Zebra Mussels in Lake Michigan

Gazette Article by: Barbara Joyce
Appeared in the Gazette: Summer 1996

The water at the beach has become so clear that bathers can wade in up to their necks and, looking down, still count their toes. To the delight of swimmers, Lake Michigan is cleaner now than at any time in this century. But biologists see a disturbing sign in these sparkling waters: the invasion of the zebra mussel.

Charles W. Shabica, coastal geologist/coastal engineer, admits he’s never seen the lake this clear. Clearer water lets in more sunlight, which promotes plant growth.  While aquatic weeds pose problems for boaters, they provide tremendous habitat for fish.

Dr. Shabica interprets the mussels’ presence as part of a natural process. “Organisms from one environment invade another environment.”

Known in Latin as Dreissena polymorpha, meaning “many forms,” the mussel is remarkably adaptable. The Dreissana was accidentally introduced into this country in 1986, arriving in the hold of a ship from the Caspian Sea. The freighter, probably a grain carrier, jettisoned its ballast water into Lake St. Clair, between Lakes Erie and Huron. Here the expelled zebra mussels survived, adapted, and reproduced—rapidly and prolifically. In waters which contained none of their natural enemies, they spread throughout the Great Lakes.

Zebra mussels are “filter feeders.” An individual mussel draws a quart of water through its body every day. With billions of them inhabiting Lake Michigan, it doesn’t take long to filter a large body of water. They have already caused rapid change. Yet, according to Shabica, their ecological impact is “still in the early stage.”

Zebra mussels are identified by their brown and white banded shells, about the size of pistachio nuts. Their most destructive habit is attaching themselves to any submerged fixed object. In droves they cling to water pipes, buoys, and boat launches. They have adhered to underwater archaeological artifacts and sunken shipwrecks.

“They’re everywhere,” said Dr. Shabica. Zebra mussels clog intake pipes at water treatment facilities and power plants. They filter valuable nutrients from lakes and rivers. Because they eat plankton, they disrupt food chains and displace native species. By the end of this century, efforts to control them will have cost a projected five billion dollars.

“To us they’re a big nuisance,” said Pat Freeley, superintendent of the Winnetka Water Plant. “We didn’t wait until our pipes clogged up.” Since 1992 the plant has been using a heat treatment to prevent the mussels from blocking their intake pipes. They backflush hot water through the pipes to kill the mussels; screens are set up to catch the shells.

While Freeley couldn’t estimate the cost of this process, he noted that they use recycled cooling water from the adjoining electric plant. Neighboring suburbs treat the mussels chemically, often using chlorine. “We’re the only community using hot water,” said Freeley.

One thing is certain. According to Freeley, “They’re here to stay.”

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