Crustacean plankton in northeastern Ontario lakes subjected to acidic deposition

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 a major species group containing B. longirostris, D. minutus, H. gibberum, and M. edax 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 cyclopoids, Daphnidae, L. kindtii and E. lacustris and high relative abundance of D. minutus. Stepwise multiple linear regression of physico-chemical lake characteristics against percent composition of individual species failed to explain much of the variation in species proportions. However, 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.