Mechanims of extracellular acid-base regulation as temperature changes in decapod crustaceans.

In the crab Carcinus maenas, as in other decapod crustaceans, the extracellular pH varies with temperature so that the relative alkalinity remains approximately constant. However, as temperature changes, the blood acid-base behavior is not quite the same in an in vitro closed system and the living animal. In fully acclimated crabs, the higher the temperature, the lower the blood total CO2 concentration. After an abrupt temperature increase in vivo a new acid-base state is established instantaneously, comparable to that observed in vitro; but during the following hours, both PCO2 and bicarbonate concentration decrease concomitantly at constant pH. The relative gill ventilation, evaluated as the ratio of the ventilatory flow rate to the oxygen uptake rate, does not vary significantly as a function of temperature. No significant change in the base output can be detected during the hours following a temperature shift. These observations suggest that the mechanisms involved in the temperature-dependent acid-base regulation act mainly to control the blood bicarbonate level.