Zebra (left) and quagga mussels
Credit: USGS

zebra mussel
Dreissena polymorpha

History:

Believed to be introduced to the Great Lakes during ballast water exchange from a cargo ship from the Black Sea
Since being discovered in Great Lakes in 1988, the species has spread widely into freshwater habitats across North America
Native to Black, Caspian, and Azov Seas

Characteristics:

Named for the striped pattern on its shell - Black or brownish shell with cream or white stripes
Shells colors vary widely; some pale or completely white
Maximum size less than 2 in (5 cm) long; often less than 1 in
Zebra shell is stable when placed on it's flattened hinge side while quagga mussels, lacking a flat side, fall over
Valves (shell halves) are symmetrical, forming a straight line when closed whereas the quagga mussel valves are asymmetrical, forming a curved line when the valves are closed

Habitat:

Lakes, estuaries, streams
Attached to hard surfaces such as rocks, wood, and plants and to manmade structures of concrete, metal, and fiberglass
Tolerate salinity to 6 ppt, temperatures to approximately 29 degrees C

Known Distribution:

21 states and 2 provinces including Quebec, New York, Vermont, Massachusetts, and Connecticut

Impacts:

Voracious filter feeders, removing microscopic plants and animals from the water, reducing food available to other aquatic animals
May cause declines in fish populations
Clog intakes for power plants, industrial facilities, and public drinking water supplies
Foul boat and ship hulls
Economic impacts in the billions of dollars

Common Vector(s):
Overland transport (e.g. boats, equipment)Shipping: Ballast waterShipping: Fouling

Zebra mussels (Dreissena polymorpha)
Credit: Whitney Cranshaw, Colorado State University