Seagrasses Can Store More Carbon Than Forests

A new international study, published this week in the journal Nature Geoscience, 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.

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 can 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.

The researchers, including Karen McGlathery, an environmental scientist in the University of Virginia\’s College of Arts & Sciences, also estimate 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. 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.

“One remarkable thing about seagrass meadows is that, if restored, they can effectively and rapidly capture carbon dioxide from the atmosphere, possibly helping to slow climate change,” said McGlathery, one of the study\’s authors and lead investigator of the Virginia Coast Reserve Long Term Ecological Research Project. “Our research over the last decade shows the importance of protecting and reestablishing these habitats.”

According to the study, seagrass meadows store 90 percent of their carbon in the soil and continue to build on this for centuries. In the Mediterranean – the geographic region with the greatest concentration of carbon identifed in 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, and at least 1.5 percent of seagrass meadows are lost every year. This study estimates that the destruction of seagrass meadows can potentially cause the release of up to 25 percent as much carbon as from terrestrial deforestation.

Seagrasses have long been recognized for their many ecosystem benefits: They filter sediment from the oceans; protect coastlines against floods and storms; and serve as vital habitats for fisheries production.

The research was led by scientist James Fourqurean of Florida International University, in partnership with U.Va.\’s McGlathery, the Spanish High Council for Scientific Investigation, the Oceans Institute at the University of Western Australia, Bangor University in the United Kingdom, the University of Southern Denmark, the Hellenic Center for Marine Research in Greece and Aarhus University in Denmark.

Several of the paper\’s authors are members of the Blue Carbon Initiative\’s Scientific Working Group, the first integrated program with a comprehensive and coordinated global agenda focused on mitigating climate change through the conservation and restoration of coastal marine ecosystems. The initiative is a collaborative effort between Conservation International, the International Union for Conservation of Nature and the Intergovernmental Oceanic Commission of UNESCO.