The presence of the quagga mussel, a cousin to the zebra mussel, was confirmed for the first time in the Duluth-Superior Harbor. Using DNA analysis, researchers for the U.S. Environmental Protection Agency (EPA) confirmed the finding of one small fan-shaped quagga mussel. If allowed to thrive, quagga mussels, which are about the size of an adult’s thumbnail, may pose a serious threat to the harbor and Lake Superior ecosystems.

As filter feeders, both the quagga and zebra mussels accumulate pollutants that they pass up the food chain, damage the food chain by consuming food sources of native species, negatively impact fisheries, and clog water intakes. Quagga mussels are widespread in the lower Great Lakes, especially Lake Michigan, Ontario and Erie, where they have out-competed zebra mussels in deep and shallow waters.

The quagga mussel became the 84th non-native species found in Lake Superior waters. Native to the Ukraine, quagga mussel were probably introduced to the Great Lakes from the ballast water discharges of transoceanic ships as were zebra mussels and dozens of other harmful invasive species. First seen in the Great Lakes in 1989, quagga mussels had not, until now, been found in the Duluth-Superior Harbor or elsewhere in Lake Superior.

Quagga mussels are now widely distributed in Lakes Ontario, Michigan and Erie. Their recent rapid expansion in Lake Huron coincides with a large fisheries decline and other changes to the local food web.
Since 1989, zebra mussels have infested the Duluth-Superior Harbor but have not taken hold in Lake Superior. Of the two species, the quagga mussel has lower temperature tolerance and tends to colonize deeper waters of the lower lakes.