Two If by Sea: Invasive Species Are Changing the Ocean Environment. (Currents)

By Hrastar, Laura M. | E Magazine, May-June 2002 | Go to article overview

Two If by Sea: Invasive Species Are Changing the Ocean Environment. (Currents)


Hrastar, Laura M., E Magazine


For decades, the coastal United States has been under siege from an invasion of foreign animals and plants (see second feature this issue). New species arrive daily, and in a variety of ways. According to the Pew Oceans Commission, ship ballast water is the primary carrier of marine species throughout the world, although intentional introductions to control other species or mismanaged aquaculture also often lead to the spread of new populations.

These invaders do harm by not only wiping out native species, but also change the habitat structure around them. Economic costs to shipping can be in the millions of dollars when non-natives foul nets or eat commercial market fish and crustaceans important for area industry.

According to Pew's James T. Carlton, new species are being introduced into U.S. coastal waters faster than ever, and the rate may be snowballing due to larger, more frequent shipping operations. Ballast water is pumped into vessels to maintain stability, and it is discharged in new ports. Linda Sheehan, director of the Pacific Regional Offices of the Ocean Conservancy, says ballast water is the second-most significant problem after habitat destruction nationwide.

Plants and animals arrive as plankton (drifters), nekton (free-swimming), fouling organisms (attached inside and on the hulls, propellers, and intake systems of vessels), and benthos (bottom dwellers). Plankton has proven to be the heartiest, and therefore most potent, form to arrive. Not all organisms that disperse to new areas can establish themselves however. Reproductive biology, and the presence of predators, competitors and parasites all play a role in a newcomer's survival chances.

Often reported as a maintenance problem, invading species take hold in dry dock areas such as marine oil-drilling/production sites or floating repair structures. Others make a home near land at nutrient run-off points from farms and power plants. Enriched or chemically altered waters in harbors are also key areas.

The invaders' arrival is not always accidental, however. In the past, Hawaiian resource managers introduced the red mangrove and Philippine seaweed. In 2001, Virginia officials released sterile Japanese oysters in Chesapeake Bay to boost the fishing industry, a move opposed by neighboring Maryland.

Another possible source of invasive species is aquaculture, which regularly imports exotic organisms. "Nearly one-third of the world's seafood supply is derived from aquaculture, and the government has reduced regulation to promote it," says Susan Williams, director of the University of California at Davis' Bodega Marine Laboratory. "The aquaculture industry can help itself by protecting cultured organisms through the control of invasive marine parasites," Williams says. In 1998, farmed Atlantic salmon escaped from a Pacific Northwest fishery and entered the wild population.

At the Monterey Bay Aquarium in California, senior marine biologist Steven Webster often deals with exotic species in their tropical exhibits. "We ensure that invasive species do not enter local waters by recycling water and by heavily filtering and applying ozone or ultraviolet light to our systems."

Scientists battle invasive species with everything from handpicking seastars/snails off the ocean floor to mowing down salt marsh grasses. One highly debated idea is the use of chemical control, as was tried in Darwin, Australia in 1999. There, Asian mussels were treated and effectively wiped out with aqueous chloride, sodium hypochloride and copper sulfate. …

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