Impact of Permethrin on Zooplankton Communities in Limnocorrals

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Abstract
A series of in situ aquatic enclosures or limnocorrals (5 × 5 × 5 m deep) was used to evaluate the impact of the insecticide permethrin (3-phenoxybenzy[(1RS)-cis,trans-3-(2,2-dimethyl-3-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate) (50.0 and 5.0 μg∙L−1 in 1979 and 5.0 and 0.5 μg∙L−1 in 1980) on the pelagic zooplankton community in a 10-ha mesotrophic lake in southern Ontario. Permethrin was acutely toxic to the macrozooplankton (Cladocera and Copepoda) at all concentrations; microzooplankton (Rotifera) showed acute toxicity only at 50.0 μg∙L−1. Despite this initial toxicity, the density of microzooplankton increased dramatically 15–20 d post-treatment in all treated enclosures, and the rotifer populations dominated the zooplankton community for 3–4 wk. The high densities of microzooplankton were attributed to their inherent reproductive capabilities when released from competition and predation pressures. Resilience of the different zooplankton taxa was variable and depended upon both the species and the exposure concentration. Diversity of zooplankton was significantly reduced in communities exposed to permethrin. The limnocorral technique has proved to be an important tool for assessment of direct and indirect impacts of pesticides on and probable recovery of a zooplankton community under natural conditions.