The effects of colonization by Sargassum muticum on tidepool macroalgal assemblages

The impact of colonization by Sargassum muticum (Phaeophyta: Fucales) on the resident macroalgal assemblage in tidepools was investigated in northern Spain. Sargassum muticum was allowed to colonize and spread in some tidepools, and was periodically removed in others. Changes in the abundance of macrophytes were recorded at three sites over two years. The colonization by S. muticum and the subsequent changes induced on the native assemblage was extremely variable among sites. Where the invader colonized profusely, it induced changes in the macroalgal composition of tidepools. The leathery group of macrophytes was significantly affected and changes were also observed in the foliose group. It was suggested that S. muticum may take advantage of their perennial and opportunistic traits in the interaction with groups of algae with different survival strategies. However, the spatial patchiness of the colonization may mitigate the impact of the invasion at local and regional scales.