A Rotating Respirometer to Monitor Voluntary Activity and Associated Exchange of Respiratory Gases in the Land Hermit Crab (Coenobita Compressus)

A rotating respirometer was designed which enabled respiratory gas exchange in the land hermit crab Coenobita compressus to be correlated with voluntary submaximal sustained pedestrian activity. In the laboratory, crabs remained spontaneously active for up to 150 min, maintaining velocities of 0.6cm s−1. Comparable activity patterns were observed in the field. Quiescent O2 uptake (MOO2) increased logarithmically as a function of load rating of the adopted molluscan shell. Steady-state MOO2 and MCOCO2 were measured after 30 min of spontaneous activity and both increased linearly with velocity. There was good correspondence between Y-intercept values and those measured in inactive crabs. At the mean locomotory speed, MOO2 and MCOCO2 were increased 3.4-fold and 2.6-fold respectively above settled rates. Minimum and gross energetic cost of transport were estimated and compared with values in the literature. MOO2 and MCOCO2 returned to settled levels within the first hour of recovery. The activity profile and concomitant changes in gas exchange are discussed in the context of acquisition of the shell-dwelling habit.