EFFECTS OF EXPERIMENTAL ACIDIFICATION ON ZOOPLANKTON POPULATION AND COMMUNITY DYNAMICS

We provide experimental evidence of indirect ecological changes occurr ing through alterations in both competitive and predatory interactions within zooplankton communities during acidification. Acidification ex periments were conducted on zooplankton in 16-m3 enclosures suspended in a Precambrian Shield lake in central Ontario in order to identify m echanisms of community change. Changes in abundance, body size, egg ra tio, and lipid status in zooplankton populations reflected changes in biotic interactions during acidification to pH between 5.0 and 6.0. Ab undance of small cladocerans (especially Bosmina longirostris) increas ed following acidification despite increases in abundance or dominance of their cyclopoid predators. Increased reproduction of Bosmina, in t he absence of detectable changes in edible phytoplankton biomass, sugg ests that this was due to competitive release from larger cladoceran s pecies that did not survive acidification.