Grazing impact of micro- and mesozooplankton during a spring situation in coastal waters off the Gironde estuary

The aim of this study was to characterize the grazing link between phytoplankton and zooplankton. Quantifying rates of phytoplankton utilization by micro- and mesozooplankton is an attempt to understand the control of phytoplankton populations in marine ecosystems aid the export Aux of organic matter to the depths. Samples were taken in the plume of dilution of the Gironde estuary during spring (May 1995). The mesozooplankton community was dominated by the heterotrophic dinoflagellate Noctiluca scintillans and by copepods. Our estimates showed that on average, 26% of the total primary production was grazed daily by mesozooplankton. However, the pressure exerted by microzooplankton on the primary production was estimated to be approximately four times higher. As a consequence, during this spring situation in the plume of dilution of the Gironde estuary when small cells dominated, microzooplankton represented the most important grazing community and could potentially control the growth of phytoplankton.