Grazing of phytoplankton by copepods in eastern Antarctic coastal waters

Chlorophyll a, primary productivity and grazing by copepods on phytoplankton were measured in the upper water column during the summer of 1994/1995 at a coastal site near Davis Station, East Antarctica. Chlorophyll a was at a maximum in mid-December, then dropped markedly as the coastal fast ice melted and broke-out. Phytoplankton biomass increased again from mid- to late-February. Copepods accounted for at least 65% of zooplankton biomass in the water column before sea ice break-out, whereas larval polychaetes and ctenophores dominated after ice break-out. Oncaea curvata was the numerically dominant species throughout the study. The highest grazing rate (8.7 mg C m(-3) d(-1)) was recorded on 21 December when O. curvata accounted for 64% of the total. Grazing had decreased markedly by 28 December (0.9 mg C m(-3) d(-1)); again O. curvata accounted for over 50% of the total ingested. Copepod grazing increased after ice break-out until the last experiment on 20 February (similar or equal to 5 mg C m(-3) d(-1)). The main species responsible for grazing during this period were O. curvata, Oithona similis, Calanoides acutus and unidentified copepod nauplii. It was estimated that copepods removed between 1 and 5% of primary productivity.