The potential effects of a small Chaoborus species (C. punctipennis) on the zooplankton of a small eutrophic lake

Abstract

The potential effects of Chaoborus punctipennis larvae on zooplankton were assessed bi-weekly and during three in situ enclosure experiments in a small eutrophic lake between May and September, 1991. The in situ enclosures consisted of replicated low, intermediate and high Chaoborus treatment densities, compared to natural lake densities. Due to large changes in Chaoborus densities during all three experiments, treatment effects were assessed by correlation analysis, using the calculated mean Chaoborus density for each enclosure. In the lake, Chaoborus preyed primarily on rotifers and the naupliar stages of cyclopoids and calanoids throughout the study. Only one statistically significant (p<0.05) relationship between Chaoborus and zooplankton densities was found to exist, between Chaoborus and total zooplankton densities, during the first enclosure experiment. The lack of statistically significant relationships between Chaoborus and individual prey group densities occurred despite the fact that Chaoborus densities were enhanced up to 20 times the lake density during one of the enclosure experiments. These results contradict the strong impacts of large Chaoborus species documented in previous studies. Chaoborus punctipennis may be too small to have a significant predation impact on the zooplankton.