Treatment options to mitigate transport of harmful algal species and pathogens via ships' ballast water and shellfish translocation
Creators: name: Gregg, Matthew David
Publisher: name: University Of Tasmania
Year: 2023

description: The worldwide transfer of non-indigenous invasive aquatic organisms via ships' ballast water and shellfish translocation has been widely shown to cause significant ecological, economic and human health impacts. In 2004 the International Maritime Organisation (IMO) adopted the International Convention for the Control and Management of Ships' Ballast Water and Sediments. This legislation (still to be ratified) requires all ships to introduce by 2016 approved systems capable of treating ballast water to strict microbial standards. The latter has reinvigorated interest in the application of chemical biocides, because mechanical separation and physical treatment are unable to kill bacteria. The present work examined the effectiveness of several proposed chemical ballast water treatment options using toxic dinoflagellate resting cysts, vegetative marine microalgae and bacteria as model organisms. The chemicals tested included the ballast water biocides Peraclean¬¨vÜOcean and SeaKleen¬¨vÜ, the chlorine dioxide biocide Vibrex ¬¨vÜand the hull antifouling agent Econea¬¨vÜ. All biocide tests were conducted using filtered seawater (28 %o) and natural estuarine water ranging in salinity from 23.7-28.6%o. Peraclean¬¨vÜOcean was biodegradable within 2-6 weeks, could effectively eliminate vegetative microalgae at 100 ppm, inactivated resting cysts of marine dinoflagellates (Gymnodinium catenatum, Alexandrium catenella, A. pseudogonyaulax, Protoceratium reticulatum) at 200-2000 ppm, and could control bacterial growth of Escherichia coli, Staphylococcus aureus, Listeria innocua and Vibrio alginolyticus at 125-250 ppm. SeaKleen¬¨vÜeliminated vegetative microalgae at 2 ppm and could control dinoflagellate cysts at 6-20 ppm but displayed poor bactericidal properties (100-200 ppm required) and poor biodegradability. The burial of dinoflagellate cysts in 0.5 and 1 mm of ballast tank sediment severely reduced the effectiveness of Peraclean ¬¨vÜ Ocean and SeaKleen¬¨vÜ. Vibrex¬¨vÜis not a suitable treatment option due to the need for hydrochloric acid as an activator, however it was found to be the most effective against bacteria (complete inhibition at 15 ppm) indicating that onboard chlorine dioxide generators may provide an effective bacterial treatment. Econea¬¨vÜcontrolled vegetative microalgae at 0.5 ppm but failed to inactivate G. catenatum cysts even at a concentration of 1000 ppm, suggesting that the product lacks the penetrability required to infiltrate the walls of dinoflagellate cysts. The applicability of ballast water biocides is limited by factors such as cost, biological effectiveness, reduced efficacy in the presence of sediments and lower water temperatures (6¬¨‚àûC compared to 17¬¨‚àûC), and possible residual toxicity of the discharged ballast water. Translocation of bivalve shellfish for outgrowing purposes or to establish new shellfisheries also poses a significant risk for transport of harmful algae. This study showed that viable microalgal cells of A. catenella, Cryptoperidiniopsis brodyi, G. catenatum, Karenia papilionacea, Kryptoperidinium foliaceum, Pfiesteria shumwayae and cysts of G. catenatum can readily pass through the digestive tract of adult Pacific oysters and blue mussels. Several treatment options currently used by shellfish farmers for controlling fouling and pathogens were tested against Pacific oysters. Vegetative cells of A. catenella, G. catenatum and K. fohaceum could not be eliminated from the digestive tract of Pacific oysters following 24 h immersion in freshwater or by 48 h exposure to hydrogen peroxide (400-600 ppm) or chlorine dioxide (40-60 ppm). Depuration in filtered seawater for 7 days was identified as the only effective treatment option. Recommendations for future research, along with potential alternative treatment options, are identified and discussed.