Aliens Among Us

by Dan McCosh

On July 14, 1994, Michigan became the first state to call out the National Guard to battle an alien species. That evening, I turned on the TV and saw what looked like a scene from War of the Worlds. Governor John Engler stood on the shore of Lake St. Clair, the 400- square-mile lake between Michigan and Canada that helps connect Lake Erie with Lake Huron. Helicopters flew overhead as the U.S. Coast Guard patrolled the area. Cleanup ships from the Marine Pollution Control struggled to subdue a floating green mess. A six- mile-wide island of rotting seaweed had washed ashore, smothering the public beach.

That was an awakening for me. For years I have driven along the western edge of this lake while distant freighters passed on their way from the Great Lakes ports to the Atlantic. The lake dominates the local horizon, yet I had never given it more than a passing thought.

The upheaval had its origins some 10,000 miles away. When the U. S. government lifted the Russian grain embargo in 1981, Russian freighters headed for the United States. For ballast during the ocean crossing, they filled their holds with brackish water from the river ports on the Baltic Sea. But the ballast pumps also sucked up larvae of the zebra mussel - a mollusk scarcely larger than a thumbnail when fully grown.

In the summer of 1986, scientists say, a northern European freighter - probably Russian - dumped some of its ballast water into the lake to reduce its draft. In so doing, it released zebra mussels that attached to the rocks near the Canadian shore and began breeding. (Since then, the Coast Guard has insisted that ocean freighters purge their ballast tanks before entering the St. Lawrence Seaway.)

To a biologist, an alien species is any organism introduced into an environment in which nature hadn't intended it to be. Without natural enemies, alien species can reproduce unchecked and throw an ecosystem off kilter. This is what happened in the shallow waters of Lake St. Clair. The shellfish reproduced so rapidly that they soon covered the lake bottom with a shell layer several feet thick. They started latching onto intake pipes at water treatment plants and clogging them solid.

By 1991, the mussels became so plentiful they filtered most of the water in the lake each day, digesting plankton and microorganisms in the process. The water, historically greenish-brown with algae, began to clear up. Suddenly, the aliens didn't seem so bad, particularly since a little bleach in the water intake pipes killed them off. Waterfront locals began joking about zebra mussel soup; a tugboat operator even repainted his vessel and renamed it the Zebra Muscle. But the optimism was short-lived. Without murky water, large pike could easily spot their prey. They began to feed voraciously on smaller game fish. Fisherman caught fewer fish, and a whole generation of fry disappeared.

Even more insidious was the seaweed. With light penetrating to the lake bottom, beds of seaweed flourished where little had grown before.

Finally came the blue-green slime. These noxious algae grow on the lake bottom, then bubble to the surface where they release an odor like rotting carp. It was when the combined masses of weeds and algae came ashore that the governor called out the National Guard.

The Great Lakes have hosted alien species before. The sea lamprey came in with the opening of the Welland Canal in the early part of the 19th century, eventually devastating one of the largest commercial fisheries in North America. In the 1960s, alewives (a type of Atlantic herring) piled up so high on Chicago beaches bulldozers had to remove them. And prior to the ban on purging ballast tanks, the ruffe, a spiny perch, was dumped by a Russian freighter and has since made its way east to threaten Lake Superior's bays and shallows.

As it has survived other invasions, Lake St. Clair will likely survive the zebra mussels. Some biologists believe that black bufflehead ducks, recently settled in the area, will control the mussel population; others are not so sure. The seaweed may remain forever, however, rolling onto the beaches at midsummer, restricting activities and turning St. Clair from a pickerel and perch lake into a bass and pike lake.

But whatever happens, the lake that spans half my horizon will never be the same. The aliens are out there, mute testimony to man's intrusion into the delicate chain of marine life.

Ocean Planet Exhibition Floorplan

gene carl feldman ( (301) 286-9428
Judith Gradwohl, Smithsonian Institution (Curator/Ocean Planet)