The EASIN Catalogue is the core of the EASIN. It contains the information needed to efficiently link EASIN to existing databases and retrieve spatial information for alien species distribution in Europe – the Alien Species Geodatabase. The Catalogue currently includes information on about 14,000 alien taxa.
The EASIN Catalogue was initially based on an inventory of all species reported to be alien in Europe (or part of) by one or more of 43 online information systems: 7 with global coverage, 2 with European coverage, 5 with supranational coverage, 26 with national coverage, and 3 with sub-national coverage.
Alien species names were extracted for all European countries, considering 27 EU Member States, 5 Candidate countries to the European Union, and 32 other neighboring countries.
To have full coverage of the four seas surrounding Europe, alien marine species reported from the entire Mediterranean Sea were included, i.e. also from North African and Near East Mediterranean countries.
For species that are alien in some regions of Europe and native in others (e.g. Ponto-Caspian species invading the Baltic and the North Sea through inland canals), the native has been defined (at a country level for terrestrial and freshwater species and at a marine basin level for marine species).
Since the initial compilation, the EASIN Catalogue has been regularly updated, revised and validated through a formal protocol, which includes several steps to achieve high quality standards, with the engagement of external experts and the editorial board members. A unique identification code is assigned to each valid name in the Catalogue, and it is used to connect it with additional information for each species (environment, taxonomy, information on pathways of introduction and level of impact).