‘R’ You Ready to Eat Oysters All Year Long?

This story is published in partnership with The Food Section.

For Patricia Langley, a bartender and server at Sea Level, a seafood restaurant in Charlotte, the questions start in June: Isn’t it the wrong time to order those raw oysters?

“They don’t understand why,” she said. They’ve just heard the old rule that you’re only supposed to eat oysters during months with an “R” in their names: September through April. 

“I’m like, ‘They haven’t killed me yet,’” Langley tells them. She eats uncooked oysters almost every day. Sea Level and its sister restaurant, The Waterman Fish Bar, run specials on their house oyster—from the Morris Family Shellfish Farms in Pamlico Sound—year-round.

For decades, oyster farms, raw bars, and marine biologists have been reassuring customers that the “R” rule is a relic of the pre-refrigeration era, and modern aquaculture has come a long way. But with the ocean in historic flux, some eaters are getting skittish again—and considering the many factors at play, scientists are understandably reluctant to issue comforting blanket statements about either flavor or safety. 

After all, for something that is basically a salty gray blob lolling on a shell as hard as layered rock, an oyster is a complicated creature. In the face of environmental upheaval, it’s hard to boil them (or grill them, if you prefer) down to an easy-to-remember saying. 

In Hot Water

No one questions that coastal waters are warming. According to Sea Grant, a research center based in Morehead City, data on water temperatures since 1880 shows the water in estuaries—where rivers meet the ocean and oysters like to live—have been hitting record highs for the last 30 years.

What isn’t clear is how that affects oysters. 

“There are so many ways climate change could impact oyster aquaculture,” said Dr. Ami Wilbur, a professor of marine biology at the University of North Carolina Wilmington who specializes in aquaculture.

“We could think of a single factor, say, warmer water,” she continued. But it’s almost impossible to separate out the consequences of rising water temperature from the presence of pathogens that accompany it. 

“Temperatures go up and down; salinity goes up and down, and each change brings a different scenario,” Wilbur said. “The potential impacts are great. It’s just difficult to know how it’s going to play out.”

Dr. Martin Posey, also at UNC-Wilmington, is Wilbur’s counterpart in the wild-oyster world. He agreed that things like water temperature are hard to interpret from the perspective of oyster populations.

“Long-term warming is well documented,” he said. “But you have three- to four-year cycles when you might get more rainfall and cooler waters. It’s an oscillation. So, the effect on [wild] oysters, year-to-year, will vary.”

Beyond safety for human consumption, warmer water can wreak havoc on oysters. It cuts down on available nutrients and oxygen levels, causing oysters to grow more slowly and reproduce later in the season—just as the worst of hurricane season is most likely to hit.

Stormy Waters

Warmer waters also contribute to more intense storms, which pose a tremendous threat to the state’s shellfish industry. In addition to damaging boats and equipment, storms create shifts in water temperatures and volume, resulting in higher or lower salinity. “Storms can wipe out two years of income for oyster farmers,” Wilbur said.

Warming water and higher salinity are among the many proposed explanations for recent mass mortality events, a phenomenon defined by its speed and severity. Several die-offs happened in 2022 along 115 miles of the North Carolina coastline, according to a March report in the Sea Grant publication Coastwatch. Oyster losses reached 90 percent. 

“We don’t know what’s causing it,” Wilbur said, citing disease, pathogens, and genetics as other possibilities.

While most consumers are primed to think that something harvested in the wild is better than its farm-raised counterpart, even in the best conditions, wild oysters can be mealy in warmer months when they’re reproducing, Posey said. As they get closer to the end of summer, after they’ve put all their energy into creating more oysters, they get small. 

Farmed oysters are a different story—and a slightly racy one, by mollusk standards. 

Oysters in the wild are mostly diploids, meaning they have two sets of reproductive organs. Farm-raised oysters, usually kept in boxy cages in shallow water, or stacked columns of cages in deeper water, are developed so they can’t breed solo.

“By manipulating the reproductive process, you can create oysters with three sets of reproductive organs instead of two,” Wilbur said. “That means the gametes (the eggs and sperm that make baby oysters) are depressed, so (the oysters) stay plump and delicious, even in summer.”

Wilbur describes it as being like the process of creating a seedless watermelon or cucumber: With three sets of organs, the oyster doesn’t make many seeds, and it doesn’t spend its energy making baby oysters. 

“If you go to the beach in July and order a platter of oysters on ice, that’s what you’re getting,” she said. 

Safety concerns aside, since farmed and wild oysters are raised in the same water, farmed are the better choice in summertime from a taste standpoint. As Wilbur sees it, the deliciousness allows you to “eat them with gusto, even though July doesn’t have an ‘R’ in it.”

The Real Risks

There’s an issue of contamination that can make it risky to eat raw oysters any time of the year.

While contamination may come from several possible sources, the overall risk is smaller than it used to be, said Paul Manley, the owner of Sea Level and The Waterman in Charlotte.

In accordance with USDA policy, every batch of oysters, wild or farmed, has a tag so it can be tracked—where it was harvested, when, and how. Oysters have to be chilled within three hours of leaving the water, reducing the potential growth for pathogens such as vibrio vulnificus, a bacteria that lives in salt water and is the most common contaminant for oysters. Cooking oysters thoroughly destroys the bacteria. (It isn’t true, as some internet reports claim, that hot sauce or lemon juice can kill it in raw oysters.)

“A lot of things would have to go wrong for us to serve a contaminated oyster,” Manley says. “You’d have to harvest when you’re not allowed to, or you haven’t managed the time out of refrigeration, or you haven’t tested the water.”

Unlike the so-called “R” rule, those rules are real—and well worth heeding.

Kathleen Purvis is a longtime journalist, food writer, and author in Charlotte, North Carolina.