The neglected role of environmental fluctuations as modulator of stress and driver of rapid evolution.

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Climate change will not only shift environmental means but will also increase the variability around means and specifically the intensity of extreme events. This variability in abiotic factors will either exert additional stress to organisms and ecosystems or potentially offers transient refuge from stress. The role of increased variability vs. increase in mean stress (from e.g. ocean warming) is a recently emerging topic in climate research but is virtually unexplored for marine systems. We hypothesize that fluctuating temperature stress will very differently affect marine organisms as compared to constant stress of the same mean, and that the two additional dimensions of a stress regime, amplitude (stress intensity) and frequency (stress duration), differ in their capacity to modulate the stress sensitivity of organisms. We further hypothesize that environmental variability is a key driver for rapid evolutionary change. These hypotheses will be tested over three years on Baltic Sea key species, using novel computer-controlled indoor mesocosm facilities. By including the new aspect of variability into experimental assessments, we will be able to substantially improve our predictions of future ecosystem shifts in response to global change.