En-route investigations of plankton in ballast water on a ship's voyage from the Baltic Sea to the open Atlantic coast of Europe

Ballast water of ships has been recognized as a major vector for the uninte ntional transfer of exotic aquatic organisms between and within many parts of the world. Studies in several European ports have, shown that most of th e ballast water discharged originates from nearby sea areas indicating the importance of secondary introductions. However, the patterns of interregion al transfer of exotic species within Europe remain largely unknown. The pre sent study examined the transport of phyto- and zooplankton organisms in th e ballast water to assess the potential for the transfer of invasive aquati c species between the Baltic Sea and the open Atlantic coast of Europe. Six potentially toxic phytoplankton species were found in the ballast water ex amined. In four ballast water sampling trials no significant changes in abu ndance of both phyto- and zooplankton organisms were observed during first 3-4 days of experiment. Even in the end of the longest sampling trial (15 d ays) millions of plankton organisms were found. The results obtained indica te the importance of interregional European shipping in the dispersal of ex otic plankton organisms.