Zebra Mussel

The zebra mussel (Dreissena polymorpha) is an invasive freshwater bivalve native to Europe. Zebra mussels are easily introduced from one water body to another, altering the ecosystem of their invaded habitat and costing millions in damage to municipal and industrial facilities.

How were zebra mussels introduced to the Bay watershed?

Zebra mussels are native to the Caspian and Black seas in Eastern Europe. In 1988, the first zebra mussel was found in North America in Lake St. Clair in the Great Lakes region. It was most likely introduced there via ballast water from a European ship. By 1989, zebra mussels were well established throughout the Great Lakes, and by the end of 1993 they had found their way to many major rivers and lakes in eastern North America and Canada.

In the Chesapeake watershed, zebra mussels have spread to water bodies in Maryland, New York, Pennsylvania and Virginia, including:

• The lower Susquehanna River in Maryland.
• Eaton Brook reservoir in Madison County, New York, on the upper Chenango River of the Susquehanna River basin.
• Canadarago Lake and Oaks Creek into the Susquehanna River in Otsego County, New York.
• The upper Susquehanna River to Binghamton, New York.
• Richland Quarry in eastern Pennsylvania.
• Milbrook Quarry in Prince William County, Virginia. (This population has been successfully eradicated.)

Why are zebra mussels considered to be invasive?

Zebra mussel research in North America has shown that these bivalves severely impact their invaded environment.

• Zebra mussels are extremely efficient filter feeders. While filtering increases water clarity, zebra mussels significantly reduce the amount of plankton available to native filter feeders.
• Zebra mussels are major biofouling organisms. They can encrust native mussels and crayfish and attach themselves to buoys, ropes, docks and boat hulls, seriously impacting navigation and boating.
• Large clumps of zebra mussels clog pipes that provide cooling water to power plants, processing water to industrial plants and raw water for municipal water treatment facilities. It is estimated that zebra mussels cost the power industry more than $3.1 billion from 1993 to 1999.
• Sharp zebra mussel shells that litter beaches and swimming areas can harm people and animals.

What is being done to manage zebra mussels?

In most cases, eradication of zebra mussels is relatively impossible once a population becomes established in a large body of water. This reaffirms the importance of prevention efforts in areas like the Chesapeake watershed, where there has been little colonization thus far.

Some efforts to limit and control the spread of zebra mussels to the Bay watershed include:

• An established zebra mussel monitoring program in Pennsylvania.
• Citizen reports to state environmental agencies.
• Federal laws that identify zebra mussels as an invasive species and prohibit their sale and transport into the United States.
• Public outreach efforts that teach citizens to clean their boat hulls, trailers and other recreational equipment before moving them to a new lake.
• Chemicals, dredging and hand harvesting have been used to control zebra mussel populations. However, treatments need to be repeated often because the mussels re-colonize very quickly.