Heart

Erinn Muller should have reason to despair. The marine biologist studies coral health in Florida, a state whose reefs have been devastated by extreme heat, increasingly ferocious hurricanes and deadly infectious diseases (SN: 6/15/23; SN: 9/13/23; SN: 7/9/19).

“We’ve lost 98 percent of our living coral cover,” says Muller, of the Mote Marine Laboratory in Sarasota, Fla. While among the hardest hit, Florida isn’t alone. From Australia’s Great Barrier Reef to the Caribbean, coral reefs globally are in trouble.

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But innovative efforts to protect and restore coral reefs buoy Muller’s hopes. She just has to visit Mote’s Caribbean king crab nursery, a project of reef restoration expert Jason Spadaro. There, tiny specks of crustaceans will grow into salad-loving foragers. Once they are set loose on nearby reefs, Maguimithrax spinosissimus eat away suffocating seaweed.

“I’m optimistic because there is really truly so much work being done” to restore coral reefs, says Tali Vardi, a marine biologist and executive director of the Coral Restoration Consortium, a global community of scientists, managers and restoration experts dedicated to helping coral reefs. While safeguarding the future of coral reefs ultimately depends on halting climate change, “we’re trying to maintain pockets of biodiversity” that can serve as a springboard for the long-term recovery of reefs.

Given how diverse coral reefs are, Vardi says, researchers need a diversity of solutions to match. “There’s no silver bullet here.”

Around the globe, coral biologists are trying everything from low-tech seaweed removal to high-tech artificial fog production to protect corals. Here’s a closer look at three projects that researchers are developing to help save coral reefs.

Sea-weeding, literally

In Australia’s Great Barrier Reef, it’s not crabs doing the weeding. It’s volunteers with Earthwatch Institute — an international environmental organization — snorkeling and diving underwater to pluck macroalgae, the weed of the sea. The volunteers’ goal is to free parts of the reef from a seaweed scourge to see if that leads to a resurgence in coral.

“There’s been this issue with increases in macroalgae versus corals for a long time,” says David Bourne. “If something’s out of whack” with the reef ecosystem, “the corals lose out and the macroalgae take over.”

Though they seem like a cross between plants and rocks, the hard corals that form reefs are actually giant colonies of tiny animals called coral polyps. The polyps secrete a hard skeleton made of calcium carbonate, and skeleton by skeleton, they build an undersea city. Tiny photosynthetic algae partners living inside the polyps give the corals their brilliant colors and generate energy for their hosts.

Seaweed, however, takes up space and soaks up light that could otherwise be used by corals. If corals decline in number due to stressors like heat or disease, seaweed can quickly proliferate and take their place.

Bourne, a marine biologist at James Cook University in Townsville, Australia, wanted to know if the seaweed-removal program being run by Earthwatch was effective. From 2018 to 2021, volunteers pruned seaweed from 24 sections of the reef — each 5 meters by 5 meters — several times per year, while leaving other seaweed-laden areas alone. In total, they removed a whopping 2,148 kilograms of seaweed.

At the start, the tended plots had enough corals to cover only about 34 square meters. Removing macroalgae from those plots led to a total gain of nearly 203 square meters of coral cover, enough to blanket a tennis court, Bourne’s team reported September 13 in the Journal of Applied Ecology. This change wasn’t seen in the plots left unpruned.

After volunteers removed suffocating seaweed from sections of Australia’s Great Barrier Reef, coral cover expanded dramatically in just a few years. These photos show the same part of the reef in May 2019 and May 2023.Hillary Smith

“It’s not surprising that we saw some recovery,” Bourne says. “What was surprising was the amount of recovery and how quickly it happened.” Sea-weeding is a straightforward way to skew the reef’s competitive balance and help corals thrive, he says.

Bourne hopes the simplicity of the approach will help it spread. “The advantage of sea-weeding is it’s really low tech; anybody can do it,” he says. Plus, seaweed tends to be an issue on reefs that are close to shore and known to local communities, “so there’s active groups that are interested in helping.”

‘Re-skinning’ a coral skeleton

Though it may sound macabre, the calcium carbonate skeletons of dead reefs can serve as vital scaffolding for new corals to flourish. “Re-skinning” a dead reef takes advantage of coral microfragments, small bits of coral polyps. Growing microfragments in the lab and then transplanting them onto reef skeletons can, in a way, bring a dead ecosystem back to life.

