Lychaete herpestica (Cladophoraceae): a New Alien Species in the Black Sea

This is the first record of the alien species Lychaete herpestica (Mont.) M.J. Wynne from the Black Sea. This macroalga is of Indo-Pacific origin and was previously included in the database of Exotic Macrophytes in the Mediterranean Sea developed by a CIESM. The immigrant species was found in the water area of the Cape Martyan Nature Park located at the Southern coast of Crimea (SCC) in the pseudolittoral zone. This corresponds to its confinedness to the littoral zone within its modern range limits. The studied specimens correspond to the taxonomic diagnosis, their key morphological and morphometric characters are specified for the new region and illustrated. The species entry into the Azov-Black Sea Basin probably occurred as a result of accidental introduction with a spat of mollusks directly from the primary range in 2023–2024. Within the boundaries of the new region, L . herpestica can widely disperse and successfully naturalize, while its development will likely have a pronounced seasonality peaking in summer. However, given its narrow biotopic confinedness and increased vulnerability to hydrodynamic factors, mass development of the species with subsequent structural transformation of native communities is unlikely. At the same time, the import of hydrobionts from donor regions and self-dispersal of invasive species from the Mediterranean Sea leave no doubt that the detection of new alien macrophytes in the Black Sea and the Sea of Azov will become more frequent. Against the background of global climate change, naturalization of some of them may seriously affect the structure of biota and the state of the natural environment of this semi-enclosed basin.