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This work reports on 60 marine alien mollusks from nine countries across the Mediterranean Sea and the Sea of Marmara collected by two Belgian citizen scientists. Some of their published observations concerning collection dates are compared with the year of first publication for these alien mollusks reported in the literature, which enable us to backdate some of their introductions and set new first Mediterranean records for two species. This underlines the importance of collaboration between volunteers and institutional scientists in tracing variations and changes in the environment and biodiversity. [ABSTRACT FROM AUTHOR]

Simple Summary: Human activities and interventions, such as creating sea basin connections (e.g., the Suez Canal), shipping, and aquaculture can serve as pathways for marine species introductions to new ecosystems beyond their natural geographical range. These species are called aliens and may become invasive, negatively impacting the recipient ecosystem. The effective management of invasive species requires understanding and assessing their impacts on the native biota. In this study, we mapped and quantified the cumulative impacts of invasive species on the marine habitats of the Aegean Sea, a Mediterranean ecoregion that is heavily affected by biological invasions. Our findings show that coastal habitats were more impacted by invasive species than the open sea. A higher frequency of strong impacts was observed in the South Aegean compared to the North Aegean, primarily due to alien fish and macrophytes. Shallow hard substrates were the most impacted habitat type, followed by shallow soft substrates and seagrass meadows. The worst invasive species varied depending on the habitat type and impact indicator used. Our study aligns with European guidelines for managing invasive species' impacts on native biodiversity and can serve as an essential tool for managing biological invasions and mitigating their impacts in the Aegean Sea. Biological invasions are a human-induced environmental disturbance that can cause major changes in ecosystem structure and functioning. Located in the northeastern Mediterranean basin, the Aegean Sea is a hotspot of biological invasions. Although the presence of alien species in the Aegean has been studied and monitored, no assessment has been conducted on their cumulative impacts on native biodiversity. To address this gap, we applied the CIMPAL index, a framework developed for mapping the cumulative impacts of invasive species, to identify the most affected areas and habitat types and determine the most invasive species in the region. Coastal areas showed stronger impacts than the open sea. The highest CIMPAL scores were four times more frequent in the South than in the North Aegean. Shallow (0–60 m) hard substrates were the most heavily impacted habitat type, followed by shallow soft substrates and seagrass meadows. We identified Caulerpa cylindracea, Lophocladia lallemandii, Siganus luridus, Siganus rivulatus, and Womersleyella setacea as the most impactful species across their range of occurrence in the Aegean but rankings varied depending on the habitat type and impact indicator applied. Our assessment can support marine managers in prioritizing decisions and actions to control biological invasions and mitigate their impacts. [ABSTRACT FROM AUTHOR]

To enrich spatio-temporal information on the distribution of alien, cryptogenic, and neonative species in the Mediterranean and the Black Sea, a collective effort by 173 marine scientists was made to provide unpublished records and make them open access to the scientific community. Through this effort, we collected and harmonized a dataset of 12,649 records. It includes 247 taxa, of which 217 are Animalia, 25 Plantae and 5 Chromista, from 23 countries surrounding the Mediterranean and the Black Sea. Chordata was the most abundant taxonomic group, followed by Arthropoda, Mollusca, and Annelida. In terms of species records, Siganus luridus, Siganus rivulatus, Saurida lessepsianus, Pterois miles, Upeneus moluccensis, Charybdis (Archias) longicollis, and Caulerpa cylindracea were the most numerous. The temporal distribution of the records ranges from 1973 to 2022, with 44% of the records in 2020-2021. Lethrinus borbonicus is reported for the first time in the Mediterranean Sea, while Pomatoschistus quagga, Caulerpa cylindracea, Grateloupia turuturu, and Misophria pallida are first records for the Black Sea; Kapraunia schneideri is recorded for the second time in the Mediterranean and for the first time in Israel; Prionospio depauperata and Pseudonereis anomala are reported for the first time from the Sea of Marmara. Many first country records are also included, namely: Amathia verticillata (Montenegro), Ampithoe valida (Italy), Antithamnion amphigeneum (Greece), Clavelina oblonga (Tunisia and Slovenia), Dendostrea cf. folium (Syria), Epinephelus fasciatus (Tunisia), Ganonema farinosum (Montenegro), Macrorhynchia philippina (Tunisia), Marenzelleria neglecta (Romania), Paratapes textilis (Tunisia), and Botrylloides diegensis (Tunisia). [ABSTRACT FROM AUTHOR]

