Influence of persistence period of an insecticide on recovery patterns of a zooplankton community in experimental ponds.

An insecticide, carbaryl, was applied singly or repeatedly to experimental ponds in order to control the residue of the chemical, and the subsequent changes in the zooplankton community were investigated. In ponds where a single application of carbaryl, which degraded rapidly in the water, was made, cladocerans were reduced, but recovered soon and suppressed rotifers through competition. On the other hand, in ponds receiving repeated chemical applications, the treatment suppressed cladocerans for longer and induced the occurrence of abundant rotifers. The rotifer abundance after the treatment seemed to depend on the persistence period of the chemical. From these findings it can be hypothesized that applications of chemicals which have different degradation rates induce different zooplankton community structures.