CAMBRIDGE, Mass. -- Foreign marine life invading waters where they are not normally found has grown into a multibillion dollar problem as fishermen continue to dump exotic species, bacteria and viruses from their boats, biologists warned Tuesday.
The sea life is often found lurking in cargo holds or in ballast water pumped in to stabilize ships during their voyage and then pumped out when they reach their destination.
Once the invaders take hold, they can devour native species, alter food chains and change whole ecosystems, biologists say.
"There are a lot of global marine hitchhikers and now is the time to take action," said Secretary of the Interior Bruce Babbitt, who spoke Tuesday at the first international Marine Bioinvasions Conference at the Massachusetts Institute of Technology.
Bioinvasion costs government and industry $123 billion a year to control on land and at sea, according to a study released at a meeting of the American Association for the Advancement of Science, Babbitt said.
In the San Francisco Bay area -- where there are more than 250 known exotic invaders -- one of the most voracious predators has been the Asian clam introduced in the 1980s.
The mud-dwelling clams feed by filtering out food particles in the water column.
"The clams have been filtering out so much of the water that we haven't seen annual blooms of phytoplankton since the 1980s," said Andy Cohen, a marine biologist for the San Francisco Estuary Institute in Richmond, Calif.
That means animals who eat phytoplankton have been stripped of an essential food source, he said.
In New England, a type of Japanese algae is now aggressively taking root along the coast. Meanwhile, an organism from New England -- called a comb jelly -- was exported to the Black Sea and has decimated an economically important anchovy fishery.
One thing scientists did in the past was introduce predator species to control invaders. But now, fearing new species could further threaten ecosystems, scientists have been developing methods that would stop the invaders before they make it to foreign waters.
Babbitt on Tuesday called for mandatory ballast water exchange programs and urged Congress to work on bioinvasion before it becomes a crisis.
Proposals include giving agencies the muscle to enforce what could amount to international regulations, he said.
Ballast exchange programs would require a ship coming from the Mediterranean, for example, to dump its ballast water in the deep seas -- at least 200 miles from shore and about 2,000 feet deep -- then replace it with deep sea water.
The theory is that organisms found in deep sea water have a harder time surviving in water closer to the coasts, and vice versa.