THE IMPACT OF SALINITY ON THE MINERALOGY OF THIN OYSTER SHELLS FROM THE CHESAPEAKE BAY

The Chesapeake Bay is the largest estuary in the U.S. and is home to a wide range of organisms, one of which is the Eastern Oyster. Oysters are valuable commodities in the shellfish industry, are great indicators of environmental health as filter feeders, and are environmental record keepers in their shell layers. In 2018–2019, oyster farmers near the Smithsonian Environmental Research Center (SERC) noted that oyster shells became noticeably fragile. This period of time also corresponded to an unusually low and prolonged dip in salinity in the Chesapeake Bay recorded by SERC, leading to concerns for how lower salinity levels affects the health of the shellfish. In this study, we tested how differences in mineralogy and crystal structure were influenced by salinity by comparing the thin versus healthy, robust shells from 2018–2019, as well as juvenile oyster spat incubated in low versus high salinity conditions. Mineralogy and crystallography measurements were taken on several scales: centimeter-scale micro X-ray CT scanning, micron-scale scanning electron microscopy, and atomic-scale X-ray powder diffraction. Rietveld refinements of XRD data allowed us to model calcite unit cell parameters to show nuances in crystal structure across salinity conditions and shell microstructures. Bulk shell density measurements revealed that healthy shells are less dense and have more “chalk” microstructures than the thin shells. Future work testing the structural integrity of these chalk structures is encouraged to evaluate the health of oyster shells under changing environments.