Heat Stress and Predation Risk in Intertidal Turban Snails

Intertidal organisms alternately experience terrestrial and marine conditions with changing tides. During daytime low tides, individuals can experience high body temperatures. Because high temperatures can affect physiological functions, we hypothesized that intertidal snails exposed to high low-tide temperatures would experience greater risk of predation than those at low low-tide temperatures. To assess the tidal height distribution and abundance of our study organisms in the field, we surveyed four turban snail species, (Agathistoma eiseni, Chlorostoma aureotincta, Chlorostoma gallina, and Chlorostoma funebralis) and a predator (Pisaster ochraceus) at three Southern California rocky intertidal sites. At each site we established at least three 25m transects parallel to the water. We surveyed snails in 0.25m²quadrats (n=10 per transect) and sea star abundance in a 2m band along each transect. In lab we used incubators to simulate four-hour low-tide exposures using three treatments (20˚, 30˚, and 40˚ C) and an unexposed control. We assessed predation risk following simulated low tide exposure using two tests: (1) latency of response of snails to sea star tube feet, and (2) predation by sea stars or whelks (Kelletia kelletii) in tanks with snails from each treatment. Snail abundance was inversely proportional to predator abundance at one field site. Snails in lab exposed to higher low-tide temperatures responded more slowly when exposed to a predator. However, predators did not prey more strongly upon snails exposed to simulated higher low-tide temperatures. Awareness of temperature and predation associations in marine ecosystems is important in understanding how high temperatures affect predation risk.