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.

The recent paper by Bariche Fricke (2020) presents an updated checklist of the marine fish species in Lebanon including 367 fish species, 70 non-indigenous and 28 new records. According to Bariche Fricke (2020), the inventory is based on the published scientific papers related to the marine fishes in Lebanon, since Gruvel (1928, 1931), as well as grey literature, images published in newspapers or on local websites and social media. However, important scientific papers and published reports, providing important data on marine fishes in Lebanon, were missed. Hereby we cite twelve scientific papers: [Nafpaktitis (1963), Bath (1977), Shiber (1981), Moosleitner (1988), Lakkis et al. (1996), Bariche (2006), Bariche et al. (2006); Bitar et al. (2007), Bariche Trilles (2008), Bitar (2010), Khalaf et al. (2014), and Bitar (2015) in Zenetos et al. (2015)], twelve national reports [the national report of Abboud Abi Saab et al. (2003) under the framework of a Libano-Franco cooperation, the national report of Majdalani (2005) under the framework of the Ministry of Agricultue (MoA), the two reports in cooperation between the Food Agriculture Organisation (FAO) and the National Council for Scientific Research (CNRS) Lelli et al. (2006), and Sacchi Dimech (2011), and the eight national reports in collaboration with the Ministry of Environment (MoE) and the organizations of: (i) aecid/Tragsa as MoE/aecid/Tragsa (2009), (ii) International Union for Conservaion Nature (IUCN)- Specially Protected Areas Regional Activity Centre (SPA/RAC) as IUCN-SPA/RAC (2017), (iii) the SPA/RAC as Bitar (2008), RAC/SPA-UNEP/MAP (2014), IUCN-SPA/RAC (2017), and SPA/RAC-UN Environment/MAP (2017, 2018a, 2018b), and finally, the book of Lakkis (2013)]. Concerning the publication of Lakkis et al. (1996), and the book of Lakkis (2013), only the valid and confirmed/ or proofed marine fish species were listed in Table 1. While, the questionable/ doubtful marine fish records from those two references were listed in Table 2 and Table 3 (see suppl.file 2, and 3). In this context and based on the Lebanese literature, Bariche Fricke (2020) missed the reports of 9 species (Table 1). Therefore, the list of marine fish of Lebanon (Bariche Fricke, 2020) is enriched reaching 376 species, 71 of which are non-indigenous species (See suppl.file 1). In agreement with Zenetos Galanidi (2020) we state that even the current update may contain errors, as species invasions are dynamic phenomena, where new information continually comes to light, whether from new observations or from re-examination of older material, changes in nomenclature and phylogenetic studies.

New records of fish of the genus Abudefduf observed and photographed in the Lebanese coastal waters are reported in the paper. The individuals from photos were examined on the basis of visible external morphological characters and geographical location already known in the Mediterranean Sea, as well as compared with photos taken elsewhere in their natural environments from various origins. In agreement with that reported by other authors, a careful analysis of these photos shows uncertainties in the validity of the visual characters previously used to distinguish between the two congeners A. vaigiensis and A. saxatilis already reported in the Mediterranean Sea, and even their possible confusion with A. troschelii. In some individuals, new morphological features are emphasized and may provide visual evidence for the presence of Abudefduf cf. troschelii (Gill, 1862). Sympatry and possible hybridization are discussed.

The presence of the black wing flyingfish Hirundichthys rondeletii (Valenciennes, 1846) was reported for the first time from the Lebanese waters. It was caught by a professional fisherman in Beirut on 27 December 2009. The present note reports details about this record.

