Whole animal and gill tissue oxygen uptake in the Eastern oyster, Crassostrea virginica: Effects of hypoxia, hypercapnia, air exposure, and infection with the protozoan parasite Perkinsus marinus

The Eastern oyster, Crassostrea virginica, lives in shallow coastal waters and experiences many different environmental extremes including hypoxia, hypercapnia and air exposure and many oysters are infected with the protozoan parasite Perkinsus marinus. The effects of these conditions on oyster metabolism, as measured by oxygen uptake, were investigated. Mild hypercapnia had no effect on the ability of oysters to regulate oxygen uptake in hypoxic water, as measured by the B2 coefficient of oxygen regulation. The average B2 was −0.060×10 −3 (±0.01×10 −3 S.E.M.; n=20; low and high CO 2 treatments combined) in oysters uninfected with P. marinus and −0.056×10 −3 (±0.01×10 −3 S.E.M.; n=16; low and high CO 2 treatments combined) in infected oysters. There was no significant effect of light to moderate infections of P. marinus on oxygen regulation. Nor did the presence of P. marinus have an effect on the rate of oxygen uptake of whole animals in well-aerated water. In well-aerated conditions, oxygen uptake was significantly reduced by moderate hypercapnia in oysters when data from uninfected and infected oysters were combined. Mean oxygen uptake of infected oysters under hypercapnia ( pCO 2=6–8 Torr; pH 7) was 9.10 μmol O 2 g ww −1 h −1 ±0.62 S.E.M. ( n=9), significantly different from oxygen uptake under normocapnia ( pCO 2 ≤1 Torr; pH 8.2) (10.71 μmol O 2 g ww −1 h −1 ±0.62 S.E.M.; n=9). Similar to what occurred in infected whole animals, mean oxygen uptake of uninfected gill tissues under high CO 2, low pH conditions was 9.44 μmol O 2 g ww −1 h −1 ±0.95 S.E.M. ( n=10), significantly different from oxygen uptake under low CO 2, high pH conditions (12.30 μmol O 2 g ww −1 h −1 ±0.95 S.E.M.; n=10). This result is due primarily to the low pH induced by hypercapnia rather than a CO 2-specific effect. The presence of P. marinus had no effect on oxygen uptake in gill tissues. Intertidal oysters from South Carolina take up very little oxygen from the air when they are air exposed. Mean oxygen uptake in air at 25°C (5.66×10 −4 μmol O 2 g ww −1 h −1±2.65×10 −4 S.E.M.; n=11) is less than 0.1% of oxygen uptake in seawater, suggesting that upon air exposure, oysters close their valves and isolate themselves from air. Oxygen uptake in air is slightly elevated at 35°C (9.28×10 −4 μmol O 2 g ww −1 h −1 ±5.57×10 −4 S.E.M.; n=11). There was not a strong correlation between oxygen uptake and P. marinus infection intensity at either 25 or 35°C.