On Determining Changes in Intertidal Marine Species Ranges

Helmuth et al. (2011) begin their study by noting that "virtually every physiological process is affected by the temperature of an organism's body, and ... with the advent of new molecular and biochemical techniques for studying organismal responses to thermal stress ... there has been a renewed interest in the effects of temperature extremes on the ecology and physiology of organisms given the observed and forecasted impacts of global climate change."

Using a simple heat budget model that was ground-truthed with approximately five years of in situ temperature data obtained by biomimetic sensors, in their own experiment Helmuth et al. "explored the sensitivity of aerial (low tide) mussel body temperature at three tidal elevations to changes in air temperature, solar radiation, wind speed, wave height, and the timing of low tide at a site in central California USA (Bodega Bay)."

The six U.S. scientists say their results suggest that "while increases in air temperature and solar radiation can significantly alter the risk of exposure to stressful conditions, especially at upper intertidal elevations, patterns of risk can be substantially reduced by convective cooling such that even moderate increases in mean wind speed (~1 m/sec) can theoretically counteract the effects of substantial (2.5°C) increases in air temperature." They also indicate that "shifts in the timing of low tide (+1 hour), such as occur [when] moving to different locations along the coast of California, can have very large impacts on sensitivity to increases in air temperature," noting that "depending on the timing of low tide, at some sites increases in air temperature will primarily affect animals in the upper intertidal zone, while at other sites animals will be affected across all tidal elevations." In addition, they report that "body temperatures are not always elevated even when low tide air temperatures are extreme," due to "the combined effects of convective cooling and wave splash."

Helmuth et al. say their findings suggest that the timing and magnitude of organismal warming "will be highly variable at coastal sites, and can be driven to a large extent by local oceanographic and meteorological processes." Thus, they "strongly caution against the use of single environmental metrics such as air temperature" for "making projections of the impacts of climate change."