TEACH Calendar of Events
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2 | The Zebra Mussel
Zebra mussels are a stark example of the explosive growth potential of non-native species. Zebra mussels were first discovered in the Great Lakes in the 1960s. Just one year after introduction, their population was estimated at densities of 35,000 per square yard (30,000 per square meter). Many scientists now consider the ecosystem changes caused by zebra mussels to be more significant than the changes caused by nutrient and toxic loadings combined.
Zebra mussels (Dreissena polymorpha) are small, fingernail-sized mussels native to the Caspian Sea region of Asia. They are believed to have been transported to the Great Lakes via ballast water from a transoceanic vessel. The ballast water, taken on in a freshwater European port was subsequently discharged into Lake St. Clair, near Detroit, where the mussel was discovered in 1988. Since that time, they have spread rapidly to all of the Great Lakes and waterways in many states, as well as Ontario and Quebec.
Detailed Map: The Great Lakes-St. Lawrence River systemZebra mussels have had extensive economic impacts. According to a 1995 Ohio Sea Grant study, large water users on the Great Lakes spend an annual average of $350,000 to $400,000 per user just to clear zebra mussels from their intake pipes. The mussels are also affecting the tourism industry, as their sharp-shell remnants clutter beaches and are encrusting historically significant shipwrecks throughout the Great Lakes. Quagga mussels, a near relative of the infamous zebra mussel, are able to survive in deeper waters and different sediment types, effectively expanding the infestation to new areas of the lakes.
Graphics: Zebra mussels (with black stripes) attached to freshwater snails, courtesy Univ. of Michigan, Center for Great Lakes and Aquatic Sciences; Zebra mussels cover a car pulled from the bottom of the Great Lakes, courtesy R. Griffith/Ontario Ministry of Natural Resources.