David Vaughan discovered the restorative potential of coral microfragments through what he calls a “eureka mistake.” Vaughan, formerly executive director of Mote and now head of the nonprofit Plant A Million Corals in Summerland Key, Fla., accidentally broke off shards of a branching coral while moving it to a new tank. Some coral polyps remained on the bottom of the tank. Vaughn assumed the tiny animals wouldn’t survive. But when he checked on them about two weeks later, he saw instead that they had quickly grown and multiplied.

Large corals grow slowly, Muller says, because they have to put a lot of energy into creating more of their calcium carbonate skeleton. If you instead affix multiple microfragments, consisting of a thin skeletal layer with a small bit of live coral tissue on top, near each other on a hard surface, they grow rapidly and fuse together. Mote scientists “hacked the biology of a lot of these slow-growing species to encourage them to put a lot of their resources into creating tissue faster,” Muller says.

Microfragments of slow-growing corals that are placed near each other on the skeleton of a dead coral will quickly grow and merge together. Coral fragments, like these pictured at Mote Marine Laboratory, can be grown in land-based nurseries.Mote Marine Laboratory

A 2018 study found that microfragments of the mountainous star coral (Orbicella faveolata) grew 10 times as much tissue over a 31-month period as the normal, larger fragments that were previously used for reef restoration. For every square centimeter of coral that was planted at the beginning of the experiment, microfragments grew an average of 3.38 square centimeters of new tissue, while larger fragments grew only 0.35 square centimeters. Ocean plantings of coral microfragments have since withstood disease, bleaching and hurricanes, and grown large enough to reproduce within several years.

“Spawning after five years,” Spadaro says, “was definitely a game changer in terms of restoration.” Re-skinning with microfragments can give you functional reef ecosystems in a fraction of the time as previous methods. Mote scientists have since shared their knowledge with others working to restore corals around the world, such as in Hawaii and the Caribbean.

Making shade

Bleaching is the dramatic outcome of great hardship; pushed to the brink by extreme stress, a strained coral belches out its symbiotic photosynthetic algae, turning stark white and losing its primary food source. Excessive heat is the most common culprit, but it’s not the only one.

Excess light can lead to bleaching, too, says Peter Butcherine, a biologist at Southern Cross University in Coffs Harbour, Australia. Too much light during photosynthesis, performed by the corals’ algae partners, leads to an abundance of toxic oxygen-containing molecules that are highly reactive and can cause cell death. Protecting corals from too much sun exposure can help prevent bleaching, but “you can’t roll out thousands of square meters of shade cloth” to shield an area the size of the Great Barrier Reef, Butcherine says.

Instead, Butcherine and others have turned to a more ephemeral approach: creating fog. “It’s essentially a sea mist,” Butcherine says. Though misting the entire Great Barrier Reef isn’t feasible, marine fog could be used to protect sensitive parts of the reef during the time of day when sunlight is at its harshest.

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Too much sunlight can lead to coral bleaching, much like excessive heat can. By creating artificial marine fog using arrays of misters mounted to ships, like what’s seen in this video, researchers hope to shield reefs such as Australia’s Great Barrier Reef from harmful rays.

Butcherine and colleagues showed that shading corals for just four hours a day can delay bleaching even when water temperatures are high, such that corals could withstand three extra weeks of bleaching-level heat. The results of that laboratory study were published in the Sept. 20 Frontiers in Marine Science. This delay could help corals hold on to their algal partners until the environment around them cools.

Because it’s still being developed, marine fogging is quite expensive; it requires large arrays of misters mounted to ships. But Butcherine is excited by the potential of using solar power, including sun-powered drones mounted with misters, to implement the technique at a wider scale, and even at other reefs around the world.

 “I’m optimistic that we can make a difference,” Butcherine says. More

Saima Iqbal is the fall 2023 science writing intern at Science News. She holds a bachelor’s degree from Harvard College, where she studied the history of medicine, conducted research on cancer immunotherapies, and fell in love with narrative science writing. More

PITTSBURGH — Salmon may now have their own version of human air conditioning.  

