In the Chesapeake Bay, saving seagrasses can fight ocean acidification

Surprisingly, minerals formed in restored seagrass beds can offset human-caused acidification miles away.

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A crab swims above a waving seagrass bed in the Chesapeake Bay.

When scientist Wen Jun Cai and his colleagues boated across the pea-soup-like waters of the upper Chesapeake Bay in the summer of 2016, water sampling kits and pH sensors in hand, they didn’t expect to find chemical magic at play.

The scientists were taking stock of a looming problem facing the 200-mile-long bay: the acidification of its waters, a human-caused phenomenon that threatens the health of the crabs, oysters, and fish iconic to the large estuary.

They started collecting their samples in the recently restored, vibrant underwater grass beds of the Susquehanna Flats near the top of the bay, and motored their way some 60 miles downstream to the deep central channel.

When they rounded up their hundreds of data points and analyzed them, they found evidence of something surprising and encouraging: Gently waving seagrasses in the bay are performing a magnificent chemical trick. As they photosynthesize in the beating sunshine, they produce tiny granules of a carbon-based mineral that acts like a miniature antacid tablet.

And those acid-neutralizing “micro-Tums” don’t stay put. They’re swept miles down the length of the bay, eventually dissolving into the deepest waters, which have long been soured by acidification caused by human sources like agricultural runoff and untreated waste.

“It’s like the seagrasses are producing antacids that counter the indigestion of the bay,” says Jeremy Testa, a marine ecologist at the University of Maryland and an author of the paper in Nature Geoscience describing the newly discovered phenomenon.

Without this acid-neutralizing trick, the bay’s...

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