DYNAMICS OF THE PLANKTON COMMUNITIES OF THE LAZAREV SEA (SOUTHERN-OCEAN) DURING SEASONAL ICE MELT

Size-fractioned primary production and zooplankton grazing impact were estimated along a repeat grid during seasonal ice melt in the Lazarev Sea aboard the MV 'SA Agulhas' (voyage 77) in austral summer (Decembe r/January) 1994 1995. During the survey, the phytoplankton size compos ition shifted from a community dominated by nano- and picophytoplankto n (<20 pm) during the first grid to one dominated by microphytoplankto n (>20 pm) during the second grid. Total areal production during the f irst grid was generally dominated by nanophytoplankton and ranged betw een 133 and 356 mg C m(-2) d(-1). During the second grid survey, total areal production was higher, ranging between 263 and 400 mg C m(-2) d (-1). Protozoan grazing removed between 0.5 and 31% of the initial phy toplankton stock or between 33 and 94% of the potential phytoplankton production per day during the first grid, and between 0.5 and 8% of th e initial phytoplankton stock or between 9 and 25% of the potential ph ytoplankton production per day during the second grid. The grazing imp act of meso- and macrozooplankton during the first grid corresponded t o <0.5% of chlorophyll stock or <23% of the daily primary production. During the second grid, the grazing impact of meso- and macrozooplankl on was higher, removing on average 1.12% of integrated chlorophyll or 28.7% of daily production. These results suggest that the partitioning of carbon between the various size classes of zooplankton during seas onal ice retreat is largely determined by the size structure of the ph ytoplankton.