In this study we present a list of invasive/potential invasive alien species in the East and South European Network for Invasive Alien Species (ESENIAS) countries with marine borders. The species were classified according to the existing literature and experts’ judgment, as established, casual, invasive and expected. Finally, factsheets were compiled for ten species of high importance based on their expanding/invading character. Of the 160 species comprising the list, 149 were already present in the ESENIAS countries, while eleven were invasive species either present in the Mediterranean or in other European Seas, likely to be recorded in the ESENIAS countries. The majority of the species were of Red Sea/IndoPacific origin (97 species; 60.6%). Italy, Turkey and Greece were the countries with the highest representation of species (159, 152 and 139 species respectively), due to their extended coastline and the number of scholars working on marine invasive species. The highest number of established species was recorded in Turkey (116 species), whereas in Italy and Greece the most numerous species were the “expected” ones (85 and 48 species, respectively). The eastern Adriatic Sea countries (i.e. Albania, Croatia, Montenegro and Slovenia) had generally low numbers of species in this list, many of which are still “expected” to arrive from the neighbouring countries of Greece and Italy. Finally, the most frequently potential pathway was transfer stowaways (ship ballast water: 41 cases; ship hull fouling: 55), whereas unaided spread of Lessepsian immigrants followed (95 cases). This list is intended to serve as an early warning system that through horizon scanning process would assist ESENIAS countries to prioritise invasive alien species, their pathways and the areas of higher likelihood to appear, in order to take management measures.

A survey conducted in inshore waters along the Romanian coast of the Black Sea from 1994 to 2000, yielded 24 polychaete species belonging to 10 families as follows: Polynoidae (2), Phyllodocidae (2), Syllidae (3), Nereididae (5), Spionidae (5), Capitellidae (3), Nerillidae (1), Sabellidae (1), Serpulidae (1), and Spirorbidae (1). Polydora websteri (Hartman, 1943) is a new record for the Mediterranean and Black Sea region. P. cornuta (Bose, 1802) is first recorded in the Black Sea. Additionally, two other species, namely Harmothoe imbricata (Linnaeus, 1767) and Typosyllis hyalina (Grube, 1863), are new to the Romanian fauna. The systematic position of some species is discussed. The information on geographical distribution within the Mediterranean region of species found is also provided.

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Populations of Alitta (=Neanthes) succinea (Frey and Leuckart, 1847) collected from two closely situated locations on the Romanian coast of the Black Sea were analysed from March 2007 to May 2008 in order to elucidate their population dynamics and genetics. The mean density was 655 ind. m −2 , presenting two peaks, the first in June 2007 with 950 ind. m −2 and the second in November 2007 with 1633 ind. m −2. The mean biomass over entire period of survey was 4.33 g dry weight (DW) m −2 , with a minimum of 1.15 g DW m −2 in September 2007 and a maximum of 8.08 g DW m −2 in June 2007. The decrease of density and biomass in winter is determined by the mortality of adults, whereas the increase in numerical abundance in late spring-early summer and especially in the autumn can be explained by the recruitment of juveniles. The analysis of the size frequency histograms indicated the existence of two recruitment periods: the first in May-June and the second in September-November. From June 2007 to May 2008, the annual secondary production, mean biomass and the production/biomass ratio (P/B) for the entire population were estimated to be 5.66 g DW m −2 year −1 , 4.22 g DW m −2 and 1.34 year −1 , respectively. Extracts for isozyme analysis were prepared from 23 individuals from the polluted Danube-Black Sea Canal (population C) and 25 individuals from relatively pristine area situated at only 2 km distance (population A). A genetic analysis was conducted with 29 DNA markers on 10 individuals from population A and 10 individuals from population C. The value of Nei's genetic index was h = 0.1873 for population A, h = 0.2099 for population C and h = 0.2172 for the total, while the gene flow was Nm = 1.12. The results showed that the two sampled populations are genetically close and could be considered as a single population and genetic pool.

Ecosystem engineers create habitat and provide conditions otherwise unavailable for the development of diverse communities. In marine soft-bottoms in particular, the biodiversity sustained by a matrix of relatively uniform sediments can be drastically enhanced by the presence of ecosystem engineers such as seagrasses. Unfortunately, the influence of seagrass meadows on the diversity of surrounding sediments is often unrecognized in spite of its importance, especially in coastlines exposed to multiple sources of pollution. This study examined composition and diversity associated with a bed of Zostera noltei Hornemann, 1832, and its surrounding bare sediments in a highly urbanized coastal area of the Romanian Black Sea. Dissimilarity levels were quantified and key species driving the differences between uniform (bare) and complex (eelgrass) sedimentary habitats were identified. 48 taxa were collected and counted, with epifaunal and infaunal species each accounting for nearly half of that diversity. Abundance, richness and diversity were strikingly higher in eelgrass-associated sediments, a difference driven primarily by various species of snails, crustaceans, polychaetes and bivalves. Between-habitat differences remained significant even after the removal of epifaunal species and each dataset undergoing strong data transformation. These results suggest that even small eelgrass beds, located in the vicinity of multiple sources of stress, can act as hotspots and make a substantial contribution to local benthic diversity.