Zebra mussels first appeared in Lake St. Clair (yellow star, north of Lake Erie), possibly from ship’s ballast water from the Black Sea region. They rapidly spread downstream with the current, and upstream and to other watersheds on boats, with bait, and by other man-mediated mechanisms.
Our herbicides and algaecides do not affect the Zebra Mussels. Zebra Mussels pose significant social, economic and ecological concerns for the Great Lakes and other inland North American waters. The prolific mollusk tends to biofoul and restrict the flow of water through intake pipes, disrupting supplies of drinking, cooling, processing and irrigating water to the nation’s domestic infrastructure. The mussel also attaches to boat hulls, docks, locks, breakwaters and navigation aids, increasing maintenance costs and impeding waterborne transport.
Besides these commerce-related disruptions, heavy infestations of zebra mussels also can alter freshwater ecosystems, possibly defeating aquatic resource restoration and development efforts. First observed in the mid-1980s in Lake St. Clair, zebra mussels are not just a Great Lakes problem. Carried mainly by the normal flow of water and boat traffic, zebra mussels have already colonized the Hudson, Ohio, Illinois, Tennessee, Susquehanna, Mississippi and Arkansas rivers. Zebra mussels now inhabit 12 states and the Province of Ontario.
While the zebra mussel invasion and its immense impact on the Great Lakes ecosystem has focused attention on the issue, the introduction of non-indigenous (exotic) species is not a new problem. An estimated 130 non-indigenous species have been introduced to the Great Lakes, most of them arriving since the St. Lawrence Seaway opened in 1959. Several of these species – including the sea lamprey, alewife, smelt, carp and milfoil – have contributed to massive changes in Great Lakes fish and plant communities.
Nor is the introduction of non-indigenous species a problem isolated to the Great Lakes. An estimated 350 non-indigenous species of marine and estuarine plants and animals have been introduced to U.S. coastal waters. These invaders can be a serious threat to native biotic communities and important fish species.
Control and Prevention:
Most scientists believe that zebra mussels cannot be eradicated, so the goal now is to learn to control or accommodate them. Better strategies to prevent the spread of zebra mussels and the introduction of new species are required. The quagga mussel, believed to be a new species of zebra mussel, has been found in Lake Ontario, and it also is spreading. The vehicles for this spread are numerous and include the hundreds of thousands of recreational boats trailered to and from the Great Lakes each year, and commercial vessels moving between ports.
Ecological Impacts:
Zebra mussels are filter feeders. Each adult is capable of filtering a liter of water per day, removing almost every microscopic aquatic plant (phytoplankton or algae) and animal (zooplankton). Zebra mussel colonies in Lake Erie have reached astounding densities of 70,000 per square meter, and experts estimate that Lake Erie’s zebra mussel population filters the entire volume of the lake’s western basin once a week. The mussel has increased Lake Erie’s water clarity up to 600 percent and reduced some forms of phytoplankton, the basis of the lake food web, by as much as 80 percent. The increased water clarity has allowed light to penetrate deeper into the water column, allowing rooted aquatic vegetation to increase greatly in density. Bottom-dwelling (benthic) forms of algae appear to be increasing, as do several forms of insect-like benthic organisms. Researchers have also found that zebra mussels even colonize the shells of freshwater clams and have almost totally eliminated some native species in certain areas.
Because of the huge volumes of water they filter and their high body-fat content, zebra mussels accumulate about 10 times more PCBs and other toxic contaminants than native mussels. These contaminants are transferred up the food-chain to waterfowl and fish that eat zebra mussels. This potential to significantly affect contaminant cycling is of great concern in the Great Lakes, where health advisories already exist for consumption of some species of fish.
Impacts on Commerce and Industry:
Zebra mussels rapidly colonize water intakes, forming layers up to eight inches thick. Such infestations along Lake Erie have disrupted the water supply to Monroe, Mich., on several occasions. Millions of dollars are being spent annually by Great Lakes cities and industries to unclog intake pipes and prevent further infestation. Much research is underway to help in this endeavor, and more is needed. In collaboration with the Erie County Water Authority, Sea Grant-funded engineers are currently field-testing a cable-crawling, robotic submarine to locate zebra mussels in water intakes and perhaps to remove them as well.
Hot water has been shown to be an effective treatment for zebra mussels, but it is not always a practical alternative. Chlorine is probably the most popular treatment currently in use, but increased chlorination clearly contradicts the efforts of the Great Lakes community to reduce the amount of chlorine entering the ecosystem. Research has shown potassium, bromine, ozone and ultraviolet light to be possible alternatives to chlorine. More than 30 other compounds are also being studied to determine the effectiveness against zebra mussels and their environmental impact.
Our herbicides and algaecides do not effect the Zebra Mussels.
