Two if by sea: invasive species are changing the ocean environment - Currents

E: The Environmental Magazine, May-June, 2002 by Laura M. Hrastar

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. However, much of the surrounding sea life was also killed off. In the summer of 2000, an unsuccessful attempt in Southern California with similar chemicals left high mortalities, but could not eradicate, the nuisance seaweed Caulerpa taxifolia.

"Scientists are wary of chemicals because of the lack of knowledge of all the effects they can have on the surrounding environment," says Carlton. "Chlorination is used when the impacts of it are thought to be less than the impact of the invading species. Most often, target species cannot be selected out and destroyed." Another possibility that needs further research is the use of benign anti-fouling agents on ships. Scientists recommend that companies develop new agents with lower chemical half-life that would have a lesser impact on other sea life. In the future, biocontrol--the use of one species to control another--may become a tool also.

On the federal level, former President Bill Clinton created the Invasive Species Management Plan, which went into effect in 2001. The plan charges the Coast Guard, National Oceanic and Atmospheric Administration, the Environmental Protection Agency (EPA) and the Department of the Interior with researching new technologies, and it strengthens the National Invasive Species Act (NISA) of 1996. The problem with NISA, critics say, is that ballast exchange reporting for ships is voluntary, and some vessels are exempt from participation, as is the case with oil tankers in coastal trade and passenger vessels with "treatment" systems. Today, a National Ballast Water Clearinghouse reports data of transfers/invasions of species through a survey meant to oversee the rate of compliance of the voluntary regulations.