In 2019, scientists set out to map the extent of seagrass in Seychelles, an island nation off the eastern coast of Africa. There, they hit upon a startling number: More than 90% of the country’s “blue carbon,” or the carbon stored in marine ecosystems, is contained within seagrass meadows.
Under the Large-scale Seagrass Mapping and Management Initiative (LaSMMI), the seagrass mapping effort is now expanding to Kenya, Tanzania, Mozambique and Madagascar, covering 2 million square kilometers (772,200 square miles) of seas hugging 9,500 km (5,900 mi) of coastline in the Western Indian Ocean.
LaSMMI is a collaboration involving the Pew Charitable Trusts in the U.S., the Western Indian Ocean Marine Science Association based in Tanzania, the University of Southampton in the U.K. and regional research organizations in participating countries.
“Currently, there is no standardized seagrass map for the [Western Indian Ocean] region, and the ecosystem is not widely included in management or policy,” Stacy Baez, a senior officer with Pew’s advancing coastal wetlands conservation campaign, told Mongabay by email. Baez added that less than a fifth of the world’s seagrasses are fully mapped.
Seagrasses are not actually grasses but a group of flowering marine plants, with 72 known species, growing close to shorelines everywhere except in Antarctica.
Like plants on land, seagrasses store carbon both as biomass and in the soil that they help bind. However, unlike their more glamorous marine cousins, mangroves and coral reefs, seagrasses are often overlooked in conservation efforts and carbon accounting.
The team that mapped Seychelles’ seagrass cover, led by Gwilym Rowlands who was then at the University of Oxford, U.K., estimated it stood at 160,000 hectares (about 400,000 acres).
Rowlands told Mongabay that “on a per-hectare basis” there is less carbon under seagrasses than under mangroves. But there is a lot more seagrass in Seychelles, which helps explain why it stores so much more blue carbon, Rowlands, now with the University of Southampton, added.
Seychelles has committed to including seagrass blue carbon estimates in its national carbon inventory by 2025 as part of its nationally determined contributions (NDC).
Seagrass meadows are also important underwater habitats, contributing to a fifth of the world’s top fisheries and protecting shorelines. But these habitats suffer when there is nutrient overloading in coastal waters, producing algal blooms that block sunlight. Dredging that damages the seafloor also destroys seagrass beds. Fishing equipment like propellers, nets and anchors can hack away at seagrass habitats.
Researchers estimate that the planet lost at least a third of its seagrass cover in the past century.
The LaSMMI aims to complete seagrass maps and a baseline assessment of carbon stocks by 2026. It’s “ambitious,” Baez said, adding there is an “urgent need to advance the data collection, collaboration and policy inclusion for seagrass ecosystems.”
Banner image: Blue and gold fusilier fish above a seagrass meadow, Desroches Atoll, Seychelles. Image courtesy of Seychelles Seagrass Mapping and Carbon Assessment project.
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