The Impact of Multiple Anthropogenic Stressors on the Colour Change and Antipredator Behaviours of the Common Shore Crab, Carcinus maenas

Abstract

The marine environment is increasingly subject to environmental change driven by anthropogenic stressors, which may alter species’ key behaviours and necessitate rapid behavioural and phenotypic plasticity. Such stressors rarely occur in isolation, yet our understanding of their potential interactions and the resultant effects not only on individual species, but upon trophic interactions, is still relatively limited. Here I study the combined impacts of a major global stressor, temperature increase, and a local stressor, anthropogenic noise, upon traits key to the survival of the common shore crab, Carcinus maenas, within a laboratory setting. First, I use image analysis and a relevant predatory vision model to determine the impact of concurrent temperature increase and noise pollution on the camouflage and growth behaviours of juvenile C. maenas. I demonstrate that anthropogenic noise detrimentally impacts crab camouflage, negating the positive influence of increased temperature, while growth increases under higher temperatures, negating negative effects of noise pollution. With this data, I reveal, for the first time, the potential for mitigative antagonism, with the biological response to one stressor reduced by the presence of the other. Following this, I further extend my investigations by studying the impact of the above stressor interaction on the movement and antipredator retreat behaviours of C. maenas. Using a series of behavioural trials, consisting of simulated predatory events and a directional movement trial, I demonstrate that anthropogenic noise pollution reduces likelihood, and increases latency, of antipredator response, whilst also prompting directional avoidance behaviour. I reveal that increased temperatures may have a complex impact upon C. maenas movement and antipredator behaviour, with the potential to impair continuity of movement, reducing distances covered and increasing pausing behaviour. This thesis provides novel insight into the cross-modal impacts of a global and local stressor interaction upon an intertidal crustacean which is native to the UK and globally invasive. It is my hope that the themes discussed in this thesis will contribute to the growing body of studies focussing on the impact of stressor interaction upon marine ecosystems, and provide valuable insight into potential management and conservation efforts.