Spatial and seasonal heterogeneity of sea ice microbial communities in the first-year ice of Terre Adélie area (Antarctica)

Abstract

Spatial and temporal changes in sea ice microbial communities were investigated at 4 stations located along a south-north transect on the land-fast ice of Dumont d'Urville station area (Adélie Land, 66°40' S, 141°01' E) during the ice coverage period (April to December). A seasonal pattern was observed in microalgae, bacteria and protozoan abundance distribution. A maximum chlorophyll a concentration occurred during fall ice formation in the surface layer with the highest values at the near-shore station (100 to 215 μg l-1). A second maximum was observed before ice breaking in the bottom ice (50 to 90 μg l-1). Microalgal communities were dominated by diatoms (>86% of the total cells), mainly represented by Fragilariopsis, Nitzschia, Navicula and Pseudonitzschia species. Fragilariopsis curta was the dominant species during the first bloom whereas Fragilariopsis cylindrus, Nitzschia longissima and Tropidoneis sp. were the main contributors during the second bloom at the bottom ice core. Maximum protozoan abundance was recorded during the fall bloom in the surface layer with dominance of ciliates, which contributed more than 75 % of total cell numbers. During this period, the maximum ciliate abundance was associated with the maximum bacteria and diatom numbers and microalgal biomass. The dramatic decrease of the ice algal biomass from south to north paralleled that of the underlying water phytoplankton available for new ice incorporation. The spatial algal biomass decrease could explain the parallel decrease in the abundance of bacteria and heterotrophic ciliates through trophic interactions. © Inter-Research 2006.