New drone footage shows that 97% of corals on a reef on Lizard Island have died following mass bleaching last summer

Last summer, the Great Barrier Reef experienced its worst coral bleaching event on record. Our new data shows the devastating damage the bleaching has caused to a reef near Lizard Island – a finding that does not bode well for the rest of this natural wonder.

A colleague collected drone images of North Point Reef on Lizard Island in March this year and we reproduced his image collection this month. The results show that more than 97% of the bleached coral on North Point Reef has now died.

This is the first quantitative assessment of coral mortality since the last mass bleaching event. We don’t know how much coral has died outside of this reef. But we do know that according to other aerial surveys, nearly a third of the Great Barrier Reef experienced “very high” and “extreme” levels of coral bleaching last summer.

If Australia wants to preserve the Great Barrier Reef’s World Heritage status – or even conserve the reef at all – we must act now to prevent further coral deaths.

Damage measurement

Bleaching occurs when corals expel algae from their tissues into the surrounding water, usually due to heat stress. This causes the corals to turn white, starved, and more susceptible to disease. Some corals die immediately. Others can recover when conditions become more favorable.

The Great Barrier Reef has experienced five mass bleaching events in the past decade – the most recent in March this year. It was the most severe and widespread mass bleaching event ever recorded there. The tragedy was part of the world’s fourth global coral bleaching event, a declaration based on significant bleaching in both hemispheres of each ocean basin due to intense ocean heat stress.

Not all coral bleaching causes death – it can recover. We wanted to find out how many corals affected by coral bleaching in March were still alive three months later.

In March, George Roff from CSIRO documented North Point Reef at Lizard Island using drone imagery. We replicated his images in June by flying drones over the reef and then snorkelling over the area to observe the situation first hand.

The drones flew at an altitude of about 20 meters and collected images at set times. We then stitched the images together to create two large maps of the reef – one for March and one for June.

The first map showed that corals were bleaching or “fluorescing” – they appeared brightly colored as they released algae. The June map showed that more than 97% of the same corals had died.

Four experts independently assessed the condition of each coral in designated areas on North Point Reef, allowing us to present our findings at North Point with a high degree of confidence.

looking ahead

The Australian Institute of Marine Science will reportedly release its annual report on the state of coral reefs later this year. UNESCO this week expressed its “extreme concern” about mass coral bleaching and called on Australia to make the extent of coral deaths public “as soon as possible”.

Our data suggest that an immediate action plan is needed to determine the extent of coral loss on the Great Barrier Reef. This should include the use of remote sensing technologies such as drones and remotely operated underwater vehicles to efficiently monitor large areas. Both methods can provide standardized data and images of reefs from shallow to deeper areas, providing baseline data for future research.

It is important that this data is made available to those who want to use it. Many scientists, tourists and commercial operators also collect data on the reef. Making all data available free of charge will help improve and update our understanding of reef health, which will ultimately lead to better decisions.

We now have more data on the Great Barrier Reef than ever before – and we need better systems to support open science. And if we are serious about maintaining the health of the reef, Australians must take their international climate commitments seriously and take swift action to reduce greenhouse gas emissions.