OXYGEN-UPTAKE AND HEART-RATE OF THE CLAM POLYMESODA-CAROLINIANA BOSC IN AIR AND IN SEAWATER

The rates of oxygen uptake and heart beat, and tissue levels of alanine and succinate of the marsh clam Polymesoda caroliniana Bosc were measured in animals exposed either to air and or isosmotic, aerated seawater (SW). The oxygen consumption rate was variable, the mean rate was approx. 380-mu-l/h/g dry weight in SW and in air. Animals exposed to air for 24 h did not accumulate an oxygen debt. The heart rate of animals with the valves ajar was 13 in SW and 11 in air. In clams exposed to air for 24 h, the levels of alanine and succinate in the gill were, respectively, 6.5 and 3.9-mu-mol/g wet weight. The alanine content of gills from animals maintained in SW was 5.6; succinate was 4.4-mu-mol/g wet weight. The adductor muscles of clams in SW contained 8.9-mu-mol/g wet weight alanine and 2.8-mu-mol/g succinate. The adductor muscles of animals exposed to air for 24 h contained 9.7-mu-mol/g alanine and 2.4-mu-mol/g succinate. Polymesoda caroliniana is capable of the same rate of O2 uptake wether in air or submerged in SW. There is no marked bradycardia during emersion, and no evidence of the accumulation of metabolites indicative of anaerobic metabolism. While these responses are typical of those found in other bivalve species that occur in high intertidal habitats, the air-breathing capacity of P. caroliniana is exceptional.