Ecologist Christian Voolstra (left) and a colleague collect coral fragments for a quick stress test to determine their resilience. Photo credit: Pete West

When ecological genomist Christian Voolstra started working on corals in Saudi Arabia in 2009, diving on the beautiful reefs was one of the greatest advantages of his job. Things have changed. “I was only back in September and was shocked,” says Voolstra, now at the University of Konstanz in Germany. “There’s a lot of rubble there. The fish are missing. The colors are missing. ”

It’s a sad, but now well-known story. In October, the Global Coral Reef Monitoring Network published the first-ever report compiling global statistics on corals and documenting the status of reefs at 12,000 locations in 73 countries over 40 years. Overall, they report, the world lost 14 percent of its corals between 2009 and 2018 – that’s around 11,700 square kilometers of coral.

“If that had happened to the Amazon, if it had turned white or black overnight, it would be all over the news, ”says Voolstra. “Because it’s underwater, nobody notices.”

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Corals are facing tough times from global warming: Longer and more frequent ocean heat waves are leading to this that corals expel their symbiotic algae (so-called zooxanthellae), making the bleached corals weak and vulnerable. Local pollution remains a problem for corals, but global warming is emerging as the predominant threat. In 2018, the International Panel on Climate Change reported that global warming of 1.5 degrees Celsius would cause global coral reefs to shrink by 70 to 90 percent (warming is currently 1.2 degrees C). A world warmer by 2 degrees Celsius would lose more than 99 percent of its corals.

There are some glimmers of hope. The Global Coral Reef Monitoring Network report shows that corals around the world can recover if they are spared hot water for about a decade. Some spots – notably the Coral Triangle in East Asia which is home to nearly a third of the world’s corals – have bucked the trend and seen coral growth. There is evidence that corals may adapt to warmer conditions. And research is flourishing to find creative ways to improve coral restoration, from selectively growing super corals to distributing probiotics on stressed reefs.

“I’m hopeful,” says Voolstra. But it takes a lot of quick action, he says, and even then we won’t be able to save all of the reefs. “That’s impossible. The point is, you’re saving some reefs so they can survive the dark ages of climate change.”

Hard corals have been on the reefs since 1978, when the Global Coral Reef Monitoring Network began collecting data The world was relatively stable for decades. That changed dramatically with the first global mass bleaching event in 1998. Warm water around the world, largely caused by a strong El Niño, wiped out about 8 percent of the world’s living corals, making a total area of “The whole drama started in 1998,” says David Souter, coordinator of the Global Coral Reef Monitoring Network and researcher at the Australian Institute of Marine Science in Townsville it takes months, we see real problems. “

Amazingly, however, the global coral cover was up until 2010 e almost back to the pre-1998 level. “That is good news,” says Souter. “Although reefs were demolished, they came back up.” When “old” corals are wiped out, the new ones that move in are often faster-growing, more weed species (just like trees after a forest fire), says Souter. It’s great to have this growth, he says, but these opportunistic corals are often more prone to disease, heat, and storms.

A global decline has largely been the trend since 2010 for corals to fall back below 1998 levels leaves. This is in large part due to two other global bleaching events in 2010 and 2015-2017 that didn’t give corals enough respite. There has been a tiny 2 percent increase in live corals since 2019, though it’s too early to say if this could continue. “If you were a really optimistic person, you could say that this also happened at high temperatures, so we might see an adjustment,” says Souter.

During the long, relatively stable and healthy period for corals in the In the 1990s and early 2000s, the average reef was roughly 30 percent live hard corals and 15 percent macro algae such as algae and turf. That is twice as many corals as algae. Since 2009, that ratio has dropped to around 1.5 as reef macroalgae boomed 20 percent. Although algae also make for a productive ecosystem, it is not the same as the complex architecture of reefs and supports various fish.

Fortunately, the so-called Coral Triangle of the East Asian Seas stands out as a bold exception. This region is home to almost a third of the world’s coral reefs – and despite rising water temperatures, it is home to anomalously more living hard corals and less macroalgae than in the early 1980s. This is believed to be due to the genetic diversity of the region’s 600 species of coral, which allows corals to adapt to warm waters. “Perhaps the diversity offered some protection,” says Souter, while a healthy population of herbivorous fish and sea urchins keeps algae down.

The other three major global regions for corals – the Pacific, which accounts for more than a quarter of the global total contains; Australia with 16 percent; and the Caribbean with 10 percent – all of which have fewer corals today than when the measurements began. “The Caribbean is a really tragic and desperate case,” says Voolstra, with only about 50 species of coral and one new disease wiping them out.

Things could get worse, Souter notes. “The reefs are, on average, probably doing better than I thought,” he says. “The fact that the reefs retain the ability to rebound is amazing.”

