Warren W. Burggren 1, Brian R. McMahon 2
1Zoology Department, University of Massachusetts, Amherst
2Biology Department, University of Calgary, Calgary, Alberta, Canada
Abstract
Hemolymph oxygen transport, acid-base status, and hydromineral regulation have been measured at 28-30°C in Cardisoma carnifex, Birgus latro, and Coenobita brevimanus in their normal hydrated state, following a period of severe dehydration, and after a subsequent 24-hour period of rehydration.
Cardisoma and Birgus tolerated a maximum loss of body water of 20%, which developed in 3-4 days without water, and resulted in an 25-30% increase in hemolymph osmolality. Ion concentrations also increased considerably, with the largest percentage increases in ion concentration occurring for Mg++, Ca++, and K+.
A metabolic acidosis and a resultant fall in HCO developed in Cardisoma and Birgus, but PCO2 showed no large changes, suggesting little respiratory compensation. Oxygenation of postbranchial hemolymph was not affected during dehydration, since PaO2 and hemolymph O2 capacity increased, the latter because of a hemoconcentration. Within 24 hours of rehydration, a restoration of the original levels of hemolymph ions and osmolality occurred, and a nearly complete return to normal acid-base status developed.
Coenobita was distinctive, since dehydration to the maximum tolerated 28% loss of body water appeared to be accompanied by a closer regulation of hemolymph ion levels. Only protein increased, which probably accounted for some of the rise in hemolymph osmolality. However, hemolymph O2 capacity fell, and that, in conjunction with a significant reduction in PaO2, suggested a more severe disruption of O2 transport than in either Cardisoma or Birgus. The metabolic acidosis and the fall in HCO during dehydration were also more profound, and Coenobita showed the least recovery of these three species after 24 hours of rehydration.
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