Why does oxygen concentration in the mantle cavity drop when

Why does oxygen concentration in the mantle cavity drop when a clam closes its valves (shells)? Does pH in the mantle cavity increase or decrease when the valves are closed? What might explain this change in pH?

Solution

Oxygen concentration drops because the livingbeing starts respiration.

The pH increases due to the secretion of CaCO₃

The mantle secretes maintains the shell in organism that have shells. The epithelial layer of the mantle secretes a matrix on which calcium carbonate crystals grow. Epithelium concentrates it and the shell forms.