Per capita invasion probabilities: an empirical model to predict rates of invasion via ballast water

Authors

  • Deborah A. Reusser,

    Corresponding author
    1. U. S. Geological Survey, Western Fisheries Research Center and Oregon State University, 2111 SE Marine Science Drive, Newport, Oregon 97365 USA
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  • Henry Lee II,

    1. Western Ecology Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, 2111 SE Marine Science Drive, Newport, Oregon 97365 USA
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  • Melanie Frazier,

    1. Western Ecology Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, 2111 SE Marine Science Drive, Newport, Oregon 97365 USA
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  • Gregory M. Ruiz,

    1. Smithsonian Environmental Research Center, 647 Contees Wharf Road, P.O. Box 28, Edgewater, Maryland 21037 USA
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  • Paul W. Fofonoff,

    1. Smithsonian Environmental Research Center, 647 Contees Wharf Road, P.O. Box 28, Edgewater, Maryland 21037 USA
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  • Mark S. Minton,

    1. Smithsonian Environmental Research Center, 647 Contees Wharf Road, P.O. Box 28, Edgewater, Maryland 21037 USA
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  • A. Whitman Miller

    1. Smithsonian Environmental Research Center, 647 Contees Wharf Road, P.O. Box 28, Edgewater, Maryland 21037 USA
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  • Corresponding Editor (ad hoc): H. J. MacIsaac. For reprints of this Invited Feature, see footnote 1, p. 287.

Abstract

Ballast water discharges are a major source of species introductions into marine and estuarine ecosystems. To mitigate the introduction of new invaders into these ecosystems, many agencies are proposing standards that establish upper concentration limits for organisms in ballast discharge. Ideally, ballast discharge standards will be biologically defensible and adequately protective of the marine environment. We propose a new technique, the per capita invasion probability (PCIP), for managers to quantitatively evaluate the relative risk of different concentration-based ballast water discharge standards. PCIP represents the likelihood that a single discharged organism will become established as a new nonindigenous species. This value is calculated by dividing the total number of ballast water invaders per year by the total number of organisms discharged from ballast. Analysis was done at the coast-wide scale for the Atlantic, Gulf, and Pacific coasts, as well as the Great Lakes, to reduce uncertainty due to secondary invasions between estuaries on a single coast. The PCIP metric is then used to predict the rate of new ballast-associated invasions given various regulatory scenarios. Depending upon the assumptions used in the risk analysis, this approach predicts that approximately one new species will invade every 10–100 years with the International Maritime Organization (IMO) discharge standard of <10 organisms with body size >50 μm per m3 of ballast. This approach resolves many of the limitations associated with other methods of establishing ecologically sound discharge standards, and it allows policy makers to use risk-based methodologies to establish biologically defensible discharge standards.

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