Transport of toxic dinoflagellates via ships' ballast water: bioeconomic risk assessment and efficacy of possible ballast water management strategies

The results of 10 yr of Australian research efforts on transport of toxic dinoflagellate cysts via ships' ballast water are reviewed, supplemented with the conclusions of similar studies now underway in Europe, Israel, North America, Canada, Japan, China and New Zealand. Toxic dinoflagellates are probably the best studied model organism to assess the bioeconomic risks of ballast water introduction of nonindigenous marine pests. A plausible scenario for their successful introduction and establishment in Australian waters is: (1) ballast water intake during seasonal plankton blooms and to a lesser extent via resuspended cysts in sediments from Japanese or Korean ports; (2) survival as resistant resting cysts during the ballasting process, the voyage in a dark ballast tank, and subsequent ballast water discharge (inoculation); (3) successful germination of cysts, sustained growth and reproduction of plankton cells in an Australian port; and (4) further spreading via coastal currents or domestic shipping, culminating under suitable environmental conditions in harmful algal blooms impacting on aquacultural operations (causative organisms of paralytic shellfish poisoning). Until international agreement and acceptance of a fully effective, practicable, safe, economically viable and environmentally friendly ballast water treatment is achieved (mid-ocean ballast water exchange and heat treatment are the only options offering promise at present), an international warning network for algal blooms in ports appears to be an effective way to minimise risks. It is also recommended that aquaculture operations and marine parks should be sited well clear of the ballast water influence of shipping ports.