First Global Study: Seagrass beds can store twice as much carbon as forests

Madagascar RAP 2010; Mangroves; Seagrass; Vohemar Bay © Keith Ellenbogen/iLCP, Conservation InternationalMadagascar RAP 2010; Mangroves; Seagrass; Vohemar Bay © Keith Ellenbogen/iLCP, Mat close –up: A peat-like deposit, usually called mat or matte, of dead belowground parts of the plant has been accumulating for the past 1,200 years. This particular mat accretes about 80gC/m2/yr. © Miguel Angel Mateo, Conservation InternationalMat close –up: A peat-like deposit, usually called mat or matte, of dead belowground parts of the plant has been accumulating for the past 1,200 years. This particular mat accretes about 80gC/m2/yr. © Miguel Angel Mateo, Conservation InternationalGlobally threatened seabed areas are hotspots for carbon storage according to a paper published in the journal Nature Geoscience this week (20.5.11 doi:10.1038/ngeo1477 ). The study “Seagrass Ecosystems as a Globally Significant Carbon Stock” is the first global analysis of carbon stored in seagrass meadows.

Dr Kennedy of the School of Ocean Sciences and co-author of the paper explains: “Our study demonstrates that, per unit area, seagrass soils can store around twice as much carbon as soils in the temperate and tropical forests. Even more amazing is that, although seagrass meadows occupy less than 0.2% of the of the world’s oceans, they store 90% of their carbon in the soil year on year, making them responsible for more than 10% of carbon buried annually in the oceans. Seagrasses, which vegetate our coastal seas are unique in this regard, being able to continue to store carbon in their roots and soil. In the Mediterranean, which our study found is the geographic region with the greatest concentration of carbon, seagrass meadows will store carbon for thousands of years.”

This research has added importance, as seagrass meadows are among the world’s most threatened ecosystems. Approximately 29% 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 destruction of seagrass meadows can potentially emit as much as 10% of the carbon currently released through changes in land use in the terrestrial environment. This destruction also leads to the loss of other benefits as the meadows provide habitats and nurseries for fish and shellfish, stabilize sediments, reducing erosion and protect coastlines against floods and storms.  

Madagascar RAP 2010; Vohemar Bay, Seagrass (Syringodium isoetifolium) with epiphytes © Keith Ellenbogen/iLCP, Conservation InternationalMadagascar RAP 2010; Vohemar Bay, Seagrass (Syringodium isoetifolium) with epiphytes © Keith Ellenbogen/iLCP, Conservation InternationalDr Kennedy says: “These losses can be reversed through restoration but it would take time. Initially, the causes of seagrass loss - water quality degradation and reduced light penetration to the seagrasses - have to be treated so that the habitat can support seagrass growth again. Once a meadow is restored the carbon concentration in the soils begins to increase again and has been shown to double in around 10 years.”

Overall, the results show that seagrass meadows are key sites for carbon storage. Conserving and restoring seagrass meadows has the capacity, as proposed in “Blue Carbon” initiatives, to reduce greenhouse-gas emissions and increase carbon stores while delivering key ecosystem services to coastal communities.

Publication date: 22 May 2012