Effects of heat stress on predation risk for intertidal molluscs

Intertidal organisms experience different threats during high and low tides. During high tides, organisms might encounter predators.  During daytime low tides, individuals can experience high body temperatures. We asked: does temperature during low tide affect predation risk during high tide? We hypothesized that prey items exposed to higher temperatures at low tide would be consumed more than individuals exposed to lower temperatures. We tested this hypothesis using seastar predators (Leptasterias hexactis and Pisaster ochraceus) and two different groups of molluscan prey items in two regions:  turban snails in southern California and limpets in Washington State. In each region, we quantified tidal height distribution, abundance, and environmental conditions experienced by prey and predators in the rocky intertidal zone.  At each site we established multiple 30m transects parallel to the water. We surveyed prey in 0.25m²quadrats (n=15 per transect) and seastar abundance in a 2m band along each transect.  In lab we simulated four-hour low-tide exposures (at 20˚, 27˚, and 33˚ C) and compared the escape response and susceptibility to predation by sea stars among prey in these treatments with unexposed control prey items. We assessed predation risk after low tide in two ways: (1) measuring short-term escape response to a predator stimulus and (2) consumption by sea stars over 48 hours.  Our results indicate that the effect of temperature differs among prey species.  This research is important because we need to see how current temperatures are affecting animals now to understand how climate change will impact animals in the future.