The city also lost its natural protection from once-in-a-lifetime megastorms such as Hurricane Sandy, which caused massive flooding when winds sent ocean waves crashing into the harbor in 2012, according to the study. It was undertaken by researchers at the University of Massachusetts at Amherst, the Woods Hole Oceanographic Institute and the the Stevens Institute of Technology who set out examine sand deposits Sandy left behind in various coastal pools on Staten Island.

Sure enough, an “event layer” of tell-tale signs from Sandy was present at every site the researchers studied, along with those of big storms dating back two centuries, said Jonathan Woodruff, the lead author of the report, published March 3 in the journal Earth Surface Processes and Landforms. But in the 200 years before the 1800s, they started to fade, and the 1600s when European settlers arrived, signs were virtually wiped away.

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“Something the early colonist did seemed to increase storm-induced overwash at the study site,” said Woodruff, an associate professor and geo-scientist at UMass. “The million-dollar question was what.” They scratched their heads and their search for answers hit dead ends. Then “we considered one of the largest impacts European settlers had on New York Harbor, the decimation of its natural oyster beds,” Woodruff said.

New York’s living, natural barrier to storms went into the stomachs of the people who built the place. And also on their farm fields, where it was used as a type of lime, and in their building construction, where it was used as mortar. The reefs they decimated over four centuries could have stopped a significant portion of the flooding that cost the city more than $40 billion in repairs.

Oysters piled atop each other on a reef are a force of nature. Capt. John Smith’s eyes popped open when he saw them as he first explored the Chesapeake Bay, worrying that they would rip his ship to shreds. Not only do oysters filter pollution from water as they dine on microorganisms, but their collective brawn can also smack down wave energy when waters are whipped by angry winds.

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Using a model, the researchers, who included UMass doctoral student and second author Christine Brandon, simulated the impact of storm surge with oyster beds in place and when they were removed. They determined that wave energy increased as much as 200 percent when the reefs were gone.

“Reefs provided significant coastal protection from waves prior to their disturbance between 1600 and 1800,” the scientists concluded.

When the first evidence of overfishing emerged, laws were written to keep the reefs from being destroyed, but they were poorly enforced. New York’s oyster trade nearly went on life support before officials struck a deal to import oyster seed from the Chesapeake region and planted new beds.

Now the Chesapeake is beset by its own oyster decline, with biologists in Maryland and Virginia working hard to bring them back. Both states have teamed with the Army Corps of Engineers to build reefs with the hope of restoring oysters, the bay’s health by filtering pollution and the dwindling oyster harvest. Maryland recently completed the world’s largest man-made oyster reef in Harris Creek on the Eastern Shore.

Maryland set out to build 10 reefs and stock them with more than 1 billion oysters protected from fishing. Harris Creek’s reef built with the help of the Corps, National Oceanic and Atmospheric Administration, Nature Conservancy and others, was the first, possibly a blueprint for restoring devastated oyster populations nationwide.

The Harris Creek reef might have to do that on its own, because Gov. Larry Hogan’s administration suspended the building of other reefs, saying plans based on science needed further study. Hogan (R) made that call after watermen who harvest oysters complained that it was a waste of time and money building reefs. Maryland oyster fishermen are campaigning to open the reefs to harvesting, even as the bivalves are disappearing from overharvesting and disease.

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Except for a few details here and there, that’s pretty much New York’s story. At one time, the city’s harbor was thought to contain half of the world’s oysters, according to The Big Oyster, written by Mark Kurlansky. Ellis Island was once dubbed “Little Oyster Island.” Traders sold tens of millions of oysters.

Now the state is conducting research that could lead to the construction of a man-made barrier that might cost billions of dollars to recreate what oysters did naturally.

Losing them as a buffer “translates into increased vulnerability of the area to storms… a result most likely shared by other coastal areas that have lost their natural oyster beds,” the study said. It was paid for by the Hudson River Foundation, the National Science Foundation and NOAA, among others.

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