By Sarah Beland and MaryRose Hall
Can the stress induced by the presence of a predator be measured?
Predation can directly lower the abundance of prey through consumption but can also indirectly lower abundance by inducing stress which may lead to disease and subsequent early death. Predation has also previously been shown to reduce prey survival by reducing habitat availability and altering trophic structures.
The blue crab is both economically and environmentally important. Stress in blue crabs has been implicated in leading to bacterial infections such as pepper disease. Infections like these greatly reduce the marketability of the crabs and therefore decrease profits. Blue crabs are a main predator of snails and therefore vital to a healthy, balanced marshland ecosystem. Snails have been shown to decimate marsh grasses thereby increasing erosion.
Stress in blue crabs can result from fluctuations in the physical environment such as oxygen levels, water temperature, or salinity. However, in the local St. Augustine, Florida area, blue crabs can be found in freshwater rivers and in the open ocean, as well as in the estuaries in between. This species is therefore highly adapted and tolerant of changing physical conditions. Another potential form of stress on blue crabs is predation. Recently a new predator has been identified, which may play an additional role in the stress of blue crabs. The American alligator has been found to journey from freshwater inland ponds to the estuaries and feed on blue crabs. Presumably, the blue crab will have a markedly different response to dealing with the stress of having a predatory alligator in its presence than it does to the stress of quickly changing physical parameters of their surrounding water habitat.
Previous studies have shown that prey can experience an increase in cellular respiration due to the increase in energy expenditure during a predation event. Similarly, an increased metabolism has been shown to increase the production of stress proteins.8 This study has limited the type of stress to only predator-induced stress by use of a controlled environment. Studying stress on a molecular level will determine precisely which genes are affected by predator-induced stress and shed light on the physiological pathways that are coupled to stress.