Diminishing international seagrass meadows key sites for carbon storage

TWO researchers from The University of WA (UWA) have contributed to the world’s first global analysis of carbon stored in seagrasses, which showed that the plants could hold as much carbon as temperate and tropical forests.
Seagrass Ecosystems as a Globally Significant Carbon Stock was published in the journal Nature Geoscience and provided further evidence of the important role that the world’s declining seagrass meadows have to play in mitigating climate change. In a statement, UWA said that results gathered from 3640 observations of 946 distinct seagrass meadows across the globe had shown that coastal seagrass beds stored 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,” the university stated.
The research also estimated that although seagrass meadows occupied less than 0.2 per cent of the world’s oceans, they were responsible for more than 10 per cent of all ‘blue carbon’ stores buried annually in the ocean, which generally rival carbon stores in the extensive peat deposits of mangrove trees.
Data sets as deep as 1m below seagrass beds were concentrated in Florida Bay in the US; off the Spanish coast of the Western Mediterranean; and in Shark Bay, WA.
“The greatest concentration of carbon found was in the Mediterranean where seagrass meadows stored carbon many metres deep,” UWA stated.
According to the study, seagrass meadows stored 90 per cent of their carbon in soil and continued to build on their stores indefinitely.
UWA professors Gary Kendrick and Carlos Duarte contributed to the study which was led by Florida International University biology professor Dr James Fourqurean.
“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: about 29 per cent of all historic seagrass meadows have
been destroyed, mainly due to dredging and degradation of water quality, and it is estimated that a further 1.5 per cent of the world’s existing seagrass meadows are lost each year. The study undertaken on seagrass carbon storage found that emissions from the destruction of seagrass meadows could contribute up to 25 per cent as much carbon as deforestation on
land.
“The good news is [that] 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.

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