The first record of Antithamnion hubbsii E.Y. Dawson, Grateloupia turuturu Yamada and Sargassum muticum (Yendo) Fensholt in the Ancona Harbour (Middle Adriatic) is reported. These non-indigenous macroalgae have colonized the hard substrata of the harbour, probably introduced by international shipping, in the ballast water or by hull-fouling. At the moment there is not evidence of their occurrence on surrounding natural rocky substrata.
