Environmental and phenotypic heterogeneity of populations at the trailing range-edge of the habitat-forming macroalga Fucus serratus

Empirical work on the dynamics of range limits of species distributions often lack replications of edge populations. We compared the local environment and performance of two groups of geographically peripheral populations of the foundation intertidal alga Fucus serratus L. at its southern range boundary in the NW Iberian Peninsula. Two populations were located on the Western Galician coast in large embayments or rias, and the other two on a Northern open coastal stretch in Lugo province. Sharp differences were detected in the local environment and performance of the two groups of populations. While recruitment was quite consistent throughout the year in rias, it was very limited and variable in Lugo. Furthermore, thalli from rias were severely damaged following their transplantation in Lugo, and poor conditions of local adult plants were detected there in subsequent years. These results suggest a higher vulnerability of Lugo populations under new climate conditions, while western rias, strongly influenced by upwelling events, feasibly act as contemporary refugia for this species. If sustained over time, these refugia may mitigate the retreat of the seaweed' rear-edge predicted by large spatial scale models.