ABSTRACT: 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 (December/January) 1994-1995. During the survey, the phytoplankton size composition shifted from a community dominated by nano- and picophytoplankton (<20 µm) during the first grid to one dominated by microphytoplankton (>20 µm) during the second grid. Total areal production during the first grid was generally dominated by nanophytoplankton and ranged between 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 phytoplankton stock or between 33 and 94% of the potential phytoplankton production per day during the first grid, and between 0.5 and 8% of the initial phytoplankton stock or between 9 and 25% of the potential phytoplankton production per day during the second grid. The grazing impact of meso- and macrozooplankton during the first grid corresponded to <0.5% of chlorophyll stock or <23% of the daily primary production. During the second grid, the grazing impact of meso- and macrozooplankton 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 seasonal ice retreat is largely determined by the size structure of the phytoplankton.

KEY WORDS: Southern Ocean · Marginal Ice Zone · Phytoplankton production · Zooplankton grazing impact

Published in MEPS Vol. 149 (1997) on April 10
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1997