Biological invasions represent one of the main threats to marine biodiversity. From a conservation perspective, especially in the context of increasing sea warming, it is critical to examine the suitability potential of geographical areas for the arrival of Range‐Expanding Introduced and Native Species (REINS), and hence anticipate the risk of such species to become invasive in their new distribution areas. Here, we developed an empirical index, based on functional and bio‐ecological traits, that estimates the Invasive Potential (IP; i.e. the potential success in transport, introduction and population establishment) for a set of 13 fishes that are expanding their distributional range into the Mediterranean Sea, the most invaded sea in the world. The IP index showed significant correlation with the observed spreading of REINS. For the six species characterized by the highest IP, we calculated contemporary and future projections of their Environmental Suitability Index (ESI). By using an ensemble modelling approach, we estimated the geographical areas that are likely to be the most impacted by REINS spreading under climate change. Our results demonstrated the importance of functional traits related to reproduction for determining high invasion potential. For most species, we found high contemporary ESI values in the South‐eastern Mediterranean Sea and low to intermediate contemporary ESI values in the Adriatic Sea and North‐western Mediterranean sector. Moreover, we highlighted a major potential future expansion of high ESI values, and thus REINS IP, towards the northern Mediterranean, especially in the northern Adriatic Sea. This potential future northward expansion highlights the risk associated with climate‐induced impacts on ecosystem conservation and fish stock management throughout the entire Mediterranean Sea. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A review of the scientific literature and an analysis of unpublished material identified ~ 50 possible alien molluscs from Greece, four of which were newly reported here. Records of ~ 100 additional taxa, which would strongly inflate the alien species numbers, were excluded. Among the ~ 50 candidate species, 43 were confirmed as alien and 12 as cryptogenic. Twenty-nine alien species were considered established, and four deemed invasive. Our results are consistent with the position of Greece in the east-west Mediterranean gradient, as well as the Aegean marine environment. The contribution of well-informed citizen scientists appears to be crucial to our overall knowledge of alien molluscan biotas because only 12 alien taxa were detected during formal research projects, while 31 were first found by amateurs. No molluscan introductions were confirmed from Greece pre-1960s, and subsequent periods had variable numbers of introductions, ranging from 0 (1976–1980) to 9.5 (2006–2010). The areas with the highest alien species concentrations were the Saronikos Gulf, near the Piraeus port area, and the Dodekanisa, near the Levantine coastline. Despite a general decline in taxonomic expertise and in local knowledge, we show that these are still needed when compiling and analyzing alien species inventories that subsequently influence policy and management decisions. [ABSTRACT FROM AUTHOR]

