Renowned coral expert Terry Hughes, a connection on social media, reported on this only last week.
For the fifth time in just the past eight summers – 2016, 2017, 2020, 2022 and now 2024 — huge swathes of the Great Barrier Reef are experiencing extreme heat stress. Thi has triggered yet another episode of mass coral bleaching,
Inclusive of Including two earlier heating episodes – in 1998 and 2002 – this brings the tally to seven such extreme events in the past 26 years.
The most conspicuous impact of unusually high temperatures on tropical and subtropical reefs is wide-scale coral bleaching and death. Sharp spikes in temperature can destroy coral tissue directly even before bleaching unfolds. Consequently, if temperatures exceed 2 degrees Celsius above the normal summer maximum, heat-sensitive corals die very quickly.
What is coral bleaching?
Bleaching happens when marine heatwaves disrupt the relationship between corals and their “photosynthetic symbionts” – tiny organisms that live inside the corals’ tissues and help power their metabolism.
Severe bleaching is often fatal, whereas corals that are mildly bleached can survive.
Before 1998, coral bleaching on the Great Barrier Reef was infrequent and localised. But over the past four decades, bleaching has increased in frequency, severity and spatial scale, as a result of human-induced climate change.
How bad is 2024?
Climate scientists can measure the accumulation of heat stress throughout the summer by using a metric called “degree-heating weeks” or DHW, which factors in both the duration and intensity of extreme heat exposure. The Great Barrier Reef is now a chequerboard of reefs with different recent histories of coral bleaching. Reefs that bleached in 2017 or 2016 have had only five or six years to recover before being hit again this summer – assuming they escaped bleaching during the 2020 and 2022 episodes.
Ironically, the corals that are now prevalent on many reefs are young colonies of fast-growing, heat-sensitive species of branching and table-shaped corals – analogous to the rapid recovery
*Terry Hughes is a distinguished professor at James Cook University. This article (in full) fist appeared on The Conversation.
