The relentless march of mass coral bleaching: a global perspective of changing heat stress

W J Skirving,E F Geiger,B L Marsh,J L De La Cour,C M Eakin,G Liu,S F Heron

doi:10.1007/s00338-019-01799-4

Abstract

The global coral bleaching event of 2014–2017 resulted from the latest in a series of heat stress events that have increased in intensity. We assessed global- and basin-scale variations in sea surface temperature-based heat stress products for 1985–2017 to provide the context for how heat stress during 2014–2017 compared with the past 3 decades. Previously, undefined “Heat Stress Year” periods (used to describe interannual variation in heat stress) were identified for the Northern and Southern Hemispheres, in which heat stress peaks during or shortly after the boreal and austral summers, respectively. The proportion of reef pixels experiencing bleaching-level heat stress increased through the record, accelerating during the last decade. This increase in accumulated heat stress at a bleaching level is a result of longer stress events rather than an increase in the peak stress intensity. Thresholds of heat stress extent for the three tropical ocean basins were established to designate “global” events, and a Global Bleaching Index was defined that relates heat stress extent to that observed in 1998. Notably, during the 2014–2017 global bleaching event, more than three times as many reefs were exposed to bleaching-level heat stress as in the 1998 global bleaching.

Highlights

The global coral bleaching event spanning 2014–2017 was the longest, most extensive, most intense and probably most damaging ever recorded (Eakin et al 2017)
The average percentage of reefs with heat stress (HS C 1 °C) for each month revealed an expected result—that the minimum extent of coral stress occurred during the winter in each hemisphere (Fig. 1)
Since most of the austral heat stresses occurs in the later year of the period, we refer to the austral heat stress year (HSY) using the year in which the period ends

Summary

Introduction

The global coral bleaching event spanning 2014–2017 was the longest, most extensive, most intense (in terms of accumulated heat stress) and probably most damaging (in terms of coral mortality) ever recorded (Eakin et al 2017). HS is a positive anomaly product based on the difference between the daily sea surface temperature (SST) and the maximum monthly mean (MMM) climatology, whereas DHW is an accumulation of HS values (Liu et al 2013, 2014, 2017) Using these products, we assess global- and basin-scale variations for 1985–2017 and place the global coral bleaching event of 2014–2017 into the context of heat stress over the past 3 decades. Developed by the NOAA CRW program, the recently released CoralTemp Version 1.0 SST data product provides, for the first time, a single dataset at a resolution comparable with the scale of many coral reefs (* 5 km) that is spatially and temporally replete. Since all analyses were initially performed as either Northern or Southern Hemisphere, counts of reef-containing pixels (Table 1) were used to weight results from individual regions for the basin and global analyses

Results

Discussion

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