SYDNEY • The world's southernmost coral reef has been hit by bleaching this summer, Australian scientists said yesterday, as they warned that rising sea temperatures from climate change were affecting even the most isolated ecosystems.

The corals off Lord Howe Island - about 600km from Sydney - were affected by elevated temperatures this summer despite escaping severe bleaching that damaged the Great Barrier Reef in 2016 and 2017.

"It's a canary in the coal mine that we are seeing bleaching at this very isolated southernmost reef, which is worrying," Associate Professor Bill Leggat of the University of Newcastle told Agence France-Presse.

"It's just another indicator that climate change is affecting everywhere around the world. Here is a reef that is 600km from the mainland and we are seeing bleaching there in a beautiful ecosystem."

Prof Leggat and other scientists from several Australian universities and the US National Oceanic and Atmospheric Administration found severe bleaching of up to 90 per cent at Lord Howe's inshore, shallow lagoon reefs.

Deeper-water corals in the marine park, which contains species not found anywhere else and, like the Great Barrier Reef is a World Heritage site, were still "looking quite healthy" having mostly escaped the bleaching, Dr Leggat said.

He said increasing baseline temperatures caused by climate change, and local factors such as elevated temperatures in the area this summer, caused the bleaching to occur.

The scientists are set to return to Lord Howe in the next few months to find out if some corals have been so severely bleached they cannot recover.

Bleaching occurs when abnormal environmental conditions, such as warmer sea temperatures, cause corals to expel tiny photosynthetic algae, draining them of their colour.

Corals can recover if the water temperature drops and the algae are able to recolonise them.

Coral reefs make up less than 1 per cent of earth's marine environment, but are home to an estimated 25 per cent of ocean life, acting as nurseries for many species of fish.

AGENCE FRANCE-PRESSE