Thermoregulatory behavior, heat gain and thermal tolerance in the periwinkle Echinolittorina peruviana in central Chile

The amount of solar radiation absorbed by an organism is a function of the intensity of the radiation and the area of the organism exposed to the source of the radiation. Since the prosobranch gastropod Echinolittorina peruviana is longer than it is wide, its areas of the lateral sides are approximately twice as large as the areas of the frontal and dorsal faces. We quantified the orientation of the intertidal prosobranch E. peruviana with respect to the position of the sun and solar heat gain in the different orientations. In the field, 80.9% of the E. peruviana monitored on sunny summer days tended to face the sun frontally or dorsally while only 19.1% faced the sun with the larger lateral sides. On overcast summer or on winter days, this trend was not observed. We then show that the body temperature of individuals increases more rapidly and reaches higher equilibriums when the lateral sides are facing the sun than when they face the sun with either of the smaller frontal or dorsal sides. These results therefore show that the orientation behavior of E. peruviana is thermoregulatory and that it permits the organisms to maintain lower temperatures on hot summer days.