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Ecological memory modifies the cumulative impact of recurrent climate extremes


Climate change is radically altering the frequency, intensity and spatial scale of severe weather events, such as heatwaves, droughts, floods and fires1. As the time interval shrinks between recurrent shocks2,3,4,5, the responses of ecosystems to each new disturbance are increasingly likely to be contingent on the history of other recent extreme events. Ecological memory—defined as the ability of the past to influence the present trajectory of ecosystems6,7—is also critically important for understanding how species assemblages are responding to rapid changes in disturbance regimes due to anthropogenic climate change2,3,6,7,8. Here, we show the emergence of ecological memory during unprecedented back-to-back mass bleaching of corals along the 2,300 km length of the Great Barrier Reef in 2016, and again in 2017, whereby the impacts of the second severe heatwave, and its geographic footprint, were contingent on the first. Our results underscore the need to understand the strengthening interactions among sequences of climate-driven events, and highlight the accelerating and cumulative impacts of novel disturbance regimes on vulnerable ecosystems.

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Fig. 1: The bleaching response of corals on the Great Barrier Reef was diminished in a second summer heatwave, despite higher exposure to heat stress.
Fig. 2: Ecological memory of the 2016 bleaching event unfolds differently in the northern, central and southern Great Barrier Reef.
Fig. 3: Legacy effects of multiple disturbance.

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The authors acknowledge support from the Australian Research Council’s Centres of Excellence programme, Australian Institute of Marine Science and US National Oceanic and Atmospheric Administration. The scientific results and conclusions, as well as any views or opinions expressed herein, are those of the authors and do not necessarily reflect the views of NOAA or the US Department of Commerce.

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Authors and Affiliations



The study was conceptualized and led by T.P.H., who also wrote the first draft of the paper. All authors contributed to writing subsequent drafts. J.T.K. coordinated data compilation, analysis and graphics. J.T.K. and T.P.H. conducted the aerial bleaching surveys in 2016 and 2017. Underwater assessments and ground-truthing of aerial scores were performed by A.H.B., A.S.H., M.O.H., M.S.P. and G.T. S.F.H., C.M.E., G.L. and W.S. provided satellite data on heat stress. S.R.C. and M.J. contributed statistical and modelling expertise.

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Correspondence to Terry P. Hughes.

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Supplementary information

Supplementary Information

Supplementary Figures 1–4

Reporting Summary

Supplementary Movie 1

Video footage from helicopter over Beesley Island Reef (143.21° E, 12.25° S) during aerial surveys of mass coral bleaching in March 2016

Supplementary Movie 2

Underwater video footage of widespread coral mortality at Zenith Reef (143.61° E,12.77° S) during coral surveys in November 2016

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Hughes, T.P., Kerry, J.T., Connolly, S.R. et al. Ecological memory modifies the cumulative impact of recurrent climate extremes. Nature Clim Change 9, 40–43 (2019).

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