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Alien marine life eats locals for lunch

Invasive foreign species - some damaging - are spreading around globein ship ballasts

By Lori ValigraSpecial to The Christian Science Monitor / February 11, 1999


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.

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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.

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.

In the US, it costs more than $5 billion a year to control marine bioinvaders, according to Cornell University ecologist David Pimentel. The zebra mussels in the Great Lakes alone cost $3 billion.

Last week, President Clinton signed an executive order expanding government efforts to combat foreign predators on land and sea. The order creates an interagency Invasive Species Council that will have 18 months to devise a plan to contain the spread of bioinvaders (see related story page 12).

Zooplankton eat phytoplankton

About 1 percent of the hundreds of sea immigrants in American waters breed and cause a major, damaging invasion. For example, about a year ago, the US Fish and Wildlife Service discovered four new species of tiny zooplankton in Alaska's Prince William Sound brought in ballast water from East Asia via San Francisco. Those zooplankton eat phytoplankton, a food for the Dungeness crab. "These four species of zooplankton may in the long run prove to be infinitely more devastating than the Exxon Valdez oil spill itself, because the species may insert themselves into the food chain," Secretary of the Interior Bruce Babbitt told a recent conference on marine bioinvasions.

One of the more recently discovered predators, an Asian snail found in Virginia's lower Chesapeake Bay, threatens to deplete stocks of oysters and clams on which it preys. The snail, Rapana venosa, was identified about five months ago by Roger Mann, professor of marine science at the Virginia Institute of Technology in Gloucester Point, and his colleagues. But they suspect it may have invaded the Chesapeake's waters as long as four years ago. They worry the hardy snail, which can live in wide temperature and salinity ranges, might also infest the even richer oyster and clam beds of Long Island Sound.

"They can eat one clam every two or three days for the 10 years of their life. That's a lot of clams," Professor Mann says. "I think they are a real cause for worry."

Mann and colleague Juliana Harding, senior marine scientist at the institute, started a project in August 1998 to study the Rapana snail. They say the animal's eggs likely were transported in ballast water around 1940 from its native Sea of Japan to the Black Sea, the eastern Mediterranean, and then via coal ships to Hampton Roads, a major coal-exporting channel in southeast Virginia linked to the Chesapeake Bay.

So far, the snails are not known to have spread outside the lower Chesapeake, Mann says. But ships thought to transport snail eggs in their ballast have regular routes from the bay through Baltimore, Philadelphia, New York, and Boston. "We have a problem in Virginia that I can guarantee will be a big problem in Connecticut in 20 years," Mann says.

Although the Chesapeake Bay is home to about 160 foreign species, the Rapana snail is the only one proving to be particularly hardy and destructive.