Abstract:
Dinoflagellate cysts are well-recognized biological constituents of ships' ballast tanks. They are present in ballast water, sediments and
residual water in drained tanks, and in biofilms formed on interior tank surfaces. Therefore, cysts have the potential to be released during
ballast discharge. The International Maritime Organization's (IMO) Ballast Water Management Convention (promulgated February
2004) stipulates a performance standard (Annex, Regulation D2) requiring discharged ballast water contain <10 viable organisms
between 10 and 50 µm per ml and <10 viable organisms ≥ 50 µm per m³. The proposed size limit has potential to exclude both the smallest
toxic and the largest toxic and non-toxic dinoflagellate (and other microalgal) cysts from discharged ballast water. Despite the appropriateness
of size cutoffs however, ballast water containing predominantly small cysts (<50 µm)could be deemed in compliance with the
performance standard, even without treatment, while ballast water having the same concentration of larger cysts (>50 µm)could require
a multiple-log reduction in abundance before its permissible discharge. Also of concern, it remains uncertain whether ballast-water treatment
can remove sufficient organisms, including dinoflagellate cysts, to meet the performance standard.
