Quantification of the invasiveness risk of non-native macroalgae in the Azores to support conservation measures

Non-native species (NNS) might become invasive and threaten biodiversity, economy and public health. Therefore, it is essential that their invasiveness risk be quantified to support conservation measures.The Azores, located in the mid-northern Atlantic, is the crossroad of macroalgal native distributions and also present almost three times the global ratio of macroalgae reported as NNS.Aquatic Species Invasiveness Screening Kit, a decision-support tool consisting of 49 questions for the Basic Risk Assessment (BRA) and six for the Climate Change Assessment (CCA), was applied to the 42 marine macroalgae classified as NNS in the Azores.The results indicate that 21 species pose a medium risk of becoming invasive, and 15 present a high risk under current climate conditions (BRA scores only). The combined BRA + CCA scores show that Laurencia dendroidea poses a high risk instead of a medium risk.Thirty-three Rhodophyta species were screened, with 10 (BRA) and 11 (BRA + CCA) classified as high risk. All four Chlorophyta species ranked as high risk. Only one of the five Ochrophyta species was classified as high risk, namely Rugulopteryx okamurae, one of the most invasive species in European waters.High-risk species are present in all islands, likely spread by the continuous maritime traffic between islands. Six of the high-risk species are restricted to single islands (BRA and BRA + CCA scores), and efforts should be made to contain their further expansion. Asparagopsis armata, a species introduced in Europe in the 1920s, is the only high-risk species present in all islands.Conservation measures for prevention, monitoring and control of NNS are proposed for the different islands of the Azores, including regulation of introduction pathways, prospection of areas with high risk of invasion, risk screening, eradication and containment of NNS. The involvement of stakeholders and maritime workers is also recommended.