Life on the Edge: Morphological and Behavioral Adaptations for Survival on Wave-swept Shores

Wave-swept rocky shores serve as a home to a great diversity of organisms and are some of the most biologically productive habitats on earth. This burgeoning community exists in spite of the fact that the zone between the high and low tide marks can be one of the most physically harsh environments on earth. Large forces imposed by breaking waves and wide swings in temperature require the organisms living on rocky shores to adapt to a constantly changing environment or risk extirpation by physical forces. I have explored a number of hypothesized adaptations for survival on rocky shores and discuss how the results influence the evolutionary and ecological processes shaping shoreline communities. I developed a biophysical model to predict body temperatures for high shore littorine snails in order to address the role of evolved morphological and behavioral traits for controlling body temperature during extreme temperature exposures. The results demonstrate that while the behaviors of these snails allow them to reduce body temperatures by several degrees, the hypothesized roles of shell shape and color contribute relatively little to controlling body temperature. A similar biophysical model for predicting organismal body temperature was combined with a physiological study to examine the role of temperature stress in setting the distributional limits of an important mid-intertidal limpet, Lottia gigantea. With a temperature exposure protocol based on realistic field conditions, I measured sub-lethal and lethal temperature limits for this species, and found that the vertical distribution of L. gigantea may be set directly by high temperatures within certain microhabitats on the shore. The final section describes the role of behavior in barnacles in compensating for limits in the phenotypic plasticity of their feeding appendages. By directly monitoring the feeding activity of barnacles under breaking waves, I show that fast reaction times allow barnacles to avoid damaging water flows while still exploiting much of the available time for feeding. The studies in this thesis provide a number of new insights into the role of the abiotic environment in the evolution and ecology of organisms living on wave-swept rocky shores