Microbial dynamics in coastal waters of east antarctica: Bacterialproduction and nanoflagellate bacterivory

Abstract

Bacterial production and heterotrophic nanoflagellate (HNAN) bacterivorywere determined concurrently with measurements of abundance and biomass atweekly intervals between 30 December 1993 and 11 February 1994 at a shallow,coastal location in Prydz Bay, eastern Antarctica Bacterial production wasmeasured by [3H]thymidine incorporation and HNAN bacterivory by the uptakeof fluorescently labelled bacteria. Bacterial abundance, biomass andproduction ranged from 2 to 8 x 108 l-1, 13 to 64 μg C l-1 and 8 to 14μg C l-1, respectively, with maximum values recorded in mid January. TheHNAN community comprised choanoflagellate, non-collared and colonial taxa,with non-collared forms dominating abundance and biomass in late January andearly February. Total HNAN abundance and biomass ranged from 1.6 to 4.2 x106 l-1 and 8 to 16 μg C l-1, respectively. HNAN cellular ingestion andclearance rates differed between taxa with maximum rates of 8.28 particlescell-1 h-1 and 9.32 nl cell-1 h-1 recorded for large non-collaredforms. During the study period the HNAN community grazed 0.9 to 4.7 μgbacterial C l-1 d-1, equivalent to 3 and 12% of bacterial biomass, and 10and 36% of daily bacterial production; however, these values are likely to beminimal estimates and grazing impact may have been higher on occasion.Choanoflagellates were responsible for inch of the grazing impact at thebeginning of the study period, while non-collared HNAN were the dominantgrazers in late January and early February. The HNAN community thereforeappears to graze substantial bacterial production in Antarctic coastal watersduring the austral summer, although alternative sources of bacterialmortality are likely to be of importance.