document; https://hal.archives-ouvertes.fr/hal-01248027/file/dupuy%20et%20al%202000a.pdf; https://doi.org/10.3354/ame022227

International audience To assess the in situ impact of oysters, Crassostrea gigas, on planktonic protist and bacteria communities and the potential contribution of protozoa to their food resource intake, the abundance and the diversity of protists and bacteria were followed in 2 Atlantic coastal ponds, with and without oysters. The protist biomass in such ponds was high, with a maximum in spring of 982 μg C l-1 and a minimum in winter of 179 μg C l-1. Whatever the season, the presence of oysters (20 m-2 corresponding to on average 23 mg dry weight m-2) induced a significant decrease in > 5 μm protist abundance. On the contrary, planktonic organisms < 5 μm, such as Chlorophyta flagellates and bacteria, developed similarly in both ponds. It can be assumed that such a depletion in micro-sized protists was especially related to the grazing activity of C. gigas, which efficiently retains > 5 μm particles. In spring, oyster grazing triggered dramatic changes in the protist community by lowering the taxonomic diversity. In autumn and winter, the presence of oysters deeply influenced the taxonomic structure of the protist communities: > 5 μm protists could only develop in the control pond, whereas they were removed by filtration into the oyster pond; on the contrary, < 5 μm protists that were not retained, were favoured in the oyster pond. The set of results showed that hetero/mixotrophic protists represent an important potential resource in coastal ponds: flagellates > 5 μm were the main protist resource for C. gigas; ciliates represented the second resource with a substantial contribution in autumn; diatoms and dinoflagellates, though efficiently removed represented a weak carbon resource. Our study supports the hypothesis that oysters may access to the strong bacterioplanktonic production through hetero/mixotrophic protists, which would thus allow the transfer of carbon from the microbial loop towards C. gigas.