Intertidal algae in sub-polar and temperate regions experience frequent and severe freezing during tidal emersion in the winter. The ability to survive repeated freezing is an important adaptation, and may greatly influence vertical zonation. In contrast to higher plants, relatively little is known about the ecological or physiological effects of freezing on marine macroalgae. This research will focus on the role of freezing as a sub-lethal stress, which reduces growth and perhaps competitive ability, by examining the effect of freezing on photosynthesis. The research will address the following questions: (1) what mechanisms are responsible for freezing resistance, (2) does the same mechanism confer resistance to both freezing and desiccation, (3) are interspecific differences in freezing resistance correlated with tidal height due to genetic adaptation or phenotypic acclimation, and (4) does the relative importance of freezing acclimation vary between upper-shore, stress tolerant, and lower-shore, competitive algae? This investigation will contribute to our knowledge of freezing as an ecological factor, and also address questions of general importance to all scientists studying the intertidal zone.
