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    Seagrass extent change within Shark Bay's Marine Park before (2002) and after (2014) the marine heat wave in 2010-11 - Arias-Ortiz etal 2018

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Blue Carbon stocks and losses in the iconic Shark Bay World Heritage Area

Seagrass ecosystems have been identified as long-term carbon sinks whose conservation could serve as a tool to mitigate carbon emissions. Shark Bay, in Western Australia, contains one of the largest (4,300 km2) continuous seagrass meadows in the world, occupying between 0.7 and 2.4% of the world seagrass area. Seagrasses colonised Shark Bay's seafloor about 8,000 yr ago and its continuous growth has stimulated carbon biosequestration.  CMER’s blue carbon team has been studying the role of Shark Bay’s seagrass in capturing and storing carbon, and assessing the impacts of the 2011/12 marine heatwave on seagrass ecosystem dynamics in the bay, including the assessment of carbon dioxide emissions to the atmosphere resulting from seagrass losses.

Our major activities and findings to date are:

  • After conducting an extensive field survey of seagrass soil cores across the Bay, (complete dataset available here), we estimated that Shark Bay seagrass sediments contain up to 1.3% of the total carbon stored in the upper meter of seagrass soils worldwide (refer article here ).
  • A marine heatwave impacted Western Australia in summer 2010-2011, resulting in extensive losses or reduced density of the dominant seagrass Amphibolis antarctica, and to a minor extent Posidonia australis. Joining forces with the Department of Biodiversity, Conservation and Attractions (DBCA), we estimated that Shark Bay host 4,300 km2 of seagrass (~1% of global seagrass area), and that at least 1,000 km2 of meadows were impacted across the entire Bay, with about 36% of all the dense seagrass meadows in 2002 converting to either sparse seagrass or sand in 2014 (refer article here ).
  • We have assessed the potential effects that the heatwave-associated mortality event had on seagrass ecosystems and their C stores. Between 2 and 9 million metric tons of carbon dioxide would have been released during the following three years after the event. This amount is roughly the equivalent to the annual CO2 output of 800,000 homes, two average coal-fired power plants or 1,600,000 cars driven for 12 months. It also potentially raised Australia’s annual estimate of national land-use change CO2 emissions by up to 20% per annum.
  • This release of carbon as CO2 will only cause further heating of the atmosphere and the oceans, reflecting evidence for the potential feedback of heatwaves on climate change through the destruction of ecosystems that are global hotspots for organic carbon storage, such as the Shark Bay World Heritage Area.

Conservation of seagrass meadows and their millenary soil C deposits is key to mitigate climate change. With increasing frequency of extreme events, there is a necessity to predict the response of seagrass ecosystems to global change threats. Our research provides insights for the building resilience for mitigation through management actions.

Key Media:

Australia’s hidden opportunity to cut carbon emissions, and make money in the process

Seagrass research key to fighting climate change

Carbon emissions from seagrass sediments triggered by a marine heat wave

Shark Bay seagrass loss during ocean heatwave released up to 9m tonnes of CO2, scientists say

Marine heatwave set off 'carbon bomb' in world's largest seagrass meadow

'Unprecedented' marine heatwave triggered huge carbon-dioxide release

Research finds major carbon emissions from Shark Bay heat wave

Key publications:

O. Serrano, A. Arias-Ortiz, C.M. Duarte, G. A. Kendrick, P. S. Lavery (in press). Impact of marine heatwaves on seagrass ecosystems. Springer, Ecosystem Collapse and Climate Change.

Arias-Ortiz, A., Serrano, O., Masqué, P. et al. A marine heatwave drives massive losses from the world’s largest seagrass carbon stocks. Nature Clim Change 8, 338–344 (2018). https://doi.org/10.1038/s41558-018-0096-y

Researchers

Dr Oscar Serrano
Professor Paul Lavery
Professor Pere Masque
Ariane Arias Ortiz - University of California

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