Many reproduce rapidly and when they are introduced into waters where conditions are favorable, their numbers can explode. Young microscopic zebra mussels, for example, are believed to have established themselves in the Great Lakes in the 1980s, after arriving in the ballast water of an ocean-going vessel. In only five years, zebra mussels spread to the waters of 20 states.   

Oceangoing vessels also export creatures from U.S. waters to other areas of the globe, where they have caused serious problems. The most recent and insidious example is the comb jelly, a native of the Western Atlantic, which arrived in the Black Sea from ballast water in the 1980s. By 1990, the jellies had grown to a volume of one billion tons in the Sea and were out-competing the native anchovies for food. The result: the anchovy catch in the Black Sea fell by 80 percent, which had a devastating effect on fishermen and local economies. 

Ballast water is the largest source of invasives, but it is by no means the only one. As Carlton points out, "A minor vector can lead to a major invasion."  And mollusks, crustaceans, and jellyfish aren't the only aquatic species causing problems. Hydrilla, an aquatic plant native to Africa, was brought to the United States as an aquarium plant. But not until it left aquariums did it show its true strength. Growing up to an inch per day, it can blanket the surface of waterways, cutting off light to other aquatic plants below and eventually killing them. It grew so thick in the Potomac River -near Washington, DC that it had to be mowed to open channels for boats to pass. And hydrilla can reproduce via fragments: bits of hydrilla that attach to boats and propellers have been carried to new waterways where they quickly establish themselves. 

Invisible to the naked eye, but equally dangerous, are invasive microorganisms. A recent sampling of ballast water from ships in Chesapeake Bay revealed that every liter of water contained about one billion bacteria and seven billion virus-like particles. Many forms of red tide-algal blooms that render shellfish inedible and potentially toxic - are believed to have originated outside the United States. Msx and Dermo, two devastating diseases that helped to decimate the Chesapeake's once-abundant oyster population, are also thought to have originated outside the Chesapeake Bay. "Some of the most studied and feared potential invaders to the Gulf of Mexico are shrimp viruses," says Lukens. "We know that they regularly enter the U.S. via shrimp imported for aquaculture, although there are no documented cases of the Viruses being found in the wild."

Getting Them Under Control

So how can we control invasive species? Well, it's no simple task, particularly after an alien species has settled in. In some regions, scientists and fisheries managers have considered controlling exotics with exotics. In the Chesapeake, the states of Maryland and Virginia have hotly debated introducing an Asian species of oyster that has shown to have excellent resistance to msx and Dermo. But the unknown impacts of intentional introduction have caused many to question the wisdom of such measures.

Scientists agree that, regardless of how an aquatic species arrives in an ecosystem, once it is established, eradication is nearly impossible. Prevention is clearly the best hope for stemming the tide of invasives. And since ballast water is the most significant source of coastal aquatic invasive species worldwide, measures are being developed to prevent the large-scale transfer of organisms from port to port. Both the U.S. government and the International Maritime Organization recommend that ships "exchange" ballast water in the open ocean, rather than in coastal waters, where exotic species have a better chance of establishing themselves. And some ports, like Vancouver, British Columbia, and states, like California, Washington, and Oregon, have adopted their own mandatory regulations that require exchange in the open ocean. But ballast water exchange is not fail-safe, since hardy species can still cling to the tanks and survive in ocean water. Technologies to treat ballast water before loading and discharging, such as filtering and treating the water with uv radiation, ozonation and de-oxygenating the water, have shown promising results.

Kathy Metcalf, the Director of Maritime Affairs for the Chamber of Shipping of America, says that her constituents major shipping companies are complying with ballast water exchange Programs. "But we would like to see more funding for research and development in treating ballast water," Metcalf says, "particularly for those technologies that will remove invasive species before they come on board."

