Oxygen Transport and Acid-base Balance in the Haemolymph of the Lobster, Homarus Gammarus, during Aerial Exposure and Resubmersion

Submerged lobsters at 15°C were normoxaemic (CaO2 = 0-52 mmol 1~ 1 at a PaO2 of 6-53 kPa) and normocapnic (Paco2 = 0-44kPa; [HCO3~] = 9-3mequivl~ 1 and pHa = 7-78). After 3h in air the haemolymph was markedly hypoxic and hypercapnic (Paoj= 1-6 kPa; C a o ^ 0-2 mmol I"; Paco2 = 0-7kPa and pHa = 7-64). Disturbance after 3h in air caused a greater increase in PacO2 to 1-28 kPa and a fourfold increase in lactate levels to 3-6 mmol I". The combined respiratory and metabolic acidosis reduced pHa to 7-39. After 14 h in air, undisturbed lobsters remained hypoxic and hypercapnic (PaC)2= l-2kPa; PaCO2= l-2kPa). Lactate levels had increased to 6-2 mmol I" . Despite this clear limit on respiratory gas exchange in air, oxygen transport by the haemolymph was restored. A rise in buffer base ([HCC>3~] = lS-Smequivl") compensated for the potential respiratory and metabolic acidosis and pH was unchanged at 7-63. The combined effects of the increase in lactate (AlogPso/ Alog[lactate] = -0-175) and calcium (AlogP5o/Alog[Ca] =-0-20 at pH7-63) levels contributed to an increase in oxygen affinity of haemocyanin at constant pH. Consequently, mean Cao2 increased from 0-2 to 0-38 mmol I" 1 between 3h and 14 h in air. Resubmergence after 14 h in air resulted in a transient alkalosis due to retention of bicarbonate; oxygen and CO2 were rapidly restored to submerged levels. The lobster possesses the appropriate respiratory adaptations for survival during the relatively long periods of exposure in air encountered during commercial shipment.