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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]

The Greek Seas are greatly exposed to the proliferation of marine alien species. At least 242 alien species have been reported within Greek territorial waters, three-quarters of which are considered established, while their rate of introduction is increasing. Some of these species exhibit high invasiveness, imposing severe impacts on native ecosystems and ecosystem services. The spatiotemporal proliferation of these species outside their natural boundaries depends on several parameters, including their biological characteristics, native distribution range, introduction pathway, and time of initial introduction. Knowing the current and potential alien species distribution is essential for the implementation of effective management actions. To investigate the distribution of impactful cryptogenic and alien species (ICAS) in the Greek Seas, we combined all records available until the end of 2020 from eight types of data sources: (1) scientific literature, (2) grey literature, (3) offline databases, (4) online scientific databases, (5) personal observations of independent researchers, (6) communications with divers and diving centers, (7) in situ underwater sampling, and (8) social networks. The results of 5478 georeferenced records refer to 60 marine ICAS belonging to 16 taxonomic groups. The number of records and the overall number of ICAS present an increasing trend from the northern to the southern parts of our study area, and there is a clear distinction in community composition between the northern and southern subregions. This latitudinal gradient is mainly due to the large number of thermophilous Lessepsian species of West Indo-Pacific origin, which reach the southern parts of the study area through unaided dispersal. On the other hand, transport stowaways appear to be more prevalent in areas located near large ports, which show significant differences in ICAS numbers and community composition compared to sites located far from ports. Most records (>40% of the total) were associated with rocky reefs, partly reflecting the preference of divers for this habitat type but also the presence of conspicuous, reef-associated impactful fish. The number of published records, as well as the number of reported ICAS, shows a dramatic increase with time, highlighting the urgent need for immediate proactive management actions and scientifically informed control measures. [ABSTRACT FROM AUTHOR]

Urocaridella pulchella Yokeş & Galil, 2006 is a palaemonid cleaner-shrimp of Indo-Pacific origin that was first described from the Mediterranean Sea in 2006. However, limited information is available about its distribution and ecology due to the small size and cryptic habit of the species. We hereby report the first records of U. pulchella in marine caves and crevices of Greece, updating the species distribution that now spreads from the Levantine Sea to the South Aegean. Species identification was based on morphological examination and DNA barcoding of collected samples and in situ photographs. We also report on the fish cleaning behaviour of the species (based on observations of cleaning behaviour to the native Mediterranean moray eel, Muraena helena), the finding of an ovigerous-female and a wide distribution range, attesting to the establishment of the species in the area. [ABSTRACT FROM AUTHOR]

Synaptula reciprocans was reported in the Mediterranean Sea for the first time back in 1986. Since then there have been numerous reports, following the species' gradual expansion and establishment in the eastern Mediterranean basin. Here we report, by using citizen science methods, from the project titled "Is it Alien to you? Share it" of iSea, the most recent known expansion sites of S. reciprocans, including its new northern-most frontier. Furthermore, the provided photographic evidence testifies for possible interspecies relationships, for the first time. [ABSTRACT FROM AUTHOR]

Data on the distribution and ecology of cryptobenthic fish of marine caves in the Mediterranean Sea are extremely scarce but necessary for scientists and marine managers alike in order to understand these fish's ecological role and assess their conservation status. Broadscale surveys by implementing underwater visual census and photographic sampling in marine caves of the northeastern Mediterranean Sea, within different expeditions during the last 5 years, brought to light new records of eight rarely reported cryptobenthic fish species. To a smaller extent, complementary citizen science data from diving professionals of Crete were used to fill distribution gaps. A total of 36 new records (66 individuals) from 18 marine caves and caverns of the Aegean and northeastern Levantine Seas were assembled, belonging to the gobies Corcyrogobius liechtensteini, Didogobius splechtnai, Gammogobius steinitzi, and Thorogobius ephippiatus, the blenny Microlipophrys nigriceps, the tripterygiid Tripterygion melanurum, the speleophilic bythitid Grammonus ater, and the gobiesocid Lepadogaster cf. lepadogaster. The above species have been rarely reported from the Eastern Mediterranean Sea, with D. splechtnai and G. steinitzi being recorded for the first and second time from Greek waters, respectively, while L. cf. lepadogaster constitutes the second record of a clingfish species in a marine cave of the Aegean Sea. Interesting behavioral and ecological habits were also noted for some species, based on in situ observations and photographic evidence. Our study contributes to filling gaps in the knowledge of cave fish diversity and demonstrates that cryptobenthic mobile species in understudied cryptic habitats are more common than previously thought in the Mediterranean Sea. [ABSTRACT FROM AUTHOR]