The invasive brown seaweed Rugulopteryx okamurae (Dictyotales, Ochrophyta) continues to expand: first record in Italy

The brown seaweed Rugulopteryx okamurae (Dictyotales, Ochrophyta), native to the Pacific Ocean and widely distributed in Asia, has been recently recognized as an emblematic case of biological invasion by marine macroalgae in European waters. Since 2015 and from the Strait of Gibraltar, R. okamurae has rapidly spread towards Atlantic and Mediterranean coastal areas exhibiting an invasive behaviour with significant ecological and economic impacts. Here, we report by morphology and genetics the first observation of this species in Italy along the north-western coast of Sicily (Gulf of Palermo), as drifted material and an established population on Posidonia oceanica , representing its new eastern distribution limit in the Mediterranean Sea, previously established in Marseilles (France). Furthermore, we have performed with the current introduced distribution of the species a favorability distribution model for the Mediterranean, which shows most of the western Mediterranean, including the Balearic archipelago, Corsica and Sardinia, central Mediterranean, including Sicily, and the northern coast of Africa together with eastern Mediterranean basin, as highly favorable for R. okamurae . Arrival of the species into this new area is suggested by means of sea currents and maritime traffic, including fishing activities, hypothesis supported by some of the ranked variables that entered the favorability model, i.e, current velocity, and proximity of fishing ports. These results are a warning that the species can cover large sea distances favored by sea currents, thus also threatening the ecosystems and marine resources of the central and eastern Mediterranean, highly favorable regions for the species. We suggest coordinated actions at the European level regarding prevention, among which those that have the complicity of the fishing sector should be considered, both because it is a highly affected sector and because it potentially has a very important role in the dispersion of the species. ### Competing Interest Statement The authors have declared no competing interest.