Alien species of the Romanian and Bulgarian Black Sea coast: state of knowledge, uncertainties, and needs for future research

In order to assist the implementation of the European policies on Invasive Alien Species (IAS Regulation) and mitigate the impact of alien species that threaten the marine ecosystem services and biodiversity, accurate lists of alien species per European Member State are required. Although inventories of marine alien species and relevant information about them have been reported for the Black Sea marine region of Romania and Bulgaria, a validated list of alien species for the two countries is still lacking. In this paper we (i) propose a validated list of the marine alien species occurring in the Romanian and Bulgarian Black Sea regions, and (ii) address errors, gaps and uncertainties associated with listing alien species from the marine waters of the two countries. The list of alien species includes 37 species for Romania and 26 for Bulgaria, with the highest number of alien species belonging to the phylum Arthopoda for both countries. The majority of alien species have been classified as successfully established in the marine waters of both countries. Thirteen alien species were classified as invasive in Romania whilst eight alien species were classed as invasive in Bulgaria. The historical overview indicates that the number of alien species has steadily increased over the last 50 years both in Romania and Bulgaria. The results of our study provide the baseline list and information for addressing marine alien species at a national level and a starting point for selecting the invasive alien species for risk assessment towards an effective implementation of the IAS Regulation. In conclusion, this study provides supporting information for implementing measures to tackle the introduction of alien species in the western region of the Black Sea. These measures are needed to build an early warning, prevention, and control of invasive alien species in the Black Sea, a unique and fragile ecosystem.