ABSTRACT: Predation rates of the 9 most abundant Antarctic meso- (4 copepods) and macrozooplankton (3 euphausiids, 1 hyperiid and 1 salp) species on microplankton (20 to 200 µm) were estimated using in vitro incubations during the fourth cruise of the South African Antarctic Marine Ecosystem Study (SAAMES IV) to the ice-edge region of the Lazarev Sea during austral summer (Dec/Jan) 1994/1995. Chlorophyll a concentrations during the incubations ranged between 0.187 and 1.410 µg l^-1 and were dominated by ice-associated chain-forming microphytoplankton (>20 µm) of the genera Nitzschia and Chaetoceros. The microplankton assemblages were entirely dominated by protozoans comprised of ciliates and dinoflagellates. Densities of protozoans ranged from 1375 to 2690 cells l^-1. Based on previously published results, meso- and macrozooplankton species generally consumed >120% of their minimum daily ration, i.e. minimum carbon uptake (MCU), when offered microplankton. Exceptions were Euphausia crystallorophias and Vibilia antarctica for which microplankton carbon contributed 68 and 30% of MCU, respectively. Microplankton carbon contributed between 17 and 24% of the total carbon requirements for the 4 copepod species examined and between 21 and 73% for the macrozooplankton. The daily rations of juveniles were, however, twice those of the adults, suggesting that the relative importance of microzooplankton to the daily ration of macrozooplankton shifts with life stage. Carnivory by metazoan grazers may, therefore, potentially reduce the high grazing impact of microzooplankton on the local phytoplankton stock.

KEY WORDS: Antarctica · Carnivory · Zooplankton · Microzooplankton

Published in MEPS Vol. 143 (1996) on November 14
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1996