In this study, we have performed a large-scale assessment on the native distribution range of the marine non-indigenous species (NIS) found in at least one of the European Seas (Mediterranean, NE Atlantic Ocean, Black, Baltic Sea). As a basis, we have used the most updated pan-European NIS inventory, provided by the European Alien Species Information Network. All taxonomic groups have been considered for this analysis, taking into account established NIS in European Seas (824 taxa in total). The vast majority of the European marine NIS have their native distribution in the Western and Central Indo-Pacific, being mostly associated with introductions into the Mediterranean Sea through the Suez Canal. However, this overall pattern is heavily influenced by the fact that 76% of all NIS primary introductions in Europe have been reported first from the Mediterranean Sea. A more detailed analysis revealed various patterns of the dominating native distributions of the primarily introduced NIS in Europe, depending on the European marine subregions where they have been initially introduced and their associated pathways. There seems to be a general decrease in NIS introductions in Europe, especially when it comes to NIS with native distribution in the Temperate Northern Pacific, although this trend should be treated with caution. The information provided in the current study can be useful for tailored management of specific primary pathways per marine subregion, supporting prioritization efforts.
Refined baseline inventories of non-indigenous species (NIS) are set per European Union Member State (MS), in the context of the Marine Strategy Framework Directive (MSFD). The inventories are based on the initial assessment of the MSFD (2012) and the updated data of the European Alien Species Information Network, in collaboration with NIS experts appointed by the MSs. The analysis revealed that a large number of NIS was not reported from the initial assessments. Moreover, several NIS initially listed are currently considered as native in Europe or were proven to be historical misreportings. The refined baseline inventories constitute a milestone for the MSFD Descriptor 2 implementation, providing an improved basis for reporting new NIS introductions, facilitating the MSFD D2 assessment. In addition, the inventories can help MSs in the establishment of monitoring systems of targeted NIS, and foster cooperation on monitoring of NIS across or within shared marine subregions.
Standardized tools are needed to identify and prioritize the most harmful non-native species (NNS). A plethora of assessment protocols have been developed to evaluate the current and potential impacts of non-native species, but consistency among them has received limited attention. To estimate the consistency across impact assessment protocols, 89 specialists in biological invasions used 11 protocols to screen 57 NNS (2614 assessments). We tested if the consistency in the impact scoring across assessors, quantified as the coefficient of variation (CV), was dependent on the characteristics of the protocol, the taxonomic group and the expertise of the assessor. Mean CV across assessors was 40%, with a maximum of 223%. CV was lower for protocols with a low number of score levels, which demanded high levels of expertise, and when the assessors had greater expertise on the assessed species. The similarity among protocols with respect to the final scores was higher when the protocols considered the same impact types. We conclude that all protocols led to considerable inconsistency among assessors. In order to improve consistency, we highlight the importance of selecting assessors with high expertise, providing clear guidelines and adequate training but also deriving final decisions collaboratively by consensus.
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