Recovery of Zooplankton Communities to Whole-Lake Disturbance

Community assembly following disturbance is a key process in determining the composition and function of the future community. However, replicated studies of community assembly at whole ecosystem scales are rare. Here is described a series of whole-lake experiments in which the recovery of zooplankton communities is tracked following an ecosystem-scale disturbance. Fourteen lakes in eastern Washington were chosen: seven lakes were treated with rotenone, while the remaining seven were reference. Each lake was monitored up to six months before and one to two years after the rotenone treatments. Zooplankton tows were taken monthly, at a shallow, intermediate, and deep site in each lake, and were later enumerated and identified. A depth profile of environmental variables was taken at the deepest site. Community responses following disturbance were assessed using coarse metrics of abundance and diversity, community composition measures, and the relative importance of species traits was assessed by grouping taxa into functional groups. Communities were considered recovered if there was no significant difference between treatment and reference in zooplankton community metrics of abundance, diversity, and composition. There was a steep decline in the abundance and diversity of the zooplankton community post-treatment. In many of the lakes, cyclopoid copepods, the group with a unique dormancy strategy, were the first group to recover, remained dominant for a few months, and may have exhibited priority effects advantages. Calanoid copepods were the slowest group to recover, perhaps due to their slow rate of development. There were varying recovery times and patterns between lakes, potentially based upon geographic location and severity of the winter season. These findings suggest that dormancy strategies, rate of development, and abiotic conditions following disturbance may be important in helping to understand recovery processes. Results of this study may give insight to disturbance ecology and the relative importance abiotic versus biotic characteristics that structure post-impacted communities