Water quality - crustacean plankton relationships in northeastern Ontario lakes

During the summer of 1981, crustacean plankton was sampled in 249 northeastern Ontario lakes, including a large proportion of acidic lakes. Species cluster analysis showed that overall, the lakes were typified by a major species group containing B. longirostris, D. minutus, H. gibberum and M. edax which was common to most lakes. Two species subgroups most associated with more productive waters (D. retrocurva, D. oregonensis, T. p. mexicanus and Diaphanosoma sp.) and less productive waters (D. longiremis, C. scutifer, D. g. mendotae, C. b. thomasi, E. longispina and E. lacustris) in the study area were identified. Acidic lakes were characterized by reduced numbers of species related to declines in the importance of cyclopoida, Daphnidae, L. kindtii and E. lacustris and high relative abundance of D. minutus. The observed general community alterations (ie. apparent shift from larger (Daphnidae) to smaller (D. minutus) grazers and scarcity of predatory plankton) may have important implications to energy cycling in acidic lakes. Stepwise multiple linear regression analysis of physico-chemical lake characteristics against percent composition of individual species failed to explain much of the variation in species proportions, accounting for on average, only 11% of the variation among near-neutral lakes and 25% in highly or slightly acidic lakes. Of the limnological characteristics considered, variables related to lake thermal structure were most frequently the primary correlates with species proportions in near-neutral lakes while in acidic lakes the best statistical predictors of species percent composition were most often variables directly related to lake acidity.