PHYSIOLOGICAL AND METABOLIC RESPONSES OF THE SHORE CRAB CARCINUS-MAENAS (L) DURING ENVIRONMENTAL ANOXIA AND SUBSEQUENT RECOVERY

The degree of hypoxia experienced by Carcinus maenas (L.) in littoral rock pools varies throughout the year. In summer, conditions may become extremely hypoxic or even anoxic at night. Crabs which remain in the pools utilize anaerobic metabolism for energy production as indicated by an increase in tissue lactate. In the laboratory, L-lactate was found to be the major end-product of anaerobic metabolism for although fumarate and alanine accumulated during anoxia, the amounts accumulated indicate that alternative metabolic pathways are of only very limited importance in C. maenas. Survival for long periods under anoxic conditions necessitates a considerable reduction in metabolic rate. Calorimetric measurements indicated that, during anoxia, the metabolic rate of C. maenas is reduced to < 20% of the normoxic rate. Exposure to anoxia resulted in significant acid-base disturbances. Although a marked metabolic acidosis developed, there was no indication that exoskeletal carbonates were important in buffering these changes. Recovery from anoxia resulted in a pronounced increase in the rates of O2 consumption and heart rate. A transient but significant increase in tissue lactate concentration was observed during the initial stages of recovery suggesting that anaerobic glycolysis may also be important in meeting the high energy demands of the crabs at this time.