A study is continuing in Lake Minnetonka this year on a potential new method to manage zebra mussel populations.
Researchers from the Minnehaha Creek Watershed District (MCWD) and the Minnesota Aquatic Invasive Species Research Center (MAISRC) are testing the use of a copper-based product to reduce the survival of zebra mussel veligers (larvae). By targeting the youngest zebra mussels, it’s hoped the overall zebra mussel population can be decreased. The study, funded by a $30,500 grant from Hennepin County, is the first known field test of its kind in the country.
"We're targeting veligers for this study for several reasons," said Dr. Michael McCartney, MAISRC Research Assistant Professor. "They're in a life stage that is more sensitive to our applications, we can lower the risk of larvae accidentally spreading through recreational boats, and we think we can significantly knock back zebra mussel populations by reducing the number of veligers in the lake."
The first year of the study, in 2016, provided a good opportunity to figure out best practices. During this second year, very low levels of a federally-approved copper-based product, EarthTec QZ, are being applied in two enclosures in Lake Minnetonka’s West Upper Lake, which has some of the largest concentrations of zebra mussels in the lake.
The study area is near the shoreline of Lake Minnetonka Regional Park and applications will occur over the course of three separate weeks through the end of July. Following each application, researchers will evaluate the impact of different concentrations of the product on the young zebra mussels.
The product is species-specific and poses no health risks to humans or other aquatic life. Recreation and enjoyment of the bay will not be impacted during the study.
“The first year of this study was a good learning year and provided us with useful baseline knowledge. In this second year, we are looking forward to building on last year’s efforts and seeing how well this method of control works,” said Eric Fieldseth, MCWD Aquatic Invasive Species Program Manager. “We are grateful for the partnership with MAISRC to better understand how to control this invasive species.”
Long term impact
Since zebra mussels were discovered in Lake Minnetonka seven years ago, they have spread throughout the lake. Because zebra mussel adults live only three to five years, they rely on veliger production to maintain their populations. Reducing veliger survival could ultimately reduce the overall population of adult zebra mussels and may be an approach to management, particularly of newly infested lakes.
Zebra mussels have long-term water quality and recreational impacts. They alter the food chain critical to fish and other aquatic life, they attach to docks, boats and other hard surfaces and their sharp shells litter beaches and lake bottoms.
The first round of trials began in June, the second round is underway and the third round is set for the week of July 17, based on conditions. The Hennepin County grant funding to support the study comes from a state appropriation for aquatic invasive species (AIS) prevention and management programs.