(full paper is archived in the Miller Library)
Title: Predation, heat stress and morphological variation in the intertidal barnacle Tetraclita squamosa rubescens
Student Author(s): Weston, Galen
Faculty Advisor(s): Watanabe, Jim
Location: Final Papers Biology 175H
Date: June 2001
Abstract: The barnacle Tetraclita squamosa rubescens exhibits a high degree of variation in shell morphology. Research on other barnacle species suggests that a variety of factors, parlicularly whelk predation and temperature stress may influence the nature of this morphological variation. By sampling T. squamosa rubescens in several sites in Monterey and Pacific Grove, California, we established that barnacle morphology varies significantly with respect to location and the vertical orientation of the substrate. One of the major aspects that differed between locations is whelk predation and the verticle orientation of the barnacles' substrate. Barnacles are taller on vertical substrate, and barnacles in areas of high whelk predation have more enclosed, recessed opercular plates. By exposing whelks to barnacles with artificially exposed opercular plates in caged experimental treatments, we found that the whelks perferentially prey on barnacles with exposed opercular plates. Our predation field experiment corroborates the field sampling data insofar as the exposure of the opercular plates decreases with increased whelk abundance, and decreased exposure of the opercular plates significantly decreases the risk of whelk predation. Moreover, by measuring the heat flux through barnacles with different shapes, we ascertained a significant difference in the temperature budgets of taller, narrower barnacles versus barnacles with a shorter, broader shape. It appears that barnacles with tall, narrow shells shead heat to the air more rapidly. These observations and experiments support the hypothesis that the shell morphology of the Tetraclita barnacle has significant effects on its susceptibility to predation and temperature change.