Interaction between anthropogenic stressors affects antipredator defense in an intertidal crustacean.

The marine environment is increasingly subject to changes driven by anthropogenic stressors which may alter species' key behaviors and impact phenotypic plasticity. Such stressors rarely occur in isolation, yet our understanding of how simultaneous stresses affect marine organisms is limited. Here, we study the combined impacts of a major global stressor, temperature increase, and a local stressor, anthropogenic noise, upon key defensive traits of the shore crab, Carcinus maenas. We tested the color change and behavioral responses of crabs in relatively colder and warmer water, and in the presence of natural ambient or ship noise. Using image analysis and a model of predator vision, we demonstrate that crabs change color, and improve camouflage, fastest in warmer water in the absence of anthropogenic noise. When anthropogenic noise was present, it adversely impacted crab color change and camouflage, to the extent that the accelerated change due to temperature was negated. In addition, anthropogenic noise affected C. maenas' behavior, reducing the likelihood and increasing the latency of antipredator response to stimuli. This reveals an interaction between the 2 stressors, with the combination of temperature and noise eliciting different biological responses compared with the effects of each stressor in isolation. Our study demonstrates how such interactions between anthropogenic stressors may impact marine life.