issue has emerged and has become better understood by resource professionals, the impacts across are becoming more widely known. As a result, various regions have been identified as areas that are highly susceptible to aquatic hitchhikers.
San Francisco Bay, a center of extensive international trade, hosts more than 210 introduced aquatic species. For nearly 150 years, this highly disturbed and vulnerable ecosystem has been exposed to continuous, large-scale introduction of non-native species through activities associated with commercial shipping and oyster farming. The importation of commercial oysters has allowed non-native species to hitchhike on the shells of oysters and packing materials shipped from the eastern U.S. coast and Japan. In the last decade, a new species has arrived about every 12 weeks.
In Chesapeake Bay, an area where
Chesapeake Bay Click image to enlarge
large quantities of foreign ballast water are discharged, it is estimated that more than 100 harmful non-native aquatic species are established in the bay.
Ecosystems of Pacific and Atlantic coastal waters suffer from infestations of the European green crab, a harmful hitchhiker that preys on commercially valuable oysters and clams. In the Pacific Northwest, the list of introductions is growing rapidly due to ballast water.
In the Gulf of Mexico, the marine brown mussel, displaces native mollusks and threaten mangrove communities. Like the zebra mussel, the brown mussel encrusts hard surfaces. As its range expands, there is rising concern over the economic impacts that could result from fouling of water intake systems, shipping areas and offshore oil platforms.
Gulf of Mexico Click image to enlarge
Inland waters. Once introduced into the Great Lakes or coastal waters, many hitchhikers spread to inland lakes, rivers, wetlands and waterways by way of barges, recreational users, bait buckets, fish stocking and other human-assistedtransport mechanisms. The zebra mussel, hydrilla, and others have taken great advantage of these opportunities to hitch a ride and have proved to be devastating to freshwater lakes and rivers. (Adapted from the Great Lakes Regional ANS Panel, "Biological Invasions," 1988)