Assessing Low-Dose Copper Treatment for Dreissenid Mussels: Effects on Nontarget Organisms

Zebra mussels (Dreissena polymorpha), an invasive dreissenid mussel, have been established and caused considerable effects in many North American aquatic ecosystems. In response, copper-based pesticides have been used to manage zebra mussel populations. We evaluated the effects of a low-dose (60 µg Cu/L for 10 d) copper-based molluscicide for zebra mussel suppression on nontarget species in Lake Minnetonka (Minnesota, USA). Specifically, we assessed changes in four fish species, a native mussel species, adult zebra mussels, chlorophyll-a concentrations (as a proxy for phytoplankton productivity), the zooplankton community, and the benthic invertebrate community before and after treatment. Chlorophyll-a concentration increased in both the treated and reference bays 1 and 4 d posttreatment. Non-target zooplankton community composition changed in both bays over the course of this study; zooplankton abundance and diversity initially decreased in the treated bay but gradually recovered and was back to pretreatment and reference bay levels after one year. We observed no significant differences in non-target benthic invertebrate abundance or diversity between the treated and reference bays, although abundance and diversity estimates were dynamic and uncertain. Among caged non-target organisms, copper bioaccumulation was higher in both mussel species than in fish, and among fish, was highest in fathead minnow (Pimephales promelas). These findings contribute to our understanding of the potential effects of copper-based pesticides on aquatic ecosystems and provide insights for zebra mussel management.