Early zooplankton response to experimental acidification in Little Rock Lake, Wisconsin, USA
The distribution of zooplankton is influenced by habitat pH conditions. A general trend of reduced species number with higher acidity has been shown in across-lakepH gradients that can be attributed to both natural and anthropogenic causes (SPRULES 1975, ROFF \& KWIATKOWSKI 1977, YAN \& STRUS 1980, CONFER et al. 1983, BREZONIK et al. 1984). Similar patterns of reduced zooplankton diversity have been observed when a lake’s pH was experimentally lowered over a series of years (MALLEY et al. 1982, SCHINDLER et al. 1985).In contrast with the overall pattern of species reduction at lower pH, some taxa are favored by acid conditions (MALLEY et al. 1982,CHENGALATH et al. 1984). Despite the information available on the distribution of zooplankton relative to pH, however, little is known about the mechanisms by which acid conditions influence zooplankton occurrence. Here we report some early results from the Little Rock Lake Experimental Acidification Project. One major component of this project has been designed to examine the direct and indirect effects of changing pH conditions on zooplankton. Although the data we report at this time are primarily concerned with patterns of zooplankton abundance, they provide the background for more detailed, experimental analyses of the effects of changing acidity on zooplankton. Specifically, in this paper we describe characteristics of Little Rock Lake’s zooplankton community and, focusing on the abundance patterns of four dominant zooplankton taxonomic groups, a preliminary comparison between the lake’s two basins during a one-year baseline period and two years in which the North basin was acidified.