Last summer, the Great Barrier Reef suffered this worse Mass coral bleaching event. Our new data shows just how devastating the damage bleaching has done to a reef on Lizard Island – a finding that does not bode well for the rest of this natural wonder.
A colleague collected drone images of Lizard Island’s North Point Reef in March this year, and we repeated his image collection this month. The results show that more than 97% of the bleached corals on that reef are dead.
This is the first quantitative assessment of coral mortality from a past mass bleaching event. We don’t know how much coral died across this reef. But we know according to Other aerial surveysNearly a third of the Great Barrier Reef experienced “very high” and “extreme” levels of coral bleaching last summer.
Clearly, if Australia wants to retain the Great Barrier Reef’s World Heritage status – indeed, if it wants to preserve the reef – we need to act now to prevent further coral deaths.
Measuring the damage
Bleaching occurs when corals expel algae from their tissues into the surrounding water, usually due to heat stress. This causes the coral to become white, hungry and more susceptible to disease. Some corals die immediately. Others may recover too if conditions become more favorable.
The Great Barrier Reef has experienced five mass bleaching events in the past decade – the Last in March this year. It was the most severe and widespread mass bleaching event ever recorded there. Part of the tragedy was World’s fourth global coral bleaching event. This statement was based on significant bleaching in both hemispheres in every ocean basin due to widespread marine thermal stress.
Not all bleached corals will die – they can recover. We wanted to find out how many corals affected by the March bleaching event were still alive three months later.
In March, George Roff of the CSIRO documented North Point Reef on Lizard Island using drone footage. We reproduced his images in June, also flying over the reef with a drone. We then snorkelled the area to observe the situation first-hand.
The drone flew at an altitude of about 20 metres and collected photos at scheduled times. We then stitched the images together into two large maps of the rock – one for March and one for June.
The first map showed that corals were bleached or “fluorescent,” appearing brightly colored as they shed algae. The June map showed that more than 97% of the corals were dead.
Four experts independently assessed the condition of individual corals in selected areas of the North Point reef. This allows us to present our results at North Point with high certainty.
looking to the future
Australian Institute of Marine Science It is believed will release its annual report on the state of coral reefs later this year. This week, UNESCO Express “Extreme concern” about mass coral bleaching and called on Australia to make public the extent of coral loss “as soon as possible”.
Our data suggest the need for an urgent action plan to assess the extent of coral mortality on the Great Barrier Reef. This plan should include the use of remote sensing technologies such as drones and remotely operated underwater vehicles to efficiently survey large areas. Both methods can provide standardised data and images of reefs from shallow to deep areas, providing baseline data for future research.
It is important to emphasize that this data should be made available to anyone who wants to use it. Many scientists, tourists and commercial operators also collect data about the reef, and making all data freely available will help improve and update our understanding of the health of the reef. Ultimately, this will lead to better decision making.
We currently have more data about the Great Barrier Reef than ever before, and we need better systems to support open science. And if we really want to keep the reefs healthy, Australians must take international climate commitments seriously and act quickly to reduce greenhouse gas emissions.
, Jane WilliamsonProfessor of Marine Fisheries Ecology, Macquarie University, Karen JoyceAssociate Professor – Remote Sensing and Geospatial Technology, James Cook University it is Vincent RaoultFull Professor in Marine Ecology, Griffith University
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