Invasive species
Marine plants, animals and microbes are being carried around the world attached to ships’ hulls or in their ballast tanks. The following are among species that already have spread: NORTH AMERICAN COMB JELLY Native to: Eastern seaboard of the Americas Introduced to: Black, Azov and Caspian Seas Impacts: Reproduces rapidly under favorable conditions. Feeds excessively on zooplankton and depletes zooplankton stocks. Contributed significantly to the collapse of Black Sea and Asov Sea fisheries in the 1990s. It now threatens to have a similar impact in the Caspian Sea. ZEBRA MUSSEL Native to: Eastern Europe (Black Sea) Introduced to: Western and Northern Europe, including Ireland and the Baltic Sea, and the eastern half of North America Impacts: Attaches to hard surfaces in mass numbers. Displaces native aquatic life. Blocks water intake pipes, sluices and irrigation ditches. The economic cost to the U.S. was $750 million to $1 billion between 1989 and 2000. TOXIC ALGAE Native to: Various species with broad ranges Introduced to: Several species have been transferred to new areas in ships’ ballast water Impacts: May form harmful algae blooms that, depending on the species, can kill marine life through oxygen depletion, release of toxins and/or mucus. Can hurt tourism, and some species may contaminate filter-feeding shellfish and cause fisheries to close. Human consumption of contaminated shellfish may cause severe illness and death. CHOLERA Native to: Various strains with broad ranges Introduced to: South America, Gulf of Mexico and other areas Impacts: Some cholera epidemics appear to be directly associated with ballast water. One example is an epidemic that began at three ports in Peru in 1991, sweeping across South America and killing more than 10,000 people by 1994. This strain had previously been reported only in Bangladesh. EUROPEAN GREEN CRAB Native to: European Atlantic coast Introduced to: Southern Australia, South Africa, U.S. and Japan Impacts: Competes with and displaces native crabs and becomes a dominant species in invaded areas. Consumes and depletes a wide range of prey species.