When only the strong shells survive: Archaeology’s fresh approach to turn oyster shells into tools of conservation

Key Points

As global oyster populations decline and fisheries collapse, archaeologists may be able to inform effective management with valuable, long-term perspectives of the human-oyster connections stretching back millennia.
Oyster shells found in archaeological middens are difficult to measure accurately because of their irregular shapes and tendency to break apart. Traditionally researchers only measure whole left valves and ignore the fragments.
In a new study, researchers from the Florida Museum of Natural History and the Smithsonian National Museum of Natural History show that shell fragments matter. Including them in calculations can improve archaeologists’ insight into past oyster populations.

We’ve feasted on them, built economies around them and in some places nearly erased them from our coasts. Today, 85% of the world’s oyster reefs are gone. Many fisheries are collapsing, and those in Florida are no exception: Many estuaries in the state have lost up to 90% of their oyster reefs. Scientists and conservationists are racing to rebuild sustainable oyster populations, something that Indigenous communities were able to steward for millennia. By looking at ancient oyster populations, archaeologists may be able to guide this restoration in the present.

“We know what happens in the past shapes the present and the future, whether that was five minutes ago, five years ago or 50 million years ago. There are tangible and intangible links through time, and these archaeological perspectives of oysters can act as a baseline for the present,” said Michelle LeFebvre, associate curator of South Florida archaeology and ethnography as well as Caribbean archaeology collections at the Florida Museum of Natural History.

The eastern oyster (Crassostrea virginica), found in brackish waters along North America’s eastern coast, is a modern delicacy but was once a staple food for Indigenous peoples along Florida’s Gulf Coast. The evidence of this remains in middens — heaps of shells, bone and other debris built by ancient communities — dotting Florida’s landscape. By studying these middens, archaeologists can gauge the health of oyster populations at the time the shells were tossed into the pile hundreds or thousands of years ago.

One of the most basic metrics archaeologists look to is shell size, which can act as a substitute for age (a more complicated and labor-intensive metric to collect). By tracking changes in size over time, scientists can interpret how intensively communities harvested oysters. A reduction in average shell size, for example, may indicate that oysters were being gathered faster than their populations could sustain themselves.