Response of the invader Sargassum muticum to variability in nutrient supply

Fluctuations in resource availability are a key factor controlling the susceptibility of an environment to invasion by non-indigenous species. Increases in the availability of resources will facilitate the invasion of habitats and assemblages. In this study, we tested experimentally the combined effects of intensity and temporal variability of nutrient supply on the invasion of a low intertidal macroalgal assemblage along the rocky shore of Galicia (northwest Spain) by the brown seaweed Sargassum muticum (Yendo). We estimated invasibility by measuring the number of plants, length of plants and biomass of S. muticum. Specifically, we tested the hypothesis that intensity and temporal variation of nutrient addition would affect interactively the invasion of macroalgal assemblages with high temporal variability emphasizing the effects of a high intensity of nutrient addition. Results indicated interactive effects between intensity and temporal variability of nutrient addition on the number and length of plants of S. muticum. Moreover, temporal variability of nutrient addition had an effect on biomass of S. muticum. In addition, intensity of nutrient enrichment and temporal variability to some extent affected native assemblages, with intensity of nutrients being mainly an important driver of the percentage cover of the most abundant functional groups.