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 galeate mendotae are presented for Middle and Hannah lakes, two metal-contaminated lakes near Sudbury, Ontario, whose acidity was neutralized by additions of base in the mid-1970s. A comparison of allozyme frequencies and abundances of D. g. mendotae in Middle, Hannah, and numerous reference populations indicates that the taxon has fully recovered at both the population and genetic levels of analysis. However, the timing and pace of recovery of D. g. mendotae differed between the two Sudbury lakes. Two 21-day bioassays were conducted to examine the survival and brood production of D. g. mendotae in five treatments simulating 18 years of changes in Cu, Ni, and Cd concentrations in the lakes. The bioassays indicated that metal concentrations, i.e,, habitat quality, regulated the pace of recovery of this important zooplankton taxon in the study lakes.