Great Barrier Reef at 'very high risk' of severe coral bleaching due to El Niño

The Great Barrier Reef is at very high risk of severe and widespread coral bleaching that may tip parts of it into ecosystem collapse, scientists warn as a record-strength El Niño builds in the Pacific.

Researchers told the International Coral Reef Symposium in Auckland on Tuesday that the coming event could kill coral across vast stretches of the reef and wipe out some species in particular areas, AFP reported.

The reef runs for 2,300km along the coast of Queensland in northeast Australia, roughly equivalent to the length of Britain travelled three times over. It’s the largest living structure on the Earth and among the country's biggest tourist draws.

Coral bleaching occurs when water stays unusually warm for weeks at a time. The heat causes corals to expel the algae living in their tissue, which supply most of their food and give them their colour, leaving them white and starving. Corals can recover if the water cools quickly enough, but repeated events kill them.

Morgan Pratchett, a marine conservation ecologist at James Cook University in Queensland, said the strength of this year's El Niño was a significant concern. "It's a very high likelihood that we'll see very high severity and large-scale mass bleaching on the Great Barrier Reef," he told the symposium.

Professor Pratchett said it was "not outside of the realm of possibility that the next major disturbance will lead to localised species extinctions and widespread ecosystem collapse".

El Niño is a natural cycle that turns surface waters in the central and eastern equatorial Pacific warmer than usual, shifting winds, pressure and rainfall patterns worldwide. This year's event is forecast to break records for overall strength, and warmer seas around Australia increase the likelihood of the sustained heat that triggers bleaching.

The reef is already weakened. Hard coral cover fell substantially across the reef in 2024 and 2025 after above-average water temperatures caused its sixth mass bleaching event since 2016.

Ocean acidification, caused as seawater absorbs carbon dioxide from the atmosphere, is also making it harder for new coral to grow.

Earlier this month, the reef avoided being added to the list of world heritage sites in danger despite the UN expressing what it called utmost concern about mass bleaching and the effects of climate change.

Unesco has monitored the site every year since 2021, when it first warned the listing was possible.

Bleaching isn’t the only pressure. Extreme weather, run-off from farmland along the Queensland coast, coastal development, and outbreaks of the coral-eating crown-of-thorns starfish have all damaged the reef in recent years.

Ove Hoegh-Guldberg, a professor of marine studies at the University of Queensland, said a lack of action by governments had put the future of coral reefs worldwide in doubt, and that this damage should be read as a warning of what lay ahead more broadly.

"This could be the precursor to the loss of humans," he told the symposium, according to Oceanographic Magazine.

"If you were on a big boat, like the Titanic, and someone comes up to you and says the boat's going down, you bloody well get on those lifeboats and start acting and do stuff."

He added that the response so far had not matched the scale of the problem. "We're not doing that. The ship is starting to sink in a really massive way, and we're not seeing it as what it is.”