To predict the effects of climate change, we first need information on both the current tolerance ranges of species and their future adaptive potential. Adaptive responses may originate either in genetic variation or in phenotypic plasticity, but the relative importance of these factors is poorly understood. Here, we tested the tolerance of Fucus radicans to the combination of hyposalinity and warming projected by climate models for 2070-2099. We measured the growth and survival responses of thalli in both current and future conditions, focusing on variations in tolerance among and within different clonal lineages. Survival was 32% lower in future than in current conditions, but the weight and length of the thalli which survived was respectively 267% and 178% higher when exposed to future conditions. The relatively high tolerance to the future conditions suggests that F. radicans is likely to persist in its current distributional range, which is limited to the Gulf of Bothia and Estonian coast in the Baltic Sea. Furthermore, this species may be able to expand its distribution southward and replace its congener F. vesiculosus, which, in previous studies, has not tolerated the future conditions as well. In addition, we discovered variation in tolerance to future conditions within one of the clonal lineages, which have been hitherto presumed to lack adaptive variation. The discovery of intra-clonal phenotypic plasticity means that this alga has the potential for adaptive responses to climate change, which may be the key to the future persistence of F. radicans in the Baltic Sea.
Keywords: Baltic Sea; adaptation; climate change; clonality; marine seaweed; plasticity; salinity; temperature; tolerance.
© 2018 Phycological Society of America.