Winter Conditions Linked to Future Coral Bleaching Risk on Great Barrier Reef

New research from James Cook University (JCU) has found that winter conditions may play a significant role in determining how coral on the Great Barrier Reef responds to heat stress during the following summer.

The study, recently published in the journal Coral Reefs, suggests coral bleaching is influenced not only by extreme summer temperatures but also by ocean conditions months earlier during the cooler season.

JCU researcher Valerie Cornet, who led the study, said most forecasting tools currently focus on summer temperatures when predicting bleaching events.

“Most bleaching prediction tools focus on summer heat and assume that corals start each summer in the same condition,” Ms Cornet said.

“We wanted to see how cooler seasons, particularly winter, influence bleaching in the following summer.”

The research team analysed aerial and in-water bleaching observations along with sea surface temperature data across the central Great Barrier Reef between Townsville and Port Douglas, focusing on the 2016 and 2017 bleaching seasons.

Study supervisor Scott Heron said those years provided a unique opportunity to examine how coral responds to repeated heat stress.

“The scale and severity of these mass bleaching events were unprecedented, affecting vast areas of the reef,” Professor Heron said.

“This gave us a rare opportunity to study how repeated heat stress and recovery periods interacted, including effects before summer conditions set in.”

The research found that prolonged warmer winter temperatures can worsen bleaching in the following summer, while moderate winter warmth may actually help corals cope better with future heat.

“It’s a Goldilocks range –– it’s not too hot, not too cold, it’s just right,” Professor Heron said.

“We think that corals living in these conditions might be better prepared for a stressful summer because they are exposed to a little bit of prior heat.”

Researchers say incorporating winter conditions into reef monitoring systems could improve early warning systems and help guide future reef protection efforts.

Heart Reef View Great Barrier Reef Stock Photo 2512856481 | Shutterstock

CAPTION: 2016 and 2017 were the first consecutive years of severe bleaching on the GBR. Photo credit: Mikael Djavadi

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