Variation in calanoid copepod resting egg abundance among lakes with different acidification histories

The maintenance of species and genetic diversity within zooplankton egg banks may be crucial to the re-establishment of zooplankton communities following historical disturbance, such as anthropogenic acidification which globally caused widespread damage to ecological communities. Despite this, no other study has described basic characteristics of zooplankton egg banks among lakes with different acidification histories, such as variation in resting egg concentration. Theoretically, habitats with frequent periods of harsh environmental conditions are expected to select for resting egg production or prolonged dormancy in zooplankton, which would increase the size of the resting egg bank in lake sediments. In this study, we compared abundances of viable and inviable calanoid copepod resting eggs among three freshwater lakes with different acidification histories. While Swan Lake underwent major chemical and biological changes from acid and metal deposition, Teardrop and Bat lakes were relatively unaffected by historical acidification and had comparatively constant, but different pH over time. We also tested the effect of age on the viability of resting eggs. As predicted, higher numbers of viable resting eggs were found in recent sediments from acid-recovering Swan Lake compared to study lakes with relatively temporally constant environments (Teardrop and Bat lakes) when the total number of eggs was held as a covariate. We detected this result in spite of similar pelagic abundances of Leptodiaptomus minutus, the dominant species in zooplankton communities of these lakes. This pattern did not necessarily hold for inviable egg concentrations since these eggs were more abundant in both Swan and Bat lakes compared to Teardrop Lake in older sediments (1939–1951, 1800s). Within study lakes, the abundance of viable resting eggs declined with increased egg age. Further study is required to test mechanisms underlying these patterns. Handling editor: S. I. Dodson