This past summer, hundreds of fish in the Wrights River in Nova Scotia, Canada, found reprieve from the heat in human-generated plumes of cold water, civil engineer Kathryn Smith reported October 17 at the Geological Society of America meeting. The work, though only proof of concept, could aid efforts to conserve cold-water species amid the widespread warming of rivers due to climate change (SN: 10/20/22).

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When water temperatures get too hot, fish can become stressed or even die. In rivers, Atlantic salmon and other cold-water species sometimes escape the heat by flocking to cooler areas, which often arise near groundwater springs or relatively cool tributaries.

Lots of work has been done to preserve and augment these naturally occurring refuges, said Smith, of Dalhousie University in Halifax, Canada, “but there hasn’t really been an emphasis or focus on if we can create cold-water habitat.”

So she and her colleagues pumped groundwater that was about 9° Celsius (or about 48° Fahrenheit) from a nearby well into the river, manifesting an artificial plume of water that could be as much as 20 degrees Celsius cooler than the surrounding water.

Researchers pumped groundwater into the Wrights River during the summer to create a plume of cooler water that fish could shelter in (image on the left). A thermal image (right) shows the effect: Cooler water appears darker purple while warmer water and sun-baked rocks are orange and yellow.Kathryn Smith

The plume attracted several hundred fish of varying life stages and species, including Atlantic salmon and brown trout. Most were alevins — juvenile fish still attached to yolk sacs — that occupied the plume throughout the tests. But when a heat wave brought on maximum water temperatures of about 30° C, more mature fish also took shelter in the plume.

For a pump-free approach, the team also rerouted some water from the river into an underground trench, where it cooled before reentering the river. Though this method lowered the water temperature by only a few degrees Celsius, fish were observed frequenting the passively cooled flow throughout the summer.

More work lies ahead to determine how many of these sites would need to be constructed and sustained to significantly benefit fish populations, and how to do so while keeping energy costs low, says John Ackerman, a consulting engineer based in Hazleton, Pa., who was not involved in the research. But the researchers are demonstrating that these solutions can work, he says. “The concept is solid.” More

Nearly 20 years ago, the first global assessment of amphibians found the animals facing widespread declines. Now, a second, updated report shows that many amphibians are still in trouble, but with some silver linings, researchers report October 4 in Nature.

“We are realistic and hopeful at the same time,” says Jennifer Luedtke, a conservationist at the International Union for Conservation of Nature, which tracks extinction risk trends for species around the world.

In particular, the wealth of data in the new report, which includes about 8,000 amphibian species, could help focus conservation efforts for years to come, says Luedtke, who also works from Washington, D.C., for Re:wild, a conservation organization based in Austin, Texas. That’s what happened after the first Global Amphibian Assessment in 2004, which brought awareness to the amphibian crisis and galvanized researchers to coordinate efforts.

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Having two assessments that can be compared is a big deal, experts say. “It’s important not just to have a picture, but actually to have a sequence of pictures … where you can see what’s happening over time,” says conservation ecologist Ana Rodrigues of CNRS in Montpelier, France, who worked on the first assessment but was not involved in the second. “I’m really happy to see this done.”

Here are five big takeaways from the new report.

1. Amphibians remain more threatened with extinction than any other vertebrate group.

About 41 percent of amphibian species, which include frogs, toads and salamanders, are threatened with extinction, Luedtke and her colleagues found. That’s more than any other group of vertebrates, beating out sharks and rays (37 percent), mammals (27 percent), reptiles (21 percent) and birds (13 percent).

Amphibians held this title in 2004 too, when 39 percent of species were threatened. As part of the 2022 update, researchers also used data to reconstruct the situation in 1980. They found that even in 1980, that number was already high, at 38 percent. Basically, amphibians have been really threatened for a really long time, Luedtke says.

The most common threat that affects amphibians is habitat loss and degradation, with agriculture affecting as many as 77 percent of the studied species. Other threats include climate change and disease, each affecting 29 percent of species. Of course, “these things are never completely isolated,” says Rodrigues, and each threat may increase the likelihood of other threats.

