Implementing a structured decision outcome for invasive mussels

Project manager: James A. Luoma, Research Fisheries Biologist, Upper Midwest Environmental Sciences Center

Funded by: MAISRC and the Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources

Project title: Copper-based control: zebra mussel settlement and non-target impacts

Project timeline: 2018-2020

Research findings:

This study tested a low-dose copper treatment to suppress zebra mussels in St. Albans Bay, Lake Minnetonka, Minnesota. Copper concentrations were maintained at 60 μg/L in the water above the thermocline for 10 days, with Robinson Bay serving as a control site. The treatment effects were measured by examining zebra mussel veliger (larval stage) abundance, juvenile settlement, benthic populations, and adult survival. Researchers also evaluated the impact on non-target organisms, such as native fish, mussels, zooplankton, and benthic invertebrates, as well as water chemistry and clarity. 

The copper treatment significantly reduced zebra mussel populations. Veliger density dropped to near zero within two weeks, juvenile settlement decreased, and adult survival was substantially impaired. However, non-target effects included reduced zooplankton abundance, lower chlorophyll a levels, and decreased survival of fathead minnows. Other impacts included copper residues in fish and mussels, declines in benthic invertebrates, and lower dissolved oxygen and water clarity. 

This study provides valuable data for evaluating low-dose copper treatments as a zebra mussel control strategy. While effective against zebra mussels, the observed effects on non-target species and ecosystem health highlight the need for careful consideration when using such treatments in aquatic environments.

Publications/data:

Luoma J.A., Barbour M.T., and Severson T.J. (2020). Data Release: Copper-based control: zebra mussel settlement and non-target impacts. U.S. Geological Survey. Data Release. https://doi.org/10.5066/P9B9NUQM.

Project manager: Diane Waller, Research Fishery Biologist, Upper Midwest Environmental Sciences Center

Funded by: MAISRC and the Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources

Project title: Assessing and refining copper-based treatment to suppress zebra mussel populations

Project timeline: 2020-2022

Research findings:

Researchers aimed to develop lake-specific, low-dose copper treatments to control zebra mussels while minimizing harm to native species and maximizing ecosystem benefits. In St. Alban’s Bay, Lake Minnetonka, two years of monitoring after a 2019 low-dose copper treatment were analyzed, and the findings were compiled into a manuscript for publication. Additional funding allowed for a third year of monitoring to better understand zebra mussel recolonization following suppression efforts. 

In Pelican Lake, trials were conducted to study the non-target impacts of copper and refine its concentration for future treatments, including the 2022 application. Although the trial did not yield valid data on veliger (zebra mussel larvae) toxicity, plans were made to repeat the experiment in conjunction with a broader bay-wide treatment. These efforts aimed to determine the lethal copper dose for veligers during acute exposures and enhance treatment effectiveness. 

Plans for a 2022 shoreline treatment in Maxwell Bay, Lake Minnetonka, were finalized in collaboration with the Minnesota Department of Natural Resources (MNDNR). Public outreach, including an open house, provided updates on the project and addressed community questions. Pre-treatment sampling in Maxwell Bay and a reference bay (North Arm) established baseline data on the aquatic community and water chemistry. Permits were secured, ensuring the treatment could proceed as scheduled.

Project manager: Diane Waller, Research Fishery Biologist, Upper Midwest Environmental Sciences Center

Funded by: MAISRC and the Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources

Project title: Assessing and refining copper-based treatment to suppress zebra mussel populations

Project timeline: 2023-2024

Research findings:

The project examined the complexities of managing zebra mussel populations in lakes and bays, emphasizing the dynamic nature of these aquatic systems. Key variables influencing treatment outcomes included lake size, organic matter levels, wetland presence, depth, abundance of aquatic plants, connections to other water bodies, and wind conditions. Despite this complexity, water temperature emerged as the most reliable indicator for treatment timing. 

A lower dose of copper proved effective for reducing veliger (larval mussel) populations, though variability across microhabitats within bays highlighted the challenges of uniform application. Sensitivity of adult zebra mussels to copper led researchers to refine treatment timing to maximize effectiveness. The optimal period was identified as the third week of July, aligning with peak water temperatures and the energy-intensive spawning season, which made the mussels more vulnerable. For resource managers, the findings suggested targeting treatments during the highest water temperatures to optimize impact. The lack of long-term monitoring before and after treatments indicates a critical need for continuous assessment to fully understand ecological impacts. The study also observed an increase in zooplankton populations following treatment, highlighting potential ecological benefits. It presented a unique opportunity to shift from an "eradication-only" mindset to an integrated pest management approach for zebra mussels. The evidence suggested that controlling populations, rather than complete eradication, could be a more realistic and achievable goal for resource managers.

Publications:

Dahlberg, A.D., Waller, D.L., Hammond, D. et al. Open water dreissenid mussel control projects: lessons learned from a retrospective analysis. Sci Rep 13, 10410 (2023). https://doi.org/10.1038/s41598-023-36522-5