On a recent spring evening at Crave Fishbar in New York City, the oysters resting on beds of ice hailed from Long Island, Virginia, Washington, Cape Cod, and British Columbia. But once they’d been slurped, all of their shells went to a single place­: New York Harbor.

As a participant in the Billion Oyster Project, Crave Fishbar is in its eighth year of collecting shells to help restore the oyster reefs in New York Harbor. The restaurant’s servers, who include many aspiring actors, tell the origin stories of the daily array of oyster options—the better the story, the greater the popularity of that brand, said Jeremy Benson, general manager of the Upper West Side location.

But the best story the team tells is that of the Billion Oyster Project, a nonprofit founded in 2014 that has organized 15,000 volunteers and 60 restaurants to restore oysters at 15 reef sites across New York’s five boroughs.

The effort seeks to bring back the harbor’s oyster population—which was destroyed by overharvesting and pollution in less than 100 years—by collecting used shells, installing them in critical locations, and “seeding” baby oysters on top to form reefs.

In addition to donating shells, Crave Fishbar employees have learned about the bivalve’s ability to clean the water and make shorelines more resilient to climate change. Every year, they join other volunteers who remove plastic forks from shell piles, clean cured shell, and load cages destined for the harbor, a body of water that The New York Times has described as “once an open sewer.”

“Now there are dolphins in the Bronx River. There are whales in New York Harbor. There are harbor seals underneath the Verrazano Bridge,” Benson told me during a recent visit, wrapping up his story with a happy ending also due in no small part to the Clean Water Act of 1972 and subsequent changes to wastewater handling.

When it comes to oyster reef restoration, the enthusiasm of the Crave Fishbar crew is not unusual, and that type of engagement is a driver of environmental activism that’s not to be underestimated.

“When the community is enthusiastic, the aquaculture community is enthusiastic, the conservation community is enthusiastic, then the regulators are sitting there saying, ‘Wow, this is great.  Let’s go!’ So, this has been enormously powerful,” said Boze Hancock, senior marine habitat restoration scientist at The Nature Conservancy (TNC).

Though some oyster reef restoration projects, like those in the Chesapeake Bay, operate at unprecedented scale globally, others are small, community efforts. They have involved Rotary Club members, public school kids, nonprofits, community shellfish commissions, universities, federal, state, and local governments, even the lawyers who won the Deepwater Horizon oil settlement. (Baby oysters are now growing on some of the 33 reefs built along Florida’s Gulf Coast as a result of that payout.)

In addition to New York Harbor, Pew Charitable Trusts points to reef restoration efforts in the Chesapeake Bay, Florida, Louisiana, New Jersey, North Carolina, South Carolina, and Texas—and throughout the world.

With 20 years of momentum behind them, the people and groups undertaking these conservation projects have garnered both funding and expertise. But one thing that’s in short supply is the oyster shell itself. That scarcity has led to concerns about what to use instead, with disagreements playing out in heated meetings, court battles, and op-eds. And the challenges are often amplified because so many different players have a stake in restoration efforts.

“If you have five different people in a room, you’re going to have six opinions,” said Taylor Goelz, a marine scientist and senior program manager focused on the ocean and the climate for the Aspen Institute, who also hosts The Ocean Decade Show podcast. She was the lead author on a paper, “Alternative Substrates Used for Oyster Reef Restoration,” when she was a research associate at Virginia Institute of Marine Science. Although approaches may differ, Goelz said most people can agree on one thing: “They all want more oysters.”

Ecosystem Engineers

“Oysters are an incredibly carbon-, space-, and resource-efficient source of protein, which are really yummy,” said Hancock of TNC. “But they also provide ecosystem services.”

Like all bivalves, oysters are multitasking ecosystem engineers. They feed by filtering algae from the water—more than 50 gallons a day. That process removes excess nitrogen, which can create harmful algae blooms, and leaves cleaner water behind.

As they build their shells from calcium carbonate, oysters sequester carbon in a way that is cost effective and energy efficient. Clustered on reefs, they also help protect shorelines from erosion and storm surges. The reef itself provides shade and traps moisture during low tide, giving heat-stressed intertidal marine life a cool microhabitat that helps them adapt to rising temperatures.

The clearer water resulting from filter feeding also allows sunlight to penetrate and promote the growth of seagrass, “one of the other really important habitats that we are missing,” said Hancock. Ecosystem engineers themselves, seagrasses also clean the surrounding water and help take carbon dioxide out of the atmosphere, while sheltering a wide array of marine life.

Oyster reefs provide habitat for hundreds of species, a benefit TNC started to quantify as early as 2012. Mussels, barnacles, and sea anemones settle on reefs and provide food for many species. Crabs and fish also hide from predators in reef crevices. “These reefs pump out fish. It’s amazing,” added Hancock, who has worked in shellfish restoration in the U.S. since 2004.

The wallets of fishermen benefit—but so do community coffers. In Greenwich, Connecticut, for example, a National Oceanic and Atmospheric Administration (NOAA) fisheries study calculated that oysters provided the town with an annual financial benefit between $2.8 and $5.8 million. Without shellfish, the town would need to invest that much in wastewater treatment, septic system upgrades, and better storm water management.

Experts agree that the general public is increasingly aware of both these economic and environmental benefits. It’s one reason there has been such a boom in oyster reef restoration, Goelz said. Crave Fishbar’s Benson agreed. “In the restaurant, I have four or five in-depth conversations with people every week about oyster restoration,” he added.

Oyster Reef Restoration Also Spawns Controversy

Wild oysters grow by continually settling on top of other oysters or older shell, rocks, and piers and then reproducing. They fuse together, creating rock-like, three-dimensional structures. But overharvesting, pollution, disease, and dredging have destroyed more than 85 percent of oyster reefs globally. And now climate change poses an added threat.

The scale is enormous and because different locations have seen different arrays of impacts. But all successful reefs require two things: healthy oysters and strong foundations on which they can grow.

Generally, the reefs in the Southeast and Gulf of Mexico tend to have enough native oysters but not enough substrate for the babies to latch on to, Hancock explained. In other places, such as the West Coast and the northern portion of the East Coast, there are too few oysters left to settle a reef.