Invasion of Zebra Mussels Threatens U.S. Waterways

CHICAGO — A tiny, astoundingly prolific Eastern European shellfish has invaded the Great Lakes, permanently altering the fragile aquatic ecosystem and threatening a water supply that tens of millions of Americans and Canadians depend upon for drinking, electricity, industry and recreation.

Zebra mussels--pinto bean-sized mollusks marked with brown and white zigzag stripes--are creating environmental havoc in the Midwest now. In coming years, scientists believe they will cause problems throughout the United States.

“This isn’t like a localized (oil) spill,” said Margaret Dochoda, a biologist with the Canadian-American Great Lakes Fishery Commission. “The zebra mussel will be plaguing a large part of North America in the next 100 years.”

“It’s a horror story,” said Gerry Mackie, a mollusk expert at Canada’s University of Guelph. “They spread so quickly.”

The tiny mollusk, with a five-year life span, reproduces in quantities and with a speed that suggests science fiction. It has few natural predators and no commercial value, and it is a voracious eater of food that fish depend upon.

“In August of 1988, we found 50 per square meter. In August of 1989--one year later--we were seeing numbers of about 700,000 per square meter,” said William P. Kovalak, a biologist at Detroit Edison’s Monroe, Mich., electric generating plant. “These animals have this explosive capability of increasing.”

In recent months, the barnacle-like zebra mussels have clogged drinking-water intakes in Lake Erie and plugged hundreds of miles of plumbing in Canadian and American factories. Natives of the Caspian, Black and Azov seas, they apparently hitchhiked into the Great Lakes in the ballast water of a ship.

Though they weigh only about an ounce each, and up to 99% of them do not survive more than a year, they have accumulated in such numbers on navigation markers that their total weight has pulled the heavy buoys under water. They are so bountiful on some Canadian beaches that swimmers are warned to wear running shoes to avoid cutting their feet on 12-inch-deep layers of mussels. And they have built up into 6-inch-thick blankets on shoals where fish have historically spawned.

Besides covering spawning areas, zebra mussels compete with juvenile fish for food. The mussels eat by filtering water through their bodies, taking from the food chain algae and plankton that young fish need. A single zebra mussel can filter up to a liter of water a day. “What frightens us is that in western Lake Erie, water clarity readings have doubled,” Dochoda said, indicating there is much less food for maturing fish.

Fish Threatened

“If 50% of the (food) is being consumed by the zebra mussel, something has to be starving,” said Ronald W. Griffiths, an ecologist with the Ontario Ministry of the Environment.

Across the Atlantic, the zebra shellfish have spread from their Eastern European home waters as far north as Scandinavia. And they have been sighted in western Asia, traveling both in the ballast water of cargo ships and on the bottoms of those vessels. The Germans call the creature “the wandering mussel.”

In America, the Mississippi and Ohio river basins are particularly vulnerable because of their proximity to the Great Lakes and because the Mississippi is linked directly to Lake Michigan by the Chicago and Illinois rivers. Lakes, rivers and reservoirs face infestation because the mussels can live out of water for at least several days and can easily be transported attached to the bottoms of recreational boats.

Zebra mussels have already been found in Ohio’s Grand and Maumee rivers. “Within a few years, if they continue to spread at the present rate, they’ll be all over the state,” said Richard L. Shank, director of Ohio’s Environmental Protection Administration.

Rapid Spread Feared

“Interstate 77 is the perfect transportation corridor for these organisms,” Griffiths said. “There are an awful lot of Americans that take their boats out of Lake Erie (in the winter), put them on a trailer and hike it right down I-77 to South Carolina and Georgia.

“They can make the trip in eight to 24 hours. It could be that right now you have little founding populations in the Southeast U.S.”

Scientists expect the zebra mussel to spread throughout the country faster than the Asian clam, which first showed up in North America in the 1920s and has been a problem for electric plants and paper mills ever since. Also capable of prolific reproduction and having few natural predators, this fresh-water creature is now found in 35 of the 50 states. It was first sighted in the waters off Vancouver Island, British Columbia, in 1924. Asian clams were found at the mouth of the Columbia River in 1938, and they appeared in Southern California in 1952.

