Zebra mussels are a type of freshwater mollusk. The scientific name for this mussel is dreissena polymorpha. This freshwater mollusk is native to Asia and Eastern Europe, and is slowly invading the Great Lakes and other fresh waters of the United States. Zebra mussels have a distinct striped pattern on each mussel shell, or valve. These small freshwater mollusks are considered to be a threat to the ecosystem, and have caused millions of dollars in damage to power plants and other structures.
The shell of the zebra mussel is tan or beige and exhibits a dark zigzag pattern across each valve. Not all zebra mussels have the same appearance. Some may be darker brown with less prominent stripes. Rarely, mussels with very little striping are found. They generally are no larger than an inch (2.54 centimeters) to 2 inches (5.08 centimeters) long and have a lifespan of approximately five years.
These mussels are algae eaters and feed by filtering large amounts of water each day. Female zebra mussels can lay as many as one million eggs during spawning season, and may even lay eggs twice in a season. Young mussels are microscopic and free swimming. They can be easily spread by currents and are also transported in the ballast waters of ships. Older and larger mussels often attach themselves to ship structures and are carried into to other fresh waters.
The original habitats of these mollusks were the freshwaters of Russia, Poland, and the Balkans. It is believed they were picked up in ballast waters of a ship in European waters and later released in Lake St. Clair in Canada, where they were found in 1988. Lake St. Clair is a small body of water connecting Lake Erie and Lake Huron. The invasive zebra mussels have since invaded the entire Great Lakes region and many of the other freshwater lakes and rivers of the eastern United States. Zebra mussels have been found in the Mississippi, Cumberland, Tennessee, Hudson, and Ohio rivers.
Numerous water treatment plants and factories have spent millions of dollars as a result of damage caused by zebra mussels. The tiny mollusks attach themselves to intake pipes and other structures, resulting in massive damage. Zebra mussels are also an extreme danger to other hard-shelled aquatic wildlife. They attach themselves to the shell of lobsters, clams, native mussels, and other hard-shelled species, rendering them incapable of movement and unable to eat, breath, or reproduce.