Seasonal changes of Antarctic marine bacterioplankton and sea ice bacterial assemblages

Abstract

The distributions of bacterial populations in sea ice and underlying seawater were investigated on the continental shelf of the “Terre Adelie” area. A reference station was sampled weekly from January 1991 to January 1992. In winter, the survey included a minimum of six sampling layers: surface and bottom ice, brine, seawater from the interface, and at 0.5 and 2 m depth. In seawater, the total bacterial abundance ranged from 0.5 × 105 cells ml−1 in July to 6.0 × 105 cells ml−1 after ice break. Values reaching 2.5 × 106 cells ml−1 were recorded in the overlying ice cover. Mean cell volumes were twice as high in brine as in seawater. The saprophytic bacterial abundance ranged from 5.0 × 104 CFU (colony-forming units) ml−1 in some winter interface samples to less than 1.0 × 103 CFU ml−1 in most of the summer seawater samples. In sea ice a clear decreasing gradient for most of the studied bacterial parameters from the surface layers towards the bottom layer was found. The ice cover had a discernible impact on underlying seawater, but its influence was restricted to a limited interface layer.