The zebra mussel, Dreissena polymorpha, is a small freshwater
mussel. This species was originally native to the lakes of
southeast Russia. However, it has been accidentally introduced in
many other areas, and has become an invasive species in many
different countries.
Zebra mussels superficially resemble marine mussels in the
family Mytilidae, and like them, are attached to solid substrates
with a byssus. However, zebra mussels are not at all closely
related to the mytilids; they are much more closely related to the
Veneridae, the Venus clams.
Zebra mussels get their name from a striped pattern which is
commonly seen on their shells, though not all shells bear this
pattern. They are usually about the size of a fingernail, but can
grow to a maximum length of nearly 2 in (5.1 cm). The shape of the
shell is also somewhat variable.
North American Invasion
In the U.S. and Canada, they were first detected in the Great
Lakes in 1988, in Lake St. Clair, located between Detroit,
Michigan, and Windsor, Ontario. It is believed they were
inadvertently introduced into the lakes in the ballast water of
ocean-going ships traversing the St. Lawrence Seaway. Another
possible often neglected mode of introduction is on anchors and
chains, although this has not been proven. Since adult zebra
mussels can survive out of water for several days or weeks if the
temperature is low and humidity is high, chain lockers provide
temporary refuge for clusters of adult mussels that could easily be
released when transoceanic ships drop anchor in freshwater ports.
They have become an invasive species in North America.
From their first appearance in American waters in 1988, zebra
mussels have spread to a large number of waterways, including Lake
Simcoe the Great Lakes region and the Mississippi, Hudson, St.
Lawrence, Ohio, Cumberland, Missouri, Tennessee, Colorado, and
Arkansas Rivers. They disrupt the ecosystems by monotypic
colonization, and damage harbors and waterways, ships and boats,
and water treatment and power plants. Water treatment plants were
initially hit hardest because the water intakes brought the
microscopic free-swimming larvae directly into the facilities.
In July, 2009, The Massachusetts Department of Conservation and
Recreation confirmed that zebra mussels had been found in Laurel
Lake in the Berkshires, the first documented case in a
Massachusetts body of water.
In September, 2009, the Minnesota Department of Natural
Resources announced that live zebra mussels have been found in
Pelican Lake, Minnesota. This was the first confirmed sighting in
the Red River Basin, which extends across the international border
into the province of Manitoba. In July, 2010, the North Dakota Game
and Fish Department confirmed the presence of zebra mussel veliger
in the Red River between Wahpeton, N.D. and Breckenridge, Minn.
In 2010 California reported invasions.
A common inference made by scientists predicts that the zebra
mussel will continue spreading passively, by ship and by pleasure
craft, to more rivers in North America. Trailered boat traffic is
the most likely vector for invasion into Western North America.
This spread is preventable if boaters thoroughly clean and dry
their boats and associated equipment before transporting them to
new bodies of water. Since no North American predator or
combination of predators has been shown to significantly reduce
zebra mussel numbers,[citation needed] such spread would most
likely result in permanent establishment of zebra mussels in many
North American waterways.
The cost of fighting the pests at power plants and other
water-consuming facilities is $500 million a year in the U.S.,
according to the Center for Invasive Species Research at the
University of California, Riverside.