Hemocyte Responses of the Oyster Crassostrea hongkongensis Exposed to Diel-Cycling Hypoxia and Salinity Change

Marine hypoxia caused by nutrient enrichment in coastal waters has become a global problem for decades, especially diel-cycling that occurs frequently the summer season. On contrary, sudden rainstorms, and freshwater discharge make salinity estuarine ecosystems variable, which often with hypoxia. We found mass mortality of Hong Kong oyster Crassostrea hongkongensis field where fluctuation co-occur season during past several years. To investigate effects changes on hemocyte immune function C. , oysters were exposed to combined effect two dissolved oxygen (DO) concentrations (24 h normal 6 mg/L, 12 2 mg/L) three salinities (10, 25, 35‰) 14 days. Subsequently, all treatments restored constant (6 under 25‰ 3 days study recovery from stress. Hemocyte parameters analyzed flow cytometry, including (HM), total count (THC), phagocytosis (PHA), esterase (EST) activity, reactive species (ROS), lysosomal content (LYSO), mitochondrial number (MN). The experimental results showed have obvious interactive various parameters. In detail, decreases led increased HM, low heavier impacts. addition, salinity, also LYSO, EST, THC, while decrease PHA only early stage. ROS production significantly hypoxic conditions. After 3-day recovery, PHA, MN basically normal, HM still affected change, indicating stress had latent . Our highlight change may impair health survival be key factors this field.