We herein review the Adriatic opisthobranch fauna, provide an updated checklist of 223 species and assess their distribution at regional and country levels. New Adriatic records are provided for 67 opisthobranch taxa, adding three new records for the Italian coastline, five new records for Albania, eight for Croatia and 15 for Montenegro. The presence of Hermaea bifida (Montagu, 1815), Hermaea variopicta (Costa A., 1869) and Facelina annulicornis (Chamisso & Eysenhardt, 1821) is reported for the first time from anywhere in the Adriatic Sea. Including the new findings, our inventory includes 28 species from Albania, 163 from Croatia, 178 from the Italian coastline of the Adriatic, 41 from Montenegro and 74 from Slovenia. No records were available from Bosnia and Hercegovina. Ninety species (40.4%) are widespread, and were recorded from all three main divisions (Northern, Western and Eastern Adriatic), whilst 79 species (35.4%) were reported from only one of them. At sub-division levels, the Albanian inventory is the most dissimilar to the other country/regional lists, presumably because of the lack of targeted field surveys. The highest similarity is observed amongst the Western Adriatic, Croatia and the Italian Ionian coastline. Seven alien, one possible alien and three cryptogenic opisthobranchs were reliably recorded from the Adriatic Sea. The first Mediterranean records of five species were in the Adriatic Sea, of which four species have not been found elsewhere in the Mediterranean. Shipping and aquaculture are the probable pathways for most of the alien species. A steady rate of one to two alien introductions per decade since the 1970s was evident. The Northern Adriatic coasts are the most affected by alien invasions, probably due to repeated local introductions along with shellfish transfers (oysters, mussels, Manila clams), and heavy maritime transport. [ABSTRACT FROM AUTHOR]

The number of alien species in the Mediterranean Sea is increasing rapidly, but few attempts have been made to evaluate impacts on specific habitat types. The present study investigated alien biodiversity in Mediterranean marine caves, both by contributing new records of Eastern Mediterranean cave aliens, and by reviewing the scattered existing literature; the main goals were to highlight potential impacts and investigate the importance of cave environments for the expansion of alien species. Seven new alien species were found in marine caves of the Aegean and Ionian seas, raising the total number of aliens reported from Mediterranean marine caves to 56 species, classified as molluscs, cnidarians, bryozoans, polychaetes, crustaceans, macroalgae, fishes and tunicates. Most cave aliens (66%) were recorded from the Southeastern Levantine coasts, specifically from Lebanese caves. Shipping and Lessepsian migration have been suggested as the main pathways of alien introduction into caves of the Mediterranean Sea. The comparison of alien cave biodiversity with the updated Mediterranean alien inventory (32 species added to the latest inventory) showed similar patterns and trends for species richness, biogeographical origin and major introduction pathways, corroborating previous findings on the high local representativeness of Mediterranean cave biodiversity. Alien species seem to have invaded mostly the entrance and semi-dark zones of shallow and/or semi-submerged caves and tunnels, whereas only a few have reached the dark inner sectors or caves of the anchialine type; thus, the unfavourable cave environment seems to be naturally protected from impacts related to opportunistic invasive species, at least to a certain point. Currently there is no research confirming any direct impacts of alien biota on the native cavernicolous one. However, some issues have emerged, implying potential threats that need to be further explored: (i) the presence of a considerable proportion of aliens in most studied marine caves of the Southeastern Mediterranean basin, (ii) the recently observed population explosion of alien cave-dwelling fishes in the same area, (iii) several indications that alien diversity in marine caves is much higher than we know today. Quantitative surveys and monitoring schemes are needed in order to evaluate potential effects of alien diversity on cave community structure and the role of marine caves as stepping stones for its expansion in the Mediterranean. [ABSTRACT FROM AUTHOR]

The distribution of the alien crab Percnon gibbesi in the Mediterranean Sea was assessed, based on new data from four independent surveys in Albania-Montenegro, Tunisia, Libya, and Crete (Greece), personal observations of the authors and a thorough compilation of existing information. The species is reported herein for the first time from Albania, Algeria, Cyprus, Israel, and Lebanon. Percnon gibbesi rapidly increased its spatial distribution in the Mediterranean Sea after its first report in 1999. At present, twelve years after its introduction, P. gibbesi is established in most Mediterranean coasts, especially in middle latitudes. It is absent from the Adriatic Sea (except from its southern limit in the Albanian part of Otranto Strait), the Ligurian Sea, the Corsica Island, and the northern Aegean Sea, possibly because of the low winter temperatures prevailing in these areas. In the North African coasts, P. gibbesi has not yet been observed in Morocco. After its initial introduction, its further spreading in the Mediterranean basin seems to be governed primarily by natural dispersal via larval transport by currents. The invasion rate of P. gibbesi was assessed in the Kaş -- Kekova Marine Protected Area in southern Turkey, based on a time series of monitoring data from 2002 to 2010. The species was first observed in 2006 in two sites and rapidly increased its occupancy and abundance the following years. Its occupancy (probability of presence in 500 m length of coastline) reached 23% within four years from its first sighting. Its abundance increased exponentially with an intrinsic rate of increase r=0.79, corresponding to more than doubling of the population per year. [ABSTRACT FROM AUTHOR]

