Biochemical responses to anoxia and hypoxia in the ark shell Scapharca kagoshimensis

Abstract

Metabolic adaptation to 7-d sustained anoxia, and the activation of anaerobic metabolism by a series of O2concentrations during a 12-h period, were examined in the ark shell Scapharca kagoshimensis. Laboratory experiments and biochemical analyses were conducted under summer conditions. The pattern of metabolic adaptation to prolonged anoxia was clearly biphasic, similar to that in many other bivalve species. The first, transition stage lasted 12 h and was characterized by sharp decreases in adenylate energy charge, aspartate consumption, and accumulation of succinate and alanine. The second, stationary stage was characterized by glycogen depletion and propionate accumulation. In a series of dissolved oxygen (DO) conditions, the onset of anaerobic metabolism (as indicated by a decrease in fermentative substrate, aspartate; and increase in the end-products, succinate and alanine) was detected only under hypoxic conditions (< 2 mg O2L-1) and was accompanied by depressed physiological performance, as measured by clearance rate and ammonium excretion rate. However, under milder hypoxia (1-2 mg O2L-1), a significant clearance rate was still observed, suggesting that both aerobic and anaerobic metabolisms were contributing toward the ATP yield. Lower DO (< 0.61 mg O2L-1) resulted in an increased rate of anaerobic metabolism and inactivated aerobic ATP production due to impaired filter feeding. © 2012, The Plankton Society of Japan, The Japanese Association of Benthology. All rights reserved.