Overwintering populations of Mesodinium rubrum (Ciliophora: Haptorida) in lakes of the Vestfold Hills, East Antarctica

The autotrophic ciliate Mesodinium rubrum Lohmann was observed during winter and spring in saline lakes ranging in salinity from 2 to 78& in the Vestfold Hills, Antarctica. The ciliate remained active during winter, and contained chlorophyll even though the level of light available for photosynthesis was minimal. No evidence of encystment as a means of survival during winter was observed. A seasonal study in one of the lakes, Ace Lake, revealed that M. rubrum was present throughout the year at abundances ranging from 1]104 to 3.5]105 cells l~1. During the winter period, when little light penetrated the lake‚àövâ‚àÜv¿‚àövá‚Äös ice cover, cells were most common immediately under the ice at 2 m, where cell numbers were typically 8]104 cells l~1.