Chaoborus americanus predation influences Bosmina mucro lengths in fishless lakes

Size attributes of the cladoceran taxon Bosmina are known to vary in response to the intensity and dominant type of predation. Using a paleolimnological approach, we tested the hypothesis that Bosmina size structure differs between fishless lakes and those with presumed populations of planktivorous fish. We measured sedimentary remains of Bosmina longirostris and assessed assemblage structure of the gape-limited invertebrate predator Chaoborus within the surface sediments of 29 lakes in remote, northwestern Ontario, Canada. Mean B. longirostris mucro, antennule, and carapace lengths did not differ significantly between lake predation categories. However, within fishless lakes, a significant (r = 0.68, P = 0.01) positive correlation was apparent between B. longirostris mucro length and Chaoborus americanus percent abundance. We thus suggest that B. longirostris mucro length may be sensitive to C. americanus predation, however further information on the interactions with predators is needed.