The Invasion of Zebra Mussels in North America

The first living North American species of the zebra mussel was collected on June 1, 1988 near the Belle River in Lake St. Clair. Most scientists agree that the mussel was probably introduced in 1985 or 1986 in ballast water discharged from foreign shipping. No matter how the zebra mussel arrived, in the six years since its discovery in North America, it has quickly spread to all of the Great Lakes and entered eight river systems (the St. Lawrence, Hudson, Mississippi, Ohio, Illinois, Tennessee, Susquehanna, and Arkansas rivers). Don Schloesser, a biologist at the US Fish and Wildlife Service National Fisheries Research Center in Ann Arbor, Mich. said, "We thought it would take these mussels five years to reach all the Great Lakes, but in less than a year we've found them in every one of the lakes." By 1989 the mussels had infested Lake Erie; by 1990 the had spread to Lake Ontario, Huron, Michigan, and Superior.

Unfortunately, it is not only the main waterways used by shipping that are susceptible to infestation by the zebra mussel. Biologists have suggested that virtually any body of water that can be reached by boaters and fisherman within a few days' travel of the Great Lakes, particularly Lake Erie, seems to be at risk. It is only a matter of time, then, before the zebra mussel reaches even small lakes, ponds, and streams.

Despite the large negative impact it can have on the economy and environment, the zebra mussel does have its good points and a place in the ecological scheme. Like all bivalves, zebra mussels are significant natural biofilters, playing an important role in biological purification and improving water quality in aquatic systems.

Zebra mussels can also affect nutrients and mineralization pathways by removing dissolved nutrients, phosphorus, calcium carbonate, and other minerals. They can also accelerate the conversion of toxic nitrogenous metabolic wastes (e.g. ammonia and nitrite) to consumable nutrients for phytoplankton.

Several biologists speculate that zebra mussels can contribute to the restoration of lakes and other bodies of water by removing excessive amounts of algae. For example, H. Reeders, a biologist, has reported that the current zebra mussel population in Dutch lakes are sufficient to filter lakes at least once or twice a month, and he has suggested the use of the mussel in biomanipulation programs.

The zebra mussel can be used as an important tool for bio-monitoring programs. Because the zebra mussel is very sensitive to water contamination and cannot live in bodies of water polluted with industrial wastes, it becomes an effective monitor of such contamination. The zebra mussel thrives only in clean, oxygen-saturated, non-turbid water.

Parallel to the ecological benefits of the zebra mussel is the negative impact it is having on native aquatic species and phytoplankton. In addition to the natural consequences is the equally devastating effect the mussel is wreaking on utilities, industries, and municipalities that use fresh water.

The growth of zebra mussel populations can cause ecological consequences throughout a community, especially because they remove large percentages of primary producers, which may reduce the energy available to food webs. Another negative impact of the zebra mussel is its ability to remove contaminants from the water and concentrate them on the lake floors and shorelines. For example, De Kock and Bowmer examined the transfer of cadmium and organachlorine contaminants from zebra mussels to the tufted duck, and showed subsequent transfer to the duck eggs with disastrous effects. Negative impacts of the zebra mussel on native mussels and clams have been observed in Lake St. Clair and Lake Erie. Zebra mussels are not selective and are colonizing all species of clams and mussels in Lake St. Clair and Lake Erie. Clams with 15,000 zebra mussels on their shells were found. Often clams were not able to open their valves and as a result were smothered to death. Thus, as a direct consequence of zebra mussel invasion, the rich diversity of the mussel and clam community in these lakes may be reduced because of the extinction of some native species.

The most expensive problem caused by the zebra mussel is its potential to foul raw water intakes such as those at reservoir pumping stations, electric generating plants, and industrial facilities. Zebra mussel communities are abundant on human-built structures such as dams, pipes, and water intakes.

Reservoirs and cooling ponds have especially good conditions for zebra mussels. Favorable hydrochemistry and water temperature, plentiful food, and the presence of excellent settlement sites on the solid surfaces of underwater structures encourage mass development of mussel colonies at these sites.

In North America, the problem has just begun, but already the Detroit Edison power plant has reported mussel densities as high as 750,000 animals per square meter in its intake canal. There is little doubt that other power plants will be severely affected as the zebra mussel takes hold in lakes and rivers.

In industrial raw-water facilities, the infestation is also severe. The zebra mussel fouls waterways, inlet pumping tubes, settling tanks, etc. The greatest impact is from clusters of shells that clog the equipment, thus causing severe reduction of water flow and sometimes resulting in plant shutdowns. "Water coming in was reduced to a trickle," says Wilfred LePage, superintendent of treatment and pumping at Monroe, Mich. "Not only do the mussels decrease the diameter of the pipe, but the rough surface they create causes turbulent water flow, which substantially reduces the flow rate through the pipes." The problem in North America with the zebra mussels is that they reduce the water flow in fouled piping, block small-diameter tubes and piping, because of single shells and shell clusters. Finally, the zebra mussels are negatively affecting both commercial navigation and recreational boating, infesting barges, ships, boats, docks, and piers. Even recreational beaches at the shoreline of Lake Erie are being affected: some swimming areas are littered with sharp shells and the air is polluted with the smell of decaying mussels. Thus, the tourism economy is beginning to feel the zebra mussel's impact as well.

