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Shrinking sea meadows store more carbon than forests. Scientists are racing to track what’s left.


Human activity is helping destroy the equivalent of a soccer field of these sea grasses every 30 minutes around the world, according to the U.N. Environment Program (UNEP). And scientists are now racing to take stock of what remains.

“There are a lot of unknowns — even things as simple as how much sea grass we have,” said Gwilym Rowlands, an Oxford University earth observation scientist who is helping the Seychelles government map the island nation’s sea grass and estimate how much carbon it stores.

Sea grasses play a large role in regulating ocean environments, storing more than twice as much carbon from planet-warming carbon dioxide (CO2) per square mile as forests do on land, according to a 2012 study in the journal Nature Geoscience.

Countries that hope to earn credit toward bringing down their CO2 emissions could tally their sea grasses and the carbon they store, a first step toward accrediting carbon offsets for eventual trading on an open market. The grasses also curb the acidity of surrounding waters — an especially important function as the ocean absorbs more CO2 from the atmosphere and becomes more acidic.

But sea grasses provide some buffer from acidification, which can damage animals’ shells and disrupt fish behaviors. In one study published March 31 in the journal Global Change Biology, scientists at the University of California at Davis found that sea grasses dotted along the California coast could reduce local acidity by up to 30 percent for extended periods.

The plants also help clean polluted water, support fisheries, protect coasts from erosion and trap microplastics, the study’s lead author Aurora Ricart said. “What is even cooler is that these habitats are present everywhere,” she said.

While most sea grasses fringe coastlines around the world, the shallowness of Saya de Malha allows sunlight to filter to the seabed, creating an aquatic prairie in the Indian Ocean that provides shelter, nurseries and feeding grounds for thousands of marine species.

The bank’s isolation has helped protect it from coastal threats, including pollution and dredging. But even such remote stretches of international waters face increasing incursions from shipping and industrial fishing.

In March, scientists from institutions including Britain’s Exeter University traveled with Greenpeace on an expedition to collect some of the first field data on the area’s wildlife, including its little-studied beds of sea grass.

With the boat bobbing for days above the plateau, the researchers gathered bits of grass floating in the water, tweezering them into bottles for analysis back on shore.

Data on sea grass meadows are patchy, but research so far estimates the grasses cover more than 115,000 square miles, distributed across all continents apart from Antarctica, according to UNEP. That would be an area the size of Italy.

It is not yet known how much carbon is locked into Saya de Malha, but globally the tangled roots of sea grasses are estimated to trap more than 10 percent of the carbon buried in ocean sediment per year.

“This has massive implications for the [world’s] climate change mitigation efforts,” said Dimos Traganos, lead scientist on a German Aerospace Center project developing software to improve sea grass tracking using satellite imagery and other data. That effort has been helped by recent advances in cloud computing and data storage, he said. “We are in such an exciting period.”

Sea grass meadows are believed to be retreating about 7 percent per year globally, according to the most recent sea grass census published in a 2009 study in the Proceedings of the National Academy of Sciences.

It notes the estimate was based on incomplete data available at the time.

The more closely studied areas illustrate the harm human activity can cause. Pollution from mining and damage by fisheries, for instance, may have helped to eliminate 92 percent of mainland Britain’s sea grasses in over a century, according to a March 4 study in the journal Frontiers in Plant Science.

If still intact, these could have supported about 400 million fish and stored up to 11.5 million tons of carbon — equivalent to 3 percent of Britain’s CO2 emissions in 2017, the study said.

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