The zebra mussel is a small freshwater mollusk, native to the Caspian and Black sea region of Eurasia. Adult zebra mussels attach themselves to firm surfaces with strong hair-like fibers called byssal threads. Each female zebra mussel can lay up to one million eggs during the summer months when water temperatures rise above 50°F. The fertilized eggs hatch into microscopic juveniles called veligers, which can travel great distances following water currents or when transported on boats and trailers. These methods of spread lead to rapid infestation of new waterbodies. Once settled on a firm surface, the veligers grow rapidly into "D" shaped, one inch size adult mussels. Colonies of adults can attain densities of up to 700,000 individuals per square meter. Zebra mussels generally live for two years in North American waters, but can survive for as long as 4-5 years.

In 1988 the zebra mussel was first identified in the United States in Lake St. Clair of the Great Lakes region. It is believed that the emptying of ballast water from commercial transatlantic ships introduced the mussel into the Great Lakes. Since then, zebra mussels have spread throughout the interconnected waterways in the eastern U.S. and were confirmed in Lake Champlain during the summer of 1993. Adult zebra mussels can now be found throughout much of Lake Champlain and the lower reaches of many of the lake's tributaries. In 1998 adult zebra mussels were discovered in Lake Bomoseen in Hubbarton and Castleton, Vermont. Adult zebra mussels have not found in any other Vermont lake or pond.

Zebra mussels can clog the intake pipes of industrial and water facilities such as the water supply plants along Lake Champlain. Similar effects can occur in small lakeside residential water systems and agricultural irrigation systems. Fortunately, most facilities and home owners on Lake Champlain averted serious impacts by installing control technologies at the beginning of the infestation. However, the costs for installing and maintaining such technologies has been significant. Zebra mussels also attach themselves to the hulls, engines and other submerged parts of moored boats. Boaters on Lake Champlain must now take special precautions to prevent damage to their boats and to avoid spreading zebra mussels to other waterbodies when trailering their boats. Zebra mussel shells are very sharp and swimmers at many of Lake Champlain's popular swimming areas must now wear protective footwear to avoid painful cuts. Additionally, Lake Champlain has numerous historic sunken ships and other artifacts which are at risk of becoming obscured or damaged by colonies of zebra mussels growing on them.

Zebra mussels can have numerous ecological impacts as well. Most significantly, the mussels are extremely efficient filter-feeders, consuming large portions of the microscopic plants and animals which form the base of the food chain. Over time, this feeding behavior can affect a lake's entire ecological balance, causing significant shifts in native species populations. Zebra mussels can also attach themselves to the shells of native mussels, impeding movement, feeding and respiration. As the native mussels become heavily encrusted they suffer increasing stress, losing body weight until they eventually succumb from either starvation, disease, or osmoregulatory problems. As a result of the invasion of zebra mussels into Lake Champlain, and their direct impact on our native mussel populations, several native mussels are listed as endangered or threatened in the state of Vermont.

The following native mussel species are listed as Endangered:

• Ligumia recta, Black sandshell
• Anodontoides ferussacianus, Cylindrical papershell
• Lasmigona costata, Fluted shell
• Leptodea fragilis, Fragile papershell
• Potamilus alatus, Pink heelsplitter
• Lampsilis ovata, Pocketbook

The following native mussel species are listed as Threatened:

• Pyganodon grandis, Giant floater

• Aquatic Nuisance Species Spread Prevention Information
• Aquatic Nuisance Species Watchers Program
• Lake Champlain Zebra Mussel Fact Sheet (pdf, 237 KB)
• Lake Champlain Zebra Mussel Monitoring Program
• USGS - Zebra Mussel North America Distribution Maps & Information
• Zebra Mussel Links

Updated: June 2004