A team of international scientists gathered results from 3640 observations of 946 distinct seagrass meadows across the globe show that coastal seagrass beds store up to 83,000 metric tons of carbon per square kilometre, mostly in the soils below them. In comparison, a typical land forest stores around 30,000 metric tons per square kilometre.

Seagrass key to carbon storing
The research also estimates that, although seagrass meadows occupy less than 0.2 per cent of the world's oceans, they are responsible for more than 10 per cent of all ‘blue carbon' stores buried annually in the ocean and rival carbon stores in the extensive peat deposits of mangroves.

Data sets as deep as one metre were concentrated in Florida Bay, USA, the Spanish coast of the Western Mediterranean and Shark Bay, Western Australia. The greatest concentration of carbon found was in the Mediterranean where seagrass meadows stored carbon many metres deep. According to the study, seagrass meadows store ninety per cent of their carbon in the soil and continue to build on this indefinitely.

"These results show that seagrass meadows are key sites for carbon storage and probably are far more important as carbon dioxide sinks than we realized," said Professor Kendrick from the University of Western Australia.

Meadows under threat
Seagrasses are among the world's most threatened ecosystems. Around 29 per cent of all historic seagrass meadows have been destroyed, mainly due to dredging and degradation of water quality and a further 1.5 per cent of seagrass meadows are lost each year. The study estimates that emissions from destruction of seagrass meadows can potentially emit up to 25 per cent as much carbon as deforestation on land.

"The good news is if seagrass meadows are restored they can effectively and rapidly reestablish lost carbon sinks and stores as well providing a range of other valuable ecosystem benefits, including water quality protection, and as an important biodiversity habitat," Professor Kendrick said.

The research was led by Dr James Fourqurean, a professor of biology at Florida International University, in partnership with scientists at 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, Aarhus University in Denmark and the University of Virginia. The study 'Seagrass Ecosystems as a Globally Significant Carbon Stock,' was published in the journal Nature Geoscience.

Source: University of Western Australia news release

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