CARRINGTON, E.*; HELMUTH, B.; MOORE, S.; University of Rhode Island, Kingston; University of South Carolina, Columbia; California State University, Monterey Bay: Spectral properties of intertidal organisms: reflections on the role of color.

Body temperature is thought to be one of the most important determinants of physiological performance in the rocky intertidal zone, often dictating the distribution and abundance of organisms. When emersed in air at low tide, organisms are exposed to a suite of terrestrial climatic conditions that can lead to body temperatures that deviate strongly from water temperature. Recently, we have used thermal engineering techniques (which have been used extensively with terrestrial organisms) to predict body temperature of mussels and macroalgae as a function of climatic conditions. These studies indicated that the spectral properties of an organism (the fraction of incident solar radiation is absorbed or reflected) is a critical determinant of body temperature during emersion. In this study, we used a spectroradiometer with integrating sphere to quantify the spectral properties of a broad range of organisms common to rocky intertidal shores of central California. The thirteen invertebrates surveyed were surprisingly similar, with the fraction of radiation absorbed ranging from 0.6 to 0.9. Furthermore, no clear pattern of shell color and absorptivity was evident. In comparison, the seven macroalgal species surveyed were less absorptive overall, ranging from 0.3 to 0.8 for hydrated thalli. Absorptivity increased by as much as 40% when thalli were desiccated, suggesting the rate of thermal loading for macroalgae accelerates during emersion as water is lost from the thallus. Potential explanations for the general lack of low absorptivity (or high reflectivity) in intertidal organisms will be discussed.