Recovery of photosynthesis after exposure of intertidal algae to osmotic and temperature stresses: comparative studies of species with differing distributional limits.

This study examines possible relationships between stress tolerance by marine algae and distributions of these species. The ability to recover photosynthetic activity following dehydration or temperature treatments was the assay used to evaluate stress tolerance, and Porphyra perforata, Rhodoglossum affine, Gelidium coulteri, and Smithora naiadum differed in thresholds of tolerance, even though plants were collected from low tidal sites.Limits of dehydration tolerance were well correlated with limits of tidal distribution for these species. Additionally, other high tidal species tolerated severe dehydration while subtidal and low tidal species were sensitive to dehydration. High tidal individuals of P. perforata were also more tolerant of dehydration than were low tidal thalli of P. perforata.Limits of high or low temperature tolerance were not well correlated with tidal elevation for any groups of algae studied. However, cold-tolerant species had more northerly extensions, and warm-tolerant species had more southerly distributions. Thus, differential tolerance to temperature extremes may be an important influence for latitudinal ranges of species.By comparing the experimentally determined thresholds of stress with distributions of species, we test the role of stress in influencing photosynthesis and ultimately distributions of marine algae.