Interaction between anthropogenic stressors affects antipredator defence in an intertidal crustacean

Abstract

The marine environment is increasingly subject to changes driven by anthropogenic stressors which may alter species’ key behaviours 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 colour change and behavioural 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 colour, and improve camouflage, fastest in warmer water in the absence of anthropogenic noise. When anthropogenic noise was present it adversely impacted crab colour change and camouflage, to the extent that the accelerated change due to temperature was negated. Additionally, anthropogenic noise affected C. maenas’ behaviour, reducing the likelihood and increasing the latency of antipredator response to stimuli. This reveals an interaction between the two stressors, with the combination of temperature and noise eliciting different biological responses compared to the effects of each stressor in isolation. Our study demonstrates how such interactions between anthropogenic stressors may impact marine life.