Seagrass: A Powerful Climate Solution Just Below the Ocean’s Surface

They can bolster the coastlines, break the force of hurtling waves, provide housing for fish, shellfish, and migrating birds, clean the water, store as much as 5 percent of the world’s carbon dioxide, and pump oxygen into the ocean, in part making it possible for life on Earth as we know it.

These miracle machines are not the latest shiny tech invention. Rather, they are one of nature’s earliest floral creations: seagrasses. Anchored on the shorelines of every continent except Antarctica, these plants (and they are plants, not algae, that sprout, flower, fruit and go to seed) are one of the most powerful but unheralded climate solutions that already exist on the planet.

Restoring seagrass is one tool that coastal communities can use to address climate change, both by capturing emissions and mitigating their effects, which is among the topics being discussed as leaders in business, science, culture and policy gather on Thursday and Friday in Busan, South Korea, for a New York Times conference, A New Climate.

Around the world, scientists, nongovernmental organizations and volunteers are working to restore seagrass meadows, if not to their original glory, then to something far more expansive and majestic than the barren, muddy bottoms left behind when they are damaged or destroyed.

In Virginia, parts of Britain and Western Australia, among other places, with the helping hands of committed researchers and citizen scientists alike, seagrass meadows are coming back. They’re bringing with them clearer waters, stabler shores, and animals and other organisms that used to thrive there. And yet, seagrass doesn’t get the attention it deserves, its partisans say.

It’s impossible to know exactly how much seagrass has been lost, because scientists don’t know how much there was to begin with.

Only about 16 percent of global coastal ecosystems are considered intact, and seagrasses are among the hardest hit. It’s estimated that a third of seagrass around the world has disappeared in the last few decades, according to Matthew Long, an associate scientist in marine chemistry and geochemistry at Woods Hole Oceanographic Institution. “Globally, a soccer field of seagrass is lost every 30 minutes,” Dr. Long said, “and we lose about 5 to 10 percent at an accelerated rate every single year.”

“Seagrasses are adversely affected by global stressors: deoxygenation, ocean acidification and warming temperatures,” Dr. Long said. But local stressors also have played a role in their withering, mainly in the form of nutrient pollution, largely from agricultural runoff and wastewater, and subsequent algal blooms and die-offs, which first choke out other plants like seagrass (a process called eutrophication) and then, as they decompose, take up all the oxygen in the water (hypoxia).

While the effects of climate change and growing human impacts have accelerated seagrass loss in the last few decades, it’s not a new story.

On the Eastern Shore of Virginia, a strong storm in August 1933 that followed a wasting disease and overharvesting of bay scallops, wiped out what remained of once vast eelgrass meadows. (Eelgrass is a type of seagrass.) For decades, there was no eelgrass on the shore’s ocean side, said Bo Lusk, a scientist with the Nature Conservancy’s Volgenau Virginia Coast Reserve, though some remained on the part of the coast lapped by the Chesapeake Bay.

Dr. Lusk, who grew up in the region, heard stories as a child of lush green carpets of eelgrass from his grandmother, who remembered that the shores teemed with life — until they didn’t. But then, in 1997, someone reported seeing some patches of eelgrass on the shore’s oceanside, likely from seeds that happened to drift south from Maryland and settled in a hospitable neighborhood in Virginia.

After several years of experiments, Robert J. Orth, a scientist at the Virginia Institute of Marine Science, devised a highly successful method of restoring seagrass, similar to methods used around the world: In the spring, scientists and hundreds of volunteers collect seeds, which they count and process over the summer and plant in the sediment in the fall.

Since 2003, when the restoration effort in the Volgenau Virginia Coast Reserve began, scientists and others have planted around 600 acres of seeds, and seagrass now covers 10,000 acres, according to Dr. Lusk. Later this year, the Nature Conservancy is hoping to sell the first validated blue carbon credits for seagrass, based on this restoration effort, said Jill Bieri, the director of the reserve.

However, the success of the Virginia project has been somewhat difficult to recreate around the world. “You can’t do this just anywhere,” Dr. Lusk said. “If the Nature Conservancy hadn’t started this land protection work 50 years ago, buying up parts of the coast to preserve it, the odds are we wouldn’t have the water quality we have now, and this wouldn’t have been so successful.”

Seagrass restoration will take decades of commitment, Dr. Lusk said. Richard Unsworth, an associate bioscience professor at Swansea University in Wales and the founder and chief scientific officer of Project Seagrass, a British NGO that works on seagrass restoration, said that an important part of the work was the long-term promise made to the whole ecosystem — the seagrass meadows, but also the people in the community.

“The actions of fishermen, the views of boat owners, the problems of water quality — they can all be part of a complex social-cultural situation, and in the long term it will be an amazing success, but it’s a slow process, not some silver bullet where you plant something and then you’ve saved it,” Dr. Unsworth said.

Community engagement has been a necessary part for seagrass success since it takes a lot of work to collect and plant millions of seeds. For Project Seagrass, that has also meant the development of a website and app, Seagrass Spotter, which allows users to upload photos of seagrass in the wild (which is then verified by scientists), to help researchers fully map the extent and types of seagrasses around the world, since mapping of seagrass globally is rather patchy.

But one place it’s well mapped is Shark Bay, a remote section of the coast in Western Australia, where seagrass from 10 different meadows was discovered to be actually just one plant, possibly the biggest in the world.

There, seagrass has been growing and accumulating carbon in its plant matter, but also in the sediment, for more than 3,000 years, said Elizabeth Sinclair, an evolutionary biologist at the University of Western Australia.

But during an extreme marine heat wave from 2010 to 2011, about a third of the seagrass canopy (what is visible above the sand) died, releasing as much as nine million tons of carbon, according to one estimate.

Over the last decade or so, Dr. Sinclair and her colleagues have been studying the recovery of the seagrass — the places where it’s come back naturally and where it likely never will, without some assistance from scientists as well as the Malgana people, Indigenous Australians who work as rangers.

Despite warming temperatures and changing ocean chemistry, which make complete restoration impossible, it’s still work worth doing, said Dr. Lusk, whether it’s on the crooked waterways of the Virginia coast, the rocky shores of Wales, or the sweeping, endless bays of Western Australia.

“There are so many logical reasons we should do this,” Dr. Lusk said. “The carbon storage is great, shoreline protection, all of this other stuff is great, and you can know that in your head but until you get in the water and spend some time really within this system, you don’t have the emotional connection.

“I would keep doing this if there was no carbon stored. It just feels right to be out there.”