Evaluation Of A Method For Ballast Water Risk-Release Assessment Using A Protist Surrogate

Aquatic invasive species cost the United States billions of dollars annually and are most often introduced via ships' ballast tanks. The International Maritime Organization (IMO) adopted a set of standards that sets limits on the number of viable organisms that can be discharged with ballast water. These standards require scientific research to determining the risk-release relationship (i.e. the number of propagules needed for an invasion). To examine the risk-release relationship a surrogate invader, the diatom Melosira varians, was used. Varying densities of the surrogate were added to 19-L mesocosms containing water from Duluth-Superior Harbor. Each mesocosm was sampled weekly for four weeks and the response of the phytoplankton community was measured via cell counts. Population responses varied by starting conditions but M. varians establishment was generally noted at higher inoculation densities. These findings suggest the mesocosm approach can inform the understanding of risk-release relationships.