The Chesapeake Bay—the largest estuary in the continental United States—used to be packed with oysters, more than anyone today might imagine. Native Americans had been harvesting oysters there for more than 12,000 years before the arrival of Europeans, as evidenced by piles of discarded shells left behind in trash pits. In the late 1800s, annual harvests from the bay—by then dominated by people of European descent—peaked at an estimated 600 million to 1,200 million pounds.
In 2024, wild commercial harvests were less than 5 percent of that.
Overharvesting and pollution with sediments, sewage, and fertilizer have mounted ever since the 1700s, a century after the first English settlement, Jamestown, was established on the James River that feeds into the bay. Today, global warming, sea level rise and acidification pose additional threats.
But the biggest destruction was from the method behind those record harvests: the practice of dredging, begun in the late 1800s, in which heavy metal rakes or toothed bars are dragged across the seafloor to scoop up loads of oysters at once. This obliterated most of the giant reefs formed by countless generations of oysters growing on top of each other.
Like coral reefs, these oyster reefs played crucial ecological roles, providing habitat and nurseries for many other species and filtering vast volumes of water. They offered essential services to people too, protecting coastlines and sustaining fisheries for thousands of years.
For decades, conservation organizations have been working to restore oyster populations in the bay, accruing data along the way to learn from successes and failures. Others have turned toward the distant past to understand what has been lost and assess what can be recovered.
Cliff Digging
Some years back, conservation paleontologist Rowan Lockwood of William & Mary college in Williamsburg, Virginia, went to one of the few surviving fossil reefs, near Dutton, Virginia. She had long wanted to find out what the oyster reefs of the Chesapeake Bay used to be like before people started large-scale harvesting there.
When this reef was formed 245,000 to 195,000 years ago, the sea level was higher, so that today, the fossil reef sits well out of the water in the cliff face along the Piankatank River. “The oysters are all in life positions, still articulated,” says Lockwood. “They look like they died yesterday.” To interpret the fossils, she teamed up with marine biologist Roger Mann, also from William & Mary, who has been closely monitoring the Chesapeake oyster population for decades.
Based on the Dutton-area fossil reef as well as an extensive collection of shells in the Virginia Museum of Natural History taken from fossil reefs that no longer exist, Lockwood and Mann estimated that long ago, local oysters used to live four times as long (up to twenty-one years) and grow twice as big (up to 25 centimeters in diameter) at nearly ten times the density of reefs in the area today.
This means that filter-feeding oysters would have been able to pass all of Chesapeake Bay’s water through their gills in one day, Mann and Lockwood calculated. Today, that might take close to a year.
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If these giant reefs would magically reappear today, it might solve many of the bay’s problems. Nutrient-rich agricultural runoff and sewage cause huge algal blooms, and when these algae die and sink, bacteria bloom in turn, consuming so much oxygen that few other organisms survive at lower depths. “Lots of oysters could turn much of this stuff into oyster tissue and shell instead,” says Lockwood.
Dredging On
But how much recovery is realistic?
“It would be naive to think we can restore these systems to what they were like before we put 18 million people in the watershed of the Chesapeake Bay. That’s simply not going to happen,” Mann says. “What existed even a few hundred years ago will never, ever be recreated.”
And neither Mann nor Lockwood sees much value in the current, large-scale practice of releasing live larvae or young oysters into the bay. They say it is costly and that the large majority of released larvae are probably swiftly consumed by predators. “It’s like flushing them down the toilet,” says Lockwood.
But, inspired by the astonishing size of many of the fossil shells, Lockwood argues that recovery could be significant if the practice of dredging was halted and restoration efforts were aimed at protecting large adult oysters, which filter more water, produce more offspring and help reefs grow tall.
This would require the introduction of large, solid structures that mimic the reefs that have been destroyed, she says. These would keep oysters from getting covered by the large amounts of sediment that wash into the Bay. They would also prevent dredging, which would be good for oysters—but not for fishers. “Watermen have been here for hundreds of years, and it’s a generational livelihood that we need to preserve,” she says. “So you’d have to be careful where you put these structures.”
Mann, who is working closely with the Virginia Marine Resources Commission on surveys to scientifically inform fisheries management, favors a less controversial approach: depositing empty oyster shells in select areas to entice naturally arriving oyster larvae to settle. The watermen are on board with this method, he says.
To date, this and other restoration efforts have helped to restore oyster reefs across nearly 1,800 acres in ten different tributaries to the bay. Harvesting once every three years minimizes the impact on the early life stages, and oyster production has increased about eightfold, Mann says.
Restoration Rising
Chesapeake Bay is far from the only place where people are trying to restore oyster populations. Marine ecologist Jessica Pruett of the University of Southern Mississippi and marine ecologist Rachel Smith of the University of California, Santa Barbara, coauthored a 2025 article in the Annual Review of Marine Science that found more than 2,000 restoration projects for the Eastern oyster (Crassostrea virginica) alone, and around 200 for other species, up from just a handful in the 1980s.
Restoration success depends on local circumstances, says Smith. For example, just north of the mouth of the Chesapeake Bay, along the shores of Virginia, recovery has been rapid in a project that has been running for some twenty years. The site is “a different place than the bay, relatively pristine, with few water quality issues,” Smith says. “We’ve had a lot of success just by putting out oyster shells or artificial reefs made of concrete.” A study published in 2022 found that oyster density on reefs built from loose shells reached that of natural reefs in about six years, and that oyster-eating mud crabs quickly moved in. A 2021 study, meanwhile, found that oysters were larger and their densities were greater where artificial reefs made of concrete were built taller; taller reefs also more efficiently protected the shore against waves.
In some spots on Virginia’s Eastern Shore, though, oysters aren’t settling, despite the ostensibly favorable conditions.
Oyster behavior may play a role. Early on, the larvae are very tiny and at the mercy of sea currents, explains Pruett, who has studied them in the lab. But after a few weeks, they actively seek a place to settle. “They have an impressive ability to swim,” Pruett says. “When they find a place they like, they kind of ‘dive bomb’ down. And if it turns out not to be suitable, they can eject themselves back into the current.”
Considering what attracts oyster larvae may be an important focus for future research—there is some evidence to suggest, for example, that artificial reefs in lighter colors might reduce the warming influence of sunlight on oysters already stressed by climate change, which would be helpful in a warming world. But in at least one oyster species (the Pacific oyster, Crassostrea gigas) such reefs seem to attract fewer larvae; something about these reefs must be less appealing to them, or even putting them off.
There are many reasons to want to preserve or rebuild oyster reefs, researchers say. In addition to preserving natural ecosystems and the sustainable fisheries that depend on them, reefs may help to protect coastlines from storms and floods, which will become ever more urgent as climate change and rising sea levels give rise to more dangerous storms.
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And because of all the organic material that accumulates in the reefs, oysters themselves might also help to absorb some of the carbon we emit into the atmosphere. Consumers can do their part by opting for oysters grown in cages, which are harvested without dredging and therefore without damaging reefs, Pruett says.
Oyster lovers might also ask staff in their favorite restaurant to make sure the empty shells don’t end up in dumpsites, she adds. “They can be recycled by restoration projects that return them back to the sea.” There, they can help to provide a substrate for oysters to settle on—so that perhaps, one day, our troubled world may once again become the oyster’s oyster.
This article is republished from Knowable Magazine under a Creative Commons license. Read the original article.
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