REGULATION OF ZOOPLANKTON COMMUNITY STRUCTURE OF AN ACIDIFIED LAKE BY CHAOBORUS

To test the hypothesis that the structure of zooplankton communities of acidified, fish-free lakes can be regulated by predation from larval Chaoborus, the rates of production of the principal prey species of Chaoborus in Swan Lake, a small, fish-less, acid lake near Sudbury, Canada, were compared with their estimated rates of consumption by Chaoborus. The production of Bosmina longirostris, the major crustacean zooplankter in the lake, rarely exceeded its apparent rate of loss to Chaoborus. In contrast, the production rate of Keratella taurocephala, the dominant rotifer in Chaoborus diets, virtually always exceeded the rate at which it was consumed. The unusually small contribution of Crustacea to total zooplankton biomass in the lake could be attributed to predation by Chaoborus. While Chaoborus can regulate zooplankton community structure in acidified, fish-free lakes, the frequency of occurrence of such control remains uncertain.