This study focuses on the isopod fauna of the eastern Mediterranean, mainly from the waters of Lebanon. Ninety-five samples containing isopods were obtained by scuba diving (depths 0 to 44 m) at 32 stations along the coast of Northern Cyprus, Syria, and Lebanon. The substrates most frequently sampled were caves, vertical walls, and calcareous algae crusts or build-ups. A total of 502 individuals were studied, belonging to 28 species, included in 20 genera, nine families, and three suborders. Four new species from this collection (Atarbolana beirutensis, Cirolana bitari, Cirolana zibrowiusi, Mesanthura pacoi) have already been published. Brief diagnoses and illustrations were included. The collection studied here consists mostly of Mediterranean species, some already known in the area. Ten (eleven, when cf. species is confirmed) are new records in the Levantine Sea (Apanthura addui, Cirolana manorae, Cymodoce fuscina, Cymodoce pilosa, Elaphognathia bacescoi, Gnathia illepidus, Gnathia inopinata, Heptanthura cryptobia, Kupellonura serritelson, Metacirolana rotunda, Pseudocerceis cf. seleneides). Of them, three (four, when cf. species is confirmed) are new records in the Mediterranean Sea (Apanthura addui, Cirolana manorae, Metacirolana rotunda, Pseudocerceis cf. seleneides). Eight species (28.5%) can be considered as non-indigenous (Apanthura addui, Cirolana manorae, Cymodoce fuscina, Metacirolana rotunda, Paracerceis sculpta, Paradella dianae, Pseudocerceis cf. seleneides, Sphaeroma walkeri). This manuscript also provides an inventory of the known Mediterranean isopod fauna (excluding Epicaridea, Oniscidea, and brackish water Aselloidea), which totals 295 species. The isopod fauna of various subregions of the Mediterranean, the Suez Canal, and the Red Sea / Gulf of Aden is compared, and the transit of species through the Suez Canal is discussed. The list of non-indigenous species in the Mediterranaean Sea is updated to 23.

The Indo-Pacific jellyfish Cotylorhiza erythraea Stiasny, 1920 is reported for the first time from the Lebanese waters. The species was observed and photographed by a professional diver on 28 July 2020 at a depth of 5 m in Tyre, south of Lebanon. The present note presents details about this observation.

We hereby review and update the current state of knowledge on the Lebanese gastropod biota based on published literature and the study of new samples. Review of 1543 published records yielded 237 gastropod taxa. New samples from the Lebanese coast yielded 2414 living specimens and 4003 empty shells, belonging to 188 taxa. Forty-six of the taxa are new records for the Lebanese fauna, bringing the gastropods known from Lebanon to 283 species. Literature records also included 71 nominal gastropod taxa based on type material from Lebanon, including 3 genera, 8 species, and 60 subspecific units. Of these, only 13 are retained as available. Of the 283 gastropod taxa known from Lebanon, 41 are aliens and 7 are cryptogenic. The majority of nonnative taxa were recorded only during the last decades, particularly from 1980 to 2019. Results from the present study question the common assumption that this region has extremely low native diversity. The flora and fauna of the Lebanese coast remain relatively unexplored and our data support the perception that several formerly abundant species have recently collapsed. Despite these advances, the lack of scientific data on biodiversity and community structure of Lebanese habitats and geographic zones is likely to hamper conservation actions and legal protection of critical species. We therefore recommend additional field and laboratory research to increase knowledge of both taxonomic composition and species' distributions in Lebanon and elsewhere in the easternmost Mediterranean Sea.

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.

A young specimen of the blackfish, Centrolophus niger (Gmelin, 1789) was reported for the first time from the Lebanese waters. It was caught and photographed by a professional fisherman in Beirut, on 15th November 2014. The present note reports details about this first record.

The two non-native ctenophores Beroe ovata Bruguiere, 1789 and Mnemiopsis leidyi A.Agassiz, 1865, were reported off the Lebanese waters. Beroe ovata Bruguiere, 1789, a specializedpredator on Mnemiopsis leidyi, was collected and photographed, on May 2th 2019 duringfieldwork in Beirut waters. While, Mnemiopsis leidyi was reported for the first time on April 27th2009, to date, it is widely distributed from the south to the north of the Lebanese waters. The mostpossible pathway of the introduction of those species is a spreading, or bringing with ballastwaters from the Black Sea.

