The Aegean Sea is highly impacted by biological invasions with 209 alien species being reported until the end of 2019, of which 149 are considered as established. Among these, the most abundant group is Pisces, followed by Mollusca, Crustacea, Annelida, and Macrophyta. There is an increasing trend of new species introductions in the Aegean Sea, reaching 60 new introductions between 2010 and 2019. The most common pathway of introduction in the Aegean Sea is “unaided” introduction from neighboring ecoregions, i.e., natural dispersal across the Aegean borders, without human agency. Most of these species are Lessepsian immigrants, introduced through the Suez Canal, and initially recorded in the Levantine Sea. The second most common pathway in the Aegean is “transport-stowaway,” i.e., introduction through ballast waters, hull fouling, or with angling/fishing equipment. All other pathways are of much lower importance for the Aegean Sea. The most invasive species in the region are the fish Siganus rivulatus, Siganus luridus, Fistularia commersonii, Lagocephalus sceleratus, and Pterois miles; the macroalgae Caulerpa cylindracea, Codium fragile, Stypopodium schimperi, Asparagopsis taxiformis, and Womersleyella setacea; the crab Callinectes sapidus; and potentially the molluscs Conomurex persicus, Pinctada imbricata radiata, Dendostrea cf. folium, and Fulvia fragilis.
