Effects of Hypoxia and Anoxia on Larval Settlement, Juvenile Growth, and Juvenile Survival of the Oyster Crassostrea virginica.

The effects of hypoxia (1.5 mg O2 1-1, 20% of air saturation) and anoxia (<0.07 mg O2 1-1, <1% of air saturation) on oyster (Crassostrea virginica) larval settlement, juvenile growth, and juvenile survival were studied. Settlement was reduced significantly (P < 0.05) in hypoxic treatments, as compared to normoxic treatments (7.3 mg O2 h-1, 100% of air saturation), and almost no settlement took place in anoxic treatments. After 96 h, 38% and 4% of the larvae placed in hypoxic and anoxic treatments had settled, while 79% settled in normoxic treatments. In the first 144 h after settlement, juveniles in hypoxic treatments grew one third as much as those in normoxic treatments, while juveniles in anoxic treatments did not grow at all. Median mortality times of recently settled juveniles in hypoxic and anoxic treatments were 131 h and 84 h, respectively. We conclude that hypoxic and anoxic waters have potentially detrimental effects on oyster settlement and recruitment.