Effects of Rotenone on Zooplankton Communities and a Study of their Recovery Patterns in Two Mountain Lakes in Alberta

Abstract

The devastation and recovery of the zooplankton communities were studied in conjunction with the application of rotenone to two mountain lakes in Jasper National Park. Crustacean plankters were absent for about 6 months after treatment, but rotifers and net phytoplankton were never completely absent. All crustacean species except one reached prerotenone abundance in about 3 years, probably the minimum time for recovery in these lakes.The speed of recovery is likely related to fecundity, time of reproduction, and the presence of resistant stages. Diaptomus sicilis had not reached reproductive maturity when rotenone was applied, and it was the last species to recover to its original numbers.Some species not found in samples before application were found in small numbers afterwards, probably due in part to movement from the littoral into the limnetic zone. In both lakes, blooms of small cladocerans after treatment were soon supplanted by increases in large cladoceran numbers. Most variations in composition and abundance after rotenone were likely due to changes in competition and predation pressures rather than to changes in environmental factors or to direct effects of rotenone.