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This work presents refined, updated subregional and regional non-indigenous species (NIS) inventories for the Mediterranean Sea, validated by national and taxonomic experts, with species records observed until December 2020. These datasets will be used as the baselines for the implementation of the Integrated Monitoring and Assessment Programme for the Mediterranean (IMAP) and the Mediterranean Quality Status Report 2023. In total, 1006 non-indigenous species have been found in Mediterranean marine and brackish waters. The highest numbers of NIS were observed in Israel, Türkiye, Lebanon and Italy. Approximately 45 species were categorized as data deficient, either due to lack of consensus on their alien status or the validity of their identification. Polychaeta, Foraminifera and macroalgae were the groups with the highest numbers of controversial species. There was a general increase in the yearly rate of new NIS introductions after the late 1990s, which appears to be slowing down in the last decade, but this may be confounded by reporting lags and differential research efforts. Between 1970 and 2020 there has been a steep increase in the proportion of shared species present throughout all four Mediterranean subregions, which are predominantly transported via shipping and recreational boating. While Lessepsian species are gradually spreading westwards and northwards, there is still a considerable invasion debt accumulating in the eastern and central Mediterranean. [ABSTRACT FROM AUTHOR]

Symplegma is a genus of compound ascidians (Fam. Styelidae) with warm water affinities and distribution in tropical and subtropical waters of the Pacific, Indian and Atlantic Oceans. The first record of this genus (as S. viride) in the Mediterranean was from 1951 in the Levantine Sea, presumably entering the basin from the Red Sea through the Suez Canal. Subsequently, it has been expanding its distributional range northward along the Levantine Sea coast, probably following the prevailing surface current direction. Recently, Symplegma has colonized the Aegean, Ionian and Tyrrhenian Seas, where it is spreading quickly, most likely mediated by shipping (i.e., hull fouling). Some specimens from the Ionian Sea (specifically from Tunisia, Malta) present opaque tunics resembling the Indo-Pacific Symplegma bahraini; however, morphological studies suggest that the genus in the Mediterranean Sea is represented by a single species, Symplegma brakenhielmi. The taxonomy of S. brakenhielmi, as well as its spreading routes and possible introduction vectors are analysed. [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]

Despite the hydroid fauna of the Mediterranean Sea being considered one of the best known in the world, the eastern basin of the Mediterranean Sea remains nearly unexplored. This paper reports on 38 species collected along the Levant Sea coast (mainly Lebanon), of which three are new records for the Mediterranean and nine for the Levant Sea. Six alien species, i.e. Eudendrium carneum, Sertularia marginata, Sertularia techocarpa, Macrorhynchia philippina, Diphasia digitalis and Dynamena quadridentata, are described in detail and illustrated on the basis of Levant Sea material. The last four species are considered as immigrants from the Red Sea. The synonymy of Sertularia stechowi, described from Japan, with S. techocarpa is established. Taken as a whole, the collection comprised a majority of circum-(sub)tropical species, and a reduced proportion of Atlantic–Mediterranean elements and Mediterranean endemics. The ecology (seasonality, depth distribution and habitat preference) of the indigenous species resulted similar to what is known for the more studied western Mediterranean, with some exceptions. Adding the present species inventory to the scanty published information, the total of hydroid species known from the Levant Sea rises to 70, indicating the need for future investigation in this sector of the Mediterranean Sea. [ABSTRACT FROM PUBLISHER]

An excavating sponge, which covers extensive areas of limestone rock, has been found at several locations of the Eastern Mediterranean Sea. This zooxanthellate clionaid, brown with yellow oscula, may have an extension of several square meters under the β-form, similar to what has been described in coral reef areas. It has been observed at 3–30 m depth, generally in clear water in the Ionian Sea, Crete, Cyprus and Lebanon. The gross morphology and the spicule characters are described from all the collected specimens. The spicule complement, with variable tylostyles and rare, sometimes absent, thin spirasters, is compared with that of Cliona parenzani Corriero & Scalera-Liaci 1997 from the Apulian coast (Ionian Sea, Mediterranean Sea), and of several Caribbean and Indo-Pacific clionaid species, which display the same morphology and rather similar spicule characters. The sponge is tentatively identified as C. parenzani, although there are some differences with the type specimens in the highly variable spiculation, suggesting that it may represent a species complex similar to what is known for other species in the Caribbean and Indo-Pacific areas. Although the sponge appears to be closely related to large brown spreading clionaids from tropical areas and was previously practically overlooked in the Eastern Mediterranean, it does not appear to be a recent introduction. It is suggested that it could be a survivor in the warmer area of the Mediterranean of an ancient thermophilous fauna, which did not survive in the colder Western Basin during glacial episodes of the Pleistocene. [ABSTRACT FROM AUTHOR]

Five new species of sponges are described from the coast of Lebanon in the eastern Mediterranean, Levantine Basin. Euryspongia raouchensis (Dysideidae), Liosina blastifera (Dictyonellidae) and Niphates toxifera (Niphatidae) belong to genera that are new for the Mediterranean but widely distributed in the tropics. Cinachyrella levantinensis (Tetillidae) and Ciocalypta carballoi (Halichondriidae) are described in genera with a restricted distribution in the Mediterranean, which have affinities with species from the Atlantic West African coast. These species do not appear to be lessepsian migrants, but are interpreted as remnants of an ancient thermophilous fauna that survived in the easternmost part of the Mediterranean. [ABSTRACT FROM PUBLISHER]

The geographic distribution of Verruca stroemia and V. spengleri are reviewed. Verruca stroemia ranges from the White, Barents, Norwegian, and North Seas south to Portugal to the Algarve and to Gorringe Bank. All of the records of this species from the Mediterranean Sea are considered to be V. spengleri. Verruca spengleri occurs in the Azores and Madeira archipelagos, in southern Spain (Cádiz), throughout the Mediterranean Sea from Gibraltar to Lebanon, and in the Black Sea. But a distinct deep-water Verruca species seems to occur in the deep Mediterranean. [ABSTRACT FROM PUBLISHER]