MEPS 536:135-147 (2015)  -  DOI: https://doi.org/10.3354/meps11401

ABSTRACT: The latitudinal distribution of species is primarily driven by physical factors, particularly temperature. However, several studies suggest the importance of non-climatic physical stressors, such as irradiance, which may interact synergistically with temperature as unexpected deleterious effects or, alternatively, as additive factors. We performed 1 field and 1 mesocosm experiment to evaluate the potential interactive effects of physical stressors operating at the southern distributional ranges of Fucus serratus and F. spiralis, 2 intertidal macroalgae with contrasting geographic distributions. The first experiment analysed field response to low tide stress by measuring temperature increase, desiccation rate and photoinhibition in fronds exposed to air and fronds covered by other fronds. The second experiment compared the response of these 2 fucoid species by recreating harsh vs. mild conditions of major intertidal stressors. Results suggest that the additive effects of climatic factors, namely air temperature, and non-climatic physical variables, namely irradiance and air humidity, partially explain and can help to forecast distributional shifts of intertidal macroalgae. F. spiralis was better adapted than its congener F. serratus with lower inhibition and faster recovery. This agrees with its low latitude affinity and higher position in the intertidal. The only major interactive effect observed was the antagonistic amelioration of atmospheric thermal stress by mid to high humidity conditions, particularly when irradiance was not excessive. These intertidal seaweeds retain ambient humidity and shade themselves, lowering physiological damage through self-cover with their fronds. We observed overall additive effects of stressors and higher physiological resilience of covered algae to low tide stressors than expected by their additive effects.

KEY WORDS: Biogeography · Climate change · Ecophysiology · Fucus serratus · Fucus spiralis · Seaweed · Stress