Predators are known to influence prey populations not via both direct consumption of individuals, and also through non-consumptive processes. Chemical and other cues from predators can change prey behavior and potentially reduce foraging rates, however, novel introduced predators may not be recognized by native prey. Response to predator cues may be influenced by climate driven changes in air or water temperature affecting consumer metabolism and foraging rates. When different predator species have different thermotolerances, prey NCE may no longer accurately match the amount of risk that each predator poses. To examine this, we measured how the foraging rate of an intertidal whelk (Acanthinucella spirata) on barnacles (Balanus glandula) changes in the presence of native crabs (Romaleon antennarium) or non-native crabs (Carcinus maenas) in Tomales Bay, CA. We also examined how A. spirata weight and morphology changed in the presence of the two crabs.
We found that native crabs suppressed both barnacle consumption and weight gain in A. spirata, whereas non-native crabs had no effect. Moreover, we found that A. spirata grew significantly faster in warmer waters, independent of predator presence. However, we found that both native and non-native crabs had an effect on A. spirata morphology. Thus, while it appears that A. spirata is naïve to non-native crabs, it may still be able to respond to these species and adjust its morphology accordingly. Interestingly, we found that climate driven increases in sea temperatures had a linear effect on whelk weight gain, which was additive to the measured NCE of native crabs. This result suggests that native crabs are suppressing whelk growth to its minimum at all temperatures. Overall, we expect that as A. spirata increases foraging under climate change, it will expose itself to greater predation risk, especially from the more thermotolerant non-native species.