Alternative, indirect measures of ballast water treatment efficacy during a shipboard trial: a case study

A shipboard study was conducted aboard the cruise ship Coral Princess during a scheduled cruise from San Pedro, CA, USA to Vancouver, British Columbia, Canada. The investigation involved three members of the global TestNet group, with experience in certification testing of ballast water treatment systems (BWTS) designed to eliminate entrained invasive species. A UV-based ballast water treatment system had been employed aboard the vessel for more than 10 years. A variety of established and experimental assessment techniques were employed, both aboard the ship and following shipment of samples via road (5 days) and air (7 days) to remote laboratories. The study was designed to compare the performance of different techniques in assessing BWTS compliance with international regulations, and to test the feasibility of compliance assessment by Port State Control internationally using different laboratories. Overall, biological end-points showed effective treatment of ballast water as judged by the percentage removal (mortality) of organisms in treated samples. Sample transport indicated generally good potential for 'off-site' sample analysis and displayed a possible latent effect of treatment as judged by a decline in photosynthetic yield associated with delayed analysis.