PO 2, and pCO 2 changes in the mantle cavity of Scrobicularia plana (Bivalvia) under normal and stress conditions

Abstract

Changes of heart rate, pO 2 and pCO 2 in the mantle cavity water of Scrobicularia plana have been followed during activity cycles and quiescence whilst continually immersed in seawater and under certain experimental stress conditions. During quiescence of 3 h duration, the oxygen content of the mantle cavity fell to about 50% of the active condition and carbon dioxide increased by about 200%. When subjected either to osmotic stress or aerial exposure, oxygen in the mantle cavity fell steadily until about 3 h had elapsed, when a sudden brief increase occurred. This is probably due to the slight opening of the valve margins allowing diffusion. The level of CO 2 in the mantle cavity becomes stabilised about 4 h after valve closure. Although this may in part be due to outward diffusion, it appears likely that other mechanisms are also involved.