Understanding The Local Drivers Of Beta-Diversity Patterns Under Climate Change: The Case Of Seaweed Communities In Galicia, North West Of The Iberian Peninsula

Aim To understand spatial-temporal changes (beta-diversity) in coastal communities and their drivers in the context of climate change. Coastal ecosystems are extremely exposed and dynamic, where changes in seaweed assemblages have been associated with changing water temperatures. However, at local scale, the effects of changes in the upwelling events and related stressors seek further exploration. Location Galicia rias, North West of the Iberian Peninsula. Methods Using data collected in 42 sampling localities in Galicia rias and over two time periods (1998 and 2014), we analysed changes in the seaweed community's composition through time and space. We calculated the temporal beta-diversity index and spatial beta-diversity as the pairwise composition differences between sampling localities. We use generalized dissimilarity models, to identify local environmental drivers of spatial and temporal beta-diversity. Results We found a significant change in seaweed communities of Galicia rias, between 1998 and 2014 (temporal beta-diversity). They were mostly related to species loss rather than to species replacement. The dissimilarity among localities (spatial beta-diversity) was significantly higher in 2014 than in 1998. Nitrate concentration was consistently predicted as the main driver of both temporal and spatial beta-diversity patterns. Main conclusions Unlike other studies in marine ecosystems, our results suggest that observed changes in the structure of perennial seaweed assemblages in Galicia Rias might lead to a local biotic heterogenization, indirectly linked to climate change through changes in nutrients availability and the upwelling intensity. Changes in Galicia seaweed communities call scientific attention to the importance of local stressors in climate change studies.