Making waves studying quagga mussels

Invasive species are non-native plants or animals that harm the environment, take a toll on the economy and can hurt humans.

As Katie Theissen has learned, invasives are nothing to clam up about.

Theissen, a senior in the College of Science who arrived from Missouri on a National Merit Scholarship, spent the last two years on a research project that tracks how quagga and zebra mussels – an invasive freshwater shellfish also known as dreissenid mussels – are transported across the U.S. to Idaho waterways.

“Wherever these mussels are found in the U.S., they are always a huge problem,” Theissen said. “I never really knew about these mussels until I got here and learned how important it is to prevent the spread of dreissenids into Idaho’s lakes and streams.”

Quagga and zebra mussels were introduced to the U.S. from Eurasia. They impact native fish populations by filtering large quantities of plankton necessary to feed young fish. The mussels disrupt and overwhelm aquatic ecosystems, their waste lowers oxygen and pH levels making water acidic, and by changing the environment the mussels outcompete native species. They also clog industrial and commercial water filtering systems and damage boat motors.

Theissen’s research has become more urgent as a small number of quagga mussels were detected last year in the Snake River near Twin Falls.

After arriving at U of I, Theissen, who graduates Spring 2025 with a bachelor’s in mathematics, earned a Hill Undergraduate Research Fellowship and the opportunity to work on the dreissenid mussel project.

The research was exactly what Theissen came to Idaho for.

“Attending a research university was one of my prerequisites when I was looking for colleges,” she said.

In conjunction with Professor Jennifer Johnson-Leung in the math department and James Nagler, professor of zoology, Theissen uses data collected by the Idaho State Department of Agriculture at motor vehicle check stations. The data tracks vehicles with boats traveling in, and through, Idaho, and includes lakes that motorists have visited in Idaho or surrounding states.

Any vehicle towing or carrying a watercraft, from a paddleboard to a motorboat, is required to stop at the stations where the watercraft is inspected and, if mussels are suspected, the watercraft is given a hot wash at the site to kill mussels and their offspring.

“The goal of this research is to use as many data points as we can to create a ranking of at-risk waterways in Idaho, and a list of which waterways, such as lakes, rivers and reservoirs could cause subsequent infestations,” Theissen said.

When she joined the research with professors Johnson-Leung and Nagler, Theissen was unaware of the impact her data analysis could have.

“I would argue that dreissenid mussels are at the top of the invasive animal species list for environmental damage and economic cost in the U.S. and Canada,” Nagler said. “Katie’s research is the first to model how invasive mussels could spread in an uninfected region by watercraft traffic, which is the principal vector for their slow movement across the continent.”

“Katie’s project has been great to work on because it incorporates academic components, math and biology, and it addresses an important real-world problem,” Nagler said.

Finding U of I at the behest of a high school counselor and touring the Moscow campus, Thiessen was immediately attracted to the U of I community.

“It reminded me of a town outside of St. Louis where I spent childhood summers at my grandparent’s house,” she said. “It felt like a comfortable and safe community, and it offered a lot of opportunity as the state’s premier research university.”

Theissen has already presented her mussel-related research at two conferences including an Office of Undergraduate Research Symposium and at the MAA MathFest in Indianapolis, Ind. She looks forward to publishing her findings in a journal.

“We are working on writing a paper, so hopefully we’ll get that published,” she said. “And we are working on refining our model to include more western states.”