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Points North

The creature that took control of the Great Lakes

NOAA Great Lakes Environmental Research Laboratory


John Janssen remembers the moment he realized Lake Michigan was about to change.

It was a September day in 1990 and he was diving looking for sculpin — an ugly fish with big lips that likes to hide under rocks.


“I wasn’t paying much attention to anything else — it was my dive partner who suddenly grabbed me and pointed out that first zebra mussel,” he says. 


“I just lay on the bottom for like five minutes, trying to imagine what the lake was going to look like in a year.”


Janssen is a fisheries biologist at the University of Wisconsin, Milwaukee, and he knew what was coming. Zebra mussels had already invaded Lake Erie. 

Still, diving in the lake the following year was a shock. “The next May it was like, this is a totally different lake,” he says. 


Before, the lake was murky. It was easy to lose sight of your dive partner from just a couple feet away. 


“You would throw the anchor in, and you had no idea what you would see on the bottom,” Janssen says. "And that all changed, instantly."


The shallow waters where John was diving were suddenly clear. He could see the bottom 20 feet below. 


Credit NOAA Great Lakes Environmental Research Laboratory
Zebra mussels tend to stick to hard surfaces in shallow waters, while quagga mussels thrive on the muddy lakebed. Now, they've all but displaced zebra mussels in Lake Michigan.

For several years only the coastal waters looked different. Offshore, the lake was still cloudy. That lasted until the early 2000s, when another mussel made its way to the lake that would alter it irrevocably — the quagga mussel.


Then, the whole lake became clear. 


“The arrival of quagga mussels was the single largest ecological event in the history of the lake,” says Dave Strayer, a freshwater ecologist at the Cary Institute of Ecosystem Studies. 


“It was bigger than deforesting the watershed, it was bigger than building Chicago.”


Quagga mussels haven’t only changed how the lake looks — they’ve also completely upended the food web in the lakes. Mussels control the flow of nutrients and productivity in all of the Great Lakes, except Superior, according to recent research from the University of Minnesota, Duluth.

It would be like if someone deforested the lower peninsula of Michigan and replaced it with some invasive plant

This domination is possible because quagga mussels can survive at great depths on the soft, muddy lakebed. They’ve spread across the lake with incredible tenacity.


“It would be like if someone deforested the lower peninsula of Michigan and replaced it with some invasive plant, where it just utterly changed the way that habitat looked,” says Strayer. “There’s no equivalent.”


The actual number of quagga mussels on the lakebed is mind-boggling: close to a quadrillion (that’s a million billion). There are more of these creatures in Lake Michigan than stars in the Milky Way. 


These zillions of mussels are slurping up water and hogging a key ingredient for aquatic life — phosphorus. It’s the stuff in fertilizers that algae likes so much. 


“They filter the particles in the water so fast that they are accumulating lots of phosphorus into their body,” says Jiying Li, an aquatic geochemist at Hong Kong University of Science and Technology, who led a research team that calculated how mussels affect the flow of nutrients in the Great Lakes. 


“It turns out that mussels themselves contain about as much phosphorus as there is in the entire lake,” saysTed Ozersky, a biologist at the University of Minnesota who was also involved in the research. 


Credit NOAA Great Lakes Environmental Research Laboratory
Researchers from NOAA sample the mussels in each of the Great Lakes every few years. In deeper waters, they bring up a clump of mud from the lakebed and count the mussels they find.

A lot of that phosphorus is in the form of phytoplankton, tiny plants that other creatures in the lake rely on. “That’s the base of the food web for the lakes,” says Ashley Elgin, an ecologist at NOAA’s Great Lakes Environmental Research Laboratory in Muskegon. 

“They’re creating a bit of an ecological desert for the other organisms that depend on that phytoplankton,” she says. That includes fish


In deep areas of Lake Michigan and Lake Huron, quagga mussels are — incredibly — still expanding, albeit more slowly, says Elgin. 


But researchers have noticed that many of the mussels are getting bigger. There aren’t as many small, younger animals in the mix.


"That is setting it up to be a population drop in the future," says Elgin. But there’s no sign of any decline in the quagga mussels in Lake Michigan yet.


“We’re just still waiting,” says Elgin. “We keep collecting data and saying, 'Has it happened yet? No? Okay, we’ll keep looking.'”

Lexi Krupp reports on science and the environment. Previously, she worked for Gimlet Media where she helped the Science Vs team distinguish what's fact from what's not. Her work has appeared in Audubon, Popular Science, VICE, and elsewhere.