Summer feeding activities of zooplankton in Prydz Bay, Antarctica

Grazing of dominant zooplankton copepods (Calanoides acutus. and Metridia g erlachei), salps (Salpa thompsoni) and microzooplankton was determined duri ng the austral summer of 1998/1999 at the seasonal ice zone of the Prydz Ba y region. The objective was to measure the ingestion rates of zooplankton a t the seasonal ice zone, so as to evaluate the importance of different grou ps of zooplankton in their grazing impact on phytoplankton standing stock a nd primary production. Grazing by copepods was low, and accounted for less than or equal to 1% of phytoplankton standing stocks and 3.8-12.5% of prima ry production for both species during this study, even the ingestion rates of individuals were at a high level compared with previous reports. S. thom psoni exhibited a relatively high grazing impact on primary production (72% ) in the north of our investigation area. The highest grazing impact on phy toplankton was exerted by microzooplankton during this investigation, and a ccounted for 10-65% of the standing stock of phytoplankton and 34-100% of p otential daily primary production. We concluded that microzooplankton was t he dominant phytoplankton consumer in this study area. Salps also played an important role in control of phytoplankton where swarming occurred. The gr azing of copepods had a relatively small effect on phytoplankton biomass de velopment.