BIOCALCITE MINERAL MICROSTRUCTURES SHIFT IN WEAK EASTERN OYSTER SHELLS FROM THE CHESAPEAKE BAY (Invited Presentation)

The Eastern oyster forms its biomineral shell out of biocalcite crystals that create lenses of lower-density chalk layers that are surrounded by denser, foliated layers, which together form the majority of the microstructures described in oyster shells. In 2018–2019, oyster farmers approached the Smithsonian Environmental Research Center (SERC) with concerns about oyster harvests with noticeably thinner and weaker shells, which we hypothesized could be due to shifts towards lower salinity levels in the Chesapeake Bay and resulting changes in the ratios of different microstructures being formed in the shells. Here we explore the crystallography, microstructures, and chemistry of Eastern oyster shells from the Chesapeake Bay and how these variables differ between healthy, robust shells versus the weak shells collected by the oyster farmers. On the micron to centimeter-scale, micro-X-ray CT scanning of the various densities within the oyster shells allowed us to observe an offset in chalk:foliated microstructure ratios between the weak versus healthy oysters, indicating that the weak oysters likely did take a different approach to biomineralizing their shells. Comparing the unit cell parameters of the different microstructure crystals, we also observe small crystallographic shifts between the different kinds of microstructures, including the organic-rich periostracum. This study demonstrates how classic mineralogical techniques (i.e., micro X-ray diffraction, scanning electron microscopy) and newer, complementary tools, such as micro-X-ray CT scanning, can be applied to gain mineralogical and chemical insights about environmental biominerals under different growth conditions.