Anoxic Metabolic Rate in the Mussel Mytilus edulis L. Estimated by Simultaneous Direct Calorimetry and Biochemical Analysis

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Abstract
Simultaneous measurements of anoxic metabolic rate in Mytilus edulis by direct (heat production) and indirect (analysis of anaerobic end products) calorimetry qualitatively confirmed Gnaiger's suggestion of an "excess" anoxic heat production which cannot be accounted for by the stoichiometric equations of glycogen fermentation. However, individual variability was sufficiently large that the average 35% discrepancy up to 12 h of anoxia was not statistically significant, and either method provides a reasonable estimate of anoxic energy demand. During 48 h of anoxia the discrepancy increased to 63% and was statistically significant. Excess heat production during prolonged anoxia may have included enthalpy changes owing to dissolution of calcium carbonate in the shell by the acidic end products of anaerobiosis, tissue autolysis after lysosomal destabilization, and "anoxic endogenous oxidation." Direct calorimetry of mussels exposed to air and to N₂ gas indicated a 28% aerobic contribution to total aerial metabolic rate and agreed with the results of oxygen uptake measurements. Direct calorimetry thus provides a convenient method of assessing total energy demand under environmentally realistic periods of anoxia and intertidal exposure.

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