Invasive species threaten the U.S. with severe ecological damage and huge economic costs. A substantial number of biological invaders are aquatic or marine species, ranging from microbes to fish, originating from fresh water, estuarine, and marine ecosystems throughout the world. Ocean-going ships which carry ballast water are important transporters of these nonindigenous aquatic nuisance species (ANS), and other human activities such as recreational boating and intentional introductions also spread these species in western rivers, streams, and lakes.
The effects of ANS introductions include: population declines of native (sometimes ESA listed) species; fundamental changes in aquatic ecosystem structure and function; biofouling of industrial facilities such as water intake systems; loss or decline of socio-economically important species; and spread of pathogens. For example, clogging of industrial intake structures and piping by the clam Dreissena requires corrective actions and maintenance is estimated to cost $1 billion annually.
Ballast water ANS introductions present particularly high risk to waters of the Western U.S. For instance, San Francisco Bay harbors and estimated 212 introduced species and at least another 123 cryptogenic species, whose origins are not clearly known. The occurrence of these species in the bay is primarily a result of shipping. As a result, the estuary has entire biotic communities of introduced benthic organisms, radically different from the native communities they replaced. Much less is known about other West Coast systems, but Washington State has at least 78 known non-indigenous marine species. Two western states (California and Washington) have recently passed laws to regulate ballast water discharges, and require scientific information to implement regulations. Adherence to the proposed regulations will require new treatment technologies onboard vessels to prevent invasions from ballast water organisms.
In fresh waters, ANS species (predators, competitors, plants, parasites, pathogens) pose risks to native fishes ranging from salmonids in the Columbia and other large river systems, to isolated desert spring systems which are the only habitats of ESA-listed desert fish species.