AN IN SITU STUDY ON THE SURVIVAL AND GROWTH OF CRASSOSTREA VIRGINICA JUVENILES IN BON SECOUR BAY, ALABAMA.

Experimental plots were established at a relic oyster reef on the eastern side of Mobile Bay, Alabama between July 1998 and November 1999 to determine whether elevated beds might improve oyster survival and growth. Oysters (Crassostrea virginica) were spawned in a hatchery and the spat were allowed to settle on small oyster shell fragments and on whole oyster shell. Two- month-old juveniles (15-18 mm) were deployed in polyethylene oyster bags on bottom and on underwater shell pads 20 cm and 40 cm above bottom. Oysters on whole shells were deployed outside bags in order to evaluate predation. Remote sensing data loggers were deployed near bottom and 40 cm above bottom to measure temperature, salinity, and oxygen concentration. Growth (increase in height), survival, and condition of oysters in bags at the three experimental depths were compared. Temperature and salinity varied between 11.8 °C-32.8 °C and 4.4 ppt-29.7 ppt, respectively. Periodic anoxic events, which lasted from a few hours to 6 days, were documented. Oysters at the three experimental levels grew to approximately 55 mm during the first year. Total mortality was observed at all three levels during the second summer when oxygen levels dropped to 0 mg L^-1 for five consecutive days while water temperature was 28 °C. If the 17 months monitored during this study are typical, restoration of Fish River Reef will be difficult due to periodic anoxic events. [ABSTRACT FROM AUTHOR]