In Australia, the Great Barrier Reef is undergoing a new episode of bleaching. This is the sixth since 1998, but the fourth in less than seven years. A frequency that worries researchers and bears witness to the devastating effects of global warming on our oceans, worldwide. Explanations, with three Australian specialists.
2016, 2017, 2020 and now 2022… Definitely, we keep hearing about the bleaching of the Great Barrier Reef in recent years. Listed on the UNESCO World Heritage List, the largest coral reef on the planet, which stretches for several thousand kilometers off the coast of the state of Queensland, in northeastern Australia, is undergoing these weeks a fourth major bleaching episode in just six years. About 91% of the Great Barrier would be affected, according to a new government report, published Tuesday, May 10, 2022. Is it serious? What is this bleaching due to? And why is it causing so much concern around the world? Three Australian researchers, specialists in the subject, answer our questions.
What is coral reef bleaching?
When we hear that coral is “bleaching”, we have to take it literally, explains Dr Emma Camp, marine biologist and researcher at the University of Technology Sydney. “Coral is an animal that contains microalgae in its tissues, and it is these that give it its color,” she summarizes. These algae provide resources and nutrients to the coral, and vice versa… But during stress, this crucial relationship breaks down and the coral expels the microalgae. This is why it becomes pale and white. »
A coral that discolors, until it becomes completely white, is an alarming sign that it has lost its micro-algae essential to its survival and that it is not well…
As for the representations of popular culture, which often show corals in “neon” colors, they are not really close to reality. “Fluorescent coral like in the animated film Nemo? As a coral biologist, I don’t like to see that, Emma Camp continues. Normally, corals are rather brown. When they are fluo, they are already trying to respond to a form of stress…”
What causes bleaching?
Different “stresses”, linked to a change in ambient conditions, can cause coral bleaching: “Temperature, salinity, pH, oxygen level, sedimentation… An anomaly among these conditions, and localized bleaching can be triggered! “says Emma Camp. Corals can recover if conditions improve and they recover these microalgae which provide them with energy and nutrients. But “heavily bleached corals have higher mortality rates,” said the Australian government’s recent report, a first version of which was published in March.
For now, a single factor seems to be the main cause of major bleaching events on the Great Barrier Reef: warming water, caused by climate change.
Dr David Wachenfeld is the scientific director of the Great Barrier Reef Marine Park Authority, the Australian government authority responsible for monitoring the Great Barrier Reef, which revealed the latest episode of bleaching in March. “These bleaching phenomena are often spotted during the summer (from December to February in Australia) or at the end of it, he specifies. This is the period when we logically observe a peak in the heat of the water around the Barrier Reef.”
Is this bleaching dangerous?
Scientists assure it: coral bleaching, observed all over the world, not only in Australia, represents a danger for many species… including for human beings. Emma Camp recalls that “if corals cover less than 1% of the oceans”, nearly “25% of marine biodiversity lives there or spends time there”. So inevitably, if there is danger for the Great Barrier Reef or any other coral reef, it also endangers this “wide biodiversity”, by depriving many fish and marine animals of their essential food or simply of their habitat. natural.
In the long term, there will therefore be repercussions on the human population… Disappearance of a barrier limiting the effects of natural disasters (tsunamis, storms), but also deterioration of resources and heritage on which a large economy is based: “Millions of people will be affected by a reorganization of this ecosystem”, assures Dr. Terry Hughes. Professor of marine biology at James Cook University in Queensland, he is also the founder of the Australian Research Council (ARC) Center of Excellence for studies on coral reefs. “Countries are dependent on fishing around these reefs, which are particularly rich in fish resources,” he continues. And then there will also be an effect on tourism…”
Why is the frequency of episodes worrying?
In March 2022, the Australian authority in charge of the Great Barrier Reef already pointed out that the bleaching phenomenon was observed in multiple places on the reef. In the new version of the report published in May, it specifies that of the 719 sites studied, 654 are affected.
This is the sixth major bleaching episode observed in less than twenty-five years. But what worries researchers even more is that the massive bleaching reported in March is the fourth in just seven years. A frequency that had never been observed before.
“In the 1980s”, the gap between two episodes of bleaching, then rare and localized, was “well over fifteen years, which gave the coral time to recover”, explains Terry Hugues, relying on a study released in 2018. “During the last decade (2010), this gap was six years, and we now observe gaps of only three years or even one year (2016 and 2017)! The coral no longer has time to recover…”
And if this is true for Australia, it is also the case for other reefs in the world. “The Great Barrier Reef usually gives a good overview of what’s going on elsewhere,” says Terry Hughes.