The Great Barrier Reef is experiencing its fifth mass coral bleaching

Australia’s Great Barrier Reef — the world’s most extensive coral reef ecosystem — has been hit by widespread coral bleaching for the fifth time in eight years, The Guardian reports, citing a statement by the Great Barrier Reef Marine Park Authority. Aerial surveys conducted by the Reef Authority and the Australian Institute of Marine Science covered over 300 reefs and confirmed mass shallow water coral bleaching.

What’s happening? Coral bleaching is caused by above-average sea surface temperatures which expel algae which feed the coral nutrients and give them their color. Climate-induced coral bleaching can lead to reefs’ death, while ocean acidification makes conditions unfavorable for growth.

It’s a global problem: Summer 2023 — the hottest on record — contributed to mass coral bleaching in several places around the world, with almost a dozen countries affected. Under the Intergovernmental Panel on Climate Change’s most upbeat scenario coral reefs are still projected with “very high confidence” to decline by a further 70–90% by the end of this century, with losses increasing to 99% at 2°C of warming.

Huge loss for Australia: The Great Barrier Reef — designated as a World Heritage site in 1981 — contains more than 1.5k species of fish, 400 coral species, 4k mollusk species, and around 240 types of birds, according to Unesco. It spans 348k sq km and has 2.5k individual reefs and over 900 islands of various sizes and shapes.

What’s next? More research combining spatial coverage with in-water testing is necessary to gauge the damage in deeper reef habitats, according to the Reef Authority. The recovery potential for corals depends on the duration and intensity of heat stress, and prolonged or severe heat may lead to coral death.