THE EFFECTS OF THE DIEL-CYCLING OF DISSOLVED OXYGEN AND pH ON THE EASTERN OYSTER, CRASSOSTREA VIRGINICA (GMELIN), CLEARANCE RATES AND HEMOLYMPH pH

Abstract

Chronic hypoxia and hypercapnia affect Crassostrea virginica. Less is known about how the co-cycling of these stressors, as occurs in shallow waters worldwide, affects this filter feeder. I used laboratory experiments and age-specific models to test how diel-cycling hypoxia and hypercapnia affect algal clearance rates by C. virginica and C. virginica hemolymph pH. Clearance rates were reduced during periods of low dissolved oxygen, but older oysters compensated by clearing faster when DO returned to normoxia. Models indicated that this compensatory feeding may allow older oysters to avoid decreases in average summertime clearance rates. Low hemolymph pH has been linked to decreased immune function in marine invertebrates and low water pH decreases the hemolymph pH of oysters. My hemolymph experiment also showed that hemolymph pH decreased with decreasing water pH and indicated that oysters may begin to compensate for declining water pH at water pH values between 7.60 and 7.36.