Foraging behavior minimizes heat exposure in a complex thermal landscape

Ectotherms use specialized behavior to balance amelioration of environmental temperature stress against the need to forage. The intertidal snail Nucella ostrina risks aerial exposure at low tide to feed on the barnacle Balanus glandula. We hypothesized that N. ostrina foraging behavior would be constrained by duration and timing of low tide exposure. We added snails to intertidal blocks on San Juan Island, Washington, USA, and forced them to choose between barnacles placed on the western or eastern face of each block, or to shelter and forgo foraging. Snail behavior and barnacle mortality were monitored daily for 8 wk during summer 2011. N. ostrina foraging peaked every 2 wk, when temperature was minimized by tidal cycling. Low tide timing determined which substrate orientation was coolest and coincided with the proportion of snails foraging on one substrate face or the other: snails foraged on the western faces on days with morning low tides and on eastern faces on days with afternoon low tides. Barnacle consumption rates mirrored this spatiotemporal foraging pattern. Our conceptual model predicted mobile organism presence and location: snails foraged during the days of the tidal cycle least likely to be hot and selected the coolest available surface when foraging. These results suggest that N. ostrina alters foraging behavior to minimize risk of exposure to high temperatures or other emersion stresses. Consequently, predation on barnacles varies over space and time. This spatiotemporal behavior may buffer warming air temperatures and should be considered in models of coastal population and community dynamics.