Influence ofChaoborusdensity on the effects of an insecticide on zooplankton communities in ponds

摘要

Zooplankton communities with a high or low density ofChaoboruslarvae were established in outdoor concrete ponds, to which a carbamate insecticide, carbaryl, was applied at 0.1 or 0.5 mg l−1. The lower concentration of the chemical was harmful only to Cladocera. The higher concentration damagedChaoborus, Copepoda, and some rotifer species, as well as Cladocera. In the ponds with a low density ofChaoborus, chemical application altered the cladoceran community from dominance byDaphniato that byBosminaandMoina. In the ponds with a high density ofChaoborus,Chaoborusexcluded cladocerans from the zooplankton community presumably by predation, and supported the dominance of rotifers. Cladocera did not recover after application of the chemical, even whenChaoboruswas eliminated by the higher concentration of chemical. The relatively rapid recovery ofChaoborusseemed to interrupt the recovery of Cladocer