A New Horizon-Scanning Tool to Identify Potential Aquatic Invasive Alien Species Introduced into the Baltic Sea by Shipping

Some invasive alien species (IAS) may constitute an important threat to global biodiversity due to major ecological impacts. In 2014, the European Union (EU) introduced a regulation (EU) No 1143/201 on the prevention and management of the introduction and spread of IAS. EU member states are required to carry out an analysis of the introduction and spread of potential IAS in their territories. In the case of aquatic alien species, shipping is considered as the main pathway for their introduction. In this study, a horizon-scanning tool was applied for identifying potential aquatic IAS introduced by shipping into the EU Baltic Sea Region (BSR) countries. This tool has mostly been applied on a country level, but it is more reasonable to study the invasive potentiality at a regional scale, especially for aquatic species that generally disperse over long distances. Individual Baltic countries may also benefit from the results of this study. The result of the horizon-scanning method that we applied produced a list of 27 potential aquatic invaders for the EU BSR countries introduced by international marine and inland shipping. In order, Asia (34% of the species), North America (27% of the species), and Indo-Pacific (23% of the species) were the most frequently listed geographical origins of concern. Marine habitat was the most frequent of the potential IAS, accounting for 41% of the species. Fish (26% of the species), Mollusks (18% of the species), and Crustacea (15% of the species) were the most frequent taxonomic groups. The list of potential IAS was prioritized from highest to lowest probability of invasion (establishment, spread, and impact). Eight species reached the highest probability of invasion. One of the potential IAS, Mytilus galloprovincialis, is native to the Mediterranean Region. These results provide valuable information that policy makers can use to develop more efficient prevention strategies for IAS introduced by shipping into the Baltic Sea.