2. Many of the worst amphibian declines are being caused by climate change now, instead of disease.

Luedtke and colleagues also wanted to know which threats were most responsible for driving the worst declines. So they looked at a subset of 788 species that, between 1980 and 2022, moved down an IUCN Red List status level — for instance, from vulnerable to endangered. They found that, in 2004, disease was the primary driver behind the drop in conservation status for 58 percent of that species subset. At the time, the fungal pathogen chytrid was devastating frog populations around the world (SN: 8/23/02). Climate change, on the other hand, was a significant contributor to declines in only 1 percent of species.

Now, less than 20 years later, climate change is behind a status drop for 39 percent of species. That makes it the most common primary driver of declines across the amphibian group, the researchers found. And still the finding is probably an underestimate, Luedtke says, as studies continue to emerge detailing how climate change–related temperature increases, changes in precipitation, extreme weather events and wildfires impact amphibians.

“It’s very worrying,” Rodrigues says. “We’re at the beginning of climate change.… What’s ahead of us?”

Amphibian species in the tepuis, or tabletop mountains, of Venezuela, like this Chimantá poison frog (Anomaloglossus rufulus), are particularly vulnerable to climate change, as they are unable to shift much higher in altitude to escape warming temperatures.F.J.M. ROJAS-RUNJAIC

3. It’s bad around the world. But amphibians are doing worse in some regions than others.

Each region faces its own set of threats. The chytrid outbreak, for example, has affected much of the world, but it hit Central and South America especially hard from the 1970s to the 2000s. That likely explains why that region contains the largest proportion of species in the IUCN Red List categories of highest concern, the researchers say. New Guinea and Africa were spared much of the devastation, though the pathogen has recently started to emerge in sub-Saharan Africa.

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Across Europe and East Asia, habitat loss is the leading cause of decline, followed by a newly emerging fungal pathogen in Europe called Batrachochytrium salamandrivorans, this time that affects salamanders (SN: 9/3/13). It hasn’t yet spread to North America, which would be disastrous, Rodrigues says. The continent is home to more than 200 types of salamanders, over a quarter of the world’s salamander species.

For now, North America’s amphibian declines are most associated with climate change, the report found. South and Southeast Asia are seeing an improving trend among their species’ extinction risk, probably due to better management of protected areas.

4. Scientists know a lot more about amphibians now than they did in 2004.

One of the assessment’s few bright spots is its sheer amount of data. The update includes more than 2,000 additional species — all newly described since 2004. There was also a decrease in species labeled as “data deficient” by the IUCN, from 23 percent in 2004 to only 11 percent in 2022. By comparison, though, less than 1 percent of bird species are listed as data deficient.

While there’s still a long way to go for amphibians, researchers are thrilled by the new amount of information. “It’s like, wow, all the knowledge!” Rodrigues says. “So that’s absolutely good news.” With more data, she says, conservation efforts can be better focused.

This indigo bush frog (Raorchestes indigo) has moved from critically endangered to vulnerable thanks to habitat protection efforts in the Kudremukh Massif mountain range of India.Saurabh Sawant

5. Some amphibian species have improved since 2004.

The new report didn’t just find declines — 120 species saw their IUCN conservation status improve.

About half of those species recovered unaided. Many of those had suffered declines due to chytrid and are now bouncing back, possibly as frogs become resistant to the pathogen (SN: 3/29/18). It’s a source of hope that “we have these little frogs evolving, in front of our eyes, resistance to chytridiomycosis,” Luedtke says.

The other half improved thanks to conservation efforts, the report found. One of those species is India’s indigo bush frog (Raorchestes indigo), which was classified as critically endangered in 2004. A couple years later, a legal battle led to the end of all mining in the Kudremukh Massif mountain range, and the species’ IUCN status has since improved to vulnerable.

Stories like that are evidence that effective habitat protection can make a noticeable difference, the researchers say, and yet, with most amphibians still facing declines, it’s clear that current efforts are not enough. The assessment’s accompanying State of the World’s Amphibians Report focuses on action steps based on the new findings. Among other things, it identifies 50 target conservation areas around the world — including Jamaica, Brazil’s Atlantic Forest and the Central Annamite Highlands in Vietnam — that feature a high density of threatened species.

“Yes, the number of threatened amphibians continues to increase, but our understanding is improving,” Luedtke says. “And because we understand them better, we can act in a more accurate and effective way.” More