Body temperature during low tide alters the feeding performance of a top intertidal predator

Although the direct effects of climate change on species distribution and abundance have become increasingly apparent, considerably less is known about the potential for thermal variations to influence community structure indirectly through altered species interactions. We examined how the low tide body temperature of the rocky intertidal sea star Pisaster ochraceus affected the rate at which this keystone species fed on the mussel Mytilus californianus. Patterns of intertidal distribution and sea star body temperatures were recorded in the field at Bodega Bay, California, in 2006 and 2007. Under controlled laboratory conditions, we separately examined the roles of short-term (acute) and long-term (chronic) exposures to high aerial body temperatures in driving patterns of feeding and growth. Upper limits to thermal tolerance were also quantified in the laboratory. Integrating field data on the vertical distribution, microhabitat, and body temperature of sea stars indicated that individuals typically experienced relatively high body temperatures over a series of short periods of time (acute exposures of a few days) and that they escaped from situations where they would have experienced such temperatures for longer periods (chronic exposure). Although sea stars never approached their upper thermal limit (35 degrees C), laboratory trials demonstrated that chronic exposure to realistic peak aerial body temperatures (>= 23 degrees C) negatively affected both feeding and growth rates, whereas acute exposure had positive consequences on feeding rates but no effects on growth. Variations in aerial body temperature, and more specifically the frequency of exposure to high body temperatures, can influence interaction strength in this important predator -prey system.