This article includes 23 new records of alien and cryptogenic species in the Mediterranean Sea, belonging to 4 Phyla (Chordata, Echinodermata, Arthropoda and Mollusca), distributed from the Alboran to the Levantine Sea. Records are reported from eight countries listed from West to East as follows: Algeria: new records of the Atlantic blue crab Callinectes sapidus; Spain: further spread and establishment of the sea slug Lamprohaminoea ovalis in continental shores; Tunisia: first record of the Atlantic Blue Crab Callinectes sapidus in the Gulf of Gabes; Italy: a new occurrence of the pufferfish Lagocephalus sceleratus in Northern Ionian waters; first record of Cephalopholis taeniops in the Ionian Sea; first record of the redlip blenny, Ophioblennius atlanticus in the Ionian Sea; Slovenia: first record of the isopod Paranthura japonica in Slovenia; Greece: first record of the molluscs Eunaticina papilla, Plocamopherus ocellatus and the fish Cheilodipterus novemstriatus; first record of the ascidian Ecteinascidia turbinata in Kriti; the long-spined sea urchin Diadema setosum in the Ionian Sea; Turkey: first record of the sea spider Ammothea hilgendorfi; the stomatopod Cloridina cf. ichneumon; the fishes Pempheris rhomboidea from the Sea of Marmara and Paranthias furcifer from the Aegean Sea; Lebanon: new records of the fishes Arothron hispidus, Rachycentron canadum, Heniochus intermedius and Acanthurus monroviae; first record of Acanthostracion polygonius. The records of Cloridina cf. ichneumon from southern Turkey and the fish Acanthostracion polygonius from Lebanon, both being the first Mediterranean records, are noteworthy.

Vermetid reefs are a key intertidal habitat in the warm-temperate part of the Mediterranean Sea and in some subtropical and tropical regions in the Atlantic and Pacific oceans. This unique and highly diverse ecosystems is under siege due to both the high anthropogenic pressure and the global climate change, with documented local population declines in the Eastern Mediterranean. This study aims at evaluating the conservation state of vermetid reefs along the Lebanese coast (Eastern Mediterranean), where seawater warming, habitat degradation and coastal urbanization likely threaten their presence. In order to assess the conservation status of vermetid reefs in Lebanon, five sites were randomly selected among those belonging to three impact classes: i) not impacted (i.e. protected), ii) moderately impacted, and iii) impacted. Two different non-destructive methods were applied to assess the presence of living vermetids Dendropoma anguliferum (Monterosato, 1878) and Vermetus triquetrus (Bivona-Bernardi, 1832) which shape the reef, and the associated communities. Our results highlight that no living vermetid reefs were recorded in the impacted sites where evident signs of bio-physical erosion of the reef are already underway. Living individuals of Vermetus triquetrus were found in some not impacted and moderately impacted sites, while living individuals of the endemic reef-builder Dendropoma anguliferum were found only at very low densities at the not impacted (protected) site. Such findings corroborate preliminary observations of population decline in the Eastern Mediterranean, and of vermetid reefs vulnerability to human disturbances. This raises concerns about the near future persistence of vermetid reefs in the region, and represents a call for management and conservation actions to preserve this reef-building species in the Mediterranean Sea.

The “New Mediterranean Biodiversity Records” series includes new records of marine species found in the Mediterranean basin and/or information on the spatial distribution of already established species of particular interest. The current article presents information on 20 marine taxa classified per country according to their geographic position in the Mediterranean, from west to east. The new records per ecoregion are as follows: Algeria: the first record of the fish Etrumeus golanii is reported along the Algerian coast. Tunisia: the alien jellyfish Phyllorhiza punctata is reported for the first time in the Gulf of Gabès. Italy: the first record of Siganus rivulatus in the Strait of Sicily and a new record of Katsuwonus pelamis from the central Tyrrhenian Sea are reported. The establishment of the isopod of the genus Mesanthura in the northern Tyrrhenian with some notes on its ecology are also included. Croatia: signs of establishment of the Lessepsian Siganus luridus and the occurrence of the alien mollusc Rapana venosa are reported. Albania: the first record of the elasmobranch Alopias superciliosus and a recent sighting of the rare monk seal Monachus monachus in Albanian waters are given. Greece: signs of the establishment of the fish Parupeneus forsskali and of the ascidian Hermania momus in Hellenic Aegean waters are reported. Turkey: a new record of the fish P. forsskali and of the Acarea of the genus Acaromantis and Simognathus are given, while the first case of Remora australis in association with delphinids and the occurrence of the sea star Coscinasterias tenuispina are reported. Also, the establishment of the two alien species Isognomon legumen and Viriola sp. [cf. corrugata] are presented. Egypt: the fish Bathygobius cyclopterus is reported for the first time in Mediterranean Sea waters. Also, a new record of Pagellus bogaraveo and a first record of Seriola fasciata in Egyptian Mediterranean waters are reported. Lebanon: the first record of Dondice banyulensis is presented.

