Distribution of introduced Japanese macroalgae Undaria pinnatifida, Sargassum muticum (Phaeophyta) and Antithamnion pectinatum (Rhodophyta) in the Lagoon of Venice

The present distribution of invasive seaweeds Undaria pinnatifida (Phaeophy ta, Laminariales) and Sargassum muticum (Phaeophyta, Fucales) in the Lagoon of Venice is updated in this work. The distribution of Antithamnion pectin atum (Rhodophyta, Ceramiales) is presented for the first time, All these sp ecies have quickly colonized the hard substrata competing with indigenous s pecies. Competition acts differently in the two species, U. pinnatifida com peting for the substratum and S. muticum for light. On tidal flats composed of silt and sand, the growth of two brown seaweeds is restricted owing to the lack of a solid substrata. While Undaria pinnatifida and Sargassum muti cum have colonized only some areas of the lagoon in a short vertical range (from 0 to -3 m), Antithamnion pectinatum is present on the three portmouth s, along the inner shores of the city of Venice, and in the lagoon islands with extensive vertical distribution (from +0.2 to -8 m).