Invasive mussels found to control phosphorus cycles in southern Great Lakes

Beautiful sunset Lake Superior Lake walk Canal Park, Duluth, Minnesota. Photo by LIKE HE/Shutterstock

An invasive mussel the size of your thumbnail has been found to be the linchpin to an essential nutrient in four of the five Great Lakes. A team of researchers from the Large Lakes Observatory with the University of Minnesota reported that the invasive quagga mussel is now the primary driver for how phosphorus moves through the lake ecosystems. This research illustrates how a single invasive species can upend an ecosystem, and highlights the importance of stopping the spread of invasive species before they establish.

Quagga mussels are abundant in Lake Michigan, Huron, Erie, and Ontario. The University of Minnesota researchers reported that the mussels can be found at the bottom of the lakes at densities of 10,000 individuals per square metre. The exception is Lake Superior, where the water chemistry and temperature prohibits quagga mussel spread.

Quagga mussels are filter feeders. They can remove phosphorus from the surrounding lake water while feeding, and then either excrete the phosphorus back into the water column or store it in their tissues and shells. The study found that the quagga mussels in Lake Michigan are removing phosphorus from the water ten times faster than twenty years ago, and they’re adding it back to the water column at eight times the amount.

“Phosphorus is the limiting nutrient that controls the biological productivity in a lot of freshwater lakes,” says Jiying Li, the lead author of the research and now assistant professor at the Hong Kong University of Science and Technology. Because phosphorus is a limiting nutrient that controls the rate of algae and aquatic plant growth, too much phosphorus in an aquatic system can cause excessive algae growth and affect water quality.

Phosphorus can enter the Great Lakes through sources like sewage and agricultural run-off. Managing phosphorus in the Great Lakes has involved reducing human-caused inputs of phosphorus, but the quagga mussels have thrown a wrench in these plans.

The research suggests that the future of phosphorus levels in the lower Great Lakes will depend on what happens to the mussel populations. “It’s pretty dynamic. If their population is increasing, they will be taking more phosphorus to incorporate into their biomass. If the population collapses or declines for some reason, then this nutrient would be coming back into the lake,” says Li.

“I think what this study really shows is that a single invader, even the tiniest of species like this little mussel, can have huge dramatic effects on big ecosystems like the Great Lakes,” says Rebecca Schroeder, aquatic invasive species liaison for the Invasive Species Centre, a not-for-profit based in Sault St. Marie, Ontario. “These aquatic ecosystems are completely dependent on the quagga mussels for phosphorus fluctuations.”

Quagga mussels have traits that allow them to successfully take over a body of water and even outcompete invasive zebra mussels. Unlike zebra mussels, which are limited to living on hard surfaces, quagga mussels can colonize soft substrates like sand. Quagga mussels are also prolific breeders, says Schroeder. One single female can produce up to a million eggs a year.

The most important thing cottagers can do to control quagga mussels is prevent their spread from one body of water to another. Schroeder recommends that when moving a boat, owners check their hulls to make sure there are no quagga mussels hitchhiking between lakes.

That being said, adult quagga mussels are tiny, so they’re easy to miss. And the larvae are even smaller, invisible to the naked eye. So to completely make sure they’re not transporting extra passengers, boaters and fishers should follow ‘Clean Drain Dry’ procedures on all vessels and water gear. The Canadian Council on Invasive Species provides clear steps on how to perform Clean Drain Dry steps on all watercraft, trailers, and gear.

“All of our actions out on the water can have a big impact to stop the spread,” says Schroeder.

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