The effects of an Arctic winter on benthic invertebrates in the littoral zone of Char Lake, Northwest Territories

A method was devised for sampling the frozen benthos in the littoral zone of Char Lake, Northwest Territories, a polar lake that was studied during the International Biological Program. Temperature probes indicated that during the winter benthic invertebrates in sediments at 0.5 and 1.75 m were exposed to temperatures as low as −18 and −8 °C, respectively. Mortality in animals that had overwintered in the frozen samples ranged from 13 to 84% (mean 46%) and was attributed mostly to sample processing. With the possible exception of chironomids, no conclusive evidence was found that benthic invertebrates avoid freezing by emigrating to deeper portions of the lake. Exposure to subzero temperatures for 8 months or more increased the synchrony in development of the population of the harpacticoid Attheyella nordenskioldii and shifted its peak reproductive period by about 4 months. These changes implied increases in the population's gross production, growth efficiency, and ecological efficiency. The exposure of shallow-dwelling benthic invertebrates to subzero temperatures is a widespread phenomenon, the effects of which on life cycles and population energetics are poorly known.