Douglas County Lakes Association President Steve Henry said he was disappointed by the low turnout in last week's presentation of the connection between weedy lakes and zebra mussels.
Given the weed problems in local lakes this summer, he said, he thought more people would want to find out the causes.
“I think the vast majority of people just look at zebra mussels as a nuisance," he said. "They have no idea how much the zebra mussels change the whole lake ecology.”
In Minnesota, zebra mussels are known to inhabit more than 500 water bodies. In Douglas County, they have been found in 46 lakes, including biggies like Ida, L'Homme Dieu, Carlos, Miltona and Mary, mostly discovered in the past decade.
Meg Duhr, research outreach specialist for the Minnesota Aquatic Invasive Species Research Center, told about 20 people at the Oct. 13 meeting that zebra mussels are bad news. Not only can they cut peoples' feet, but they filter the water, making it so clean that sunlight can penetrate deeper, prompting the growth of aquatic plants where none had grown before.
They also disrupt the food chain for walleye and other fish. Fish stocking by the DNR has masked the problem, but already young walleye aren't growing as fast as they should, she said. First-year walleye are 25% smaller in lakes infested with both zebra mussels and spiny water flea, another invasive species, she said.
“That really matters," she said. "The smaller you are, the more risk you are in being eaten by other fish." Smaller walleye also have smaller mouths, with fewer choices of what to eat.
One study in Michigan in the 1990s found that zebra mussels were able to filter the inner part of Saginaw Bay 1.3 times a day. Zebra mussels came from the Baltic region of Eurasia to the U.S. in the ballast water of ships and have spready rapidly. Their larva, called veligers, can't be seen by the naked eye, and they're spread most frequently by watercraft, Duhr said. Earlier this summer, they were found in imported moss balls after they had been sold to customers for use in aquariums, which Duhr said happened because federal inspections workers are underfunded.
"They become mature early on and are capable of explosive growth,” Duhr said. "We think of them as kind of an ecosystem engineer. ... They have major cascading impacts up and down the food web.”
And if you're noticing that lake bottoms are getting slimier from algae, that's no accident either, as zebra mussels filter everything except algae. To drive home the point, Duhr showed a video clip of a zebra mussel spitting out harmful algae.
Algae proliferation is complicated, Duhr said, but it is worsened by the presence of zebra mussels. The publicly-funded center she works for is trying to find a science-based solution to zebra mussels. The most promising research is tinkering with the species' RNA to prevent it from being able to form shells or other body parts, rendering it incapable of survival. A solution like that would only affect the zebra mussels themselves and not other aquatic species, she said. But it remains years away from application.
Zebra mussels do scrape easily off boats and docks, and can be composted in a garden, or transported in a closed container to a landfill, Duhr said.
Meanwhile, Henry said Alexandria area lakes are in trouble and have declined over the past five years. There are places where people can't get their boats from their lifts to open water because of weed growth, and he has noticed a dark-gray algae growing on the lake bottom.
“My grandchildren will no longer swim in L’Homme Dieu,” he said.
The chain of lakes is such a draw for the area that he wishes more people would take an interest in keeping them healthy. He said he appreciated Duhr's talk.
“There is no easy solution, but the organization she represented has made progress,” he said. “I think science and further research is where the answer is going to be and I strongly support their organization.”