Underwater and out of sight, one of humanity’s most effective weapons against climate change is struggling.
According to a new study, failure to protect the world’s seagrasses will come at a steep cost — in more ways than one.
Protecting the world’s seagrasses could avert climate damages valued at over US$ 200 billion by preventing the release of 1.2 billion tons of carbon pollution — an amount equivalent to the annual carbon footprint of 100 million homes in the United States.
“Seagrass meadows are not just important for marine biodiversity — they are a critical piece of the climate puzzle,” said Johannes Krause, the study’s lead author and assistant professor at Florida International University. “If we don’t act now, we risk losing these ecosystems and compounding the effects of climate damage. It’s time to prioritize seagrasses.”
Combining research from roughly 3,240 sites across 61 countries, the study, led by Conservation International and Florida International University, is the most comprehensive look to date at the amount of carbon stored by the world’s seagrasses.
Critically, the study shows, not all seagrass is created equal when it comes to carbon storage.
“There is huge diversity in seagrass ecosystems,” Krause said. “Those that are tall, with long leaves and deep root systems store much more carbon than other, smaller varieties.”
A seagrass bed in Honduras.
While the study finds the amount of carbon held by seagrasses globally is on average lower than previous estimates, it is a more accurate and detailed account, he said, and can help target priority areas with varieties of seagrass that capture the most carbon.
Seagrass meadows in the tropical Atlantic, the Mediterranean and southern Africa hold the highest carbon stocks, up to nearly four times as much carbon as the global average for seagrasses. A single hectare (2.5 acres) of seagrass in these regions can store the equivalent of the annual emissions of up to 22 cars.
“Our pool of data is more robust than ever, giving us a much clearer picture of what seagrass is capable of,” Krause said. “By breaking it down into different species in different regions, we can now target our efforts for the most effective action.”
As a climate ally, seagrasses are often overlooked — literally. Growing below the water’s surface, seagrasses are often difficult to study, and as a result, difficult to target for protection, he said.
Researchers estimate that vegetated coastal ecosystems including seagrasses cover only 2 percent of the ocean floor, but account for 50 percent of the carbon storage. Yet because seagrasses are so difficult to study, scientists still don’t have a complete understanding of how much exists in the world.
Seagrass’ benefits extend far beyond carbon: They help protect coastal communities from erosion, improve water quality and provide habitat and food for fish and other marine life.
But the threats to seagrasses are just as numerous. Agricultural runoff can choke out seagrass, while giving rise to algae that block out sunlight. Deforestation and erosion near coastal areas lead to excessive amounts of sediment that can smother seagrasses. And destructive fishing practices like bottom trawling can rip up seagrasses by their roots.
“Unfortunately, seagrasses are bound to the ocean floor,” Krause said. “They can't just move when a threat arrives; they're really sensitive to whatever comes their way.”
Conserving seagrass is one of the most cost-effective and powerful actions against climate change, said Emily Pidgeon, study co-author and Conservation International’s Vice President for Ocean Science.
“The vital role seagrass meadows play not only in carbon storage, but also in protecting coastal communities, is abundantly clear,” she said. “With the right policies and investments, we can protect these underwater treasures and the climate benefits they provide.”
Policies like managing water quality and preventing habitat destruction in coastal areas go a long way in protecting seagrass, Pidgeon said. But it’s critical to move quickly.
Countries must include seagrass protection in plans to tackle climate change, she said, as well as embrace financial opportunities for protection, such as carbon markets, which provide financial incentives in return for the protection of the carbon stored by trees and mangroves.
“Seagrass is underrepresented in carbon financing initiatives compared to other coastal ecosystems, like mangroves,” Pigeon said. “Not only will investing in global seagrass conservation unlock its carbon storage potential, it will also support fisheries, coastal erosion protection and improve water quality — safeguarding our planet and coastal ecosystems for humanity.”
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Mary Kate McCoy is a staff writer at Conservation International. Want to read more stories like this? Sign up for email updates. Also, please consider supporting our critical work.