Structure and distribution of chalky deposits in the Pacific oyster using x-ray computed tomography (CT)

Oysters are unusual among bivalves in that they possess chambers, often
filled with soft, chalky calcite, that are irregularly scattered
throughout the shell. Because the function of these so-called chalky
deposits is still unclear, evaluating the growth and distribution of chalk
is important for elucidating the ecological function of this unique shell
trait. Specimens of the Pacific oyster Magallana gigas, an oyster well
known for chalk expression, were grown in Bodega Harbor, Bodega Bay, CA.
At the end of an 11 month growing period, specimens were culled and
selected animals were submitted for x-ray computed-tomography (CT)
imaging. Three-dimensional reconstructions of oyster shells were used to
assess the overall distribution of chalk, and also to better understand
the relationship between chalk and other structures within the shell.
Results indicate that chalky deposits underly sculptural features on the
shell exterior, such as external ridges and changes in growth direction,
and also that there is a relationship between chalk formation and oyster
processes of cementation. Overall, chalk is useful for a cementing
lifestyle because it enables morphological plasticity needed to conform to
irregular substrates, but also acts as a cheap building material to
facilitate rapid growth.