Great Barrier Reef: the world's largest coral reef – and new hope from the lab

The Great Barrier Reef off the coast of Queensland in north-eastern Australia is the largest coral reef on Earth. It stretches for more than 2,000 kilometres and can even be seen from space. But this natural wonder is under pressure: between 1998 and 2022, extreme heat triggered six mass bleaching events, followed by another in 2024, researchers at Lancaster University noted. At the University of Sydney's research station on One Tree Island, 66 percent of the monitored colonies were bleached by February 2024, rising to 80 percent by April.

A new Stanford University study, published on 14 October in the journal Science Advances, now offers hope – for the time being in the lab. The researchers tested ten pairs of coral fragments from the same colonies, each pair made up of one healthy and one bleached piece. In five pairs the fragments touched; in the other five they were separated by a few millimetres. All bleached pieces in contact fully recovered within seven weeks, while the separated ones died. The vital algae moved in within three days; one week of contact was enough, and in some cases five days.

The method cannot yet be applied to real reefs, the authors acknowledge, because every bleached coral would need a genetically identical healthy partner. Next, they want to test ways of transferring the algae without direct contact. How urgently solutions are needed is shown by the toll at One Tree Island: by July 2024, 44 percent of the bleached colonies there had died, even though the area has a "highly protected status", according to researcher Shawna Foo.