For generations, the waters surrounding Long Island have defined its identity — from the wide-open waterfronts of the South Shore to the shellfish beds of the North Shore. But beneath the surface, a quieter transformation is underway.
Ocean acidification is often called climate change’s “evil twin,” and refers to the lowering of the water’s pH, the scale used to measure the concentration of hydrogen ions in the water. While global warming refers to rising temperatures, acidification describes a shift in seawater chemistry.
…
On Long Island, acidification is not driven by global carbon emissions alone. Local factors intensify the problem. Nitrogen discharged from wastewater, septic systems and fertilizer runoff flows into bays and harbors, fueling harmful algal blooms. When those blooms die and decompose, the process consumes oxygen and releases additional carbon dioxide in the water, further lowering pH.
The result is a compounding effect: global atmospheric carbon dioxide combined with local nitrogen pollution accelerates acidification in shallow, enclosed estuaries.
Warming waters add another layer of stress. As temperatures rise, marine organisms’ metabolic demands increase, but warmer water holds less dissolved oxygen. Together, warming and acidification can weaken shellfish during their most vulnerable larval stages, making it harder for them to survive and build shells.
For Long Island’s oyster and clam farmers — industries that have experienced both revival and setbacks in recent decades — these chemical changes aren’t just theoretical. They are measurable, seasonal and, increasingly, part of daily operations.
The ‘evil twin’ of climate change
Adrienne Esposito, executive director of Citizens Campaign for the Environment, a nonprofit advocacy organization in New York and Connecticut, describes ocean acidification as a hidden but mounting crisis for Long Island’s waters — one intensified by warming temperatures, nitrogen pollution and poor circulation in local bays.
“It’s commonly understood that roughly a third of all carbon dioxide emissions released into the atmosphere are absorbed by the marine environment,” Esposito said. That absorption increases acidity levels in bays, estuaries and the open ocean.
Ryan Wallace, assistant professor of environmental science at Adelphi University, explained that these acidity levels are not evenly distributed. Some bays and harbors on the North Shore are measured at 450 parts per million, close to the ideal level of roughly 300 ppm, while others, particularly in the western portion of Long Island Sound, measured as high as 2,000 ppm.
Wallace emphasized that while these may not sound like huge differences, even minor changes in CO2 levels can have a drastic impact.
“To put it into perspective, over the last 800,000 years or so, the carbon dioxide in the atmosphere was only about 300” parts per million, Wallace explained. “Two thousand is a lot more than that, so when you get to concentrations that are that high, this can have implications for, you know, organisms that are living in these ecosystems.”
While the data reflect a global pattern, the consequences are being felt at the regional level as well. As Esposito noted, Long Island’s problems do not exist in isolation.
“It’s being exacerbated by an increase in temperature of the waterways and more nutrient runoff, such as nitrogen, going into waterways,” she said. “All of that causes unfortunate degradation to our water bodies.”
While algae is an important part of a healthy ecosystem, excess nitrogen can fuel algal blooms that, when they die off, consume oxygen and further stress marine life — compounding the chemical impacts of acidification with biological ones.
In the South Shore’s Western Bays, limited water circulation compounds the problem. Research by Stony Brook University has shown that it can take up to 180 days for water to fully flush out through an inlet into the Atlantic Ocean. Instead, Esposito said, the water “sloshes back and forth” before eventually reaching the ocean, trapping heat and pollutants in the process.
Coastal areas such as the western portion of the Sound are especially vulnerable because of limited circulation. Wallace stressed that scientists differentiate between open-ocean acidification and coastal-ocean acidification because of the unique challenges those areas face.
In Hempstead Harbor, the issue of acidification has been a focus for local environmental organizations for decades. The Coalition to Save Hempstead Harbor was formed in 1986 to address a range of environmental issues facing the area, including acidification.
Michelle Lapinel McAllister, the coalition’s programs director, explained that pH monitoring is one of the core services that the nonprofit provides for the harbor. Measuring occurs year-round, with particular emphasis from May to October, when the harbor, in common with other waterways, sees annual spikes in nitrogen levels.
“Each season we will see periods of low dissolved oxygen, and whenever dissolved oxygen gets low, then we’ll see pH drop as well,” Lapinel McAllister said. “That will typically happen around the hottest part of the year.”
Another complication is the fact that enclosed waters respond more quickly to environmental stressors than the open ocean, meaning local ecosystems can feel the impacts sooner and more intensely.
“The more stagnant the water body is, the more these acidity levels build up,” Esposito said. “The more the temperature builds up, the more damage the increase in acidity levels can do.”
She described three primary consequences of ocean acidification: “reduced water quality, the impact on shellfish and finfish and the degradation of the overall habitat due to low oxygen.”
Shellfish such as oysters and clams struggle to build and maintain their shells in more acidic conditions, while finfish larvae have lower survival rates — threatening both the ecosystem and the region’s maritime economy.
