In Lake Superior's Duluth harbor, signs of new invading mussel
The Associated Press
Posted on Mlive.com on January 11, 2007
DULUTH, Minn. (AP) — An invasive species that can disrupt the ecosystem of waters by competing with native species and small fish for food has been found for the first time in Lake Superior, federal officials say.
The quagga mussel, discovered in Duluth-Superior Harbor, resembles another well-known invader, the zebra mussel, which has spread rapidly in North America over the past two decades and cost billions of dollars.
Carl Richards, director of the Environmental Protection Agency's Mid-Continent Ecology Lab here, said the quagga mussels were collected last summer from the bottom of the harbor as part of a broader sampling program and verified recently with new DNA testing techniques.
"These mussels are quite abundant in the lower Great Lakes and it just means that they've made the hop to Lake Superior," he said Thursday. "We don't know exactly how they got here, but there are many opportunities," including on ships that move regularly between ports, Richards said.
Quagga mussels originally came from the Black and Caspian seas of Eastern Europe and were almost certainly carried into the Great Lakes in the ballast water and sludge of transoceanic ships. They were first noticed in Lake Erie in the late 1980s and have spread widely through Lakes Ontario, Huron and Michigan.
Tom Nalepa, a biologist for the National Oceanic and Atmospheric Administration in Ann Arbor, Mich., said quaggas exploded in Lakes Huron and Michigan between 2000 and 2005 and have consumed food that's essential for small fish.
"Alewives, smelt and bloater populations have crashed in Lake Huron coincident with the expansion of quaggas," Nalepa said. The effect "trickles up," he said, so that with fewer small fish in the lakes, there's a significant shortage of food for larger fish. "As a result, Michigan has cut its stocking rates for coho and chinook salmon by 50 percent," he said.
Nalepa, who works at the Great Lakes Research Lab in Ann Arbor, said quagga mussels can live in deeper water than zebra mussels but aren't likely to spread far beyond the Duluth harbor.
The mussels need calcium to thrive, he said, and most of Lake Superior outside the harbor has relatively low levels of it. As a result, Nalepa said he does not expect the quaggas to overtake large areas of lake bottom as they have in Lake Erie and other lakes with more calcium.
Doug Jensen, aquatic invasive species coordinator for the University of Minnesota's Sea Grant program, said the discovery of quaggas "doesn't bode well" for the harbor. Jensen said he will continue to work with state and federal authorities on boater education programs to prevent the mussels and other invaders from spreading to Minnesota's interior lakes and watersheds.