EFFECTS OF SALINITY CHANGE ON LARVAL SETTLEMENT SUCCESS OF THE EASTERN OYSTER Crassostrea virginica  

The practice of transferring eyed oyster larvae from a hatchery to a different location for settlement (remote setting) has been conducted successfully for decades. Most commercial experience with remote setting has been for the production of Pacific Oysters (Crassostrea gigas) in the Pacific Northwest. Attempts to employ remote setting techniques with the Eastern Oyster (Crassostrea virginica) are more recent and are occurring primarily within the Mid-Atlantic region. Our understanding of salinity tolerances during settlement is based on experiments in waters with salinities higher than those of many of the oyster-producing regions of the Chesapeake Bay. Questions have arisen about the effects of exposing eyed larvae to low salinities and to salinities that differ significantly from those they experience during larval grow-out. This study was designed to quantify those effects.

We conducted a series of settlement experiments at the Horn Point Oyster Hatchery on the upper Chesapeake Bay. Larval cohorts produced at this facility, which typically experience salinities around 10, were placed in triplicate settlement chambers containing 12 salinities ranging from 5 to 35. Larvae remained in the chambers for 4 days and were fed cultured Chaetoceros muelleri and Tetraselmis chuii once daily. To compare the differential settlement success of larvae reared in high salinity, we exposed larval cohorts from 3 other hatcheries to the same treatments. A subset of these experiments was extended to 14 days to determine survivorship and relative growth of the newly settled spat. Initial results show that larvae from all hatcheries settled in all salinities. The final results and implications for the aquaculture industry and oyster restoration activities will be discussed.