Class : Bivalvia
Subclass : Heterodonta
Order : Veneroida
Family : Dreissenidae
Genus : Dreissena
Species : polymorpha
Length : .25-2in (.6-5cm)
IUCN Status : Not listed
Zebra Mussels were originally located in Southwest and Central Asia, in the Black and Caspian Sea regions. By the 1800s however, these little guys were invading waterways throughout Europe, making it as far as England and Ireland. In 1988, they were first discovered in the American Great Lakes, and are now considered an invasive species.
Zebra Mussels aren't particularly large, as a adults they rarely grow above two inches. They have a "D" shaped shell with an opening. Out of this opening comes a threadlike external organ called a Byssus, which allows them to attach to just about anything. They even attach themselves to other living organisms. Zebra Mussels are filter feeders; they go through about a quart of water each day and consume algae and phytoplankton.
So why are Zebra Mussels so bad? Well first off, they are prolific breeders. Females produce between 30,000 and 1,000,000 eggs every year, and adults can live as long as 6-8 years. The larvae are small and free-swimming, which makes it very easy for them to get into new water supplies and cause contamination. Because they attach to most surfaces and filter so much water, they threaten the food supplies of native species. They have also caused the decline of other Mussel species, since they will attach themselves to those as well.
Strangely, Zebra Mussels have a positive effect on some species. Because they filter so much detritus, water is clearer in certain areas, which prompts growth in underwater plants. This in turn feeds fish and other aquatic animals. Zebra Mussels are also a food source for several species. However, there are so many of them that even with rapid consumption their numbers are not put in check.