Return to the Wild - Evolving perspectives on Canadian wildlife
The zebra mussel is not native to Canada but now flourishes in the Great Lakes and beyond.

Did you know?

In one year, a female adult zebra mussel can produce from 30,000 to one million eggs.

Scientific name: Dreissena polymorpha
Average length: 2 cm–4 cm
Average lifespan: 2–4 years
A woman holds a stick with many zebra mussels attached to it.

About

Biology

The zebra mussel is named for the striped pattern usually found on its shell, which is triangular or D-shaped. The shell has a flattened underside and a very sharp edge. The species displays many variations in shell pattern, colour and shape. Although typically small, some specimens can reach up to five centimetres in length.

Using stringlike projections called “byssal threads,” the zebra mussel is able to attach itself to various surfaces underwater. The threads are so strong that removing the mussel can be very difficult.

Habitat and behaviour

This freshwater mollusc can be found in lakes, rivers and even brackish lagoons. It is most abundant on hard surfaces, particularly rocks.

One of the zebra mussel’s most striking characteristics is its tendency to congregate by the tens, even hundreds, of thousands per square metre. Because of its extraordinary capacity for invading aquatic habitats, the zebra mussel has been deemed a nuisance species throughout much of North America. It damages and clogs underwater conduits, such as pipelines and tunnels. It also corrodes the hulls of ships, covers shipwrecks and destroys habitats by re-structuring the ecosystem.

The zebra mussel acts as a filter by removing microscopic particles such as algae from the water. After consuming the algae, it deposits its feces on the lake floor. This fertilizer provides nutrients for bottom-feeding species and ultimately for the fish that feed on them.

While this process may appear helpful by increasing water clarity and reducing pollution, it actually starves native species that rely on the algae as a food source. It also allows more sunlight to penetrate the water column, forcing some fish to find a new habitat.

Although the zebra mussel reproduces prolifically, only a small number — possibly less than 10 percent — reach maturity. The zebra mussel has a number of natural predators, including crayfish, waterfowl, muskrats and the freshwater drum fish.

Range

Originally native only to Europe, the zebra mussel was inadvertently introduced into the Great Lakes some time in the 1980s, probably in the ballast water of a foreign ship using the St. Lawrence Seaway.

Many scientists predict that the zebra mussel will continue to be spread by ships and pleasure craft to increasingly more rivers and lakes throughout North America.