Oyster restoration in New York shows signs of promise, despite threats

Pollution. Disease. New predators — and a warming planet.

These are the threats facing many of New York’s oysters, whose 20- to 25-year life spans have been cut down to just four or five years.

But despite these obstacles, scientists and local officials say oyster restoration programs in the state are showing signs of promise.

"They evolved in these crazy variable environments, they can handle wild variations of salinity” and sun, Boze Hancock, senior marine habitat restoration scientist with the Washington, D.C.-based nonprofit The Nature Conservancy, said of oysters. “They are some of the toughest creatures we've got to work with.”

Nutrient filters and storm surge protection

Oysters are key to the marine ecosystem.

They shield shorelines from storm surges and remove excess nutrients that power summer algae blooms and fish kills — without requiring feeding or tending. And they excel as fish nurseries.

Each oyster filters tens of gallons of water a day. In Greenwich, Connecticut, cultivated shellfish take out about 9% of the nitrogen from local sources, according to the National Oceanic and Atmospheric Administration’s Milford Laboratory.

Said Hancock: "Oyster reefs are one of the best mechanisms for getting nutrients out of the water."

Growing oysters successfully requires a series of reefs to catch larvae that otherwise will die without something hard to stick themselves on.

Scientists model larvae’s watery routes to find the best spots for them to reach other reefs instead of disappearing into the mud.

In western Shinnecock Bay, for example, Hancock said they are "evenly distributed throughout the system; in the eastern bay, mainly all the larvae disappear in the first few days."

But once so abundant they were shipped nationwide, oysters must now contend with a series of threats.

Diseases more commonly found in southern states, for example, are killing the young adult shellfish. 

“As the water warms, those diseases are becoming more prevalent as you move north,” said Michael Doall, associate director for Bivalve Restoration and Aquaculture at Stony Brook University's School of Marine and Atmospheric Sciences.

Two culprits are salt- and warm-water loving parasites: Dermo, which thrives at 77 degrees and above, and MSX, which needs at least 66 degrees. A third, called simply a “seaside organism,” also does well in brine, said Hancock.

Warming New York waters are also bringing an increase in predators, including the cownose ray, Doall said.

"We're seeing them now on Long Island; in just the last several years, I saw a mass school of them, I was blown away,” he said.

Pollution may also be impacting oysters, Doall said.

'Just a part of nature'

Survival rates of oysters vary markedly depending on various factors including whether spat or adult oysters were planted. Larvae are called spat once they stick to a hard surface. 

Spat were planted in New York Harbor, according to the state Department of Environmental Conservation. On Long Island and in New York Harbor, The Nature Conservancy planted adult oysters — bought to keep shellfish famers in business during the pandemic — on the bottom. 

The Nature Conservancy added oysters to ongoing successful programs already permitted and the results reveal how these adults fared after a year.

In February, the Conservancy and partners began a second project, recreating reefs at 12 sites from Maine to Maryland to California and Washington state.

The survival rate for New York Harbor’s Billion Oyster Project, which will plant 1 billion oysters by 2035, was 53%, The Nature Conservancy said. Next was Oyster Bay at 66%, the Long Island Shellfish Restoration in Shinnecock and Bellport bays at 74.9%, and the Hudson River Trust at 91.5%.

In some of Suffolk’s Shinnecock Bay, the proportional survival rate was 49.7%, according to The Nature Conservancy.

The DEC said some Billion Oyster Project sites that are “more favorable” than others may be replanted, with other spots focused on education. So these sites “may not reflect the likelihood of success of a larger restoration effort.”

And spat was used, the DEC said, which “typically has a higher mortality in the first year as compared to larger oysters.”

“I would not say these restored oysters have shortened lives,” said Aaren Freeman, professor and chair of the biology department at Adelphi University, in an email.

“There is natural mortality of course, but many of the oysters have lived for three years," Freeman said. "We will need to collect more data to really draw any conclusions about their longevity.”

Islip Town Supervisor Angie Carpenter said in a statement that the town's Bay Bottom Aquaculture Program's oysters are thriving.

"As per the NYS DEC we also know that, as of 2018, the oyster production in Islip's waters rose from 0 to 20% of the cultured oysters harvested in New York State," she said, and now is 9% of both wild and cultured oysters. 

Calling New York's results "encouraging," Hancock added: “Survival rates of 20% to 50% for small oysters/spat in the first year is viewed as great. … For subsequent years, 75% is good.”

Added Doall, “Mortality is very high on these younger stages, but that’s why females spawn tens of millions of eggs. So those survivorship curves look bad, but that’s just a part of nature.”