Improving Tolerance to Hypoxia in the Eastern Oyster, Crassostrea Virginica

Abstract

The loss of oyster reefs is attributed to a variety of causes including over fishing, disease, and periodic hypoxia. Hypoxia, as well as brief periods of anoxia, is a problem in Mobile Bay, in particular. Development of hypoxia-tolerant oysters through selective breeding could assist in oyster reef restoration efforts. Eastern oysters, Crassostrea virginica, collected from a suspected hypoxic reef and from a normoxic reef, both within Mobile Bay, were subjected to anoxic conditions (<0.05mg/L) in the laboratory and their mean LT-50s and LT-90s determined. Oysters from the hypoxic reef (LT-50=102.5 h and LT-90=122.0 h) showed significantly greater tolerance to anoxia (a=0.05) than those from the normoxic reef (LT-50 = 94.0 h and LT-90 = 109.7 h). Survivors from each tested group along with controls which were not subjected to laboratory anoxia, were spawned and the LT-50s and LT-90s of the offspring (mean height 13.6 mm) determined. Mean LT- 50s ranged from 103.0 h (offspring of survivors from the hypoxic reef) to 126.6 h (offspring of survivors from the normoxic reef). Mean LT-90s ranged from 125.0 h (offspring of survivors from the hypoxic reef) to 150.8 h (offspring of survivors from the normoxic reef). The offspring of the survivors from the normoxic reef were found to be significantly more tolerant to hypoxia than the offspring of the survivors from the hypoxic reef. Although the hypoxic reef survivors did not produce the expected increase in mean LT-50 and LT-90 between generations, results from the normoxic reef survivors (LT-50=126.6 h and LT-90=150.8 h) as well as the hypoxic reef controls (LT-50 =124.1 h and LT-90 =143.9 h) suggest future selection and breeding trials.