UC San Diego

Temperature is crucial to the optimal functioning of most physiological and behavioral processes in animals. For ectothermic crabs that inhabit shorelines, temperature fluctuations and anomalies pose a challenge for maintaining optimal body temperature. Here we examine the thermal ecology of two shore crabs, the ghost crab, Ocypode quadrata, and the striped shore crab, Pachygrapsus crassipes, using non-invasive infrared thermographic (IRT) technology. We tested the hypothesis that the exoskeleton helps buffer changes in environmental temperature by recording exoskeleton surface temperature in live and dead animals exposed to external heat sources. Crabs were first acclimated to room temperature in an experimental arena, then heat was sequentially added from a hot plate (conduction), IR emitter (radiation), and a heat lamp (radiation) until peak heat was reached, then all heat sources were sequentially removed. Exoskeleton surface temperature was recorded across multiple body locations (carapace, chelipeds and 5th pereopods) throughout increased and decreased heat exposure. For both species, dead crabs had significantly greater exoskeleton temperature flux than live crabs across all body locations, as well as the substrate. Thus, the exoskeleton itself does not appear to provide much thermal buffering, but the physiology and behavior of live crabs do. While O. quadrata spent most of the time sponging, P. crassipes actively avoided areas of high heat. This study demonstrates the responsiveness of the crab exoskeleton to environmental temperature changes and lays a foundation for exploring additional thermal adaptations of crabs on land using non-invasive IRT technology.