DESCRIPTION: Zebra mussels are freshwater bivalve mollusks that typically have a dark and white (zebra-like) pattern on their shells, but may be any combination of colors from off-white to dark brown (hence the name "polymorpha"). They are alien to North America but have invaded many of our waters, east of the 100th Meridian from Ontario Canada and the Great Lakes to southern Louisiana. Zebra mussels are usually about an inch or less long, but may be larger. When healthy, they attach to hard substrates, often found in clusters much like marine mussels, but unlike any other freshwater bivalve in North America.

PATHWAYS/HISTORY: Zebra mussels are native to eastern Europe and western Asia, from the Black and Caspian Sea drainages. Until the mid 1980s there were no zebra mussels in North America. Quickly that changed when they were inadvertently introduced into waters near the Great Lakes region. It is suspected that zebra mussels hitched a ride in ballast water tanks of commercial ships. Zebra Mussels were first discovered in the United States in Lake St. Clair near Detroit, Michigan in 1988. Since the '80s, zebra mussels have spread, unchecked by natural predators, throughout much of the eastern United States. They currently infest much of the Great Lakes basin, the St. Lawrence Seaway, and much of the Mississippi River drainage system. The have begun to spread up the Missouri River and Arkansas River.

RISKS/IMPACTS: Zebra mussels reproduce quickly and in large numbers, typically creating large populations. Zebra Mussel densities have been reported to be over 700,000 individuals per square meter in some facilities in the Great Lakes area. Zebra mussels are biofoulers that occlude pipes in municipal and industrial raw-water systems, requiring millions of dollars annually to treat. They produce microscopic larvae that float freely in the water column, and thus can pass by screens installed to exclude them. Monitoring and control of Zebra Mussels costs millions of dollars annually. As filter feeders, zebra mussels remove suspended material from the habitat in which they live. This includes the planktonic algae that is the primary base of the food web. Thus, zebra mussels may completely alter the ecology of water bodies in which they invade.

MANAGEMENT: Once zebra mussels have established in a water body, there is no known method of eradication. Preventing spread remains our best course of action. Since zebra mussels have planktonic (free drifting) larvae, preventing spread to water bodies downstream from known infestations may not be possible. However, westward, overland spread is assumed to be largely due to trailered boat traffic. Thus, further westward spread of zebra mussels is highly preventable.

WHAT YOU CAN DO: As a general practice, wash and scrub your boat and equipment, allowing it to completely dry, before moving to a new water body. Tiny mussels attached to your boat may not be visible to the naked eye. High pressure water at a temperature above 104 ºF will kill zebra mussels and is the best choice for washing your boat and equipment in order to prevent spread. Be sure to drain all water from your boat, including bilges, live wells, bait buckets and coolers. Never transport water or plants from one water body to another.

PROFILE CREDIT: David K. Britton, USFWS - IMAGE CREDIT: David K. Britton, USFWS