What’s the matter with mussels?

Biology senior leads research team surveying mussel population

| Author: Eric Baerren | Media Contact: Aaron Mills

A Central Michigan University senior put his natural outdoors skills to use, leading a research team assessing the status of a population of critical freshwater critters.

What Aaron Vlasak learned about the mussels in a mid-Michigan watershed formed the core of his presentation at an event showcasing collaborative research projects, funded, in part, by the CMU Undergraduate Summer Program for Arts & Research grant involving CMU students and faculty from the Biology Department and Institute for Great Lakes Research.

Vlasak, who lives in Midland but who came to CMU from Minnesota, led a research team that surveyed the population of mussels in the upper reaches of the Tittabawassee River watershed. Mussels, sometimes called clams, are animals that live in the water, including the rivers and lakes of Michigan. They also feed by filtering small particles from the water.

The empty shells of several species of freshwater mussels sit in the mud.
Mussel shells collected by a team of CMU researchers led by senior Aaron Vlasak sit in the mud during their survey of the upper Titabawassee River watershed. The team conducted the first survey of mussels in the area in 40 years, and found that the animals, which play critical roles, are generally in decline. The shells do not contain living animals.


The animals play a critical, underappreciated role in helping us understand ecosystems, said Daelyn Woolnough, a CMU biology faculty member who  researches mussels. Vlasak, a senior, led his research team as an undergraduate researcher in her lab.

Mussels like clean water. A decline in their population could indicate that water quality has degraded. They can also filter a lot of toxins from the water and bury those down the mud, effectively locking them up, Woolnough said.

Vlasak set out to answer two very simple questions: Which species and how many mussels are in the Upper Tittabawassee, and how many of them are there? The Tittabawassee has its origins across mid-Michigan – primarily in Clare and Gladwin counties – before flowing to Midland.

The question was first asked by researchers 40 years ago, Woolnough said. Vlasak’s research updated a knowledge base badly in need of an update.

Those researchers took an inventory of mussels at 28 locations in rivers across the upper Tittabawassee. Vlasak’s team returned to those and added more sites in between the previously studied sites. They also visited six sites in Ross and Higgins lakes, which are in the watershed.

Vlasak became SCUBA certified through the Woolnough Lab and had already demonstrated considerable skill handling boats, Woolnough said. He and the researchers he led dove, swam and searched the mud of 40 sites across mid-Michigan looking for mussels.

Things changed in the 40 years since the last survey. Some sites had different mussels, including three species not previously recorded in the Tittabawassee watershed. The number of mussels had changed in some places. One site studied 40 years ago was dry, in fact, so Vlasak couldn’t survey it.

What they found pointed to a general decline in the mussel population.

It’s hard to draw any firm conclusions about what it means, Woolnough said. The time that elapsed since the first study creates challenges to understanding what role climate change might have played, for example.

Parts of the river system also saw a significant disruption in 2020, when the Edenville and Sanford dams failed. Not much was known about that area prior to the failures because the study 40 years ago only had a few sites nearby. That made it hard to understand what had changed.

Only one historic survey site was below Sanford and Vlasak’s research team found an abundance of mussels from many species. Fish also play a critical role in the reproductive cycle of mussels, so the Sanford dam is likely a barrier to the upstream travel of mussels.

The big conclusion is that 40 years is too long to go between mussel surveys, Woolnough said. Five to 10 years is probably a good time frame.

Vlasak and Woolnough shared what they learned at the 2023 Biology Undergraduate Research Symposium in mid-November. The event provided an opportunity for undergraduate students to share the fruits of research projects they worked on with CMU faculty.

A gloved hand holds a freshwater mussels covered in non-native zebra mussels.
Zebra mussels, a non-native kind of freshwater mussel, cover the shell of a native mussel. Zebra mussels latch on to native mussels and rob them of nutrients.


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