Exciting findings in recent zebra mussel research
In previous management studies, copper sulfate has been used for controlling zebra mussels. In 2019, the Minnesota Aquatic Invasive Species Research Center and United States Geologic Survey partnered to study the effectiveness of low-dose copper application to control zebra mussel populations in lake ecosystems. The concentration used in the study was substantially lower than previously used in Minnesota lakes—60 parts per billion (ppb) vs. one part per million (ppm) of free copper.
The objectives of the study were to determine the eﬀectiveness of low-dose copper treatments for reducing zebra mussel populations and to monitor the response of native species. Researchers selected two similar bays in Lake Minnetonka to conduct the study—St. Alban’s Bay was treated while Robinson Bay was used as a control.
In early July 2019, the research team conducted pre-treatment assessments of zebra mussel density, native zooplankton and benthic invertebrate communities in both bays. They then began treating St. Alban’s bay to a targeted concentration of 60 ppb of free copper. The team maintained the concentration for 10 days.
Data is currently under review, and results are still preliminary; however, the study suggests that the treatment effectively reduced zebra mussel veliger density, juvenile zebra mussel recruitment, and live zebra mussel density. Potential treatment-related impacts to native species varied. Zooplankton mean density declined after exposure in the treated bay compared to an increase in the control bay. Similar trends were observed in abundance and family richness of benthic invertebrates that were collected. No treatment-related adverse impacts were observed to the native mussels 24 hours after exposure.
Post-treatment monitoring is planned for 2020 and 2021 in order to determine the long-term effectiveness of the treatment. Follow-ups will inform the need for retreatment and will help determine the recovery response of the native community.
These findings are exciting for a number of reasons. By identifying the lowest quantity of free copper needed to effectively treat zebra mussel infestations, researchers hope to reduce the cost of future treatments and limit impacts to native species. Looking forward, our researchers hope to replicate the results observed in St. Alban’s Bay in additional lakes before providing final recommendations.