DEMOGRAPHIC AND GENETIC-EVIDENCE OF THE LONG-TERM RECOVERY OF DAPHNIA-GALEATA MENDOTAE (CRUSTACEA, DAPHNIIDAE) IN SUDBURY LAKES FOLLOWING ADDITIONS OF BASE - THE ROLE OF METAL TOXICITY

Twenty-year records of changes in abundance of Daphnia galeata mendota e are presented for Middle and Hannah lakes, two metal-contaminated la kes near Sudbury, Ontario, whose acidity was neutralized by additions of base in the mid-1970s. A comparison of allozyme frequencies and abu ndances of D. g. mendotae in Middle, Hannah, and numerous reference po pulations indicates that the taxon has fully recovered at both the pop ulation and genetic levels of analysis. However, the timing and pace o f recovery of D. g. mendotae differed between the two Sudbury lakes. T wo 21-day bioassays were conducted to examine the survival and brood p roduction of D. g. mendotae in five treatments simulating 18 years of changes in Cu, Ni, and Cd concentrations in the lakes. The bioassays i ndicated that metal concentrations, i.e., habitat quality, regulated t he pace of recovery of this important zooplankton taxon in the study l akes.