HELMUTH, Brian: How do we measure the environment? Linking ecology and physiology through biophysics

Understanding the role of thermal stress in driving the ecology of intertidal animals and algae requires that we first quantify what the body temperatures of these organisms are under field conditions. While the temperature of an ectotherm’s body during high tide is likely to be very similar to that of the surrounding water, body temperature during aerial exposure at low tide is driven by multiple, interacting climatic factors, and can be substantially different from the temperature of the surrounding air. Furthermore, the exchange of heat between an animal and the environment is determined in part by its size and shape. As a result, two organisms exposed to identical climatic conditions can display very different body temperatures. As a first step in quantifying spatial and temporal patterns in body temperature of the common intertidal mussel Mytilus californianus, I deployed a series of temperature loggers designed to mimic the thermal characteristics of real mussels, at sites ranging from northern Washington State to Point Conception, California. Results indicate a highly complex pattern of thermal stress, where the interaction of climate with the timing of low tide in summer determines the timing and magnitude of high temperature extremes. Southern sites are not necessarily hotter than northern sites, and spatial variability in body temperature within a single site can exceed that observed over a range of several thousand km, simply as a result of the effects of substratum angle. These results demonstrate that thermal stress in the rocky intertidal zone does not always increase along a latitudinal cline, and suggest the possibility of “hot spots” along the west coast of the U.S., where the timing of mid-day low tides coincides with extremes in terrestrial climate. Supported by NSF IBN-9985878.