The marine macroflora introduced into Lebanon was studied through an analysis of historical data and field studies carried out since 1991. A total of 29 introduced species have been listed: 3 Chromobionta, 13 Rhodobionta, 12 Chlorobionta and 1 Streptobionta. Among them, Caulerpa taxifolia var. distichophylla, Spatoglossum variabile and Womersleyella setacea are recorded for the first time from Lebanon. Among them, Asparagopsis taxiformis, C. taxifolia var. distichophylla, Cladophora patentiramea, Codium arabicum, Codium parvulum, Galaxaura rugosa, Halophila stipulacea, Hypnea cornuta, Laurencia cf. chondrioides, Lophocladia lallemandii, Stypopodium schimperi, Ulva lactuca and Womersleyella setacea are potentially invasive species, and several of them already occupy extensive stretches of the Lebanese coast. The distribution of species on the Levantine coast, their dynamics and the current status of their populations are discussed.

Because of its location in the warmest corner of the Mediterranean, its proximity to the northern entrance of the Suez Canal, i.e. the gateway for massive exotic biota introduction into the Mediterranean, the occurrence of high shipping activity and strong human pressure, the Lebanese coastal zone is an area that is exceptionally well-suited for investigating the effects of these extreme conditions on Mediterranean biodiversity. Bryozoans, which are among the main components of sessile communities, reflect dramatically the impact of these particular conditions. Their assemblages, sampled by diving along the whole coast of Lebanon during a pluriannual programme, mainly between 1999 and 2003, consist of 93 species (12 Cyclostomata, 2 Ctenostomata, 79 Cheilostomata). The native part of this bryozoan fauna exhibits low diversity, with an unexpected absence of many taxa, from family to species level, which are very common in the rest of the Mediterranean. It is also characterized by a high proportion of endemic species, in contrast with the general eastward trend of decreasing endemicity observed in the Mediterranean, and by the strong presence of 'southern' thermophilic species. With 27 non-indigenous species, xenodiversity is exceptionally high, particularly in the cheilostome pool (26 species), but was likely undersampled. Moreover, one may assume that new non-indigenous bryozoans (NIB) are now established along the Levantine coasts. This trend is expected to increase in the near future with the intensification of surface water warming and boost of shipping activity and propagule flux generated by the expansion of the Suez Canal.

The Action Plan for the conservation of habitats and species associated with seamounts, underwater caves and canyons, aphotic hard beds and chemosynthetic phenomena in the Mediterranean Sea follows a series of eight Action plans adopted by the Mediterranean countries within the framework of the Barcelona Convention, devoted to the conservation of species or groups of species. These Action plans are: •Action Plan for the management of the Monk Seal •Action Plan for the conservation of marine turtles •Action Plan for the conservation of cetaceans •Action Plan for the conservation of marine vegetation •Action Plan for the conservation of bird species registered in annex II of the SPA/BD Protocol •Action Plan for the conservation of cartilaginous fi shes (Chondrichtyans) in the Mediterranean Sea •Action Plan concerning species introduction and invasive species •Action Plan for the conservation of the coralligenous and other calcareous bio-concretions in the Mediterranean Sea Dark Habitats are considered as sensitive habitats requiring protection (Directive 92/43), fragile and constitute veritable reservoirs of biodiversity that, therefore, must be protected and need further attention. This draft Action plan was the result of a Meeting of the ad hoc group of Mediterranean experts, nominated in consultation with the Contracting Parties and relevant partner organizations (Marseilles (France), May 2013). It was reviewed and adopted by the Eleventh Meeting of Focal Points for SPAs (Rabat - Morocco, 2 - 5 July 2013). The Action Plan was adopted in the Eighteenth Ordinary Meeting of the Contracting Parties to the Convention for the Protection of the Marine Environment and the Coastal Region of the Mediterranean and its Protocols (Istanbul - Turkey, 3-6 December 2013).

