July 17, 2017
By Marie Zhuikov
As prior researchers have demonstrated, Wisconsin Sea Grant researchers further confirm that the tiny quagga mussel has an outsize impact on Lake Michigan. What’s novel about the study team’s work is the exploration of the age-old biological truth: what goes in must come out. They found the invasive mussels’ sheer numbers and feeding efficiency are changing the lake’s ecosystem dynamics. Perhaps the climate, as well.
Laodong Guo and his graduate student Stephen DeVilbiss, researchers at the University of Wisconsin-Milwaukee, looked at the impacts of quagga mussels from an aquatic chemist’s point of view in a paper published this year in the Journal of Great Lakes Research. They took measurements in Lake Michigan and collected mussels from the lake. They brought the mussels into the lab to assess filtration and excretion rates, and the type of things excreted to better understand their role in the lake’s carbon cycle.
The researchers found that the mussels are highly efficient; each one can filter up to 578 gallons of water every year, with younger, smaller mussels pumping more efficiently. In addition to feces, the mussels excrete dissolved nitrogen and phosphorus, and they “breathe” out carbon dioxide into the water -- so much carbon dioxide, in fact, that it could impact the climate.
“There are so many mussels that the carbon dioxide they release into the water, which gets into the air, may add to the problem of global warming,” Guo said. “Normally, in places like the ocean environment, the water absorbs carbon dioxide. However, Lake Michigan is somewhat oversaturated with carbon dioxide because of the quagga mussels. We need to look at whether this is causing acidification in the lake.”
Estimates of the number of quagga mussels in Lake Michigan by NOAA researchers range from 750 to 950 trillion. More information about how quagga mussels are impacting carbon dioxide dynamics in Lake Michigan and other Great Lakes can be found in a paper Guo and his postdoc, Peng Lin, published last year in Nature’s Scientific Reports.
Another impact the researchers found from their field studies is that quagga mussels are changing the way phosphorous is cycled in the lake. Normally, the amount of phosphorous, a vital nutrient needed for diatoms and other species important in the food web, rises during the winter when it is released from particulate matter resuspended from coastal sediment during storm events and turbulence. The sediment then gets transported from shallow areas to deeper regions in the lake.
“Because quagga mussels carpet the bottom of the lake, the resuspension of phosphorus during winter and during storms is less than it used to be,” Guo said. “When we compare data from
before and after the invasion of the quagga mussels, we find there’s only about one third to less than half of the amount of total phosphorus present in the winter water column.”