Photo: Ari O. Laine
Introduction of non-native or "alien" species has been identified by scientists and policymakers as one of the major threats to marine ecosystems. Living organisms are transferred outside their natural distribution both intentionally and unintentionally through shipping, aquaculture, fisheries, stocking, recreational activities and opening of new water links. 

Ballast water and fouling of ship hulls are considered as principal vectors of alien species transmission, and at any one time 4000-10 000 species of viruses, bacteria, algae and animals are travelling over the distances. 

The sensitive Baltic Sea 

The Baltic Sea with its low number of native species and simple food webs is vulnerable to ecological changes and offers excellent opportunities for detailed studies in invasion biology. 

The Gulf of Finland is a hot spot area for introductions, because its salinity gradient allows both fresh- and brackish-water organisms to establish and numerous geographical or man-made invasion corridors open to it. The risk for introductions will increase further as the new ports in the NE Baltic will be opened: a 4-fold increase in ship traffic in the Gulf of Finland is expected from 1990 to 2010. 
 

Baltic Sea as recipient and donor area 

Picture: Marjo Pienimäki
More than 100 alien species have been recorded in the Baltic. Some 70 of them have established reproducing populations, and 20 can be regarded as harmful. Once established, the removal of the species from the system is nearly impossible, and the area can also act as a source to secondary introductions to adjacent and remote water bodies. 

Diverse impacts 

Bioinvasions have economical, recreational and ecological impacts. Ecologically they affect both structural and functional biodiversity of the sea. In principal every successful introduction alters somehow the ecosystem, either by altering existing or adding new functions, or in the worst case, by replacing native organisms. 

Thus the theoretical framework of this project will be based on the threats to biological integrity, defined as the capability of supporting and maintaining a balanced, integrated and adaptive biological system. 
 

Picture: GEBCO Digital Atlas and World Vector
Shoreline, the US Defense Mapping Agency