M. edulis demand immersion to enable excretion of ammonia,
aerobic respiration and feeding but as an intertidal bivalve, it can tolerate
periods of emersion and temperature variation for extended
periods by closing both shells via an adductor muscle. During
prolonged hypoxic events the mussel will open the shell (gape) to
breathe air, can depress metabolic rate and respire anaerobically;
haemolymph ammonium concentration also increases during emersion
(Sadok et al., 1995)