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.

This study records the number of Peracarida (Cumacea, Isopoda, Mysida, Lophogastrida and Tanaidacea) from Algerian coastal waters. A total of 170 species are reported with the highest richness observed in the Isopoda (71 species), then the Cumacea with 43 species, the Mysida and Tanaidacea with 27 species each and the Lophogastrida with only two species. The diversity of Peracarida in Algeria is high, corresponding to 60% of the species recorded for the Mediterranean Sea. A geographical analysis of the distribution of the species shows that the Algerian fauna has a close similarity with taxa reported from both the European and African coasts of the Atlantic Ocean. This reflects the influence of Atlantic waters along the North African coasts extending from Morocco to Tunisia in the south of the Mediterranean Sea, which is related to the connection via the Strait of Gibraltar. For the Algerian coasts only five Peracarida species may be considered as Non-Indigenous Species.

The present study analyses the spatio-temporal structuration of the molluscan fauna from four tidal channels of the Gulf of Gabès. A total of 26 stations were sampled at four seasons from March 2016 to January 2017, leading to the identification of 2695 individuals and 57 species. The species richness and abundances are higher in autumn than in other seasons. The fauna is dominated by seven species, three gastropods [Cerithium scabridum Philippi, 1848, Bittium reticulatum (da Costa, 1778) and Tricolia speciosa (Megerle von Mühfleld, 1824)] and four bivalves [Abra alba (W. Wood, 1802), Loripes orbiculatus Poli, 1791, Varicorbula gibba (Olivi, 1792) and Peronaea planata (Linnaeus, 1758)], which are characteristic of habitats with detritus accumulation and seagrass meadows. These dominant species are commonly recorded in lagoons and coastal shallow waters of the Mediterranean Sea. The structure of the molluscan fauna is linked to the location of tidal channels in the Gulf of Gabès. Abundances are lower in the Mimoun channel than in the other channels, especially the Maltine channel which shows a great accumulation of organic matter and high abundances of molluscs. Low abundances are found in high-energy hydrodynamic zones with gravel sediment; conversely, the presence of macrophytes (mainly in seagrass meadows) increases molluscan diversity. Comparisons with other sites in the shallow waters of the Tunisian coast and lagoons show that the taxonomic diversity of molluscs of the tidal channels of the Gulf of Gabès is equivalent to that reported elsewhere, but the abundance per m² is among the lowest levels recorded here. Moreover, most of the dominant species found in the Gulf of Gabès tidal channel are reported as dominant in other studies covering the Mediterranean Sea. A distance-based redundancy analysis shows that depth, sediment type and the presence of marine phanerogams and filter-feeder bivalves on fine sands and gravels account for the structure of mollusc assemblages associated with each channel.

An updated checklist for 2023 is given for the amphipods recorded on the continental shelf of five countries in North Africa bordering the southern Mediterranean Sea: Morocco, Algeria, Tunisia, Libya and Egypt. This revision incorporates the checklist of amphipods from two countries, Algeria and Tunisia and provides the first checklists for Morocco, Libya and Egypt. The total number of species recorded in the entire Southern Mediterranean Sea is 454. The number of species is much higher in the western basin than in the eastern or central parts of the Mediterranean Sea. The Algerian fauna accounts for the highest number of species (with 342), while the lowest is found in Egypt (with 100). The other checklists are for Morocco (241 species), Tunisia (167 species) and Libya (138 species). Among the 454 species making up the overall checklist, 95 species (21%) are considered as endemic to the Mediterranean Sea. The Caprellidae Leach, 1814 represent the most diversified family with 34 species. Five other families account 20 species or more, i.e., the Ampeliscidae Krøyer, 1842 (33 species), the Aoridae Stebbing, 1899 (25 species), the Ischyroceridae Stebbing, 1899 (21 species), the Corophiidae Leach, 1814 (21 species) and the Maeriidae Krapp-Schickel, 2008 (20 species). Only 15 species are non-indigenous species or cryptogenic species. There is a trend of decreasing diversity of benthic amphipods from the western to the eastern parts of the Southern Mediterranean Sea; the greatest number of pelagic amphipod species has been observed in the Egyptian coast. Only eight species have been reported from abyssal depths off the Algerian coast. Twenty-seven species were found along the entire North African coast, including four Ampelisca (A. brevicornis, A. diadema, A. tenuicornis and A. typica), four Maeridae (Elasmopus pocillimanus, E. rapax, Maera grossimana and Quadrimaera inaequipes) and three Lysianassidae (Lysianassa costae, L. pilicornis, and Lysianassina longicornis). Future research should be focused on deep-sea habitats, on specific or unexplored habitats such as seagrass meadows (Posidonia oceanica, Zostera spp. and Cymodocea nodosa) and coralligenous formations as well as on the south-eastern part of the Mediterranean Sea.

An updated amphipod checklist for 2024 is given for the amphipods recorded from the adlittoralto abyssal zones of the Macaronesian archipelagos and the north-west African margin. Four marine regions are taken into account: 1) North West Africa (NWA), 2) Mauritania and Senegal (SEN), 3) Canary, Selvagens and Madeira Archipelagos (CAN MAD) and 4) the Cabo Verde Archipelago (CV). The total number of species recorded in these four regions is 509. CAN-MAD is the region with the greatest species richness (302 species), followed by NWA (297 species), SEN (152 species) and finally CV (122 species). Among the 509 species recorded, 66 have been described from this region while 59 are endemic. The most diverse family is the Ampeliscidae Krøyer, 1842 (32 species), the Scinidae Stebbing, 1888 (29 species), the Caprellidae Leach, 1814 (22 species). Then, five other families are each represented by 16 species or more, the Photidae Boeck, 1871, Maeridae Krapp-Schickel, 2008 and Ischryroceridae Stebbing, 1899 (17 species), Aoridae Stebbing, 1899 and Hyalidae Bulyčeva, 1957 (16 species). Only five species are non-indigenous or possibly non-indigenous. The biogeographical affinities of the benthic amphipods are highlighted by comparing them with communities from the continental/insular shelf of the four regions studied here as well as with three neighbouring areas, i.e.: part of the Lusitanian maritime province (BIS-IBE), the Mediterranean shores of Morocco and Algeria (MOR-ALG) and the Azores Archipelago (AZO). The CV and SEN fauna are distinguishable from the others, which form two main groups: the NWA, MORALG and BIS-IBE on the one hand, and the CAN-MAD and AZO archipelagos on the other. Future research should be focused along the coasts of Mauritania and Senegal and around the Cabo Verde Archipelago where there is a lack of knowledge not only on amphipods but also regarding marine invertebrate biodiversity in general. Special attention should be paid to biofouling in harbours since this is liable to increase the number of non-indigenous species which appears to be very low in the Macaronesian archipelagos in spite of the intense maritime traffic.