ANS Task Force
Zebra Mussels and Quagga Mussels
( Dreissena polymorpha, Dreissena rostriformis bugensis)

Zebra MusselsDESCRIPTION: Zebra mussels, species Dreissena polymorpha, 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 Latin 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 have also been detected in a few Western states. 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 native freshwater bivalve in North America.

Quagga Mussels, species Dreissena rostriformis bugensis, are nearly identical to zebra mussels. In fact, many people refer to both species as "zebra mussels." Often, it takes an expert to tell the difference between a zebra and a quagga mussel. Both species are invasive in North America.

PATHWAYS/HISTORY: Zebra and quagga mussels are native to eastern Europe and western Asia, from the Black and Caspian Sea drainages. Until the mid 1980s there were no zebra or quagga mussels in North America. Quickly that changed when they were inadvertently introduced into waters near the Great Lakes region. Although it is suspected by many that zebra and quagga mussels hitched a ride in ballast water tanks of commercial ships, some people believe that they may have arrived on anchor chains or other equipment. Zebra Mussels were first discovered in the United States in Lake St. Clair near Detroit, Michigan in 1988. Quagga mussels were first detected in the Great Lakes a couple of years later. 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. Populations of zebra mussels have been detected in California, Colorado, and Utah. Although quagga mussels began overtaking zebra mussel populations within the Great Lakes, quagga mussels did not initially spread far beyond the Great Lakes. However, in January 2007, quagga mussels were detected in Lake Mead, near the Nevada/Arizona border. Lake Mead is a reservoir on the lower Colorado River, a river that supplies drinking and irrigation water to much of Southern California, Southern Nevada, and Arizona. Artificial water diversions allowed rapid downstream spread of quagga mussels into California and Arizona.

RISKS/IMPACTS: Zebra and quagga 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 and quagga 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 and quagga mussels cost millions of dollars annually. As filter feeders, both species 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 and quagga mussels may completely alter the ecology of water bodies in which they invade.

MANAGEMENT: There is no known method of eradication once zebra or quagga mussels have established in a large water body. Preventing spread remains our best course of action. Since zebra and quagga mussels have planktonic (free drifting) larvae, preventing spread to water bodies downstream from known infestations may not be possible. However, there is evidence to suggest that overland spread is largely due to trailered boat traffic. Thus, further spread of zebra and quagga 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. Prolonged exposure to high-pressure water at a temperature above 140 ºF will kill zebra mussels and is the best choice for washing your boat and equipment in order to prevent spread. Since this is a dangerously high temperature, it is recommended that boats that have been in infested waters should be professionally cleaned. Be sure to drain all water from your boat, including bilges, live wells, bait buckets and coolers. Let everything dry for several days. Never transport water or plants from one water body to another.

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


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