What Are Zebra Mussels?

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.

Zebra mussels are small, invasive freshwater bivalves native to the lakes of southern Russia. They were first discovered in the United States in the late 1980s in the Great Lakes, likely introduced through ballast water discharged from ships. Their distinctive zebra-like stripes on their shells make them easily recognizable.

Zebra mussels can drastically alter ecosystems by filtering water, which removes plankton and decreases the food supply for native species. According to the U.S. Geological Survey, they also attach to and smother native mussels and can form dense colonies that clog water intake structures, affecting municipal water supplies and power generation.

The economic impact of zebra mussels is significant. They cause billions of dollars in damage and control costs in North America. Industries such as power plants and water facilities spend millions annually to remove and prevent clogging of their infrastructure, as reported by the National Oceanic and Atmospheric Administration.

Eradicating zebra mussels is extremely challenging once they establish in a water body. Efforts typically focus on prevention and management. Methods like chemical treatments, manual removal, and UV light have been used, but these are often costly and labor-intensive with varying degrees of success.

Preventing the spread of zebra mussels involves cleaning, draining, and drying boats and equipment before moving them to different water bodies. Educational campaigns by wildlife agencies emphasize the "Clean, Drain, Dry" mantra to raise awareness among boaters and fishermen about the importance of these preventative measures.

While zebra mussels have few natural predators in North America, some species like certain types of fish, ducks, and crayfish may consume them. However, these predators have not significantly controlled the zebra mussel population. Research into biological control methods is ongoing, but no effective predator has been identified to manage their spread effectively.