The impact of the zebra mussel in North America will only worsen until natural equilibrium is achieved, unless steps are taken to control the spread and lessen its effect.

There are many ways to kill the zebra mussel, the trick is to do it selectively without wiping out other aquatic life. A recent study found that minute traces of potassium, nontoxic to other organisms, reliably send zebra mussels into fatal shock. Paints laced with potassium might protect underwater structures from mussel invasion.

Zebra mussel spawning is triggered by odor wafting from phytoplankton. These chemical cues ensure that the eggs hatch when the food supply is plentiful. If synthetic scents could be dubbed then maybe it would create a premature spawn, which would surely doom most of the larvae. However no such synthetic scent has yet been produced.

Another proposal for trying to control the zebra mussel population is trying chlorine treatments. The chlorination kills both the adults and the larvae, but it has to be applied in such a way that it's not released into the environment. Removing the mussels by hand is safer, but the process is painstaking, and the mussels usually just reappear the next year. Ford Motor Co.'s Windsor Casting Plant were able to kill the mussels with 300 pound doses of chlorine, leaving clean-up crews to contend with mountains of dead mussels. But municipal officials have to think about purity as well as quantity. Since chlorine and mussel proteins can mix to form suspected carcinogens, Monroe officials are trying to develop a whirling scrubber that will unseat the intruders mechanically. Other communities are trying to concoct filters that will keep the mussels from entering the pipes in the first place. These devices will cost an estimated $50 million apiece, and dozens of towns may require them. "many of us are moving quickly to contain this mussel," says Michael Donahue of the Great Lakes Commission, an eight-state consortium of governments. "But I can tell you that the cost will be much more than the Exxon oil spill."

Natural predation may be another possible solution in controlling the zebra species. The mussel has turned up in the stomachs of several species of fish. Diving ducks seem to like them too, so we can cross our fingers and hope that they are hungry.

For now experts are simply monitoring the problem, waiting to see if the mussels will spread through the heartland of the US. Europeans have been living with the zebra mussel for centuries. They have learned to build water pipes and bury them under the sand. Now that the zebra mussel has made the transatlantic migration, Americans may have to prepare to redesign and maintain its water-supply facilities, like the Europeans did. Dr. Jon Stanley, the director of the US Fish and Wildlife Service National Fisheries Research Center in Ann Arbor, calculates that over the next 10 years the redesigning of the water-supply system alone will cost Great lakes municipalities, manufacturers and electric utilities $1.2 billion. On top of that, he proposes the cost to shipping, pleasure boating and fisheries in the Great Lakes to be nearly $3 billion over the next decade. Until industry comes up with better ways of controlling the mussels, we may just have to adapt.

As a counter proposal for killing zebra mussels, biologist Anna Stanczkowska- Piotowska of Poland's Agricultural- Pedagogical University believes that the zebra mussel is not without virtue and that we should learn to live with it instead of killing it. She points out the the zebra mussel's byssuss extrudes an adhesive that may have commercial value. Its appetite for foul-smelling algae can markedly sweeten the taste of drinking water. Perhaps most admirable of all, the zebra mussel has performed acts of public service by dramatizing the threat posed by tiny organisms that hitch rides around the world. Both the US and Canada are moving to restrict the discharge of ballast water into the Great Lakes, a measure of ecological prudence that is long overdue.

The zebra mussel is now well established throughout the Great Lakes and their connecting channels, as well as in numerous inland river systems in North America. There seems to be no way to eliminate these mussels from North American waters without harming other aquatic life forms. This leaves many scientists and biologists in a difficult situation, for it is up to them to try to control the impact of zebra mussels populations on aquatic ecosystems. Though the zebra mussel's invasion of the Great Lakes threatens the region's environment and economy, it has brought one unexpected benefit. Because each of the zebra mussels can filter microscopic algae from up to 1 liter of lake water per day, the bivalves have dramatically cleared Lake Erie's water. However this does not change the fact that these mussels have had a disastrous effect on the endemic species in many aquatic habitats and on sport and commercial fishing, navigation, boating, and agricultural irrigation throughout North American fresh water surfaces. I have cited many different human responses and scientific recommendations for controlling the zebra mussels yet none of these have created any significant results. Hopefully in the future new control alternatives will be developed in order to eliminate the harmful effects of the zebra mussel into the aquatic ecosystems of North America.