Habitat as a factor involved in the physiological response to environmental anaerobiosis of White Sea Mytilus edulis

The ability of blue mussels Mytilus edulis L. to withstand severe environme ntal hypoxia was studied in mussels from an intertidal population and from a suspended cultured settlement. Specimens were exposed to air for 60 h at +10 degrees C. Tissues were analysed for the amount of anaerobic metabolic end products, adenylates, phosphagen, and inorganic phosphate, and for chan ges in intracellular pH (pH(i)). Proton balance and Gibb's free energy of A TP hydrolysis were calculated. Under the experimental conditions applied su ccinate appeared to be the only anaerobic end product. Under control condit ions pHi measured using the homogenate technique ranged between 6.78 and 6. 85 in both groups. Very small decreases in pHi were observed after air expo sure; Rapid breakdown of ATP and phospho-L-arginine (PLA) was accompanied b y the accumulation of inorganic phosphate, free AMP and ADP. The Gibb's fre e energy change of ATP hydrolysis decreased from about -57 to -50 kJ mol(-1 ), showing the depletion of energy reserves in the tissues. The calculated ATP turnover rate was higher in intertidal mussels. It is concluded that mu ssels from the intertidal zone demonstrate lower abilities for metabolic de pression under the conditions of air exposure than cultured (sublittoral) o nes. The latter are characterised by higher initial PLA content. These diff erences may be related to a difference in mitochondrial density depending o n the habitat.