Meeting Abstract
Responses of many estuarine invertebrates to hypoxic conditions are well established, however many studies have investigated hypoxia as an isolated condition despite its frequent occurrence with hypercapnia, elevated CO2. We measured respiratory and acid-base parameters including Po2, pH, [l-lactate], and total CO2 in pre-and post-branchial hemolymph sampled from blue crabs before and during light walking exercise under a range of O2 and CO2 conditions. Crabs walked at 8 m min-1 on an aquatic treadmill in normoxic (100% air saturation), moderately hypoxic (50%) and severely hypoxic (20%) 30 ppt seawater at 25° C with and without the addition of hypercapnia (2% CO2). Respiration was completely aerobic in normoxic conditions, with little buildup of lactate and continued maintenance of a substantial venous O2 reserve. During exercise under moderate hypoxia, the venous reserve was tapped but not depleted, and lactate increased from 0.5 mM to 2.3 mM, indicating the some use of anaerobic respiration. Exercise under severe hypoxia was marked by substantial decreases in both pre- and post-branchial % O2 saturation, as well as a large increase in lactate from 1.4 to 11.0 mM, indicating a heavy reliance on anaerobic respiration. In all cases, the introduction of hypercapnia caused a significant depression in pH of up to 0.07 units, and a marked increase in total CO2 and Pco2, which rose on average 8.2 mM and 7 torr respectively. Although the reduction in pH caused by CO2 causes a maladaptive decrease in hemocyanin O2 affinity, molecular CO2 is known to increase the oxygen affinity of blue crab hemocyanin. This effect may be strong enough to counteract the effects of pH and maintain oxygen transport even in severely hypoxic conditions (NSF OS-1147008).
