Upwelling areas as climate change refugia for the distribution and genetic diversity of a marine macroalga

Aim Global climate change has profound and diverse effects on biological diversity. Identifying present‐day climate refugia is an increasingly recognized strategy for the management of biodiversity loss. Such refugia are potential safe havens that enhance environmental diversity by buffering the effects of large scale change, facilitating species persistence at regional scales and conserving unique genetic diversity. Although their ecological effects are well studied, the potential of upwelling centres to act as refugia in a scenario of climate warming remains largely unexplored. Here, we investigate whether upwelled waters act as refugia in a region heavily affected by recent climatic changes. Location Shores of south‐western Iberia and north‐western Africa. Methods We compared changes in distribution of the canopy‐forming macroalga Fucus guiryi with sea surface temperature patterns in five upwelling areas and adjacent warmer regions. Population diversity and structure was inferred from genotypic analyses using nine microsatellite loci. Results Fucus guiryi has disappeared from large expanses of non‐upwelling shores, currently persisting in areas characterized by strong upwelling and reduced or non‐significant rates of warming. Populations of F. guiryi were more abundant towards upwelling centres. Furthermore, the genetic characterization of populations revealed distinct genetic groups associated with each upwelling system. Main conclusions Within a large region of predominantly changing climate, we highlight the fundamental importance of upwelling areas as favourable, comparatively stable climates where F. guiryi has retreated and persists, preserving unique portions of the species’ genetic pool.