The finding of some alien opisthobranchia previously unknown from Cyprus confirms that Indo-Pacific alien species are spreading at an increasing rate in the Levantine Sea. This work reports on the occurrence of four new alien species recorded in the form of images that have been taken over a period spanning more than 8 years. These are Chelidonura fulvipunctata, Chromodoris annulata, Flabellina rubrolineata and Hypselodoris infucata. In addition, finding ofMelibe viridis, which was considered hitherto as casual, confirm its establishment success around Cyprus. Chromodoris annulata, a recent invader in the Mediterranean and little known from the Levantine basin, is currently well established on the Cypriot coast. [ABSTRACT FROM AUTHOR]

Percnon gibbesi is an opportunistic feeder, feeding primarily on algae, of the shallow infra-littoral rocky shores. It was first observed in 1999 in the Mediterranean Sea and has rapidly spread since then. The range expansion of the species in the Aegean and Ionian Seas was recorded and evidence of its further establishment in Greek waters was provided. Established populations were observed in areas where it had not been previously reported: the Saronikos Gulf (central Aegean Sea), Chios Island (central Aegean Sea), Milos Island (central Aegean Sea), Zakynthos Island (central Ionian Sea) and Syvota (north-eastern coast of the Ionian Sea). The species was also observed in new sites in the Messiniakos Gulf, Crete and Rhodes Island, where it had been previously reported. The species keeps spreading in the Mediterranean Sea with a high rate of expansion. [ABSTRACT FROM AUTHOR]

The finding of sixteen alien species collected around Cyprus reveals that Indo-Pacific alien species are spreading at an increasing rate in the Levantine Sea leading to homogenization of the basin. This work reports on the occurrence of six alien species previously unknown to Cyprus namely: Dendrostrea frons, Gafrarium pectinatum, Paphia textile, Septifer forskali, Spondylus spinosus, Psammotreta praerupta and many more that seem to be now well established. Purpuradusta gracilis notata an Indo-Pacific cowry, known from the Levantine basin, is currently well established along the Cypriot coast. The literature review after the CIESM Atlas and Ozturk et al. (2004) has revealed another three new alien species, namely Aplysia dactylomela, Melibe viridis and Thais lacera. Outstanding is the finding of Fulvia fragilis, an Indian Ocean species widespread throughout the Mediterranean. [ABSTRACT FROM AUTHOR]

By October 2007, a total of 31 alien marine macrophytic species had been recorded on Greek coasts. Following a critical review of these findings, these species were classified as established (9 species), casual (8 species) and debatable (14 species). There were also 23 species found in the Greek marine flora that are excluded from the list of alien macroalgae. Brief remarks are provided for the debatable species. Based on the distribution of the alien species, four are considered as invasive, although their impact on the native vegetation has not yet been documented. A trend analysis revealed that most alien species (65% of current total) were found in the period 1971–2007. Shipping contributes to most alien macroalgal immigration (48%), followed by progressive immigration via the Suez Canal (33%), while aquaculture plays a minor role (16%), unlike the western Mediterranean Sea where aquaculture accounts for 73% of the macrophyte introductions. [ABSTRACT FROM AUTHOR]

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/Indo- Pacific 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. [ABSTRACT FROM AUTHOR]