Effects of temephos on zooplankton communities in enclosures in a shallow eutrophic lake

An organophosphorus insecticide, temephos, was applied to large-volume (105 m3) enclosures set up in a shallow eutrophic lake. Application of the chemical at a target concentration of 500 microg litre(-1) eliminated almost all zooplankters. No recovery of cladocerans was evident at the termination of the experiment (47th day after the treatment). Copepods showed a slight recovery after having been absent for 26 days in one enclosure and 40 days in another. The residual chemical remaining in the water until the final day may have suppressed the recovery of the crustacean zooplankters. The rotifer community was reconstructed 16-20 days after the treatment. However, the species composition of this community differed from that of the rotifer community in the control enclosures. Rotifer species might therefore show differences in susceptibility to temephos.