MICROBIAL DYNAMICS IN COASTAL WATERS OF EAST ANTARCTICA - BACTERIAL PRODUCTION AND NANOFLAGELLATE BACTERIVORY

Bacterial production and heterotrophic nanoflagellate (HNAN) bacterivo ry were determined concurrently with measurements of abundance and bio mass at weekly intervals between 30 December 1993 and 11 February 1994 at a shallow, coastal location in Prydz Bay, eastern Antarctica. Bact erial production was measured by [H-3]thymidine incorporation and HNAN bacterivory by the uptake of fluorescently labelled bacteria. Bacteri al abundance, biomass and production ranged from 2 to 8 x 10(8) l(-1), 13 to 64 mu g C l(-1) and 8 to 14 mu g C l(-1) d(-1), respectively, w ith maximum values recorded in mid January. The HNAN community compris ed choanoflagellate, non-collared and colonial taxa, with non-collared forms dominating abundance and biomass in late January and early Febr uary. Total HNAN abundance and biomass ranged from 1.6 to 4.2 x 10(6) l(-1) and 8 to 16 mu g C l(-1) , respectively. HNAN cellular ingestion and clearance rates differed between taxa with maximum rates of 8.28 particles cell(-1) h(-1) and 9.32 nl cell(-1) h(-1) recorded for large non-collared forms. During the study period the HNAN community grazed 0.9 to 4.7 mu g bacterial C l(-1) d(-1), equivalent to 3 and 12% of b acterial biomass, and 10 and 36% of daily bacterial production; howeve r, these values are likely to be minimal estimates and grazing impact may have been higher on occasion. Choanoflagellates were responsible f or much of the grazing impact at the beginning of the study period, wh ile non-collared HNAN were the dominant grazers in late January and ea rly February. The HNAN community therefore appears to graze substantia l bacterial production in Antarctic coastal waters during the austral summer, although alternative sources of bacterial mortality are likely to be of importance.