Zebra mussel

The zebra mussel (Dreissena polymorpha ) is a small bivalve mollusk native to the freshwater rivers draining the Caspian and Black Seas of western Asia. This species of shellfish, which gets its name from the dark brown stripes on its tan shell, was introduced into the Great Lakes of the United States and Canada and became established sometime between 1985 and 1988.

The zebra mussel was first discovered in North America in June of 1988 in the waters of Lake St. Clair. The introduction probably took place two or three years prior to the discovery, and it is believed that a freighter dumped its ballast water into Lake St. Clair, flushing the zebra mussel out in the process. By 1989 this mussel had spread west through Lake Huron into Lake Michigan and east into Lake Erie . Within three years it had spread to all five of the Great Lakes.

Unlike many of its other freshwater relatives, which burrow into the sand or silt substrate of their habitat , the zebra mussel attaches itself to any solid surface. This was the initial cause for concern among environmentalists as well as the general public; these mollusks were attaching themselves to boats, docks, and water intake pipes. Zebra mussels also reproduce quickly, and they can form colonies with densities of up to 100,000 individuals per square meter. The city of Monroe, Michigan, lost its water supply for two days because its intake pipes were plugged by a huge colony of zebra mussels, and Detroit Edison spent half a million dollars cleaning them from the cooling system of its Monroe power plant. Ford Motor Company was forced to close its casting plant in Windsor, Ontario, in order to remove a colony from the pipes which send cooling water to their furnaces.

Although the sheer number of these filter feeders has actually improved water quality in some areas, they still pose threats to the ecological stability of the aquatic ecosystem in this region. Zebra mussels are in direct competition with native mussel species for both food and oxygen. Several
colonies have become established on the spawning grounds of commercially important species of fish, such as the wall-eye, reducing their reproductive rate. The zebra mussel feeds on algae, and this may also represent direct competition with several species of fishes.

The eradication of the zebra mussel is widely considered an impossible task, and environmentalists maintain that this species will now be a permanent member of the Great Lakes ecosystem. Most officials in the region agree that money would be wasted battling the zebra mussel, and they believe that it is more reasonable to accept their presence and concentrate on keeping intake pipes and other structures clear of the creatures. The zebra mussel has very few natural predators, and since it is not considered an edible species, it has no commercial value to man. One enterprising man from Ohio has turned some zebra mussel shells into jewelry, but currently the supply far exceeds the demand.

[Eugene C. Beckham ]

RESOURCES

PERIODICALS

Griffiths, R. W., et al. "Distribution and Dispersal of the Zebra Mussel (Dreissena polymorpha ) in the Great Lakes Region." Canadian Journal of Fisheries and Aquatic Science 48 (1991): 1381–1388.

Holloway, M. "Musseling In." Scientific American 267 (October 1992): 30–36.

Schloesser, D. W., and W. P. Kovalak. "Infestation of Unionids by Dreissena polymorpha in a Power Plant Canal in Lake Erie." Journal of Shellfish Research 10 (1991): 355–359.

Walker, T. "Dreissena Disaster." Science News 139 (May 4, 1991): 282–284.