Average global temperatures are expected to warm by 1.4-5.8C over the next century. Although the direct effects of temperature on individual performance are well-documents for many species, less well understood is how these direct effects of temperature will influence interactions among species within a community. The barnacle Balanus glandula is one of the major space occupying organisms in rocky intertidal habitats in the San Juan Islands region of Washington, and is preyed upon by the intertidal snail Nucella ostrina. Temperature is predicted to alter both the growth rate of B. glandula and the foraging activity of N. ostrina. To examine the cumulative effect of these changes, I separately manipulated N. ostrina body temperature and the size distribution of its prey (B. glandula) and followed changes in the growth rate and foraging behavior of the snail. Experiments were conducted in an outdoor tidal mesocosm system that allowed for two high tides and two low tides each day. Snails were assigned to one of three temperature treatments and one of two prey size treatments.

Results/Conclusions

Snails ate more barnacles when presented with smaller prey, but energy consumption (calories) declined. Warm temperatures reduced both snail growth and survival, particularly for the smallest snails in the experiment. When larger snails were fed on the larger prey treatment, their growth and survival under the warmest temperature treatment was not reduced relative to controls. These results present a complex picture: changes in the prey size distribution, even under unlimited prey abundance, altered the predator's performance under thermal stress. Thus it is not possible to predict the consequences of future climate change for this predatory snail without simultaneously considering its prey's response to temperature changes.