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ITHACA, N.Y. — Farmed oysters are mixing with and potentially adding to populations of wild oysters – a once-abundant species in New York’s estuaries and rivers that has declined drastically over the last century.

A new study, which published April 23 in the journal Molecular Ecology, offers genetic evidence and the first documented proof that farmed eastern oysters are adding to and breeding with wild eastern oyster populations in the western and central Long Island Sound.

“Oyster farms might provide ecosystem services to the natural system, with one of those being a boost to oyster populations that are dwindling,” said Matthew Hare, associate professor in the Cornell CALS Ashley School and 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,” Hare said.

A rise in oyster populations could be good news for these waterways because they eat organic matter such as algae, essentially filtering the water. This allows sunlight to travel further down the water column, benefiting plant life and other animals. Oysters also sequester polluting nutrients and deposit them on the estuary floor.

In the 1600s, New York’s estuaries and rivers were home to some 220,000 acres of oyster reefs until overfishing, pollution and siltation led to their decline by the 1900s. Scientists estimate wild oyster numbers have declined globally by 85% over the last century, with similar rates of declines of eastern oysters in New York occurring mostly in the 19th Century. In 2023, 84% of New York harvested eastern oysters were reared in oyster farms.