Seagrass Meadows Some 9,000 Miles Apart Show Strength of Nature-Based Solution to Climate Change

Seagrasses—flowering marine plants that form dense underwater meadows—boost coastal economies and can capture and store significant amounts of climate-harming carbon, known as “blue carbon.” But they are also one of the most imperiled ecosystems on Earth, declining globally at 7% each year. Up to 1 billion metric tons of carbon dioxide are released annually worldwide from degraded coastal ecosystems, including seagrasses—an amount equivalent to the emissions from 222 million gas-powered cars on the road for a year.

Researchers and policy experts specializing in coastal conservation in the U.S. state of North Carolina and in the Indian Ocean island nation of Seychelles led a webinar hosted by The Pew Charitable Trusts exploring how they’re assessing the ability of seagrasses along their extensive coastlines of their regions to mitigate the effects of climate change. The webinar detailed their work cataloging and conserving seagrasses in both locations and included discussion of how their documentation of carbon capture capacity can serve as models for other countries and states.

Seagrasses pack a particularly powerful punch in nature-based climate change mitigation for three major reasons. Jud Kenworthy, a researcher with the North Carolina Coastal Habitats Greenhouse Gas Workgroup who previously spent decades as a coastal marine scientist for the National Oceanic and Atmospheric Administration, explained that:

• Because they grow rooted in the soil, seagrasses capture two-to-five times more “blue” carbon below ground than in their aboveground biomass, which makes them incredibly effective at storing carbon.
• Since that soil is water-saturated—with very little oxygen—decomposition occurs very slowly, making seagrasses ideal for carbon capture and storage from other sediments.
• The way seagrasses grow promotes the capture of carbon. As much as 50% of the carbon in the soil beneath the water’s surface may come from sources other than the seagrasses themselves.

North Carolina’s Greenhouse Gas Inventory: Learn by Doing

Although North Carolina’s seagrasses are declining at a rate of 1% to 1.5% annually, resulting in a loss of nearly 17,000 acres in the past 14 years, the state still has the largest intact seagrass meadow on the Eastern Seaboard of the U.S. Beginning in 2018, North Carolina committed to creating and publishing plans to address the state’s vulnerability to climate change. In 2021, it updated its Coastal Habitat Protection Plan (CHPP) with a recommendation to assess the blue carbon benefits its seagrasses and other coastal wetlands provide. Seagrasses are one of only three marine ecosystems—alongside salt marshes and mangroves—currently recognized by the United Nations Intergovernmental Panel on Climate Change as ecosystems that can make measurable contributions to help states and countries reduce emissions.

The CHPP documented important findings and raised new questions that researchers should answer, according to Paul Cough, facilitator of the North Carolina Coastal Habitats Greenhouse Gas Workgroup that developed the state’s blue carbon inventory. Cough was also a former director of the Oceans and Coastal Protection Division for the U.S. Environmental Protection Agency.

The work group discovered that North Carolina's seagrasses store the equivalent of about 18 million tons of carbon dioxide and capture roughly the equivalent carbon of taking 14,000 cars off the road each year. However, that rate decreases as North Carolina loses seagrass acreage, and the fate of the carbon stored under former seagrass beds is not well known. “This is a big data gap, and more research is needed to figure it out,” Cough added.

States don’t need perfect data to begin assessing the carbon benefits of their coastal wetlands. Instead, Cough suggested that they “Get started and learn by doing.” North Carolina intends to complete its coastal wetlands greenhouse gas inventory this summer, becoming one of the first U.S. states to include seagrasses, allowing officials to consider developing supporting policies. For example, the state’s CHPP has a goal of protecting or restoring 191,000 acres of seagrasses and other submerged aquatic vegetation. “If North Carolina achieves this goal, what impact will it have on greenhouse gas emissions?” asked Cough. “We've learned that climate policy and coastal policy can and should be mutually reinforcing.”

Seychelles Commits to Climate Action

The vital role that seagrasses play in Seychelles’ economy and climate resilience led its government to commit to protecting all of its seagrasses by 2030 as part of its nationally determined contribution to the United Nations’ Paris Agreement, said Angelique Pouponneau, adviser to the chair of the Alliance of Small Island States on climate change and ocean negotiations and a past executive at the Seychelles’ Conservation and Climate Adaptation Trust.

According to Pouponneau, through this work, Seychelles learned important lessons, including that:

• It’s necessary to translate science to policy that can leverage the financial commitments needed to undertake the work.
• It’s important to transfer knowledge and know-how gained from science to local communities. “Even if governments are able to make ambitious, bold commitments, it’s the people who must own them,” Pouponneau said.
• Curbing greenhouse gas emissions is required to save the planet, even as nature-based solutions can help mitigate climate change.

“Nature-based solutions are supplementary and things that we can do straightaway,” Pouponneau said. “If a country like Seychelles, a small island-developing state, a country of 100,000 people can do it … we can all take climate action.”

Alex Clayton is a principal associate with The Pew Charitable Trusts’ conserving marine life in the United States project, and Kate Meyer is a principal associate with Pew’s protecting coastal wetlands and coral reefs project.