Climate change threatens world's biggest seagrass carbon stores

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A new study by an international team of researchers including researchers from The University of Western Australia highlights the devastating effects of a marine heatwave on seagrass meadows at Shark Bay – one of the world’s largest remaining seagrass ecosystems.

The study, led by the Institute for Environmental Science and Technology at the Universitat Autònoma de Barcelona (ICTA-UAB) in collaboration with scientists from Australia, Spain, Malaysia, the United States and the Kingdom of Saudi Arabia, found the death of seagrasses in the Shark Bay World Heritage Site from a 2010/11 marine heat wave released up to nine million metric tons of carbon dioxide (CO2) into the atmosphere over the following three years.

This amount is roughly equivalent to the annual CO2 output of 800,000 homes, two average coal-fired power plants or 1.6 million cars driven for 12 months. It also potentially raised Australia’s annual estimate of national land-use change CO2 emissions by up to 21 per cent.

Previous international research has estimated that Shark Bay has the largest carbon stores reported for a seagrass ecosystem, containing up to 1.3 per cent of the total carbon stored in seagrass soils worldwide.

Ariane Arias-Ortiz, PhD candidate at ICTA-UAB and first author of the study said the widespread losses in the summer of 2010/11 were unprecedented in the athropocene.

“The net loss of seagrass extent was accompanied by a dramatic decline in seagrass cover. What remained was sparser, with ‘dense’ seagrass areas declining from 72 per cent in 2002 to 46 per cent in 2014,” she said.

Collaborating researchers from the Department of Biodiversity, Conservation and Attractions of Western Australia mapped 78 per cent of the Shark Bay Marine Park area within the UNESCO World Heritage Site in 2014.

They found a 22 per cent loss of seagrass habitat as compared to the 2002 baseline, equivalent to a loss of about 1,000sqkm of meadows.

Professor Pere Masqué, UAB researcher and co-author of the study said the loss was significant. “Seagrass meadows are CO2 sinks, known as 'Blue Carbon ecosystems',” Professor Masqué said.

They take up and store carbon dioxide in their soils and biomass through biosequestration. The carbon that is locked in the soils is potentially there for millennia if seagrass ecosystems remain intact.

Professor Gary Kendrick, UWA researcher and co-author said the outcome showed the significance of seagrass loss to regional and global carbon loads to the atmosphere from a single warming event.

“To meet Australia’s responsibilities to the Shark Bay World Heritage Site and to contain our carbon footprint we need immediate action to both protect and restore these iconic seagrass ecosytems,” he said.

A marine heat wave drives massive losses from the world’s largest seagrass carbon stocks is published in Nature Climate Change.

Media references

Professor Gary Kendrick (School of Biological Sciences and Oceans Institute, UWA)(+61) 448 793 090
Ariane Arias-Ortiz (UIB, Spain)  (+34) 93 581 11 91/ (+34) 667399279
Pere Masqué (Edith Cowan University (+61) 475 238 922
David Stacey (UWA Media and Public Relations Manager)     (+61 8) 6488 3229/ (+61 4) 32 637 716

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