Estimating the relative importance of predator-prey interactions in the provision of marine ecosystem services

As such, this thesis investigated the ecosystem service provision of native elasmobranch predators to better understand how such species may be used to mitigate the effects of such a regime shift. To accomplish this, the research presented here focused on mesopredator suppression caused by predator-induce stress (fear).Chapters 2 and 3 investigated the effects of predator and prey identity, as well as habitat complexity on mesopredator suppression.

From a Marine Protected Area management perspective, this was important as understanding how different species respond to the same stimulus can help to identify whether a particular management measure will be effective across multiple species, and how habitat complexity can mediate these effects. It was found that two elasmobranch species (Raja clavata and Scyliorhinus stellaris) which display trophic overlap both caused feeding suppression in crabs (Carcinus maenas), in combination with habitat presence.

Furthermore, it was found that 3 species of crabs (C. maenas, Necora puber and Liocarcinus depurator) that display trophic overlap were suppressed by the presence of an elsamobranch predator (R. clavata), but to different intensities, i.e. nuances in anti-predator response between the species.Subsequently, Chapter 4 was designed to utilise techniques from invasive species research to investigate the effects of spatial availability and conspecific presence on mesopredator feeding.

The aim of this research was to enhance the understanding of the role which conspecifics play in the feeding success of decapod crustacean mesopredators. Combining the findings of Chapter 4 with those of Chapters 2 and 3 can enhance the understanding of how brachyuran mesopredators use space, react to conspecifics, and respond to predators while feeding. It was found that female shore crabs (C. maenas) displayed a functional response similar to that of an ecologically de-stablising invasive species, and that there were nuances in conspecific antagonistic behaviour at different conspecific and prey densities.Finally, Chapter 5 used cardiac recording techniques to explore the underlying physiological response of brachyuran mesopredators to predator cues.

This study tested for differences in how individuals reacted physiologically to predators and non-predators. This research, combined with that of Chapters 2-4, aimed to provide a holistic understanding of the interactions between brachyuran mesopredators and elasmobranch predators. The results of Chapter 5 showed that crabs (C. maenas) displayed less cardiac activity in response to a 'known non-predator' and higher cardiac activity in response to both a cryptic 'control' cue and a 'known predator' cue.