Seasonal changes in microbial biomass in the first-year ice of the Terre Adélie area (Antarctica)

Abstract

The coastal sea ice in the vicinity of Dumont d'Urville station, Antarctica (66° 40' S, 140° 01' E) supports a diverse microbial community. To investigate seasonal changes in bacterial, microalgal and protozoan biomass during the ice-coverage period, a survey was conducted on fast ice in the continental shelf of Terre Adelie. A reference station was sampled twice a month from April to December 1997. In April and May, during sea ice formation, the autotrophic biomass reached rela- tively high levels ranging from 400 to 800 mgC m -3 in the subsurface ice. A second increase reach- ing 1500 mgC m -3 in mid-December occurred in early summer in the bottom ice layer. Bacterial bio- mass ranged from 200 mgC m -3 in May. Maximal levels of bacterial biomass were detected during ice formation and just before the summer thaw. Total pro- tozoan biomass increased from May to July. Maximum protozoan biomass (31.8 mgC m -3 ) occurred in the surface ice layer in July. Except for during a short period (late May to early June), ciliates were dominant, accounting for 50 to 77% of the total protozoan biomass. During the ice-covered period, phototrophic biomass was always dominant. Microalgal biomass contributed on average 80.6% of total biomass whereas bacterial and protozoan biomass accounted for only 16.4 and 3%, respectively. Despite their low biomass, protozoa seem to play a major role in bacterial regulation.