The National Invasive Species Act of 1996 (NISA) authorizes broad?based activities intended to stem the tide of invasives. But in the federal 2000 budget, marine and freshwater invasive species projects received only one percent of the funds for controlling invasives, whereas agricultural invasive management received go percent. NISA is up for reauthorization in Congress this year, and funding will be at the forefront of the debate. "We can't advance our knowledge of the problem with only $2 Million per year for research and management," says Carlton. "There is so much that we just don't know." Lukens agrees: "We are way, way behind the curve in our ability to deal effectively with invasions."

But both Carlton and Lukens are convinced that education is as important as research, and that changing people's behaviors can have a significant, positive impact on the introduction of nuisance species. Lukens cites the series of workshops on shrimp viruses that the Gulf Invasive Species Focus Team held jointly with the National Marine Fisheries Service. "As a result," says Lukens, "shrimp aquaculturists have introduced best?practice innovations that are helping to reduce the possibility of escape and transfer of these viruses to wild shrimp."

Is the invasive species problem one we can solve? "If we can bring a rock back from the moon," says Carlton, "we can probably solve the problem of ballast water and make significant progress into other vectors, as well. The key is getting the message out and educating the public."

In addition to co-writing the first-ever state law mandating ballast water exchange in the open ocean, which was a model for similar laws in Washington and Oregon, The Ocean Conservancy's Pacific Regional Office has been working on a number of other invasive species issues. Along with other nongovernmental organizations, it petitioned EPA in 1999 to regulate ballast water nationwide under the Clean Water Act. and then sued when EPA failed to respond. At the U.S. Coast Guard's request, The Ocean Conservancy provided detailed comments and testimony on ballast water treatment standards and on the progress of the National Invasive Species Act (NISA) in controlling marine invasions. Recently, the organization has worked on new language for the upcoming 2002 NISA reauthorization. Pacific Regional. Office Director Linda Sheehan also represents coastal and marine aquatic interests on the Western Regional Panel of the Aquatic Nuisance Species Task Force and the national Invasive Species Advisory Committee, where she helped to develop the first National Invasive Species Management Plan

No area of the United States better exhibits the effects of invasive species on entire ecosystems than the San Francisco Bay and Delta. The largest estuary on the West Coast, the Bay-Delta harbors 750 species of plants and animals and supplies drink­ing water for two-thirds of California inhabitants and irrigation water for one of the world's most productive agricultural areas. Yet many scientists believe that the area has lost its identity; estimates indicate that over 234 non­native plant and animal species are now established, and up to 99 percent of the living matter in the Bay-Delta system is non-native.

The San Francisco Regional Water Quality Control Board has stated that non-native species represent one of the greatest threats to the integrity of the San Francisco Estuary ecosystem."  The most notorious alien invaders in the Bay include the Asian clam, the European green crab, the New Zealand sea slug, and the Chinese mitten crab.  All have either out-competed or preyed upon native sea life, including salmon, shrimp, and crabs.

How did San Francisco Bay earn the title "most invaded ecosystem"?  Linda Sheehan, director of The Ocean Conservancy's Pacific Regional Office, and a specialist in invasive species, says that a number of factors may be involved. The Bay receives nearly one billion gallons of foreign ballast water each year, and scientists speculate that ballast water has accounted for 53 to 88 percent of the Bay's alien invaders over the last decade. The ecosystem's diversity - ocean, bay, delta, and estuarine environments - may make it more hospitable to foreigners. Development has also taken its toll: "The San Francisco Bay-Delta area has been diked, dug up, filled in, and otherwise disturbed over many years," says Sheehan, making it easier to invade." But,” she adds, "it may simply be that the Bay has been better studied than other bodies of water, so that we're more aware of its problems."

 This awareness has inspired new legislation that may help to shield the Bay from further invasions – at least from ballast water. California became the first state in the nation to pass legislation requiring that ballast water be exchanged in the open ocean, beyond U.S. territorial limits.  The Ocean Conservancy co-wrote and  co-sponsored the bill. 

 "California was the first to pass a law in large part because of the information coming out of the Bay," says Sheehan. "The data demonstrate the importance of better invasive species information on a national basis. If we focus more research and attention on the scope of the problem, we can find solutions that work."