A marine heatwave drives massive losses from the world’s largest seagrass carbon stocks

Abstract

Seagrass ecosystems contain globally significant organic carbon (C) stocks. However, climate change and increasing frequency of extreme events threaten their preservation. Shark Bay, Western Australia, has the largest C stock reported for a seagrass ecosystem, containing up to 1.3% of the total C stored within the top metre of seagrass sediments worldwide. On the basis of field studies and satellite imagery, we estimate that 36% of Shark Bay’s seagrass meadows were damaged following a marine heatwave in 2010/2011. Assuming that 10 to 50% of the seagrass sediment C stock was exposed to oxic conditions after disturbance, between 2 and 9 Tg CO2 could have been released to the atmosphere during the following three years, increasing emissions from land-use change in Australia by 4–21% per annum. With heatwaves predicted to increase with further climate warming, conservation of seagrass ecosystems is essential to avoid adverse feedbacks on the climate system.

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Fig. 1: Shark Bay World Heritage Site with spatial distribution of seagrass.
Fig. 2: Spatial distribution of organic carbon in seagrass sediments of Shark Bay.
Fig. 3: Spatial distribution of organic carbon stocks in seagrass sediments of Shark Bay.
Fig. 4: Seagrass extent change within Shark Bay’s Marine Park before (2002) and after (2014) the marine heatwave in 2010/2011.

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Acknowledgements

This work was supported by the CSIRO Flagship Marine and Coastal Carbon Biogeochemical Cluster with funding from the CSIRO Flagship Collaboration Fund and by King Abdullah University of Science and Technology through the baseline funding to C.M.D., P.M. and A.A.-O., and M.A.M. acknowledge the support by the Generalitat de Catalunya (grants 2014 SGR-1356 and 2014 SGR-120, respectively). This work is contributing to the ICTA `Unit of Excellence' (MinECo, MDM2015-0552) and is contribution no. 78 from the Marine Education and Research Center at the Institute for Water and Environment at Florida International University. A.A.-O. was supported by a PhD scholarship from Obra Social `LaCaixa'. O.S. was supported by an ARC DECRA DE170101524. M.R. was supported by the Research University grant UKM-DIP-2017-005. N.M. was supported by a Gledden Visiting Fellowship of IAS-UWA and the Medshift project (CGL2015-71809-P) and J.W.F. was supported by the US National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research programme (grant DEB-1237517). Partial laboratory analysis was supported by the Hodgkin Trust Top-up Scholarship 2013 awarded to M.R. We thank G. Bufarale and L. Collins for their assistance in collecting the cores and C. X. Pita, King Abdullah University of Science and Technology (KAUST), for the artwork in Fig. 2 and Supplementary Fig. 1. Seagrass spatial distribution in Fig. 1 from the Department of Biodiversity, Conservation and Attractions of Western Australia.

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O.S., P.L., G.A.K. and C.M.D. designed the study. A.A.O., O.S., M.R., A.E. and N.M. carried out field and/or laboratory measurements. U.M. derived geostatistical models and A.A.O. and P.M. derived dating models. K.M. and M.R. mapped seagrass area. J.W.F. and M.A.M. contributed data. A.A.O. analysed the data and drafted the first version of the manuscript. All authors contributed to the writing and editing of the manuscript.

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Correspondence to A. Arias-Ortiz.

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Supplementary Discussion, Supplementary Figures 1–4, Supplementary Tables 1–4 and Supplementary References

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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

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