ENERGY METABOLISM DURING AIR EXPOSURE AND RECOVERY IN THE HIGH INTERTIDAL BIVALVE MOLLUSC GEUKENSIA DEMISSA GRANOSISSIMA AND THE SUBTIDAL BIVALVE MOLLUSC MODIOLUS SQUAMOSUS.

Metabolic responses to air exposure and recovery were investigated in the adductor muscles of the high intertidal mussel Geukensia demissa granosissima and the subtidal mussel Modiolus squamosus. Exposure to air for 12 h had no significant effect on the levels of high energy phosphates (arginine phosphate, ATP) in the adductor muscles of G. demissa granosissima, indicating minimal metabolic stress in this species. In contrast, there was a considerable decline in arginine phosphate and ATP during air exposure in the phasic and tonic adductor muscles of M. squamosus. In addition, there was a substantial accumulation of alanine and succinate under these conditions. Furthermore, D-lactate accumulated in the phasic muscle of M. squamosus during air exposure. During recovery, there were transient accumulations of alanopine/ strombine in both G. demissa granosissima and M. squamosus. The differences in metabolic responses between these two species reflect adaptations to specific micro-habitats. It appears that metabolism in the posterior adductor muscle of G. demissa granosissima is largely aerobic during air exposure. The subtidal species M. squamosus displays a much greater reliance on anaerobic pathways of energy production under these conditions.