Wild eastern oyster populations in New York's estuaries and rivers have declined sharply over the past century. However, a new study has revealed that farmed oysters are mixing with wild oyster populations – and may be helping replenish a species that once thrived in New York’s waterways.
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The study, published in Molecular Ecology, has provided the first documented genetic evidence that farmed eastern oysters are contributing to (and breeding with) wild eastern oyster populations in western and central Long Island Sound.
The findings suggest that oyster aquaculture may be influencing the genetic makeup and recovery of wild oyster stocks in the region.
“Oyster farms might provide ecosystem services to the natural system, with one of those being a boost to oyster populations that are dwindling,” says Matthew Hare, the senior author of the paper.
“If a farm is near an oyster population and there’s any reproduction on the farm, it’s possible that it can provide a demographic supplement and basically build up populations nearby, because the offspring from the farm could end up in the wild population.”
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New York’s oysters
In the 1600s, New York’s estuaries and rivers supported an estimated 220,000 acres of oyster reefs. But by the early 1900s, decades of overfishing, pollution and silt buildup had driven these species into decline. In 2023, 84 per cent of New York-harvested eastern oysters were reared in oyster farms.
Regulations require farmers to raise oysters in clean water, since oysters can be tainted by polluted waterways, and become harmful if eaten. As a result, aquaculture is banned in places with compromised water, where sewage and runoff can contaminate waterways.
For this reason, most of the Hudson River, the East River and the far western Long Island Sound are closed to oyster farming.
In the study, Hare and their colleagues analysed the DNA of oysters collected from the Hudson River, the East River and Long Island Sound (which lies between New York’s Long Island and the state of Connecticut).
Using genetic markers previously identified as signs of domestication, the researchers were able to distinguish between wild and farmed oyster ancestry.
Oysters from the Hudson River showed little evidence of interbreeding with farmed oysters, consistent with the absence of oyster farms in the area. In contrast, oysters from the East River and Long Island Sound carried a mix of wild and farmed ancestry, indicating that farmed oysters are breeding with wild populations.
Researchers say more work is needed to understand the long-term effects of this genetic mixing. However, some traits selected by oyster farmers, such as disease resistance, could potentially benefit wild oyster populations.
