| Mollusks (Phylum Mollusca)
are found in marine, brackish, and fresh waters. They include a diverse group
of animals such as clams, mussels, oysters, scallops, abalone, conchs, shipworms,
snails, nudibranchs, chitons, squids, and octopuses. Common methods of introduction
include ballast water introductions, aquarium releases, and accidental release
from aquaculture facilities. Displacement by competition is the most frequently
observed impact on native species. The most notable nonindigenous mussel introduction
is the zebra mussel (Dreissena polymorpha), a native of eastern Europe.
Zebra mussels were first discovered in 1988 in Lake St. Clair, Michigan; the initial
introduction is believed to have occurred in 1985 or 1986 via ballast water. Since
then, they have proven to be a very costly pest to municipal and industrial water
users. Additionally, zebra mussels can destroy entire colonies of native mussels
by interfering with such basic functions as respriation, reproduction, feeding,
growth, and movement. |