So far, zebra mussels have had their biggest impact in and around Lake Erie. Of the five Great Lakes, it has the most heavily settled and industrialized shoreline and the largest commercial and sport-fishing industry. Toledo, Ohio; Cleveland and Windsor, Ontario, are among cities where zebra mussels have already caused problems. They blocked the water intake for Monroe, Mich., last month, forcing the city of 50,000 on the western edge of Lake Erie to order restaurants and bars to close, industries to voluntarily shut down and hospitals to use bottled water.

High Costs Seen

Within the next few years, zebra mussels are expected to be established and causing similar problems in Lake Ontario, Lake Huron, Lake Michigan and Lake Superior which, along with Lake Erie, are reservoirs for 20% of the planet’s fresh surface water and vital to the economy and environment of the region’s 35 million American and Canadian residents.

Cities like Chicago; Milwaukee; Gary, Ind.; Duluth, Minn.; Green Bay, Wis., and Toronto are all threatened. Zebra mussels are expected to reach Buffalo, N.Y., this summer. They are already forming colonies near Dunkirk, N.Y., just west of Buffalo.

“We’re looking at damage for the next decade in the Great Lakes,” said Jon Stanley, director of the U.S. Fish and Wildlife Service’s Great Lakes research station. He estimates the American cost of controlling the mussels and cleaning them out of water intakes--as well as the damage to fishing they will cause--at more than $4 billion over the next 10 years. That, Stanley said, “is a crude estimate.”

Under water, the mussels attack virtually every surface. For example, Ontario provincial police pulled a mussel-encrusted red sports car out of Lake Erie off the Leamington shore last March, six months after it had been reported stolen. Every single surface--glass, metal, plastic, fabric, chrome, rubber, vinyl--was covered with a 1 1/2-inch-thick layer of zebra mussels.

“They stick to everything as if they were attached with super glue,” said Rick J. Turnbull, an analyst with the Ontario Ministry of the Environment who studied the “mussel car.”

The mussels attach themselves with scores of strong, sticky “threads.” One characteristic of the zebra mussel is that it forms colonies by attaching to a neighboring mussel. Sometimes they form balls or clusters, sometimes layers and sometimes stands or “beards.”

Although they reach 2 inches at maturity, 10 yearling zebra mussels will fit into a tablespoon. If all 10 are female, they can produce a total of 300,000 eggs in their first year and 400,000 eggs annually after they are 3 years old.

Diving ducks are one of the few zebra mussel predators. “They can eat tons of mussels over short periods of time,” Griffiths said, and there are indications that ducks have discovered this nouvelle bivalve. Off Pelee Point in western Lake Erie, the number of blue-billed ducks went up from 20 a few years ago to more than 13,000 last autumn.

For humans, however, these mussels are no feast. “We’re very fussy over here, and if the Europeans haven’t found a way to eat this thing,” Mackie said. “I doubt that Canadians will.”

Despite the impact they have already had, the history of the zebra mussel in the Great Lakes is a relatively short one.

A pair of graduate students from the University of Windsor’s Great Lakes Institute discovered the first zebra mussels in 1988 while taking samples of aquatic life from Lake St. Clair--a small body of water north of Detroit that links Lake Huron with Lake Erie. Subsequent research by Mackie suggests that they were apparently dumped into the lake either late in 1985 or in the spring of 1986, probably by one or more ships releasing ballast water they had loaded in a European port.

Warnings that they were a potential threat to the waters and ecology of North America appeared as far back as 1963 in an American report and as recently as 1981 in a study commissioned by the Canadian environmental ministry, Griffiths said. “We had at least 30 years of warning, and the governments have done nothing.”

Both the Canadian and American governments have resisted mandatory regulations aimed at keeping foreign species or biological pollution out of the Great Lakes. Opposition has centered on issues ranging from the costs of operating the program to fears about restraint of trade.

The Canadian government last year did establish voluntary guidelines. They asked captains of the approximately 1,000 ships entering the St. Lawrence Seaway each year to exchange ballast water somewhere between the U.S. continental shelf and the European continental shelf. Compliance is about 89%, said Dochoda, who monitors regulations for the Great Lakes Fishery Commission. “But it just takes one ship to introduce these things.”

Meanwhile, Congress last year gave the Coast Guard six months to report on strategies to prevent the introduction of non-native life forms into all U.S. waters. That report is due in the spring.

“There are species sitting out there that are just as bad or worse, just waiting for a free ride to America,” Griffiths said.