Acid-base status of the oyster Crassostrea virginica in response to air exposure and to infections by Perkinsus marinus

Hemolymph acid-base variables were investigated in the Eastern oyster, Crassostrea virginica, to determine its responses to air exposure and to infections by the parasite Perkinsus marinus. Infected and uninfected oysters were subjected to two treatments of temperature (21 degrees and 30 degrees C) and air exposure (5 and 24 h). Upon exposure to air, oysters underwent a respiratory acidosis that remained uncompensated in uninfected oysters but was partially compensated in highly infected oysters at both 21 degrees and 30 degrees C. The acidosis was significantly greater in oysters with high infections. Hemolymph in uninfected oysters had a greater buffering capacity (-6.80 +/- 0.76 SEM slykes) than hemolymph in highly infected oysters (-3.30 +/- 0.50 SEM slykes). Calcium ion concentrations in hemolymph increase when the hemolymph becomes acidic, suggesting that shell decalcification plays a role in buffering the acid. During air exposure, although oysters do not visibly gape, they access air and are apparently not completely anaerobic.