New York City was once the oyster capital of the world. With more than 350 square miles of oyster beds in New York Harbor, it's estimated that at one point New York contained half of the world's oysters.

Just about 100 years ago, the last of this abundant resource was deemed too polluted to eat and the oyster slipped out of our diet and into history books.

Thanks to the Clean Water Act and the recent efforts of the Billion Oyster Project (BOP), oysters in New York Harbor are set to make a comeback.

Is a Billion Oysters a Lot?

The BOP, a collaboration of more than a dozen organizations, aims to grow one billion oysters in New York Harbor, the estuary waters where the Hudson River and East River meet the Atlantic Ocean.

The New York Harbor School, the production hub for the BOP, is a public high school on Governor's Island in New York Harbor. It includes students from all five boroughs of New York, who receive maritime education in addition to the standard high school curriculum. The school's aquaculture facility has the potential to grow 100 million oysters each year.

That may seem like a lot, but compared to other commercial oyster hatcheries it’s quite modest. The BOP points out that one facility at the University of Maryland can produce 1.2 billion oysters annually. But even this pales in comparison to what a healthy oyster reef can do—a single acre can produce hundreds of billions of young oysters.

As of 2014, the BOP has restored just over an acre of reef and grown some 7.5 million oysters in New York Harbor. While just a fraction of historic levels, the BOP says this is meant to “jump-start the natural processes of restoration.” By including high school students in the process, it’s also jump-starting the next generation of leaders and workers in marine conservation—something which has just received a strong boost from the National Science Foundation, in the form of a $5 million grant.

Money from the grant will be used to establish teacher training programs at Pace University, curriculum for other New York City schools, and programming at museums and aquariums, among other programs.

What Happened to New York City's Oyster Reefs?

Historically, the oyster beds in and around New York City covered more than 220,000 acres. They provided food for Native Americans for thousands of years. After the arrival of Europeans, oysters were a key part of the New York City economy, with half a billion oysters harvested each year in the region up through the middle of the 1800s.

“The combination of having reputably the best oysters in the world, in what had become unarguably the greatest port in the world, made New York City for an entire century the world’s oyster capital,” writes Mark Kurlansky in The Big Oyster.

Such levels of harvest, combined with increasing pollution in the waters around the island of the estuary, created an unsustainable situation. By the end of the nineteenth century, the native oyster beds were largely fished out. Rising pollution levels also meant that cultivated oyster beds produced shellfish that were unsafe to eat. The last commercial oyster bed in the city was closed in 1923 due to contamination from sewage and industrial pollution dumped in the harbor.

Pollution Controls Pave the Way for a Comeback

Today, thanks to 40 years of pollution controls and a changing New York City economy, the waters around the city are much cleaner than they used to be. The summer of 2014 witnessed an increase in the numbers of whales and sharks off the shores of Coney Island, Bay Ridge, and the Rockaways. These large animals wouldn't be present if there were not enough food for them in the ecosystem.

The cleaner water, combined with an increasing awareness of the value of oyster beds in helping maintain healthy marine ecosystems, allows projects such as the BOP to gain traction. Similar oyster rehabilitation projects are underway locally in New Jersey as well.

As the BOP points out, “Oysters are the keystone species and original ecosystem engineer of the New York Harbor…. Oysters provided massive ecological benefits, including continuous water filtration, habitat for thousands of marine species, and wave attenuation.”

Oyster Beds Are New York’s Coral Reefs

Reefs, whether they be coral or oysters, act as buffers against erosion from strong waves and storms. When reefs are compromised, storm damage can be severe. This was the case with hurricane Sandy that hit the region in the autumn of 2012. Large parts of the Rockaways and a number of shore towns in New Jersey were severely damaged, transportation tunnels running under the harbor flooded, and lower Manhattan lost power for more than a week.

As the climate changes, and the severity of storms is likely to increase, natural barriers like oyster reefs become crucial tools for protecting coastal communities. The beds create contours on the sea floor close to shore that help change the way waves form, diffusing their energy. They also help create conditions for marsh grasses to grow, further stabilizing the shore against erosion.

For all the benefits in mitigating future extreme storms, climate change could prove challenging for oysters (and other shellfish) for the same reasons that coral reefs are threatened. Research shows that ocean acidification caused by increasing greenhouse gas emissions inhibits the ability of at least one type of oyster that lives on the east coast of North America to build their shells.

Despite the challenges, restoration efforts are underway. Someday oysters may be street food again in New York City.