Introduction of Invasive Species by Ballast Waters

An emergent problem of global concern that directly threatens the biodiversity of indigenous planktonic species in both marine and freshwater ecosystems is the introduction of invasive species and disease-causing agents via the ballast water of transoceanic ships.

In the Great Lakes region, two invasive cladoceran species have recently been discovered. Cercopagis pengoi, a predatory clado-ceran native to the Caspian, Azov, and Aral seas, has been introduced into Lake Ontario. And Bythotrephes cederstroemi, the "spiny water flea," is another cladoceran species that appears to have been transported in ballast waters to

Lake Erie from the Port of St. Petersburg in Russia. The former species actively preys on smaller zooplankton and is expected to harm populations of the native cladoceran species. The latter species, B. cederstroemi, is plank-tivorous and is directly competing with the native species of Daphnia for food and resources. Both invasive species are expected to alter the size and composition of the indigenous plankton community.

In the marine realm, the Atlantic comb jelly (Mnemopsis leidyi), a species native to the western Atlantic, was accidentally introduced into the Black Sea in the late 1980s from the ballast water of a grain ship. This ctenophore both fed on meroplanktonic fish larvae and outcompeted the local fish populations for zooplankton, ultimately resulting in the crash of commercial fisheries in the Black Sea.

Of graver concern is the introduction of disease-causing agents, such as invasive species of phytoplankton that cause harmful algal blooms, into uncontaminated regions. Recently, high concentrations of pathogenic strains of Vibrio cholera, the causative agent of cholera, were detected in all samples of ballast waters collected from ships in the Chesapeake Bay that had arrived from foreign ports. Cholera is an acute diarrhoeal disease, epidemics of which can result in the deaths of thousands of people. The bacterium Vibrio cholera is an inhabitant of brackish and estuarine waters, and preferentially attaches to chitinous zooplankton, such as copepods. Plankton blooms triggered by climatic events, such as El Niño, have been suggested as the underlying cause behind some recent outbreaks of cholera.

—Susan L. Richardson

See also: Arthropods, Marine; Bacteria; Cnidarians;

Lakes; Mollusca; Oceans; Protoctists


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