The Collective Article ‘New Mediterranean Biodiversity Records’ of the Mediterranean Marine Science journal offers the means to publish biodiversity records in the Mediterranean Sea. The current article is divided in two parts, for records of native and alien species respectively. The new records of native fish species include: the slender sunfish Ranzania laevis and the scalloped ribbonfish Zu cristatus in Calabria; the Azores rockling Gaidropsarus granti in Calabria and Sicily; the agujon needlefish Tylosurus acus imperialis in the Northern Aegean; and the amphibious behaviour of Gouania willdenowi in Southern Turkey. As regards molluscs, the interesting findings include Ischnochiton usticensis in Calabria and Thordisa filix in the bay of Piran (Slovenia). The stomatopod Parasquilla ferussaci was collected from Lesvos island (Greece); the isopod Anilocra frontalis was observed parasitizing the alien Pteragogus trispilus in the Rhodes area. The asteroid Tethyaster subinermis and the butterfly ray Gymnura altavela were reported from several localities in the Greek Ionian and Aegean Seas. The new records of alien species include: the antenna codlet Bregmaceros atlanticus in Saronikos Gulf; three new fish records and two decapods from Egypt; the establishment of the two spot cardinal fish Cheilodipterus novemstriatus and the first record of the Indo-Pacific marble shrimp Saron marmoratus in semi-dark caves along the Lebanese coastline; the finding of Lagocephalus sceleratus, Sargocentron rubrum, Fistularia commersonii and Stephanolepis diaspros around Lipsi island (Aegean Sea, Greece); the decapod Penaeus hathor in Aegean waters; the decapod Penaeus aztecus and the nudibranch Melibe viridis in the Dodecanese islands; the finding of Pinctada imbricata radiata in the Mar Grande of Taranto (Ionian Sea, Italy) and the Maliakos Gulf (Greece).

According to reports, the following 16 species have extended their distribution to other Mediterranean areas or have made a new appearance in other regions. The first category includes the following organisms: The rare and common Indo-Pacific seaweed Codium arabicum (Lebanese coasts), the acari Thalassarachna affinis (Marmara Sea), and the non-indigenous nudibranch Flabellina rubrolineata, which has also been found in many other areas of the Aegean Sea. In addition, the rare sea slug Thecacera pennigera (Piccolo of Taranto), the fangtooth moray Enchelycore anatina (National Marine Park of Zakynthos, Ionian Sea), the carangid Seriola fasciata (Gulf of Antalya), Lagocephalus sceleratus (SE. Ionian Sea), the reticulated leatherjacket Stephanolepis diaspros (Slovenia, N. Adriatic Sea), the marbled stingray, Dasyatis marmorata (NE Levantine), the starry smooth-hound Mustelus asterias (Iskenderun Bay, NE Mediterranean), the cephalopod Ommastrephes bartramii (Ionian Sea) have also been reported. The Atlantic crab Dyspanopeus sayi has expanded to many Italian areas and the blue crab Callinectes sapidus to a lake in N. Greece and in the S. Adriatic Sea. Finally, Farfantepenaeus aztecus has been found in the Ionian Sea, thus showing its wide expansion in the Mediterranean. The larval stages of Faccionella oxyrhyncha have been found, after many years, in the Aegean Sea and the first report of an existence on intersexual acari Litarachna duboscqi in Split (Adriatic Sea) was reported.