GRAZING IMPACT OF COPEPODS AND SALPS ON PHYTOPLANKTON IN THE ATLANTICSECTOR OF THE SOUTHERN-OCEAN

During the SO-JGOFS-Polarstern cruise in October/November 1992, grazin g of the dominant calanoid copepods (Calanoides acutus, Calanus propin guus and Rhincalanus gigas) and of Salpa thompsoni was determined. Cal anoides acutus and R. gigas were very abundant in the Polar Frontal re gion (PFr). Calanus propinquus was abundant at the ACC-Weddell Gyre Bo undary (AWE). Grazing by copepods was very low and accounted for less than 1% of the primary production (PP) for all three species. Salpa th ompsoni occurred in swarms in the southern part of the Antarctic Circu mpolar Current (ACC) where its ingestion rates accounted for more than 100% of the PP. We conclude that grazing by copepods had a negligible effect on build-up of the phytoplankton biomass recorded in the PFr a nd-to a much lesser extent-at the AWE, whereas high grazing pressure o f S. thompsoni was likely to have constrained phytoplankton biomass le vels in the ACC. (C) 1997 Elsevier Science Ltd.