Tangled thorny masses of Himalayan blackberries in Bellingham vacant lots. Dense thickets of Scotch Broom inducing sneezes along miles of Interstate 5 in Western Oregon. Invading mussels from the Black Sea displacing native ones in Montana streams. Atlantic salmon in the Pacific and Pacific salmon in the Great Lakes. In an age of hypermobility, species are moving around the planet in directions and at rates unprecedented in global history.

While organisms have evolved ingenious mechanisms to disperse on their own, human activities are enhancing that natural ability, creating large-scale introductions of non-native species in more and more areas. Some introductions, like the succulent South African freeway plant introduced around Los Angeles for erosion control, are deliberately planned by humans. Others are quite inadvertent and capable of doing tremendous damage, such as the zebra mussel, (Dreissena polymorpha), which has caused several hundred million dollars in economic and ecological damage in the Great Lakes and is spreading west at an alarming rate.

Non-indigenous species (also known as exotic species, alien species, introduced species, or non-native species) are defined as species that have been transported long distances (almost always because of the activities of humans) from the place in which they evolved. A subset of non-indigenous species, known as invasive species, are especially good at establishing viable, reproducing populations in their new homes. These invasive species, by interacting within native ecosystems, can create genuine ecological havoc in the absence of their own predators, parasites, and pathogens back home. How do species actually get moved around by people? The answer is as variable as human enterprise itself, ranging from hitchhiking on vehicles or in shipments of crops to arriving as parasites on imported pets or on ornamental plants.

Ballast water has proven to be an especially efficient mechanism for inadvertently moving critters en masse to far-off locales and new habitats. What is ballast water? Its simply water taken into holding tanks by large ships, like tankers and freighters, to keep them stable on the high seas. It typically is slurped up in coastal waters where the ship starts its journey, and released in the coastal waters near its destination. Ballast water tanks can contain up to 70 metric tons of water each! Furthermore, up to 30,000 ships are cruising the world's waters on any given day, and the size, speed, and number and routes these ships follow are increasing every day. Every gallon of water, in every ship's ballast tanks, on every journey has the potential to transport the adults or larvae or eggs of non-indigenous marine or freshwater organisms. The hardy invaders among these organisms are creating substantial new problems in West Coast ports, bays, and estuaries.

Zebra mussels are the most famous aquatic non-indigenous species, but many others are currently having dramatic effects on West Coast economies and ecosystems. For example, the vast majority of the benthic (bottom-dwelling) organisms in San Francisco Bay are now from other places, having displaced many native populations and even entire species. One species of Chinese clam there, Potamocorbula amurensis, is such an efficient filter feeder that regular blooms of phytoplankton have completely disappeared in northern parts of the delta. Phytoplankton blooms, of course, generate much of the primary productivity upon which the rest of the San Francisco Bay community depends; in this way a single exotic species may be capable of altering the entire community structure of a region. Even the local congressional delegation has noticed.

Other non-indigenous organisms may be pathogens (disease-causing organisms) to other creatures; a good example of this is whirling disease, a European protozoan parasite affecting the nervous systems of trout species in at least 11 western states. Indeed, the Madison River in Montana has seen a 90% decline in rainbow trout populations since the disease arrived, probably with introduced fish stocks. Finally, sensitive West Coast estuaries are being invaded at unprecedented rates by the exotic cordgrass Spartina alterniflora; altered substrates and hybridization with native cordgrasses is threatening these most productive of coastal ecological communities from Padilla and Willapa Bays in Washington State, all the way down to California.

Sea Grant Nonindigenous Species (SGNIS)

This address is for the Sea Grant Nonindigenous Species (SGNIS) website. Supported by this federally-funded (but run by state agencies) program, there is a wealth of information on zebra mussels and other aquatic non-native species.

Ballast Water Report

This site has a report from the National Research Council (NRC) on ballast water introductions and possible solutions. The NRC is the research arm of the National Academy of Sciences, and advises Congress on scientific issues of importance to the United States.

National Academy Press

This site, part of the National Academy Press online reading room, has the text of the comprehensive NRC report by some of the nations top marine scientists called STEMMING THE TIDE: Controlling Introductions of Nonindigenous Species by Ships' Ballast Water.

U.S. Geological Surveys

This site has the United States Geological Surveys homepage on the topic of nonindigenous aquatic species. It contains lots of links with information on specific kinds of vertebrates, invertebrates, plants, and pathogens that are getting introduced to places where they didn't evolve. Who are the main invaders in your state?

U.S. National Invasive Species Act, 1996

This site contains the complete text of the US National Invasive Species Act of 1996, which reauthorized and modified the Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990. The site also contains a list of the congressional sponsors of the act. Is your elected official among them?

Species Roulette

This fun but scary site has a game of biological roulette to explore how quite a few species have been introduced and what happened next.

Nonindigenous Species in the San Francisco Bay and Delta

This site contains a press release from California Congresswoman Ellen O. Tauscher calling for a hearing on nonindigenous species in the San Francisco Bay and Delta. The congresswoman displays a good grasp of the biology of non-native species in the Bay area and the problems they are causing there.

Translocation from World Resources Institute

This site contains guidelines from the World Resources Institute, a non-governmental organization, on translocations of living organisms. It includes sections on how nonindigenous species impact native species, gene pools, and societies.

Alaska Ballast Hitchhiking

This site contains an article from Alaska Sea Grant on ballast hitchhiking organisms in that state.

Effects of European Green Crab

This homepage describes the research interests of one scientist (Dr. Greg Ruiz, an ecologist who studies estuaries) at the Smithsonian Environmental Research Center, which include studying the effects of the invasive European Green Crab (Carcinus maenas) on native organisms in California's Bodega Bay. Green crabs arrived in Coos Bay in Oregon in the last year and, in their predatory zeal, are working their way north up the coast.

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Bederman, David J. "International Control of Marine 'Pollution' by Exotic Species." Ecology law Quarterly 18(4): 677, 1994.

Bonny, Megan. "Ballast Water: The Scourge of the Oceans." Search 25(3): 72, 1994.

Carlton, James T. "Biological Invasions and Cryptogenic Species." Ecology 77(6): 1653, 1993.

Carlton, James T. "Role in Changing the Face of the Ocean: Biological Invasions and Implications for Conservation of Near-Shore Environments." Conservation Biology 3(3): 265,1989.

Carlton, J. T. and J. B. Geller. "Ecological Roulette: The Global Transport of Nonindigenous Marine Organisms." Science 261(5117): 78, 1993.

Carlton, J.T., J. K. Thompson and L. E. Schemel. "Remarkable Invasion of San Francisco Bay (California, USA), by the Asian clam Potamocorbula amurensis." Marine Ecology Progress Series 66(1/2): 81, 1990.

Everett, R.A., G.M. Ruiz, & J.T. Carlton. "The Effects of Mariculture on Submerged Aquatic Vegetation: an Experimental Test in a Pacific Northwest Estuary." Marine Ecology Progress. Series 125:205-217, 1995.

Grosholz, E.D. and G.M. Ruiz. "The Spread and Potential Impact of the Recently Introduced European Green Crab, Carcinus maenas, in Central California." Marine. Biology 122:239-247, 1995.