Scientific Name: Dreissena polymorpha
What are Zebra Mussels?
Zebra mussels (Dreissena polymorpha) look like small clams with a yellowish or brownish "D"-shaped shell, usually with dark and light-colored stripes (hence the name "zebra"). They can grow to two inches long, but most are under an inch. Zebra mussels usually grow in clusters containing numerous individuals and are generally found in shallow (6-30 feet), algae-rich water.
These small, fingernail-sized mussels are native to the Caspian Sea region of Asia. With the opening of the St. Lawrence waterways, ships from all over the world made their way to the Great Lakes. It is believed that ships containing water from Eastern Europe, where zebra mussels are native, discharged not only water but zebra mussel larvae and juveniles as well into the Great Lakes watershed. These mussels found a welcoming environment and quickly began to populate North American waters. The first sighting of zebra mussels was in 1988 in Lake St. Clair, near Detroit, Michigan.
Zebra mussels are a cause for concern because of their incredible rate of reproduction, because they often form an impenetrable crust of shell on any hard surface. The animals clog water intake pipes used by power plants and water treatment facilities and attach themselves to docks, boat bottoms, dam structures and other human built structures. They also attach to the shells of native mussels in such numbers that they can kill the mussel by holding its shell closed. Zebra mussels are strong competitors not only for living space but for food. Each zebra mussel can filter as much as one liter of water per day plankton that would normally be food for native mussels.
Why Are There So Many?
There are many reasons that the Zebra Mussel population is being so successful in North America:
Stopping the Spread of Zebra Mussels
Zebra mussels spread to inland waters either as veligers (mussel larvae) transported in water, or as adults attached to boat hulls, engines, bait traps, or other hard surfaces. Veligers can't survive drying, but they can survive in any small pool of water. Adult zebra mussels can close their shells and survive drying for several days. This time is extended in moist environments.
The Minnesota Department of Natural Resources, in cooperation with Minnesota Sea Grant and the Bell Museum of Natural History, has published a handy field guide to exotic species with this checklist to help you prevent the spread of zebra mussels and other exotic species from one body of water to another:
Did You Know?
At Lake Onalaska, near LaCrosse WI, the Mississippi River is about 4 miles wide. The combination of water held behind Lock and Dam #7 and water held by damming the Black River form this broad reach of the Mississippi River.