Most ecosystems are affected by multiple anthropogenic stressors simultaneously; however, there is a lack of information describing the cumulative effects of many common stressor pairs. Consequently, we have but a rudimentary understanding of the roles that stressor characteristics and environmental context play in determining interactions among stressors. Nutrient enrichment often affects coastal ecosystems that may have already been affected by invasive species. To identify the effects of nutrient enrichment on communities under different invasion scenarios, the presence of the invasive fucoid algae Sargassum muticum and nutrient conditions were manipulated in the field to test for their independent and cumulative effects. Their combined effects on the diversity and functioning of rock pool communities were quantified. Rock pools with S. muticum contained fewer species, and lower macroalgal and microalgal biomass, and their overall benthic assemblage structure differed from pools without S. muticum. Both the presence of S. muticum and nutrient enrichment affected different functional groups of algae differently. Their cumulative effects, however, did not differ with increasing intensity of nutrient enrichment. Furthermore, invaded communities from which S. muticum had been removed manually tended towards greater species richness following removal than pools where S. muticum remained present, indicating a potential for recovery. These findings highlight the importance of identifying the cumulative effects of multiple stressors on the responses of individual functional groups, alongside effects on overall assemblage structure, in order to fully understand the consequences for ecosystems.