Fears have mounted that the Great Barrier Reef could be hit by the most severe mass coral bleaching event on record after an environmental group released footage showing damage up to 18 meters below the surface.
Dr Selina Ward, a marine biologist and former academic director of the University of Queensland's Heron Island Research Station, said this was the worst bleaching she had seen in 30 years of working on coral reefs, and some corals were starting to die.
Great Barrier Reef Marine Park Authority He said last week Aerial surveys of more than 1,000 individual reefs revealed that more than half were classified as experiencing high or very high levels of bleaching, and that a smaller number to the south – less than 10% of the total – were experiencing severe bleaching. Only about a quarter of them were relatively unaffected.
She confirmed that the 2,300-kilometre-long coral reef system was witnessing the fifth mass bleaching event in eight years. The authority said sea surface temperatures were between 0.5 degrees Celsius and 1.5 degrees Celsius hotter than expected for this time of year.
On Thursday, the Australian Marine Conservation Society published videos and photos that it said showed that bleaching in the southern part of the reef had extended to greater depths than previously reported this year.
Ward said the impact of bleaching was widespread across the 16 sites she visited in the reef's southern section, affecting coral species that were normally resistant to bleaching. Some corals have begun to die, a process that usually takes weeks or months after bleaching occurs.
“I feel devastated,” she said. “I've been working on coral reefs since 1992 but this [event]”I'm really suffering.”
Quick guide
What is coral bleaching?
Displays
Coral bleaching describes a process in which a coral expels algae that live in its tissues, giving it its color and many of its nutrients.
Without its algae, the coral's white skeleton can be seen through its translucent flesh, giving a bleached appearance.
Massive coral bleaching over large areas, first observed in the 1980s around the Caribbean, is caused by rising ocean temperatures.
Some corals also display fluorescent colors under stress when they release a pigment that filters the light. Sunlight also plays a role in stimulating the bleaching process.
Coral reefs can survive bleaching if temperatures are not extremely high or prolonged. But extreme marine heat waves can kill coral reefs instantly.
Coral bleaching can also have near-fatal effects, including increased susceptibility to disease and decreased rates of growth and reproduction.
Scientists say the gaps between bleaching events are becoming too short to allow coral reefs to recover.
Coral reefs are one of the planet's ecosystems most at risk from global warming. Coral reefs support fisheries that feed hundreds of millions of people, as well as major tourism industries.
The world's largest coral reef system – Australia's Great Barrier Reef – has suffered seven mass bleaching events since 1998, of which five have occurred in the past decade.
Ward said sea temperatures at two of the sites she visited were the same at the surface and 20 meters below the surface. She said this was “highly unusual” and reinforced the need for rapid action to reduce greenhouse gas emissions.
“What do we do to prevent the loss of coral reefs?” Ward said. “We cannot expect to save the Great Barrier Reef and open up new fossil fuel developments. It is time to act and there are no more excuses.”
Coral bleaching occurs when coral undergoes heat stress and expels tiny marine algae, known as zooxanthellae, that live in its tissues and give most of its color and energy. With the Zooxanthellae gone, the coral starves and its white calcium skeleton becomes visible.
If the high temperature does not continue for long, the coral reefs can recover. Otherwise, it begins to die. In severe cases, the bleaching process is skipped and the coral dies almost immediately, usually turning a dirty brown color.
Terry Hughes, an emeritus professor at James Cook University and a long-time coral bleaching researcher, said aerial surveys showed “the most widespread and most severe mass bleaching and mortality event ever recorded on the Great Barrier Reef.”
He said the extent of the damage was comparable to 2016, the previous worst year the world had seen, but there were now fewer individual reefs untouched by bleaching between southern Queensland and the Torres Strait. He said the area south of Townsville had been particularly hard hit this year.
“We are already seeing widespread coral loss at the time of peak bleaching,” he said. “It is heartbreaking to see damage this severe so quickly.”
Hughes said every part of the reef system has been bleached at least once since 1998. Some corals have been bleached three or four times. He said the cumulative damage has made it difficult for coral reefs to recover and they are likely to succumb.
The Intergovernmental Panel on Climate Change found in 2018 that most coral reefs are tropical We will lose out if global warming is limited to an average of 1.5°C Above pre-industrial levels, 99% of them would have likely lost heating reaching 2°C. They found that they would be at greatest risk when the temperature reached 1.2 degrees Celsius, which is the level of 1.2 degrees Celsius. It may have already been reached.
This year the unbleached corals are colored blue.
This is the most widespread and most severe mass bleaching and mortality event ever recorded on the Great Barrier Reef. https://t.co/eE5LCrSwtL
– Terry Hughes (@ProfTerryHughes) April 9, 2024
Dr Lisa Schindler, ecologist and coral reef campaign manager at the Australian Marine Conservation Society, called on the Great Barrier Reef Marine Park Authority to release maps showing the extent and severity of bleaching so the public has a true picture of the scale of bleaching. impact.
Schindler also urged the body, which she described as the guardian of coral reefs, to play a greater role in advocating for stronger action on emissions.
She said the body had in the past called for “strong and rapid national action” to deal with the climate crisis, but its most recent climate statement focused on global action and said nothing about Australia’s need to step up. .
“If the Albanian government is serious about its commitment to UNESCO to protect coral reefs, it must commit to net zero emissions by 2035 and stop approving new fossil fuel projects,” she said.
Scientists said the government's emissions reduction targets – a 43% cut compared to 2005 levels and net zero by 2050 – are consistent with global action that could see global temperatures rise by 2 degrees Celsius.
In an interview with ABC Radio National on Wednesday, Environment Minister Tanya Plibersek said the government was “very concerned about the bleaching that we're seeing at the moment, unfortunately, not just in the Great Barrier Reef, but around the world.”
She said the government was doing “everything we can” to reach net zero emissions. “We need to protect coral reefs because they are…unique in the world, and 64,000 people depend on them for their work,” she said.
A spokesman for the Coral Reef Authority said it confirmed in early March that widespread coral bleaching was beginning to unfold. They said that coral surveys in the waters are continuing, and a report containing data and maps will be published “in the coming weeks.”
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