Blue Carbon: Seagrasses can Store as much Carbon as Forests

Marine ecosystems, such as mangrove forests, seagrass meadows and saltwater marshes, can capture and store a significant amount of atmospheric carbon. Yet the full potential of these “blue carbon” habitats to mitigate climate change remains relatively overlooked. A new study shows that seagrasses are a vital part of the solution to climate change and that per unit area, seagrass meadows can store up to twice as much carbon as the world’s temperate and tropical forests
There is also growing evidence that the management of coastal blue carbon ecosystems, through avoided emissions, conservation, restoration and sustainable use is an important tool in managing natural carbon and climate change. Africa’s abundance of mangrove forests, seagrasses and tidal marsh ecosystems and their importance as global carbon sinks and sources, makes ‘Blue Carbon’ important for many African countries’ climate change strategies. Furthermore, these carbon benefits may also provide opportunities for African countries to attract finances for the conservation and restoration of vital coastal ecosystems.
A green turtle (Chelonia mydas) grazes on seagrass

A green turtle (Chelonia mydas) grazes on seagrass. © Luciano Candisani/iLCP

 

The paper, “Seagrass Ecosystems as a Globally Significant Carbon Stock,” is the first global analysis of carbon stored in seagrasses and demonstrates that coastal seagrass beds store up to 83,000 metric tons of carbon per square kilometer, mostly in the soils below them. For comparison, a typical terrestrial forest stores around 30,000 metric tons per square kilometer, most of which is in the form of wood. This research also estimates that, although seagrass meadows occupy less than 0.2 percent of the world’s oceans, they are responsible for more than 10 percent of all carbon buried annually in the ocean.
“Seagrasses only take up a small percentage of global coastal area, but this assessment shows that they are a dynamic ecosystem for carbon transformation,” said Dr. James Fourqurean, the lead author of the paper, a professor of biology at Florida International University and scientist with the Blue Carbon Initiative. “Seagrasses have the unique ability to continue to store carbon in their roots and soil in coastal seas. We found instances where particular seagrass beds have been storing carbon for thousands of years.”
According to the study, seagrass meadows store ninety percent of their carbon in the soil and continue to build on this for centuries. In the Mediterranean, which is the geographic region with the greatest concentration of carbon found from the study, seagrass meadows were found to store carbon in deposits many meters deep.

Seagrasses are among the world’s most threatened ecosystems. Roughly 29 percent of all historic seagrass meadows have been destroyed, mainly due to dredging and degradation of water quality.   Furthermore, at least 1.5% of seagrass meadows are lost every year. This study estimates that emissions from destruction of seagrass meadows can potentially emit up to 25 percent as much carbon as from terrestrial deforestation.

Posidonia oceanica meadow

Posidonia oceanica meadow. © Miguel Angel Mateo

 

“One remarkable thing about seagrass meadows is that, if restored, they can effectively and rapidly sequester carbon and reestablish lost carbon sinks,” said coauthor Karen McGlathery, Professor, University of Virginia.

In addition to their climate benefits, blue carbon ecosystems play a critical economic role, through the services they provide to coastal and island communities. These include nurseries for coastal fisheries, protection of shorelines, supporting of coastal tourism and cultural heritage, and the conservation of marine biodiversity. Yet despite their major contribution to sustainable development, coastal ecosystems continue to be degraded or lost at an alarming rate.

“The results of this global analysis emphasizes the importance of seagrass conservation and restoration,” according to Dr. Bill Dennison, Vice President for Science Applications at the University of Maryland Center for Environmental Science. He added “In addition to providing habitats and nurseries for fish and shellfish and stabilizing sediments to reduce erosion, we now know that seagrass meadows have a crucial role in regulating global carbon.”

This research was led by scientist Dr. James Fourqurean of Florida International University, in partnership with others from, the Spanish High Council for Scientific Investigation, the Oceans Institute at the University of Western Australia, Bangor University in the UK, the University of Southern Denmark, the Hellenic Center for Marine Research in Greece, Aarhus University in Denmark and the University of Virginia. The study emphasizes that conserving and restoring seagrass meadows may reduce greenhouse gas emissions and increase carbon stores, while also delivering key ecosystem services to coastal communities.

“Our vital seagrass ecosystems have always been a conservation priority, given their myriad benefits of ecosystem services to local communities” said Dr. Emily Pidgeon, Senior Director of Strategic Marine Initiatives at Conservation International and co-chair of the Blue Carbon Initiative. “Now we must also recognize the vital importance of Coastal ‘blue’ carbon ecosystems, such as seagrass meadows, for their importance to global climate health.”

Sources: Conservation International, South African Institute of International Affairs, UNEP

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