Invasive Marine Species

How do they get here?

Many exotics are brought intentionally. The Japanese oyster, the Manila clam, and the European mussel are all non-native species raised commercially in Washington. While these cultivated species may benefit humans, they now have abundant wild populations and are currently replacing several native species. Many destructive parasites and diseases have also been introduced accidentally along with the species we import.

Photo Courtesy of Marine Bioinvaders Web page: massbay.mit.edu/exoticspecies/ballast/index.html

Today, most marine and aquatic invaders arrive attached to ocean-going ships, or in ballast water carried in tanks inside these ships to keep them properly balanced in the water. Water taken up in one port is pumped out when the ships load cargo in another port. Any plants and or animals present in the water, including their planktonic larvae, can easily hitch a ride to a new environment.

Exotics arrive in other ways too. Serious invasions have resulted from the release of aquarium plants and animals into the local environment.

Why are invasive species a problem?

Not all introduced species become established. Of those that do, not all will become nuisance species. However, there is always the risk that the invader will harm native species or disrupt the environment it moves into. They may do this by preying on or competing with native species, or by bringing about physical changes to their new environment that impact everything else living there. They may become nuisance species without natural predators to control their numbers. In extreme cases, they may bring native species to the brink of extinction. American chestnut and elm are examples of tree species virtually extinguished in the last century by diseases and insect pests carried into this country accidentally. Regardless of the environment invaded, once an exotic species become established, it is nearly impossible to eradicate it.

The transport of marine and aquatic organisms in ballast water has received widespread attention. Current efforts to control this source of exotic organisms rely on voluntary ballast water exchange programs in offshore waters. Ships carrying water from other ports are asked to empty their tanks 200 miles offshore to reduce the likelihood that plants and animals carried in the water will reach the shore. While these programs may slow the arrival of some organisms, they are not likely to not stop the entry of animals such as tunicates that probably travel as adults attached to the ships themselves.

Go to Links for additional sites with information on non-native species.