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

The autotrophic ciliate Mesodinium rubrum was observed during winter and spring in saline lakes ranging in salinity from 2 to 78 ppt 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 1x10 super(4) to 3.5x10 super(5) cells/l. During the winter period, when little light penetrated the lake's ice cover, cells were most common immediately under 8x10 super(4) cells/l.