Interaction between anthropogenic stressors affects antipredator defence in an intertidal crustacean

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 a possible mitigative antagonism, with the biological response to
temperature reduced by the presence of anthropogenic noise. Our study
demonstrates how interactions between anthropogenic stressors may impact
marine life.