Seagrasses can store as much carbon as forests

Researchers at The University of Western Australia (UWA) have contributed to the first global analysis of carbon stored in seagrasses, which shows they can hold as much carbon as the world’s temperate and tropical forests.

The study ‘Seagrass Ecosystems as a Globally Significant Carbon Stock’, published in the journal Nature Geoscience, provides further evidence of the important role the world’s declining seagrass meadows have to play in mitigating climate change.

Results gathered from 3640 observations of 946 distinct seagrass meadows across the globe show that coastal seagrass beds store up to 83,000 tonnes of carbon per square kilometre, mostly in the soils below them. In comparison, a typical land forest stores around 30,000 t/km².

The research also estimates that although seagrass meadows occupy less than 0.2% of the world’s oceans, they are responsible for more than 10% 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 90% of their carbon in the soil and continue to build on this indefinitely.

UWA Professors Gary Kendrick and Carlos Duarte contributed to the study led by Dr James Fourqurean, a professor of biology at Florida International University.

“These results show that seagrass meadows are key sites for carbon storage and probably are far more important as carbon dioxide sinks than we realised,” Professor Kendrick said.

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

“The good news is if seagrass meadows are restored they can effectively and rapidly re-establish 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.