Niche conservatism and spread of seaweed invasive lineages with different residence time in the Mediterranean Sea

Marine algae invasions attract a lot of interest as they are altering the structure of marine ecosystems. However, niche dynamics and risk predictions of marine invasions integrating phylogeographic structure in the analyses have not yet been investigated. In this study, we perform a comprehensive analysis of two invasive lineages of Caulerpa taxifolia with different residence time in the Mediterranean Sea for a better understanding of their invasive processes. We performed lineage-based and species-based niche models to assess the risk of invasion, the spatial overlap, and the variables delimiting the distribution of the two lineages. We also compared the effect of using different extents on niche overlap and niche shift analyses. Intraspecific models with pooled occurrences accurately found two separate regions susceptible of invasion for each invasive lineage in the Mediterranean, while species-based predictions underestimated invaded regions. The invasive lineages spread across colder coastal areas than the species. Altogether, we provide evidence that different invasive lineages of algae show dissimilar environmental responses and invasive ranges that are not detectable by species-based analyses. Moreover, niche overlap and niche shift analyses seem to depend greatly on the geographical extent used. According to the most appropriate extent (worldwide), the invaded range did not show niche shift, and thus, no evidence of a post-introduction adaptation scenario was found as both lineages invaded habitats similar to their Australian native locations. Actions to prevent further spreading of the most recent invasive lineage are needed.