Scientists are trying to plant a billion oysters in New York City waters

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ARI SHAPIRO, HOST:

Oysters are slowly returning to New York City waters. After more than a decade, scientists are still far from the goal of planting a billion of them in the water. WNYC's Rosemary Misdary reports from the Hudson River near lower Manhattan on their progress.

ROSEMARY MISDARY, BYLINE: When Henry Hudson first arrived in New York Harbor in 1609, he came upon an unimaginable bounty of oysters. He described oysters as large as dinner plates. Experts estimate there were more than 220,000 acres of oyster beds, about half of all the oysters in the world. Now, oysters' best days in New York City are long gone. Experts are trying to bring them back.

UNIDENTIFIED PERSON #1: There's some fish in there.

MISDARY: Between the piers along Tribeca, scientists have dropped more than 250 man-made reefs on the riverbed. The structures are 3-foot-wide hollow concrete spheres called reef balls and steel cages called gabions that are about the size of a vintage trunk and filled with shells. Twice a year, scientists working with the Hudson River Park Trust pull the structures out of the water to check on the oysters' progress. Carrie Roble is vice president of the trust's river project.

CARRIE ROBLE: We're going to use a boat hook to get the buoy that's attached to our gabions or our reef balls. Then we're going to attach it and hoist it up with this crane here to bring it on our vessel.

MISDARY: Once the man-made reef is securely aboard, the field team takes out their calipers and measures the live oysters.

ROBLE: Twenty-four.

UNIDENTIFIED PERSON #2: Thirty-seven.

ROBLE: Twenty-two.

MISDARY: Some reefs come up empty.

ROBLE: I mean, it's, like, nothing on there, so - do you have the notebook?

UNIDENTIFIED PERSON #3: Yeah.

ROBLE: So just write it down that it's bare.

MISDARY: Others are teaming with thriving adults alongside baby oysters.

ROBLE: So the coverage on this reef ball certainly is more full. It's coming down the sides of the reef ball. And that's exciting to see, so.

MISDARY: It's a pattern the scientists have seen for years. Restoring New York Harbor's oyster glory is a hit-or-miss endeavor. The scientists are collaborating with the Billion Oyster Project, which has planted 122 million of them in waters surrounding the city. Data shows about half of those oysters die. And so far, none of the oysters are reproducing on their own.

ROBLE: One here. Dead, dead, dead.

UNIDENTIFIED PERSON #4: This is alive. This is alive.

MISDARY: The oysters die off as a result of the winter cold and predators. Meredith Comi is an oyster restoration expert for the Urban Coast Institute at Monmouth University. She says part of the problem is that there are many unknowns about jump-starting oyster reproduction. Researchers say they're focusing on increasing the population so they can reproduce independently.

MEREDITH COMI: The population of oysters here is functionally extinct. There's no larval source. It's kind of like we have to do everything from scratch. We're putting out structures, but it's like a needle in a haystack if they find them.

MISDARY: The research team says it's a build-it-and-they-will-come scenario, eventually. If they succeed, the oysters would provide huge benefits. Oysters can defend shorelines from flooding. The reefs break the intensity of waves. They're also good at cleaning up. A adult can filter 50 gallons of water per day.

COMI: Oysters are a keystone species, so they're kind of like the building block of the estuarine food web.

MISDARY: The Billion Oyster Project hopes to live up to its name by 2035. This winter, the Hudson River Park Trust will release the results of its third year of monitoring. Scientists will use the data to create more effective strategies for restoration and hopefully speed up the process.

For NPR News, I'm Rosemary Misdary in New York City. Transcript provided by NPR, Copyright NPR.