FEEDING RATES AND PRODUCTIVITY OF THE COPEPOD ACARTIA-BIFILOSA IN A HIGHLY TURBID ESTUARY - THE GIRONDE (SW FRANCE)

Acartia spp. are the dominant copepod species in the Gironde estuary, seaward of the turbidity maximum area. Acartia bifilosa develop a larg e population in spring and early summer whereas Acartia tonsa appear i n late summer. High values and high variability of chlorophyll a/suspe nded particulate matter ratio are found seaward of the turbidity maxim um area. Feeding rates of A. bifilosa were measured by fluorometry. Ph ytoplankton ingestion was found to be highly variable, between 8 to 80 % of copepod carbon body weight. Except for adult females, copepods we re heavier in summer than in winter. P/B ratios, estimated by the inst antaneous growth rate method, varied from 0.03 d(-1) to 0.14 d(-1). Th e gut contents and P/B ratios of Acartia bifilosa were related to chl a/SPM ratio. From those data, and a few obtained for A. tonsa, it is c oncluded that only in summer months phytoplankton ingestion is enough to maintain secondary production.