Meeting Abstract

P2.175  Monday, Jan. 5  Physiological adaptations of the intertidal green crab, Carcinus maenas to emersion SIMONIK, E*; HENRY, R.P.; Ohio University, Athens; Auburn University, AL henryrp@auburn.edu

The green crab, Carcinus maenas, is intertidal during the summer months, undergoing periods of emersion for up to 6 hr twice a day. The gills, whose lamellae are supported by the buoyancy of water, collapse in air, causing potential respiratory and acid-base disturbances. Elevated temperature and reduced humidity could further contribute to metabolic stress and desiccation. Field measurements showed that temperatures under rocks and seaweed, where crabs take shelter, were significantly lower, and relative humidity was higher than on the surface. Motor activity is minimal or absent during emersion. Crabs lost about 5% of their total wet weight during 6 hr emersion, and water loss came from the hemolymph whose osmolality increased by about 50-100 mOsm. Crabs were able to volatilize ammonia and thus had approximately the same rates of NH3 excretion in air and water. As a result, changes in hemolymph NH3 concentrations were minimal. Emersion resulted in an initial but transient bradycardia. Ventilatory rate, measured by scaphognathite frequency, decreased by about 67% during emersion but never ceased. Hemolymph total CO2 increased, but pH was not significantly depressed, and aerial VO2 was similar to that in water. The combination of low temperature, high humidity shelter and aerial respiration/excretion reduces the environmental stress of emersion and allows the green crab to maintain a near-undisturbed physiological state. Supported by NSF 02-30005 and by an NSF REU site award to the Mt. Desert Island Biological Laboratory.