One of the first of many things this journalist learned on moving to Virginia was to only eat oysters in months containing an “R.” And believe it or not, this rule has been in place for 4,000 years and has never been questioned – while the “R” has become associated with the word, “risk.”
And technically, this is true for wild oysters because, during the warm summer months, oysters harbor increased levels of pathogenic bacteria that may result in serious illness or, in some cases, death. In addition, oysters in the southeast U.S. spawn during the summer months and become watery in texture and unpalatable.
Just keep in mind this does not apply when it comes to eating commercially farmed oysters served in restaurants and sold in supermarkets. And because the U.S. has strict laws governing seafood, many restaurants serve commercial oysters from cold-water climates during the months of May, June, July, and August.
How do we know the rule is so old?
Researchers from the Florida Museum of Natural History were able to shed some light on the old rule, and interestingly, discovered it has been around for at least 4,000 years by examining shell rings. Their findings were reported in the journal PLOS ONE on November 20.
The scientists analyzed oysters and snails from a 230-foot-wide, 4,300-year-old shell ring on St. Catherines Island – similar to the shell rings that dot the coasts of Florida, Georgia, South Carolina, and Mississippi. The shell ring off Georgia’s coast revealed that the ancient inhabitants of St. Catherines Island only harvested their oysters during the non-summer months.
Shell rings are curved shell middens or mounds composed of mollusk shells completely or partially surrounding a clear space. Basically, a midden contains the debris of human activity. So, for archaeologists, the shell rings play a big role in their investigation.
Across what is now the southeastern United States, starting around 4000 BCE, early people began creating large shell middens. Starting around 3000 BCE evidence of large-scale gathering of oysters appears. So, how did the scientists know when islanders were collecting oysters? They measured parasitic snails.
According to Vice, Nicole Cannarozzi, an environmental archaeology collection manager at the Florida Museum of Natural History, said that she and her team were able to determine when the oysters were eaten because of a small parasite that attaches itself to their shells.
The impressed osteotome, the common name for a snail known as Boonea impressa are common parasites of oysters. They feed on oysters by injecting a stylus through the shell to slurp up the insides. Scientists know the snail has a predictable 12-month life cycle, and its length at death offers a reliable estimate of when the oyster host died.
This allowed researchers Nicole Cannarozzi and Michal Kowalewski to use the snail as a tiny seasonal clock for when people collected and ate oysters in the past.
“People have been debating the purpose of these shell rings for a very long time,” said Cannarozzi, the study’s lead author and Florida Museum environmental archaeology collection manager. “Were they everyday food waste heaps? Temporary communal feasting sites? Or perhaps a combination? Understanding the seasonality of the rings sheds new light on their function.”
The team analyzed the oysters and snails from the shell ring off St. Catherines Island, comparing them with live oysters and snails. They found that island inhabitants primarily harvested oysters during late fall, winter and spring, leading to the observation that visits to the island tapered off during the summer.
The study suggests that this finding is probably the earliest example of sustainable harvesting. Cannarozzi said oysters in the Southeast spawn from May to October and avoiding oyster collection in the summer helps to replenish their numbers.
“It’s important to look at how oysters have lived in their environment over time, especially because they are on the decline worldwide,” she said. “This type of data can give us good information about their ecology, how other organisms interact with them, the health of oyster populations and, on a grander scale, the health of coastal ecosystems.”
