Invasion of Sargassum muticum in intertidal rockpools: Patterns along the Atlantic Iberian Peninsula

•We examined the spatial variations in the invasion success of Sargassum muticum.•Relationship between native species richness and invasion success at multiple scales.•Most of the variation in invasion success was found at the smallest spatial scales.•Relationship invasion success vs. species richness varied accordingly to scale and metric.•Small-scale processes contributed the most to the heterogeneity of S. muticum success.

Spatial patterns of non-indigenous species show scale-dependent properties. Sargassum muticum is an invasive macroalga widely distributed along the Atlantic Iberian Peninsula. Despite being quite abundant from Norway to South Portugal, there is little information about its patterns of distribution, particularly at a large spatial scale (i.e. thousands of kilometres). Here, we examined the spatial variation in the invasion success of S. muticum from rockpools at multiple spatial scales using a hierarchical design. In addition, we analysed how the richness of native assemblages was related to its invasion success and how this relationship changed over different scales. Most of the variation in the invasion success was found at the smallest scales of pool and plot. Furthermore, the invasibility of native macroalgal assemblages was related to the native species richness, but causes that determined invasion success could not be separated from the effects provoked by the invader. Results suggest that small-scale (centimetres to metres) processes contribute considerably to the heterogeneity of S. muticum invasion success.