Tolerance and potential for adaptation of a Baltic Sea rockweed under predicted climate change conditions

Climate change is threating species' persistence worldwide. To predict species responses to climate change weneed information not just on their environmental tolerance but also on its adaptive potential. We tested how thefoundation species of rocky littoral habitats, Fucus vesiculosus, responds to combined hyposalinity and warmingprojected to the Baltic Sea by 2070–2099. We quantified responses of replicated populations originating from theentrance, central, and marginal Baltic regions. Using replicated individuals, we tested for the presence of withinpopulationtolerance variation. Future conditions hampered growth and survival of the central and marginalpopulations whereas the entrance populations fared well. Further, both the among- and within-populationvariation in responses to climate change indicated existence of genetic variation in tolerance. Such standinggenetic variation provides the raw material necessary for adaptation to a changing environment, which mayeventually ensure the persistence of the species in the inner Baltic Sea.</p