CONCORD, N.H. — A half million juvenile oysters the size of a thumbnail are being readied to rescue New Hampshire’s Great Bay from an environmental meltdown.
The oysters that will be placed into the bay in Newmarket will be the crowning touch on what will be New England’s largest manmade oyster bed designed for conservation reasons. With each oyster capable of filtering 20 gallons of water a day, it is hoped the marine militia will suck the excess nitrogen out of the bay and make the waters fit for generations of oysters and other species.
“We’re putting nature back in control,” said Ray Konisky, director of marine sciences for The Nature Conservancy. “We put a lot of hungry oysters in there and you’ve got the beginnings of getting your balance back.”
The excess nitrogen comes from leaching septic fields, wastewater and runoff from fertilized lawns. It makes Great Bay a less attractive habitat for oysters, eel grass and fish, with a ripple effect that leads to birds seeking other habitats from which to feed. The nitrogen promotes the growth of algae, particularly sea lettuce, which blocks light and suffocates baby oysters. It also depletes oxygen in the water, making it difficult for fish to breathe.
The Nature Conservancy is working with the University of New Hampshire to restore the oyster reefs of Great Bay. Once spanning 1,000 acres in the bay, the oyster beds have thinned to less than 50 acres.
The oyster stock was decimated largely by two diseases that struck in the 1990s that still pose a threat, Konisky said, but most strains of oysters have developed a tolerance. Over-harvesting also contributed to the decline, but not nearly as much as the diseases did.
Construction is under way on a 2.5-acre oyster reef at the mouth of the Lamprey River into the Great Bay in Newmarket. It’s a task that involves a lot of heavy lifting to build a bed the oysters will nestle into and spawn.
Each acre requires 100 tons of clamshells — quarantined and dried to kill bacteria — that are spread across the silt on the floor of the bay.
The shells arrive in 1-ton bags that are loaded onto a crane-equipped barge, hoisted above the water and spread. Konisky said the barge is moved 20 feet and the process is repeated some 225 times to create the bed, at a cost of about $75,000 per acre.
The baby oysters that will inhabit the new reef are being nurtured at a hatchery at UNH located on Adam’s Point in Durham, where Little Bay opens into Great Bay. About 25 volunteers around the bay also nurture the baby oysters in small crates anchored to their docks until they are ready for release.
The nascent oysters, called spat, start as the size of a pinhead, and will be released to settle on the new oyster bed when they reach the size of a nickel, too big for crabs to gobble.
“Our vision is a bay full of oysters again,” Konisky said. “But they need a jump start.”
UNH’s Dr. Ray Grizzle said they are raising 3 million disease-resistant oyster larvae in hopes 1 million survive. This week those larvae reached the spat stage, and will be hung in 200 cages from rafts in the bay to be sheltered as they grow.
He said even in a doomsday scenario in which none of the oysters planted in the bay survived, the manmade reef that will be unveiled Wednesday is a magnificent habitat for juvenile fish and other species to hide in as they grow beyond the size of prey. Grizzle said winter flounder in particular will thrive there.
Great Bay has the northernmost oyster beds along the Eastern Seaboard, Konisky said, ideally suited to oysters that do not like the colder, open ocean waters.
The oysters will be released to the new reef later in the summer, when the warmer waters will be conducive to spawning. Legions of organizations and partnerships are working to make the project a success, including seafood restaurants in New Hampshire and Maine that recycle tons of shells per year.
“We want to make sure we’ve made our bed before the guests arrive,” Konisky said.