Fluctuations of zooplankton taxa in ballast water during short-term and long-term ocean-going voyages

A major vector for unintentional species introductions is international shi pping. A wide range of organisms have bean transported over long distances in ships' ballast tanks and as hull fouling. Although many desk studies and ship sampling programmes have been carried out, little information is avai lable on changing numbers of individuals in ballast water during voyages. D etailed information could assist in evaluating the dimension of species imp ort and future risks of unintentional species introductions by ballast wate r. The first European study, organised as a concerted action tram and finan ced by the European Union, carried out several long-term and short-term wor kshops on board ships undertaking international voyages. The preliminary re sults from sampling the ballast water of the first four oceangoing workshop s of this Concerted Action showed a decrease in numbers of specimens and ta xa over time.