Changes in temporal variance of rocky shore organisms in response to the manipulation of mean intensity and temporal variability of aerial exposure

We tested the hypothesis that mean intensity and temporal variability of aerial exposure exert interactive effects on temporal variance in abundances of algae and invertebrates on rocky shores of the NW Mediterranean Sea. Transplantations of assemblages to different heights on the shore were used to manipulate the aerial exposure indirectly. Different periods of residency of assemblages at each height were distributed over 2 yr to generate different levels of temporal variability of aerial exposure. Total durations of periods of emersion and submersion of organisms were kept comparable across all treatments to avoid confusion between intensity and temporal variability of aerial exposure. Interactive effects between these 2 factors were observed for some response variables (filamentous and encrusting coralline algae, Chthamalus stellatus, Patella spp. and number of taxa), with mean intensity of aerial exposure either magnifying or dampening effects of temporal variability. Specific responses were related to the life histories of the focal organisms, in particular the ability to resist and to recover from aerial exposure. The experimental design we used can help in separating effects of shifts in mean values and temporal variances of climate variables in studies of climate change.