Survival of tropical ballast water organisms during a cruise from the Indian Ocean to the North Sea

In an assessment of non-indigenous species transported by international shi p traffic to German waters, commissioned by the German Federal Environmenta l Agency, the survival of tropical plankton organisms in ballast water was studied by accompanying a container vessel on its 23-day voyage from Singap ore to Bremerhaven in Germany. Two tanks, one filled off Singapore and the other off Colombo, Sri Lanka, were monitored for their phyto- and zooplankt on content by daily sampling. As already reported in previous studies, spec ies abundance and diversity, especially of zooplankton, decreased sharply d uring the first days, and only a few specimens survived the whole cruise. T he contents of the Colombo tank, however, changed dramatically during the l ast week. The harpacticoid copepod, Tisbe graciloides, increased its abunda nce by a factor of 100 from 0.1 to 10 ind.l(-1) within a few days. This is the first time that a ballast water organism has been found to multiply at such a high rate. Opportunistic species such as Tisbe are apparently able t o thrive and propagate in ballast water tanks under certain conditions. Bal last water tanks may thus serve as incubators for certain species depending on their characteristics.