The zebra mussel (Dreissena polymorpha) is an invasive

species of freshwater mollusk that threatens the Ohio River

and other fresh water systems in North America. They are a

bivalve variety of mussel, meaning that they have shells

with two hinged parts. Zebra mussels come in a wide range

of brown and tan colors, but their shells feature a

characteristic stripped pattern that makes them easily recognizable (figure 1). A rare variety of zebra mussels do not have striped shells. These mollusks are usually reach about an inch in size and can live in fresh water that is anywhere from six to twenty four feet deep. They have a maximum lifespan of 5 years. A mature female zebra mussel is capable of producing up to one million eggs each year.



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Zebra mussels are native to the Balkans, Poland, and Russia. The first zebra mussel sighting was at St Clair lake in 1988. It is thought that they were introduced to the Great Lakes via ballast water (used to stabilize boats) from European ships. Once the ships reached a harbor, this water was dumped into the lake, releasing mussel larvae. Presently, zebra mussels can be found in the Ohio River Basin, Mississippi River Basin, and all five Great Lakes. The rapid spread of these mollusks in evident in figure 2. They spread quickly because young, free swimming zebra mussels are quickly transported to new areas by currents. This invasive species is a threat to hundreds of lakes in the United States.

Zebra mussels damage habitats in several ways. They feed by filtering water for algae. Large populations of zebra mussels deplete the food sources of native mussel species and other organisms. Unlike most fresh water mussel species, zebra mussels have string-like organs called byssus that make them capable of attaching to almost any hard surface. This enables them to live on virtually any structure or slow moving organism in an aquatic ecosystem, including crayfish, turtles, other mussels, boats, and water treatment pipes.

When mass quantities of zebra mussels colonize an animal, they can prevent it from eating and reproducing. This depletes the populations of native species and disrupts the

                                     food webs of fresh water ecosystems. For instance, decreasing a

                                     crayfish population could have a major impact on several species

                                     because crayfish are both predators and food sources for aquatic

                                     and terrestrial animals. Figure 3 shows a crayfish disabled by

                                     zebra mussels. Zebra mussels have a severe impact on native

                                     mussels species in Kentucky, five of which are endangered. (The

                                     five endangered species are the pink mucket (Lampsilis abrupta), orangefoot pimpleback (Plethobasus cooperianus), fat pocketbook (Potamilus capax), clubshell (Pleurobema curtum), and fanshell (Cyprogenia stegaria) mussels.)

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Zebra mussels also threaten human activities. In addition to being unsightly, their colonies can ruin boats, docks, and other underwater equipment. They are also exceptionally difficult to remove from these structures.

Swimmers can cut themselves on the

mussels’ sharp shells. Also, their

presence can deplete stocks of fish

used for recreational fishing. These

factors can have a negative impact on

tourism in areas such as beaches and

lakes that are heavily infested with this

invasive species. Figure 4 illustrates the

vast amounts of zebra mussel shells

that accumulate on the beaches of Lake

Erie. Mussels can also clog water

treatment pipes and therefore interfere

with the productivity of water treatment plants.