Coral bleaching linked to local ocean temperatures

CSIRO research published in Nature Climate Change has revealed the importance of regional differences in sea surface temperature variability in determining the global distribution of coral bleaching risk.

The paper’s lead author Dr Clothilde Langlais of the CSIRO Climate Science Centre said the question is no longer if coral bleaching will occur, but how often and which areas might be a temporary safe haven for corals.

As our planet warms the risk of coral bleaching becomes more frequent and more severe, and as a consequence the recovery time between events is shortening, she said.

“Our research finds global warming is not the only driver of local coral bleaching impacts. Regional variability in ocean temperatures, driven by processes like El Niño, or even from seasonal changes, plays a critical role setting the spatial distribution of future bleaching risk,” said Dr Langlais.

The research shows that coral reefs situated south of the 15 °S latitude, including islands in southern Polynesia, Melanesia and parts of the Great Barrier Reef, could be the last regions globally to be affected by harmful coral bleaching.

Extreme El Niño events have been a major driver of severe coral bleaching events, including the recent third Global Bleaching Event that spanned an unprecedented 36-month period. As the climate warms, bleaching events are likely to recur more often, preventing corals the critical break needed for recovery.

Dr Scott Heron co-author and physical oceanographer with NOAA’s Coral Reef Watch said as oceans continue to warm due to climate change and summer temperatures are pushed to dangerously warm levels these reefs are likely, under the current warming trajectory, to be exposed to annually recurring bleaching-level heat stress events.

“In the Western Pacific, the absence of strong natural variations of ocean temperatures initially protects the coral reefs, but only a small warming increase can rapidly transition the coral reefs from a safe haven to a permanent-bleaching situation,” Dr Langlais said.

“These results can assist reef managers to identify which reef areas are at high risk of recurring bleaching events, and how reefs can be managed to protect biodiversity,” Dr Langlais said.

This research was conducted under the Pacific-Australia Climate Change Science and Adaptation Planning (PACCSAP) Program funded by the Australian Government (Department of Foreign Affairs and Trade, formerly AusAID) by authors from CSIRO, NOAA Coral Reef Watch, and the University of New South Wales.

The paper, Coral bleaching pathways under the control of regional temperature variability,

is available here.

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