IMPORTANCE OF MICROZOOPLANKTONIC CRUSTACEANS IN THE COASTAL FOOD-CHAIN - BAY OF MARENNES-OLERON, FRANCE

Modelling biological processes in marine ecosystems requires a good kn owledge of the relationships between the different compartments of the ecosystems, Microzooplanktonic crustaceans are often neglected in fie ld feeding studies, due to the difficulties in identification and to t heir small size. In coastal areas, difficulties are enhanced by the gr eat quantities of particulate organic matter in the water column. Eute rpina acutifrons is the major component of the zooplankton community i n the Bay of Marennes-Oleron (south-west France) during the algal spri ng bloom (nauplii strongly dominate the copepod community). The grazin g impact of the copepod Euterpina acutifrons (microzooplanktonic and m esozooplanktonic fractions) on the algal standing stock was estimated in the Marennes-Oleron Bay during this period by means of both laborat ory experiments and field data. The results suggest that grazing press ure of the microzooplanktonic stages was similar to the pressure exert ed by the mesozooplanktonic ones, underlining the significant role of small copepod stages in marine systems in terms of grazing impact. Our results indicate that the daily grazing pressure exerted by the whole population is quite low in the Marennes-Oleron Bay (about 15% of the algal standing stock). (C) Elsevier, Paris.