Microalgal spores in ship's ballast water: a danger to aquaculture

Resting spores of diatoms and dinoflagellates were found in the ballast tank sediments of Japanese cargo ships servicing Tasmanian ports. while most phytoplankton cells do not survive the long, dark voyage in ballast tanks and subsequent discharge into different temperature, salinity and nutrient regimes, phytoplankton resting spores are well capable of surviving such unfavourable conditions. Ballast tank sediments, even after being stored in the dark at 4 c for 6 months, were found to be capable of producing viable cultures of diatoms (e.g. Chaetoceros, Odontella) and dinoflagellates (e.g. Protoperidiniwn, Scrippsiella). Of special concern was the finding of the cyst of the toxic dinoflagellate Alexandrium cf. tamarense. Precautionary measures on ballast water discharge are called for, especially where ballast water and/or sediments may be carried into important aquaculture areas.