Climate change disables coral bleaching protection on the Great Barrier Reef

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Science  15 Apr 2016:
Vol. 352, Issue 6283, pp. 338-342
DOI: 10.1126/science.aac7125
  • Fig. 1 Sea temperature trajectories before and during coral bleaching stress events on the GBR.

    (A) Schematic of the three temperature trajectories on the GBR during previous (the past 27 years) bleaching level thermal anomalies, where SST reached the local bleaching threshold, 2°C above the local MMM baseline. (Top, blue line) protective trajectory; (middle, red line) single bleaching trajectory; and (bottom, green line) repetitive bleaching trajectory. The black line represents diurnal temperature variation; the colored lines reflect the nighttime-only satellite data. The pre-stress period (PS) is the duration of the pre-stress pulse exceeding the MMM; the recovery period (RP) is the duration below the MMM after the pulse. The horizontal axis spans 90 days. (B) The predominant trajectory for each reef pixel (n = 115) is shown by color as for (A), except that green shows equal incidence of repetitive and protective trajectories (no pixels were predominated by the repetitive trajectory). Black pixels indicate that the local bleaching threshold (MMM+2°C) was never reached. The histogram (inset) shows the frequency of the predominant trajectories for reef pixels (table S2).

  • Fig. 2 Effects of temperature trajectories on cell death and Symbiodinium cell density of A. aspera at bleaching.

    (A) Principal coordinate ordination plot of the gene expression patterns of the apopotic genes (Bcl-2, Bak, Bok, Bax, Bak, BI, and BIR) under ambient conditions (no thermal stress; white) and the three temperature trajectories: protective (blue), single bleaching (red), and repetitive bleaching (green). Each point represents an individual coral. PC01, principal coordinate ordination axis 1; PC02, principal coordinate ordination axis 2. (B) Coral cell death (bars) and Symbiodinium density (lines) at bleaching; colors are as for (A). (C to F) In situ end labeling of coral tissue exposed to (C) ambient conditions and the (D) protective, (E) single bleaching, and (F) repetitive bleaching trajectories. Healthy haematoxylin-counterstained nuclei are stained blue, In situ end-labeled nuclei undergoing cell death are stained red.

  • Fig. 3 Projected changes in the frequency of thermal stress events, and SST trajectories, with +0.5°C, +1.0°C, and +2.0°C SST warming.

    Stress event frequency at 50-km reef pixels (A) averaged across the GBR; and spatial distribution under (B) recent conditions, and (C) +0.5°C, (D) +1.0°C, and (E) +2.0°C projections. Proportions of events from each trajectory are as follows: (F to J) protective, (K to O) single bleaching, (P to T) repetitive bleaching. Inset histograms show the percentage of reef pixels (vertical axis) with [(B) to (E)] bleaching frequency per decade (horizontal axis) or [(G) to (J), (L) to (O), and (Q) to (T)] trajectory frequency (horizontal axis) for each projected warming. Black pixels in (B), (G), (L), and (Q) indicate that no severe stress events occurred (not present in projected warming).

  • Fig. 4 Coral cover simulations under high (A, C, and E) and low (B, D, and F) CO2 emission scenarios (RCP8.5 and RCP2.6).

    This incorporates differential mortality rates associated with protective [(A) and (B)] single bleaching [(C) and (D)] and repetitive bleaching [(E) and (G)] trajectories. Colored lines represent the average coral cover among simulations; gray lines represent the trajectory of each of the 50 simulations for each scenario.

Supplementary Materials

  • Climate change disables coral bleaching protection on the Great Barrier Reef

    Tracy D. Ainsworth, Scott F. Heron, Juan Carlos Ortiz, Peter J. Mumby, Alana Grech, Daisie Ogawa, C. Mark Eakin, William Leggat

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
    • Supplementary Text
    • Figs. S1 to S8
    • Tables S1 to S8

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