Breaking and entering: Examining the role of stress and aerial exposure in predator–prey relationships between the common shore crab (Carcinus maenas) and cultivated blue mussels (Mytilus edulis)

During benthic cultivation Mytilus edulis (blue mussels) are subject to predation pressure from a number of predators including Carcinus maenas (shore crabs). This predator can be responsible for substantial losses of mussels from the fishery and a full understanding of the predator–prey relationship between M. edulis and C. maenas is required to ensure attempts that reduce predatory pressure and subsequent commercial loss are successful. Whilst much work has examined the prey–predator size relationships between C. maenas and M. edulis, far less research has investigated how stress, such as periods of extended aerial exposure, may affect these relationships. We tested whether profit in terms of calories gained by crabs consuming mussels stressed by aerial exposure for 48h differed from that of mussels at ambient conditions and whether being stressed affected the mussel's likelihood of predation. We also tested whether the size relationship between predators and their prey differed when mussels were stressed. We found that the profitability of prey (calories gained per second of handling time) did not vary between stressed and unstressed mussels. Handling times for stressed and unstressed mussels were similar, even when crabs were presented with mussels of the maximum size that they are able to consume. Small crabs were more likely to reject a mussel of preferred size if it was unstressed, suggesting that crabs may be able to assess that these mussels would require extra effort to break into and consume. Our findings suggest that the predator–prey relationship between mussels and crabs is not altered when mussels are stressed. C. maenas remains a voracious predator and regardless of the condition of mussels laid on commercial beds there is a need to control this predator in attempt to reduce losses in the benthic fishery. This work is directly relevant to those involved in the benthic cultivation of mussels. Whilst extensive research has investigated sized-based predator–prey relationships but very little is known about how stress may alter the relationship between Carcinus maenas and Mytilus edulis. Our findings have particular relevance to the on-growing of mussels in benthic cultivation and demonstrate that efforts made during handling and transportation processes to maintain mussel condition do not increase their resilience to predation. This research can be used to inform producers on the impacts of predators on their crop and highlights the continued