EFFECTS OF EXPERIMENTAL ACIDIFICATION ON ZOOPLANKTON POPULATION AND COMMUNITY DYNAMICS

We provide experimental evidence of indirect ecological changes occurring through alterations in both competitive and predatory interactions within zooplankton communities during acidification. Acidification experiments were conducted on zooplankton in 16-m3 enclosures suspended in a Precambrian Shield lake in central Ontario in order to identify mechanisms of community change. Changes in abundance, body size, egg ratio, and lipid status in zooplankton populations reflected changes in biotic interactions during acidification to pH between 5.0 and 6.0. Abundance of small cladocerans (especially Bosmina longirostris) increased following acidification despite increases in abundance or dominance of their cyclopoid predators. Increased reproduction of Bosmina, in the absence of detectable changes in edible phytoplankton biomass, suggests that this was due to competitive release from larger cladoceran species that did not survive acidification.