“Acidification actually reduces the availability of carbonate ions that are needed for these organisms to build their shells, so that’s a major issue,” Wallace said. “Like shellfish aquaculture, it can impact fisheries, and then there’s this cascading effect that can influence things like recreational activities and tourism.”
This is especially relevant because shellfish play an important role in regulating nitrogen levels. An adult oyster can filter up to 50 gallons of water per day, depending on size and environmental conditions, while a clam can filter roughly half that.
Across Long Island, and across the country, local environmental organizations and governments are throwing their support behind shellfish hatcheries and protection programs, including the towns of Hempstead, Oyster Bay and Babylon. Lapinel McAllister explained that while these efforts serve an important role in safeguarding healthy ecosystems, they can’t singlehandedly save marine ecosystems.
“On their own, shellfish can’t improve the water quality to healthy levels,” she said, “but having a good, healthy, strong population is going to be part of that overall puzzle of maintaining the stability of pH over long term.”
While local efforts to restore wetlands, upgrade sewage treatment plants and rebuild shellfish populations are making progress, Esposito said the root cause remains global. “The main culprit of ocean acidification is the burning of fossil fuels,” she said. “The only thing we can do is support more renewable energy so that we’re not pouring more carbon dioxide into the waterways.”
The wet work of marine scientists
Across Long Island, scientists are working together to find ways to improve the quality of local waters. A leading solution is all-organic: Restoring local populations of filter-feeders could, with careful management, bear the brunt of decontamination efforts.
The Flax Pond Marine Laboratory, in Old Field, is nestled in the marshes of the North Shore, overlooking the Long Island Sound. This laboratory is a research hatchery, working toward “improving local coastal water quality and replenishing natural shellfish populations,” according to its shellfish restoration manager, Peter Martin.
The facility’s current focus is the Ribbed Mussel Bioextraction Project, in which staff test what growth strategies lead to the healthiest shellfish that could be reintroduced to coastal waters to rejuvenate them.
“There’s a lot of coastal communities and little inlets and even out-of-use small pockets of water that are just polluted and are in need of cleaner water,” Martin said. “Fundamentally … shellfish are natural filters. All they do is filter feed, so they’re cleaning the water as they grow.”’
“One of the big pollutants that we’re focused on is nitrogen removal,” hatchery Research Specialist Ashley Lopez said. “Shellfish take in the bad form of nitrogen, process it in their body, and they still expel some nitrogen, but it’s a safe and more bioavailable kind of nitrogen.”
The ribbed mussel program is exploring new methods of shellfish cultivation; according to Lopez, there is no consensus in the field about growing large amounts of these shellfish. In their nascence, ribbed mussels have delicate health — a larva is as small as a grain of sand. The Citizens Campaign for the Environment staff regularly sterilize equipment and filter externally sourced seawater to minimize diseases and infections from plankton and bacteria.
The researchers grow eight different varieties of algae to feed adult ribbed mussels, which are kept in temperature-stabilized basins. This conditioning process is meant to “ripen the gonads” of the mussels and help them reproduce as effectively as possible, according to Martin.
“What we’re doing is trying to find out the best way to grow a lot of them from birth on and have them actually survive,” Lopez said. “And the starting point, we think, is the feeding regimens that we’re giving them. So that’s why we’re doing different diets — to see what kind of spawn they produce and see how the larvae survive after that.”
“This two-year project is Phase Two of a larger project,” Martin added. “Phase One was from ’23 to ’25. Each phase is getting further and further, doing more to figure out the best way to grow these things.”
In addition to ribbed mussel cultivation, CCE staff are involved with other restoration efforts, including a Community Aquaculture Restoration and Education program, in which scientists partner with community volunteers to sow “spat-on-shell” oysters into local estuaries, from which larvae will grow and mature into underwater custodians.
The Flax Pond hatchery works with groups ranging from the Cornell Cooperative Extension of Suffolk County and Stony Brook University to the state Department of Environmental Conservation and the New England Interstate Water Pollution Control Commission. It is one ecological collective of many working toward improving the quality of local waters from the east end of Long Island to the shores of Nassau County.
Setting course for a healthier future
Even as Long Island’s waterways face the threat of rising acidification, the experts emphasize that all is not lost. Thanks to the efforts of the Coalition to Save Hempstead Harbor and other environmental groups, the region’s waters have bounced back from near-toxic levels of acidity, not to mention numerous pollution-related threats of the 1980s.
According to Wallace, the efforts of scientists and local volunteers, from the South Shore to coastal Connecticut, to monitor and address these issues have already made an impact.
“There’s been a lot of positives,” he said, “but we can’t stop there. There’s more work to be done.”
Abigail Grieco, Will Sheeline & Joseph D’Alessando, Herald Community Newspapers, 5 March 2026. Article.
