Reactive oxygen intermediate production by oyster hemocytes exposed to hypoxia

Oysters are frequently exposed to severely hypoxic conditions, especially d uring summer months. During the summer, there are also large numbers of dis ease-related oyster mortalities. This research was conducted to determine w hether exposure to environmental hypoxia reduces the ability of oyster hemo cytes to produce reactive oxygen intermediates (ROIs), an important part of their defense system. Oysters of the species Crassostrea virginica were he ld in normoxic (P-O2=20.0-20.7 kPa, pH 7.8-8.0) and hypoxic conditions (P-O 2=4.0-6.7 kPa, pH 7.1-7.4). In vivo hemolymph variables (P-O2, P-CO2 and pH ) were measured after both 1 hour and 2 days in each treatment to determine the appropriate environment for subsequent hemocyte experiments. Productio n of reactive oxygen intermediates by hemocytes was measured using luminol- enhanced chemiluminescence (CL). During CL tests, hemocytes were held under the following conditions: air (P-O2=20.7, P-CO2<0.07, pH 7.6), in vivo hem olymph conditions of normoxic oysters (P-O2=5.2, P-CO2=0.27, pH 7.6), and i n vivo hemolymph conditions of hypoxic oysters (P-O2=1.47, P-CO2=0.53, pH 7 .1). Production of ROIs under hypoxic conditions was 33 % of that under nor moxia. This decrease was the result of specific and independent effects of lower oxygen levels and decreased pH. It was not due to any direct effect o f CO2.