Description: Final Report, EU Concerted Action Introductions with Ships (MAS3-CT97-0111): Until recently, the importance of ballast water as a major transfer vector that affect aquatic ecosystem stability and modify biodiversity was not generally recognised, although studies on species transfer via ballast water in maritime countries have increased world-wide. Despite considerable research effort (national and international), there has been virtually no consideration of the effectiveness or standardisation of ballast water sampling methodology in order to monitor effectiveness of control measures. One key objective of the Concerted Action was to test monitoring systems for sampling ballast water. Two major intercalibration workshops compared sampling techniques. The largely varying conditions onboard ships require to develop a “tool box” rather than singling out one method, thereby combining qualitative and quantitative sample analysis for plankton species composition and abundance. The two intercalibration workshops delivered results allowing better comparisons of ship sampling studies around the world. The second key issue was to gain more insight on species composition in ballast water during ship voyages. This was achieved by ocean-going workshops (OGWs). The data obtained during five OGWs, using the “tool box” originated from European voyages (three OGWs) and during inter-ocean voyages (two OGWs). In total, approximately 700 samples were collected during more than 100 days at sea. More species and specimens were found in new ballast water, and communities were in general similar to outside seawater where ballasting took place. The highest number of phytoplankton species found was 52, including potentially toxic species. At most, 40 zooplankton taxa were found. Abundance and diversity of phyto- and zooplankton species remained fairly stable for 3-4 days, followed by an exponential decline. In some cases no living zooplankton were found after 9 days, in others about 10% of the taxa survived, remaining viable for 25 days (i.e. voyage Hong Kong – Hamburg). Sampling showed that in calm conditions phytoplankton exhibited a vertical zonation in ballast tanks. During rough weather mixing occurred causing increasing in mortality. For the first time in ballast water studies, traps were used with bait and light as attractants, catching taxa not seen in the net samples before. The effect of mid ocean exchange (MOE), recommended by International Maritime Organization (IMO) as a measure against unintentional introduction via ships, was studied. In many cases the number of taxa increased rather than declined while densities of specimens were diluted. A public awareness was launched, preparing a video, a leaflet, flyers, press releases, newsletter articles of International Aquatic Societies, an Internet homepage (visit the homepage at: http://members.aol.com/sgollasch/sgollasch/index.htm *) and several posters. A book on case histories, listing species previously introduced to European waters, was prepared especially to address harbour and regulatory authorities. Assessment of potential control measures (treatment) to reduce risks arising from ballast water releases included the evaluation and development of guidelines for ballast water treatment options. All participants provided input on references (e.g. grey literature, governmental reports, internal reports from harbour authorities, interim project reports) into a database kept by the co-ordinator. The Concerted Action reviewed and considered shipping studies both within and outside the EU. This provided a more balanced view of the state of the art and also enabled the Intercalibration workshops to consider and compare sampling methods as used throughout the world. During the CA many of these studies were completed and new ones studies commenced. It is recommended that the EU takes advantage of the well developed expertise within the network of the CA partners to gain momentum in an area where global solutions are urgently needed.