What do I need to know about zebra mussels?

Highlights:

• Quagga mussels came to the Great Lakes later than zebra mussels, but outcompete them in places.
• Zebra and quagga mussels make the water clear, not clean, by filtering out plankton.
• Zebra and quagga mussels appear to accumulate PFAS in their bodies.

Zebra mussels were brought to the Great Lakes in ship ballast water during the 1980s. They were joined shortly after by Quagga mussels in the early 90s. Today, both are among the most serious aquatic nuisance species in the region. But what have we learned about them?

Daelyn Woolnough in an expert on freshwater mussels and is a member of Central Michigan University’s biology department and Institute for Great Lakes Research. She shares some insights about what you might not know about invasive mussels.

Q. How far inland have zebra and quagga mussels spread?

In the mid-1980s, zebra mussels spread quickly throughout the Great Lakes and were in midwestern lakes within a few years. They are still limited in the western part of the US and weren’t found there until 2008.

Zebra mussels have also spread to inland lakes through the flow of water and human-spread (e.g., boats, bait buckets), but mostly in lakes and reservoirs because their early life stages are pelagic and can move to the next waterbody if the flow is enough. Therefore, when we are doing work in Michigan inland rivers, we often don’t find zebra mussels in the abundance you find in lakes. zebra mussels can anchor to hard surfaces and do not live as deep in lakes as quagga mussels. Lake Superior has some areas with zebra mussels, but because of the water temperatures, they don’t seem to survive in the larger numbers that they can in the other, warmer Great Lakes.

Quagga mussels also spread fast throughout the Great Lakes and, in fact, can outcompeted zebra mussels. Most of the invasive mussels currently in Lake Michigan are quagga mussels. quagga mussels can live on both hard and soft surfaces and can survive in really deep, sandy areas of the Great Lakes. So really, quagga mussels have a larger niche where they can survive and are prevalent now in our surrounding Great Lakes—except Lake Superior. Like the zebra mussels, the quagga mussels also prefer temperatures that are more like lakes Michigan, Huron and Erie than Superior. They are sometimes found places that have a lot of boat traffic like Duluth Habor.

The inland rivers of Michigan have some zebra and quagga mussels, but they essentially just live in backwater areas and most get swept into the next lake or reservoir during their microscopic early-life stages. This is why many of our inland reservoir lakes have a lot of them because the dams have decreased the flow and the young zebra and quagga mussels literally settle out into those regions.

Due to a lot of outreach about boat cleaning and other actions to decrease the spread of aquatic invasive species there are still some beautiful inland lakes that do not yet have zebra mussels or quagga mussels.

The US Geological Survey keeps a map of zebra and quagga mussel observations and data from aquatic biologists here at CMU end up in those databases: https://nas.er.usgs.gov/queries/SpeciesAnimatedMap.aspx?speciesID=5

https://nas.er.usgs.gov/queries/SpeciesAnimatedMap.aspx?speciesID=95

Q. How have invasive mussels changed the Great Lakes’ food system?

Both the zebra and quagga mussels are filter feeders and can filter up to a liter of water in a day. They filter and digest small organisms that are called phytoplankton and zooplankton and these are organisms that other larger organisms, like fish, use. The food web and systems in the Great Lakes essentially collapsed in the early 1990s due such a dramatic change in food availability because of these invasive mollusks.

The lack of food, in turn, causes declines in a variety of fish and birds that ate the fish. So even though we think of the zebra and quagga mussels having a dramatic influence on our aquatic waterbodies in Michigan they are also influencing the surrounding terrestrial environments. 

Q. Can invasive mussels tell us anything about PFAS is in our water?

Newer studies by NOAA researchers have found PFAS in the tissues of these invasive mussels. Marta Springer, a recent graduate student in my lab, working with Hunter Carrick’s lab (Biology CMU) and the Saginaw Chippewa Indian Tribe, found that there are PFAS substances also in native freshwater mussel tissues. What this tells us is that these mollusks, both invasive and native, are taking in PFAS contaminated waters. They may die because of it, or they may, like in both the NOAA and CMU studies, keep the PFAS substances in their tissue and filter them out of the water. These mollusks are all like tiny wastewater treatment plants, but the zebra and quagga mussels don’t live long (3-5 years), Those substances are released back into the water after they die. Their tissues can be indicators that they are filtering substances that belong to the group of contaminants that are PFAS.

Q. Have invasive mussels had an impact on other environmental problems?

They filter so much of the Great Lakes that people talk about how clean the water it. It isn’t actually clean but instead clear. This clear water has created a cascade of changes. More light can get to the bottom of the lakes, so more algae grows and some of the algae and biofilms create habitat for more bacteria. This has unfortunately been horrible for birds and other fauna of the Great Lakes because some of these Cladophora, a green algae that grows well in clear water, has been implicated in washing up on shorelines and it, with the bacteria it harbors, has killed many animals that fed on it and/or get caught in it. All of this is due to the invasive zebra and quagga mussels so there are lots of indirect influences that happen when new invasive species moves in.

Q. How will invasive mussels shape the Great Lakes’ future?

Invasive mussels have been in the Great Lakes region since the 1980s.  Surprisingly they are still not in all our inland lakes or rivers. These inland areas are more pristine than the Great Lakes at this point. There was lots of research during their first invasion that considered ways to use physical, chemical and biological methods to control their populations. Many options tested didn’t work at all. There are still a small number of methods, chemical and physical, that are being tested in lakes where they have recently established themselves, which could be helpful in controlling them. 

Unfortunately, the quagga mussels in the Great Lakes are so abundant that they are now part of the ecosystem. As researchers, we have had to adapt, including our research questions, to include these invasive mollusks.

About Daelyn Woolnough

Daelyn Woolnough is a member of Central Michigan University’s Biology Department and Institute of Great Lakes Research as a research professor. She received her bachelor’s and master’s degrees from the University of Guelph and her doctorate in Ecology and Evolutionary Biology from Iowa State University.

Her research interests include mussels and other mollusks in the Great Lakes and around the world, especially in the inland rivers and environmental factors affecting the distribution of their populations. She is also interested in how data can help predict the future distribution and survival of species.