STRUCTURE AND GRAZING IMPACT OF THE MESOZOOPLANKTON COMMUNITY DURING LATE SUMMER 1994 NEAR SOUTH-GEORGIA, ANTARCTICA

Mesozooplankton abundance, community structure and grazing impact were determined during late austral summer (February/March) 1994 at eight oceanic stations near South Georgia using samples collected with a Bon go and WP-2 nets in the upper 200-m and 100-m layer, respectively. The zooplankton abundance was generally dominated by copepodite stages C3 -C5 of six copepod species: Rhincalanus gigas, Calanus simillimus, Cal anoides acutus, Metridia spp., Clausocalanus laticeps and Ctenocalanus vanus. Most copepods had large lipid sacs. All copepods accounted for 41-98% of total zooplankton abundance. Juvenile euphausiids were the second most important component contributing between 1 and 20% of tota l abundance. Pteropods, mainly Limacina inflata, were important member s of the pelagic community at two sites? accounting for 44 and 53% of total abundance. Average mesozooplankton biomass in the upper 200 m wa s 8.0 g dry weight m(-2), ranging from 4.3 to 11.5 g dry weight m(-2). With the exception of Calanus simillimus, gut pigment contents and fe eding activity of copepod species were low, suggesting that some speci es, after having stored large lipid reserves, had probably started und ergoing developmental arrest. Daily mesozooplankton grazing impact, me asured using in situ gut fluorescence techniques and in vitro incubati ons, varied widely from <1 to 8% (mean 3.5%) of phytoplankton standing stock, and from 5 to 102% (mean 36%) of primary production. The highe st grazing impact was found northeast of the island co-incident with t he lowest phytoplankton biomass and primary production levels.