Commentary: reconstructing four centuries of temperature-induced coral bleaching on the great barrier reef

Hoegh-Guldberg, Ove, Skirving, William J., Lough, Janice M., Liu, Chunying, Mann, Michael E., Donner, Simon, Eakin, C. Mark, Cantin, Neal, Carilli, Jessica, Heron, Scott Fraser, Miller, Sonya, and Dove, Sophie (2019) Commentary: reconstructing four centuries of temperature-induced coral bleaching on the great barrier reef. Frontiers in Marine Science, 6. 86.

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Coral reefs are spectacular ecosystems found along tropical coastlines where they provide goods and services to hundreds of millions of people. While under threat from local factors, coral reefs are increasingly susceptible to ocean warming from anthropogenic climate change. One of the signature disturbances is the large-scale, and often deadly, breakdown of the symbiosis between corals and dinoflagellates. This is referred to as mass coral bleaching and often causes mass mortality. The first scientific records of mass bleaching date to the early 1980s (Hoegh-Guldberg et al., 2017).

Kamenos and Hennige (2018, hereafter KH18), however, claim to show that mass coral bleaching is not a recent phenomenon, and has occurred regularly over the past four centuries (1572–2001) on the Great Barrier Reef (GBR), Australia. They support their claim by developing a putative proxy for coral bleaching that uses the suggested relationship between elevated sea surface temperatures (SSTs) and reduced linear extension rates of 44 Porites spp. coral cores from 28 GBR reefs. If their results are correct, then mass coral bleaching events have been a frequent feature for hundreds of years in sharp contrast to the vast majority of scientific evidence.

There are, however, major flaws in the KH18 methodology. Their use of the Extended Reconstructed Sea Surface Temperature (ERSST) dataset (based on ship and buoy observations) for reef temperatures from 1854 to 2001, ignores the increasing unreliability of these data which become sparse, less rigorous, and more interpolated going back in time. To demonstrate how the quality of these data degrades, we plot the average number of SST observations per month that contribute to each 200 x 200 km ERSST pixel (Figure 1A, black line). Note that from 1854 to 1900 the four ERSST pixels used by KH18 averaged only 0.85 observations per month, and 82% of these months had no observations at all. Given the heterogeneous nature of SST at local and regional levels, using such broad-scale data as ERSST, is likely to produce substantial errors at reef scales (Figure 1A, red line prior to 1900).

Item ID: 59758
Item Type: Article (Commentary)
ISSN: 2296-7745
Keywords: 400 years; climate change; coral bleaching; errors; ERSST datasets; mortality
Copyright Information: Copyright © 2019 Hoegh-Guldberg, Skirving, Lough, Liu, Mann, Donner, Eakin, Cantin, Carilli, Heron, Miller and Dove. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0)
Funders: ARC Centre of Excellence for Coral Reef Studies, Australian Research Council (ARC), National Oceanic and Atmospheric Administration (NOAA)
Projects and Grants: ARC Laureate Fellowship, NOAA grant NA14NES4320003
Date Deposited: 26 Aug 2019 02:33
FoR Codes: 02 PHYSICAL SCIENCES > 0203 Classical Physics > 020399 Classical Physics not elsewhere classified @ 50%
05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050101 Ecological Impacts of Climate Change @ 50%
SEO Codes: 96 ENVIRONMENT > 9603 Climate and Climate Change > 960307 Effects of Climate Change and Variability on Australia (excl. Social Impacts) @ 50%
96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960507 Ecosystem Assessment and Management of Marine Environments @ 50%
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