According to a study, more than half of the corals on the Great Barrier Reef have been lost to bleaching due to climate change in the past 25 years.
Experts who examined the condition of the Australian reef system – one of the seven natural wonders of the world – reported that it is disappearing faster than thought.
Man-made climate change accelerates so-called bleaching episodes, in which corals lose their vital symbiotic algae, turn white and can finally die.
More than half of the corals on the Great Barrier Reef have been lost to bleaching in the past 25 years due to climate change. One study found that Pictured is a coral on the reef
VIRUS AIDS CORAL BLEACHING EVENTS
Researchers at Oregon State University in the US have found that infection aids in coral bleaching.
The team compared the viral metagenomes of coral colonies in Mo & # 39; orea, French Polynesia, during a minor bleaching event in 2016.
"After analyzing the viral metagenomes of each pair, we found that bleached corals were more likely to have eukaryotic virus sequences," said the author and Adriana Messyasz.
"Unbleached corals had higher frequencies of bacteriophage sequences," he added.
"This gave us the first quantitative evidence of a shift in viral assemblages between states."
Eukaryotic viruses are those that infect animals, while bacteriophages selectively infect bacteria.
The team also found that bleached corals have higher levels of a new type of "giant virus" that may aid bleaching.
The full results of the study were published in the journal Frontiers in Marine Science.
"We found that the numbers of small, medium, and large corals on the Great Barrier Reef have decreased by more than 50 percent since the 1990s," said Terry Hughes, paper writer and marine biologist of the University of Queensland, Australia.
"The decline occurred in both shallow and deeper water, and in virtually all species – especially branched and tabular corals."
"These were hardest hit by record-breaking temperatures that led to mass bleaching in 2016 and 2017."
Branched and table-shaped corals form structures on the reef that are important to other marine life such as fish.
Their loss serves to reduce the population and productivity of seafood.
The reef off the Queensland coast is so large it can be seen from space. It is home to the largest collection of living organisms on earth, including around 1,500 species of fish.
The Great Barrier Reef is larger than the Great Wall of China and extends for approximately 1,400 miles in an area of approximately 133,000 square miles.
When ocean temperatures are too high, corals expel their colorful symbiotic algae, which provide them with food – and turn them a bleached white.
If the ocean cools down fast enough, the expelled algae can return, but if it stays too hot for too long, the corals will begin to starve.
Studying changes in coral population can provide valuable insight into how the reef has responded to past pressures and how it is likely to evolve in the future.
Researchers studying the condition of the Australian reef system – one of the seven natural wonders of the world – concluded that it is disappearing faster than thought. Man-made climate change accelerates so-called bleaching episodes, in which corals lose their vital symbiotic algae, turn white and can finally die
In their study, Professor Hughes and colleagues documented the changes in the size of individual colonies along the length of the reef between 1995 and 2017.
"Colonies, both small and large, have become increasingly rare," said paper author Andy Dietzel of the ARC Center of Excellence for Coral Reef Studies in Queensland.
"This indicates a decline in the reproduction, recreational potential and long-term resilience of coral populations."
"We measured changes in colony size because population studies are important to understand the demographics and breeding ability of corals."
"A vibrant coral population has millions of small and large baby corals – the big mums that produce the most larvae."
"Our results show that the Great Barrier Reef's ability to recover – its resilience – is compromised compared to the past with fewer babies and fewer large adult breeders."
The researchers said there was an urgent need for better data on the demographic change of the corals that make up the Great Barrier Reef.
"If we are to understand how coral populations are changing and whether or not they can recover between disruptions, we need more detailed demographics – on recruitment, reproduction, and structure of colony size," said Dr. Dietzel.
The Great Barrier Reef consists of more than 2,900 individual reefs and around 900 islands – and is larger than the whole of Great Britain.
The natural wonder is home to around 1,625 species of fish, 3,000 molluscs and 30 different species of whales and dolphins.
"We used to think that the Great Barrier Reef was protected by its size," commented Professor Hughes.
"However, our results show that even the largest and relatively well-protected reef system in the world is increasingly endangered and in decline."
The Great Barrier Reef consists of more than 2,900 individual reefs and around 900 islands – and is larger than the whole of Great Britain. The natural wonder is home to around 1,625 species of fish, 3,000 molluscs and 30 different species of whales and dolphins
Climate change is leading to an increase in the frequency of disruptions such as marine heat waves that can damage the reef's corals.
The team found that coral colonies in the northern and central Great Barrier Reef deteriorated more steeply after the mass bleaching events in 2016 and 2017 – along with damage to the southern population after record temperatures in early 2020.
"There is no time to lose – we have to drastically reduce greenhouse gas emissions as soon as possible," warned Dr. Dietzel.
The full results of the study were published in Proceedings of the Royal Society B.
Corals drive away tiny seaweed when sea temperatures rise, causing them to turn white
Corals have a symbiotic relationship with a tiny marine alga called "zooxanthellae" that live inside and feed them.
When sea surface temperatures rise, corals drive away the colorful algae. The loss of the algae causes them to become pale and white.
These bleached states can last up to six weeks, and while corals can recover when the temperature drops and the algae return, heavily bleached corals die off and become covered in algae.
In both cases, it is difficult to distinguish healthy satellites and dead corals from satellite images.
This bleach recently killed up to 80 percent of coral in some areas of the Great Barrier Reef.
Bleaching events of this kind are four times more common worldwide than before.
An aerial view of the Great Barrier Reef in Australia. The Great Barrier Reef corals were bleached twice in a row in 2016 and earlier this year, raising concerns among experts about the reefs' ability to survive under global warming