Moving with the Flow: Nature-driven approach to control the spread of zebra mussels

Minnesotans who love to go fishing or boating and those who follow the news have likely heard a lot about invasive zebra mussels. Zebra mussels are infesting Minnesota’s beloved lakes. Miki Hondzo, Jessica Kozarek, and William Herb are researching a new old tool to protect our beloved lakes and streams from the spread of zebra mussels.

A lot of public service announcements, money, and time have been focused on cleaning boats and equipment as they come out of our Minnesota lakes. Other efforts to control zebra mussels and other invasive species include using chemicals in the water. 

Miki Hondzo and Jessica Kozarek are proposing a more nature-driven approach to controlling the Zebra mussels. Hondzo is a researcher in the Department of Civil, Environmental, and Geo- Engineering (CEGE) and at the St. Anthony Falls Laboroatory (SAFL). He is working with his co-principal investigators, Jessica Kozarek and William Herb (both of SAFL). “We are proposing to use hydrodynamics, the change of fluid motion in time, as one of the tools to control the spread of zebra mussel larvae,” said Hondzo. “Zebra mussels live and grow in streams, rivers, lakes. Surprisingly enough, researchers have not paid much attention to the fact that the fluid in these environments is moving, or how that fact affects the spread of zebra mussels. We want to study how physical processes in streams impact the spread of zebra mussels.”

Anyone familiar with adult mussels, the kind that you can buy and eat, may well wonder how they could be so difficult to stop. Hondzo explains, “In their larval stage, zebra mussels are very small, about 100 micrometers (or 0.004 of an inch). That is something that you can see without a microscope, but it would appear as just a small dot in the water. At this small larval stage, zebra mussels can easily spread through the moving fluid.” That is the challenge. 

Hondzo, Kozarek, and Herb are interested in determining where these tiny larvae settle and breed. Along a shoreline, one might notice some places with a dense population of mussels, while other places along the shore have few or no mussels. So, the question is what combination of physical, biological, and chemical parameters contribute to a hot spot of growth for zebra mussels? What areas make a good habitat for tiny, larval mussels?

To begin to untangle this question, Hondzo, Kozarek, and Herb set out to examine one physical parameter, turbulent flow intensity and intermittency from individual larva (0.1-0.2 mm) to mussel stream bed colonies (meters in size).

The researchers are also collaborating with the Minnesota Zoo, who has established a procedure for growing larvae under laboratory conditions. Zoo personnel will provide zebra mussel larvae to be exposed to various controlled experimental conditions at SAFL. The team follows specialized protocols to avoid dispersing zebra mussel larvae into the Mississippi River. 

The United States Geological Survey (USGS) program for research on Nonindigenous Aquatic Species (NAS) is funding the research with $560,998 over three years, from January 2024 through January 2027. The researchers will be in contact with USGS to implement the outcomes of laboratory measurements in the field.

The first year, researchers will be working in the laboratory designing an experimental stream that can generate a turbulent flow, but one that operates in the field. Hondzo’s expertise with ecological fluid mechanics (fluid flow-biological interactions) and water quality and transport processes in lakes, rivers, and watersheds will be especially useful at this stage. 

Hondzo acknowledges that managing stream flow in a wild environment is a challenge. Engineering practices have changed over the years. “In the past, civil engineers often restored streams, but mostly for flood control. They used to pave streams with concrete,” says Hondzo. “It was very effective for preventing erosion and floods. We realized that while concreting a stream bed did a good job in terms of flood prevention, but in terms of ecological services, it was not a good idea.” 

Over the past 15 years, engineers have moved toward green and sustainable engineering, toward understanding stream dynamics and using stream transport processes to an ecological advantage.  The idea of green engineering is to understand the nature and use it to our advantage instead trying to control nature. “On this project,” says Hondzo, “that means restoring stream substrates and geometries in a way that follows natural stream patterns” so that the fluid flow conditions can help minimize the spread of zebra mussels.