Substratum-mediated heart rate responses of an invertebrate to predation threat

Although the relation between behaviour and stress in humans and other vertebrates is well documented, few comparable observations exist for invertebrates. We addressed this issue by considering the impact of the physical environment on cardiac activity in invertebrates exposed to predation and nonpredation threat scenarios. We used cardiac activity as a proxy of stress in juvenile queen scallops, Aequipecten opercularis, under predation threat by the common starfish, Asterias rubens. Stress levels were monitored in juvenile queen scallops exposed, and not exposed, to predation threat on a substratum known to act as a refuge (live maerl) as well as substrata known not to possess refuge potential (dead maerl, sand and no sediment). In the vicinity of known refuges, stationary scallops under predation threat had significantly lower cardiac activity than individuals in habitats lacking refuges. Scallops not under predation threat did not show significant differences in cardiac activity. These are probably habitat-mediated physiological responses to the presence of a predator and possibly to the availability of suitable attachment substrata. These findings have implications in terms of behavioural physiology in invertebrates.