Invaders Abroad

If you went swimming in the lake, you might have felt the soft feathery leaves of Eurasian watermilfoil brush your legs. You probably wore water shoes to protect your feet from sharp edges of zebra mussels. What all of these species have in common is that they are not native to Minnesota. They are invaders.

“What invaders do is disrupt the way an ecosystem functions,” says Dr. Michelle Marko, associate professor of biology and co-director of the environmental studies program.

Invasive species affect our ecosystems everywhere, often having a negative impact on wildlife and humans.

The Aquatic Nuisance Species Task Force asserts on its website, “Introduced species are a greater threat to native biodiversity than pollution, harvest, and disease combined.”

Invasive plants also crowd out native species, change fish populations and clog boat motors. Marko has studied Eurasian watermilfoil, an aquatic plant that has invaded 330 lakes in Minnesota and 48 states across the country. Invasive plants like watermilfoil can grow so thick that they disrupt boating and swimming. These aquatic plants could have come from the aquarium trade, water gardening or even deliberate stocking. Whatever the source, these aquatic interlopers are becoming common.

But the problems aren’t just in the United States. We are exporters of invasive species as well. The aquatic plant elodea is native to North America but invasive in Europe. It affects water flow, recreational activities and is outcompeting native plants. Marko and colleagues are studying elodea to learn more about the process of invasion and to find whether it has weaknesses that can be exploited for control.

In summer 2015, Marko and student researchers Hunter Smith ’18 and Jordan Bolger ’16 studied two elodea species in Minnesota where they are native. Elodea, commonly called waterweed, grows along lake bottoms. Dark green leaves grow off the elodea stems in whorls of three.

The team traveled to Concordia’s Long Lake Field Station near Detroit Lakes, Minn. Smith and Bolger worked together pulling clumps of elodea into the boat and stored the plants in Ziploc bags. After long hours on the lake, they brought the samples back to the lab to study. The team compared plant shape and size of two elodea species. This understanding of the plant’s biology would help them find ways to manage it.

In addition to Long Lake, the team studied elodea in five other Minnesota lakes, getting a feel for the plants in their native habitat.

Then it was time to check out the lakes these plants had invaded in Europe. In summer 2016, Marko and student researchers Rebecca Dahl ’19 and Ruth Sexton ’18 headed to France. Gaining an understanding of the organism in its native and invasive ranges would prove crucial to their research.

While the collection and lab experiences were very similar to how they had always performed, the locals made sure they also drank in a bit of culture while they did their fieldwork.

“In the United States, we sometimes eat lunch on the boat or on our way to a field site, trying to maximize every bit of daylight we have,” Marko says. “In Europe, our hosts always made sure we stopped for lunch at a restaurant to sample the local cuisine.”

The team spent six weeks snorkeling in lakes and rivers of France, Luxembourg and Germany.

In Europe, the team gently collected plants underwater by hand. Back at the European labs, they processed the elodea samples just like they did at Long Lake. They gathered data in three different areas: plant chemistry of the two elodea species, insects living on the elodea plants and physical characteristics of the plants, such as size and shape of the leaves.

They are testing the enemy-release hypothesis to see if elodea plants do better in Europe, without their normal competitors. That’s why Marko’s team is studying elodea both here and abroad. If their hypothesis is correct, they would expect the elodea in Europe to be more robust.

The team also examined the conditions of each area. Studying both water and soil chemistry gave the team a better understanding of the whole ecology of a location. One hypothesis might be that removal of elodea in low-nutrient lakes leads to lower chances of reinvasion.

The team studied differences in defensive chemicals between two species of elodea and between plants in the U.S. versus plants in Europe. With the enemy-release hypothesis, researchers would expect elodea in Europe to have lower defensive chemicals.

They’d also expect fewer insects to feed on the elodea in Europe. Determining which insects are found on elodea may help identify insects that can help control elodea populations. Because many European countries don’t use herbicides, Marko’s team is looking to use what is already there to fight what shouldn’t be. Learning more about the ecology of elodea and the organisms feeding on it will help manage invasive species better.

The team found more than just plants in the water. When looking at physical characteristics of the two species of elodea, the team found something unexpected abroad.

“In Europe, the two species can shape-shift a bit,” Marko says. During research in France, plants they thought were one species of elodea were actually of the other species of elodea. This inspired them to go back and relook at specimens they’d collected in 2015 and check DNA to make sure of what species they are.

Marko’s team brought samples back to the U.S. and will continue to study them along with samples they collected in Minnesota during 2015. Because of this re-evaluation, the research project may continue an additional summer.

Marko and her student researchers shared preliminary results at the Upper Midwest Invasive Species Conference in October and will share at the Private College Scholars Showcase in February. When they finish analyzing their samples, they will also present at a national conference.

The entire experience is something many students don’t become involved in until graduate school. Dahl, who had just completed her first year, appreciates how many opportunities Concordia offers students, even those early in their college careers.

“It’s great that Concordia does this research and experience out of the classrooms,” she says. “I don’t think I could’ve gotten it anywhere else.”

It was a great chance to get a taste of fieldwork. While abroad, the students also got the chance to work with another professor and talk with graduate students, which opened up new ideas for their futures.

Marko says the students were passionate about the research this summer and learned to navigate a different culture on a daily basis.

“Rebecca and Ruthie worked hard and embraced the cultural experience,” Marko says. “By being there for six weeks, we had the opportunity to jump into both the lakes and the culture.”

Marko and her collaborators continue to fight invasive species, one organism at a time. 

 ^{Published September 2018}