Physical Ecology of the Rocky Intertidal: Predicting Patterns in Invertebrate Body Temperatures

University Of South Carolina At Columbia, Columbia SC

Investigators

Abstract

Intertidal animals (organisms such as barnacles, mussels and oysters) live between the regions of high and low tide along most of the world's coastlines, and must alternately contend with both the aquatic and terrestrial environments. Unlike mammals, intertidal animals often have very little physiological control over their body temperatures. As a result, their temperatures are driven by the characteristics of the surrounding environment, and can change very rapidly. During high tide, when the animal is underwater, its body temperature very rapidly equilibrates to the temperature of the surrounding water. In contrast, when the tide is low and the creature is exposed to air, its temperature is driven by a variety of climatic factors. Because of heating from the sun, these temperatures are often much higher than that of the air, making air temperature a poor predictor of body temperature. Importantly, this means that in order to accurately predict body temperatures, a variety of climatic factors must be considered, including wind speed, air temperature, cloud cover and heating from the sun. Decades of laboratory studies have shown very strong effects of body temperature on the growth, reproduction, and survival of intertidal animals and plants, which can potentially have cascading effects on the productivity of the nearshore environment. Surprisingly, while many studies have monitored water temperatures, only very recently have we begun to explore what animal temperatures are during low tide. As a result, the PIs are severely limited in connecting studies examining organismal physiology with the ecology of intertidal populations and communities. Perhaps more importantly, the PIs presently have no way of gauging the potential impact of forecasted climate changes on intertidal communities. Using a series of small weather stations and temperature recording devices, this study will test a mathematical model that uses climatic data to predict the temperatures, and thus the levels of thermal stress, of an ecologically important intertidal animal (the mussel) during low tide. It will also explore geographic patterns in thermal stress from sites ranging from northern Washington to southern California. Because the timing of low tide varies with location and time of year, geographic patterns in body temperatures are likely to be complex. For example, while summertime low tides in parts of Washington State often occur during the hottest parts of the day, those in Central California tend to occur earlier in the morning, when conditions are cooler. Therefore animals in northern regions may actually experience hotter body temperatures than those in southern regions. This study will provide an important step in predicting the effects of climate change on intertidal communities, and will attempt to provide a means of explicitly linking studies of animal physiology with those of population ecology.