On a windy morning in May,  six volunteers gathered on the deck of New York Harbor School on Governors Island. They reached into a muddy wire cage, searching out oysters identified with plastic tags, then carefully measured each oyster’s shells with calipers.

“Twenty-eight to 30″ millimeters, one volunteer called out, announcing old size compared to new. A supervisor with the Billion Oyster Project noted that finding on a spreadsheet. “Twenty-five, 25,” another volunteer called out. “This little fella didn’t grow at all.”

The volunteers come from all walks of life. None of them has had prior experience working with oysters. Occasionally, they spot surprises on the shells — a tiny sea sponge, a worm or a tiny blue crab the size of a pea. Whatever strange organisms they find, Jeremy Esposito, the oyster hatchery manager, always knows them by name — and a whole lot more.

“I just say there’s a thirst in all of us to connect to nature,” said Blyss Buitrago, the public engagement manager of the Billion Oyster Project. “They are just average New Yorkers who have this thirst to get involved in our local programs, and I say we can quench that thirst.”

Oysters are generally considered a mouthwatering treat in gourmet restaurants. What’s not as widely known is that these salt water-dwelling mollusks pack a powerful punch when it comes to filtering seawater. On average, an oyster can filter up to 80 gallons of polluted seawater a day. Their ability to clean the water makes oysters a keystone species in providing a pollution-free habitat for other marine creatures.

The Hudson estuary was once a thriving habitat, boasting 220,000 acres of oyster reefs when Henry Hudson first sailed up the river. Today, oysters are virtually extinct as a result of overharvesting, dredging and pollution. Because of environmental laws such as the Clean Water Act in 1971, water quality has improved, creating the condition for a large-scale oyster restoration project.

The “Billion Oyster Project” is a citizen science project coordinated by the New York Harbor School, a New York City public high school. The project launched in 2008 with the aim of restoring one billion oysters to the New York Harbor by 2030. The project includes cultivating oysters in the hatchery, rebuilding oyster reefs and continuing research on improving the oyster’s survival rate in the wild.

Back on deck, the volunteers are participating in a study to monitor growth in environments where oysters are exposed to their natural predators.

“What we are doing today is taking the measurement where we initially notched them,” said Jennifer Zhu, a first-year Ph.D. student in biology and a research assistant at Baruch College. Part of the research team at the Billion Oyster Project, she points to a “V”-shaped notch on the rim of an oyster. New growth from edges of the notch is measured with a caliper and carefully noted.

Zhu explains that when oysters are surrounded by predators such as blue crabs, mud crabs  and oyster drills, they send out a chemical cue to thicken their shells. Data collected by the volunteers contributes to an ongoing study that will help researchers like Zhu figure out how to increase nursery-hatched oyster survival rates when they are introduced into the river.

Mark Kasabuski just started as volunteer. He used to work on an oyster farm in Rhode Island and enjoys now the role of an oyster conservationist.

“At home, the side of the oyster farming I know was to grow them from seed and raising them. Essentially putting them on dinner tables in restaurants,” said Kasabuski.  “Whereas in here they are seeing what the best way of growing the seed is, and then they were building reefs to restore the Hudson and not to consume them. So there are two different sides of oyster farming that I am getting kind of experience from here.”

The students of the Harbor School are essentially the backbone of the restoration process, according to Buitrago. They spawn and raise the oysters, dive in to monitor reefs too deep to monitor from land and build underwater reef structures to provide habitats for the oysters.

The Billion Oyster Project works with public middle schools and high schools across New York City. Currently, 90 oyster test cages in the city’s water are stewarded by students and citizen scientists, and an estimated 20 million oysters have been restored into the river. More than 50 restoration station sites are in the city’s water, and the project is in the process of installing two new reef sites along with more reef cages. By the end of July, the number of oysters will hopefully increase by another four million, said Buitrago.

Opened to the public since 2005, Governors Island has taken on a mission of farm-to-life education. Aside from the Harbor School, the island also houses a 21,000-square-foot urban farm by GrowNYC. Tourists and city dwellers can be seen lounging on green grass or biking around the island, which seems a world away from Manhattan.  An original tenant, the Billion Oyster Project is committed to engaging the public through programs such as the volunteer program that allows New Yorkers to get their hands dirty.

“I had a really cool day helping out with the oysters, and I think it’s just really nice to hang out on the island in general,” said Robert Hillebrand, another volunteer.

Although the goal of one billion oysters seems like a long way off, Buitrago is optimistic. She is inspired by the success of the Oyster Recovery Project in the Chesapeake Bay, where 6.7 billion oysters have been replanted on 2,200 acres of oyster habitat in Maryland waters since 1998.

The work of the students, volunteers, and scientists are actively contributing to that goal. Over the course of last year, the New York project had 600 volunteers and is hoping to double that number this year through more outreach of individual and corporal volunteer programs.

“It takes a village to get to a billion,” said Buitrago. “It totally does.”