Given the harsh conditions, coral conservationists around the world are working to protect corals from pollution and to actively restore them. A recent study led by Lisa Boström-Einarsson of James Cook University in Australia scoured the literature and found more than 360 coral restoration projects in 56 countries. Most focus on transplanting pieces of coral from a flowering spot to a difficult spot, or “gardening” and planting baby corals in nurseries. It also includes innovative efforts like using electricity to calcify artificial reefs (an old but still controversial idea) and using a diamond saw to cut tiny, fast-growing microfragments from slow-growing coral.

Other researchers are running pilots to spray coral larvae on reefs that need it most – this should be faster and easier than manually planting corals, but it is still unclear how many of the larvae will survive. “If it works, it will make much bigger profits faster,” says Souter.

Boström-Einarsson and colleagues found an encouragingly high average survival rate of 66 percent for the restored corals in these 362 projects. But behind these lucky numbers are more sobering facts. Almost half of the projects were in just a few countries; most lasted less than 18 months; and the average size was a tiny 100 square feet. Worse, the coral gains were often temporary. In one case in Indonesia, a three-year project resulted in a dramatic increase in coral cover and fish – which were then decimated by a heat wave six months after the project ended.

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Such efforts are still rewarding and raising awareness about corals, says Voolstra. But there are some techniques that could make them far more effective and far larger.

One bold strategy is to selectively grow corals to create super strains that are best adapted to a warmer world – but that job is still very preliminary. “It takes longer to grow and raise corals than cows, so we have been more focused on finding heat-resistant individuals that already exist than creating new ones in the laboratory,” says Stephen Palumbi of Stanford University, a marine biologist who focuses on corals around the Pacific island nation of Palau. Palumbi has developed a tank that will heat test small samples of coral on site and is now working to make it cheaper – in part by borrowing components from the home brewery. Voolstra has also developed a tool for stress tests on site; He received $ 4 million from the Paul Allen Foundation this summer to expand his efforts worldwide.

However, heat tolerance isn’t the only thing corals need. Choosing those who can survive the heat can also inadvertently choose those who are less resistant to disease or grow more slowly, for example. “We need to understand that better,” says Voolstra.

Another strategy is to optimize the organisms that live in and around corals and help them grow, including the symbiotic zooxanthellae and bacteria. Getting corals to adopt heat-tolerant zooxanthellae is a great idea that could theoretically have a huge impact, says Voolstra, but it’s tough to implement. The connection is like an intimate marriage, and it’s hard to change. Altering the coral’s bacteria, which tend to live on a layer of slime on the outside of the coral, is easier and appears to improve the coral’s overall health. “They bleach the same way, but they recover better,” says Voolstra. A recent study led by microbiologist Raquel Peixoto of King Abdulla University showed that lathering corals in probiotics could improve coral survival after a heat wave by 40 percent. “It’s still experimental and conceptual,” says Peixoto, who is experimenting with robotic submarines that could dump slow-release probiotic pills on reefs to slowly release bacteria over weeks.

Another option that in Australia is played the idea is to lighten clouds over a reef to protect them from extreme heat. “That is a completely left-wing field,” laughs Souter, but it should work just like cloud seed for agriculture: A sprayed seawater mist promotes cloud formation and protects the soil from direct light radiation. This year researchers tested the idea; they have not yet published their results. If it worked, scaling it up would be a huge project: they figure it would take a thousand stations, each with hundreds of sprayers, to reduce solar radiation by about 6.5 percent over the Great Barrier Reef during a heat wave. Questions remain as to whether the effort would be worth the energy costs and what would be the net impact on ecosystems across the region.

To see what actually works, much more needs to be done on the practicality of these strategies, according to Voolstra. “Then you put a lot of money into what really makes a difference,” he says. Different reefs require different solutions, which is what makes all of these strategies important, says Peixoto. “Everyone’s hands are on deck.

In the meantime, Voolstra supports the idea of ​​investing heavily in protected areas: places like the northern Red Sea, where corals are already adapted to deal with hot water, but by other factors such as sewage, pollution, construction and fish farms are threatened. Local efforts to address non-climatic threats to corals can be very effective. The Belize Barrier Reef Reserve System, for example, was removed from the list of endangered world natural heritage sites in 2018 after it came to protecting this ecosystem and banning oil production.

If protecting a handful of refuges from humans does not seem big enough, have Researchers last year also started a project to build an emergency Noah’s Ark for corals in global aquariums to keep their genetic diversity alive in tanks on land.

As the 2018 IPCC stated that 99 percent of corals would be lost in a world 2 degrees Celsius warmer, says Voolstra, that is really shocking. The goal now is to reduce that 99 percent to 90 percent or less, he says, so that the reefs have at least a chance to recover. “Whatever we do, it gets way worse before it gets better.”

Nicola Jones is a freelance journalist based in Pemberton, British Columbia, just outside of Vancouver. With a background in chemistry and oceanography, she writes on the natural sciences, mostly for the journal Nature. She has also contributed to Scientific American, Globe and Mail, and New Scientist, and is a science writer at the University of British Columbia.

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The Navy has confirmed that the construction of the base damaged the corals. Jeju divers, the Haenyeo, have noticed, as have marine scientists.

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