Competitive ability of macroalgal canopies overwhelms the effects of variable regimes of disturbance

Predicting the response of natural systems to climate change is key for maintaining their functioning and the services they deliver to humans. Along with variations in the mean intensity of environmental and meteorological events, climate change is expected to generate a substantial increase in their temporal variance, the ecological impact of which has been largely overlooked. In the marine environment, these changes may result in altered natural regimes of disturbance that, interacting with the current decline of species playing key ecological roles, could influence the structure of natural communities. The aim of this study was to experimentally investigate the compounded effects of changes in the mean intensity and temporal variance of storms and loss of canopy-forming macroalgae on the abundance and diversity of benthic assemblages in temperate rockpools. Our results showed that competitive effects of Cystoseira spp. on the cover and diversity of assemblages were more important than changes in intensity or temporal variance of events of disturbance per se. As a consequence, predicted changes in the regime of disturbance due to storms do not have the potential to counteract community shifts towards the dominance by algal turfs, once Cystoseira spp. are lost.