It's been almost a decade since the Exxon Valdez spilled 11 million gallons of crude oil into the clear waters of Alaska's Prince William Sound, but it's still hard to shake the images of oil-drenched birds gasping for air. It may be even harder to imagine that foreign marine life invading new waters could cause more damage than that oil spill. Foreign species eat native species or their food sources, destroy habitats, and block undersea pipes at power stations or factories. The problem of marine invasions is worldwide, largely a byproduct of the shipping trade. Cargo ships such as this one in the port of Los Angeles flush out alien marine species in their ballast water.
Many marine species enter waters in the ballast water used to stabilize ships.
The water is picked up in one or more ports and then discharged into others. The United States port of Baltimore alone receives more than 12 million metric tons of foreign ballast each year, originating in 48 different foreign ports. Ninety percent of that carries live organisms, according to the US Department of the Interior, which is charged with safeguarding the environment. Other bioinvaders travel in imported bait and via the aquarium trade. Last week, President Clinton signed an executive order expanding government efforts to combat foreign predators on land and sea.