Citizen sleuths use DNA traces to hunt for zebra mussels in Minnesota lakes

Pulling on a pair of rubber gloves, Carrie Ruud waded into Clear Lake with a plastic bottle and a mission: search for the DNA of zebra mussels, the invasive pest that’s infested lakes across Minnesota.

Back on shore, Ruud pumped the water she collected through a filter. Using tweezers, she carefully placed the filter membrane into an envelope to send to the University of Minnesota where researchers will examine the sample for genetic residue that might signal the presence of zebra mussels.

“Pretty cool, isn’t it, what we’ve come to with our science?” she said. “I’m excited.”

Ruud and dozens of volunteers this summer collected samples of environmental DNA, known as eDNA, using test kits created by the U’s Minnesota Aquatic Invasive Species Center. It’s a novel approach that’s brought citizens and scientists together to fight invasives, and could eventually make it easier for Minnesotans to police their local lakes.

Environmental DNA can be an early warning system, “like the smoke detector in your house,” said Nick Phelps, the research center’s director.

“This is going to be a very efficient potential large-scale surveillance tool that’s going to make this haystack of where to look for invasive species much smaller,” he said.

Leaving genetic clues behind

Living organisms are mostly terrible at staying hidden. They’re constantly shedding eDNA into their surroundings.

Phelps compared it to the dust in a house, which is partially made up of human skin cells. If scientists collected some of it and sequenced the DNA, they could figure out who lives in the house, he said.

“The same premise exists for zebra mussels or carp or invasive plants in the environment,” Phelps said. “They're shedding their DNA into the water. And we can filter that water and get the molecular signature of that species.”

State and federal scientists used eDNA for years to search for invasive carp in rivers. But the complexity of the effort made them reluctant to enlist Minnesotans in the fight.

Phelps' team developed eDNA kits simple enough for citizen scientists to use. Each kit contains everything a volunteer needs to collect a sample, including gloves, filter, siphon, bottle and instructions.

Then, researchers set up a lab in St. Paul to test the samples. While this year’s pilot project is focused on zebra mussels, the method could be expanded to look for other invasive plants and animals, Phelps said, although those still need more work.

The invasive shellfish are found in about 5 percent of Minnesota lakes, where they can damage ecosystems. They filter out tiny plankton in the lake that native fish and other species depend on for food.

They make the water clearer, allowing sunlight to reach much deeper. That can fuel the growth of nuisance plants and algae.

Zebra mussels also can clog water intake pipes for water treatment facilities and power plants. And their sharp shells can cut swimmers’ feet.

New infestations often aren’t discovered until someone finds an adult zebra mussel clinging to the end of their dock, Phelps said.

“By the time they go out and actually do a survey of the lake, it’s all over the place,” he said.

But eDNA can give scientists an early warning before an invasive species becomes widespread, Phelps said.

“We can just filter large volumes of water without having to find the actual animal or the plant,” he said. “Early in invasions, when they’re hard to find, this becomes a very, very useful surveillance tool.”

Next up: DNA tests for more invasive species

Next month, researchers will start testing the samples that volunteers collected from 52 Minnesota lakes. They expect to have results in two to three months, which will be sent to the volunteers and to lake managers.

Currently, the tests can only tell whether zebra mussel DNA was detected or not. They can’t provide an estimate how many of the shellfish are in the lake.

Volunteers sampled lakes large and small, including some that are known to have zebra mussels and some that don’t. Among them were Big Sandy, Como, Leech, Ossawinnamakee, Ten Mile and Vermillion lakes.

The research center expects to have kits ready to survey more lakes for genetic traces of zebra mussels by next summer. They’ll roll out tests for other invasive species as they’re developed, Phelps said.

The research lab plans to offer eDNA testing for a fee to lake associations, local governments and others who want to help detect invasive species, he said.

Back at Clear Lake, near the town of Pequot Lakes and about 20 miles north of Brainerd, Ruud rinsed out the collection bottle before filling the sample. “We want to make sure it’s not my DNA in the bottle,” she said with a laugh.

She collected several more water samples from different spots on the lake, recording the latitude and longitude of each.

Ruud, a former state lawmaker who regularly volunteers to collect water samples, said using eDNA to detect the presence of invasive species sooner gives lake managers more options for controlling an infestation.

“If we catch them early,” she said, “we can’t eradicate it, but we can manage it.”

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