Risk assessment of ballast water-mediated invasions of phytoplankton: A modeling study

Phytoplankton, particularly toxin producing phytoplankton, is of primary concern with respect to bioinvasions in aquatic environments. I examined the risk of phytoplankton invasions through ballast water with specific reference to the likely factors important for the growth of post-discharged phytoplankton (i.e. physiological state, growth rate, lag period for growth, water dilution rate, and the size of seed population). Model results suggest that invasions are most probable when large numbers of metabolically active and fast growing phytoplankton requiring small size of seed population are introduced into relatively low flow regimes. Strategies to minimize invasions of phytoplankton therefore may require either significantly reducing the physiological state of the phytoplankton or reducing its cell density below the seed population size required, although the best strategy would be a combination of both. Incorporation of the population growth of phytoplankton at low density into risk assessments based on information such as habitat match/mismatch and invasion history may provide insights for setting up regional, cost-effective strategies to minimize the risk of the invasions of phytoplankton.