CONSEQUENCES OF SALINITY CHANGE, SALINITY HISTORY, AND SHELL MORPHOLOGY ON EARLY GROWTH OF JUVENILE OYSTERS

Estuaries provide valuable habitat for the eastern oyster (Crassostrea virginica). Although salinity at a given location fluctuates regularly with tides, upbay and downbay salinity differences span a broad estuarine salinity gradient. Higher salinity habitats downbay support faster oyster growth, whereas lower salinities upbay act as a refuge from predation and disease but slows growth. Two experiments were performed to investigate the effect of salinity, postsettlement salinity changes, and shell morphology on juvenile oyster growth. One experiment used wild oyster spat collected from three distinct Delaware Bay salinity zones that were then transplanted into various salinity conditions in the laboratory, where growth was monitored. Transplanting into low salinity led to decreased growth compared with transplanting to higher salinity, and growth of oyster spat was overall highest for spat from the lowest salinity source. Growth did not differ among shell morphologies. A second experiment used hatchery reared larvae set in one of four different salinity conditions. Those spat were maintained in settlement salinities 22, 16, 10, and 6 for 2-3 wk postsettlement, then measured before fully factorial transfer into new salinity conditions with measurement 3 wk later. Lower final salinity treatments were associated with lower growth, lower initial salinity treatments were associated with faster final treatment growth, and final growth depended on the interaction between initial and final salinity. Therefore, in addition to the effects of acute salinity changes on growth, early postsettlement hyposalinity stress can generate compensatory juvenile oyster growth. As increased freshwater events due to climate change are expected in the Delaware Bay and regionally in the Northeast, these results indicate that nonlinear early life stress responses are important to quantify to better understand oyster stock resilience and plan management.

Automated summary

Estuaries provide important habitat for eastern oysters, with varying salinity conditions affecting oyster growth. Experiment 1 found that transplantation to higher salinity led to increased growth, while oyster spat from the lowest salinity had the highest overall growth. Shell morphology did not affect growth. Experiment 2 showed that higher initial salinity and lower final salinity led to increased growth, highlighting the importance of early postsettlement salinity stress on oyster growth. These findings have significant implications for understanding oyster stock resilience in the face of climate change.