The role of the blood in the temperature dependence of oxidative metabolism in decapod crustaceans. I. Intraspecific responses to seasonal differences in temperature

Total oxygen uptake in the blue crab Callinectes sapidus doubles with a rise in ambient temperature in the range 15–25°C, and increases precipitously (Q 10 =4.92) in the range 5–15°C. Both systemic and cellular phenomena are responsible for the pattern. At summer temperatures, where motor activities are maximal, the oxygen affinity of blue crab hemocyanin is low, and considerable volumes of oxygen are delivered to the tissues. At winter temperatures, where feeding and locomotion virtually cease, the hemocyanin‐oxygen (HcO 2 ) affinity is so high that little oxygen can be extracted by the tissue and O 2 is transported entirely in the free form. At the transitional temperature of 15°C, a seasonal acclimation of HcO 2 affinity permits appreciable oxygen delivery to the tissues in the spring, but curtails oxygen delivery in the fall. Both muscle and hepatopancreas utilize the hexose monophosphate shunt (HMS) in carbohydrate metabolism. Specific activities of the enzymes participating in the HMS are greater in hepatopancreas than muscle, and the sensitivity of O 2 uptake to the glycolytic inhibitor iodoacetate (10 −2 M) is smaller. The temperature dependence of O 2 uptake in the range 15–25°C is much smaller in hepatopancreas than in muscle. The ratio of C‐1/C‐6 labeled glucose utilization indicates that, at low temperature, the activity of the HMS in hepatopancreas is five times greater than that of glycolysis. Thus, the low thermal sensitivity of O 2 uptake in hepatopancreas appears to be due to a change in the relative contribution of the two pathways to total carbohydrate metabolism. There is no evidence of a compensatory response of intermediary metabolism in muscle, which comprises the major fraction of total biomass. The thermal dependence of O 2 uptake by the animal exceeds that of either hepatopancreas or muscle, due to the large increase in HcO 2 affinity, and hence a decrease in tissue O 2 supply, at low temperature.