Sexual healing for dying coral reefs

With news that mass coral bleaching and dying across the world's reefs is accelerating - some 30 percent of Great Barrier Reef coral was lost in 2016 alone, and new findings show coral could be largely extinct by 2050 - the world's scientists are scrambling to find ways to restore these marine biospheres so they don't disappear forever. 

Although coral reefs occupy less than 1 percent of the total ocean area, their loss will upset a very delicate balance, says Dave Vaughan, who works restoring corals. "It's like looking at a desert - and we've lost all of the oases," he told DW. 

But Vaughan, who is executive director of the Mote Tropical Research Laboratory in Summerland Key, Florida, is hopeful that humans can do something about it. Within the next year, his project hopes to produce 50,000 new live corals; within two to five years, this could be a million corals. "We [will] increase the actual coverage of the entire Florida Keys reef by 25 percent," he says.

It's a bold prediction - but one that gives hope to the many who are already mourning the demise of the world's magnificent coral reefs.

Coral sex: the new hope

Vaughan's breakthrough was to find ways to build up reef corals through sexual reproduction. "The most prevalent coral is a branching coral, such as staghorn, that propagates on its own when broken apart," Vaughan explains. This is a form of asexual reproduction.

"However, 'massive corals' like brain, cavernous or star coral that actually build the reef are sexually reproduced," Vaughan continues. This wasn't even known until the 1980s, he added. "We know so little about corals - we didn't even know how they reproduce until recently."

That vital discovery was made by team of researchers that included Peter Harrison, director of the Marine Ecology Research Centre at Australia's Southern Cross University.

Most reef restoration, involving coral fragmentation and transplanting, is time-consuming and only works on a relatively small scale. "That's a key limitation," Harrison says. 

But on the Great Barrier Reef and in many other reef regions, spawning corals (pictured at top) produce literally billions of eggs and sperm. "If you harness the power of this mass spawning, you can capture the larvae and put them back into the reef system, and let the winners grow."

Lucky accident

With a background in aquaculture and fish spawning, Vaughan had long questioned the method of asexually reproducing corals by fragmenting them and putting the pieces back out into the ocean.

Initiating the first facilitated coral spawning was a slow process. "In the summer after the full moon, these corals will all synchronously spawn - but only one [fertilizes] every 25 to 100 years." This is because coral that lives to between 300 to 800 years should have plenty of time to breed. 

But with the world having lost so much coral in recent years, Vaughan needed to speed up his coral sexing. He soon created test tube coral babies in the lab, and succeeded in fertilizing coral at 10 times the natural rate. 

But once spawned, these massive coral species grew painfully slowly - at around 2 millimeters in the first year. "I got disappointed," he says. 

Then Vaughan dropped a coral by accident. After a couple weeks, he noted that the pieces were growing, and at a much faster rate. Breaking them apart "stimulated them to grow back to a three-year-old size in just a few months," he explains.

Soon enough, Vaughan was breaking off a hundred or so micro-fragments from the spawned coral. Most also grew quickly.

Now, he is confident he will soon be planting millions of corals back onto the Florida Reef, the world's third-largest. It's one part of a global reef regeneration project now taking place at Mote's new $7-million (6.3-million-euro) International Center for Coral Reef Research and Restoration, which opened last week. 

Spawning climate-resilient reefs

Even more importantly, Mote is reproducing coral that will survive in today's waters, which are warming due to climate change. "We're simulating tomorrow's conditions to see which ones will be resilient corals in the oceans of the future," Vaughan adds.

Harrison, meanwhile, is working to spread coral larvae directly onto dying reefs in the Philippines. There, corals have been badly degraded - not only from bleaching events, which are projected to increase in frequency and severity due to climate change - but also as a result of blast-fishing.

"It's the first time it's been done anywhere in the world successfully," he says. By capturing millions of larvae in gauze nets, Harrison's coral larval restoration project hopes to insure that thousands of corals are propagated on the reef before they drift off due to strong tides or superstorms.

Like Vaughan, Harrison is hopeful for widespread reef regeneration through sexual reproduction. But spreading coral from a diverse gene pool with also help to future-proof reefs, he believes.

"If you use sexual reproduction, the genetic diversity of the offspring is very high, and there is a higher chance that the coral developed from those larvae will more climate change-resistant," Harrison said.

To this end, coral restorers are also depending on burgeoning research to develop more climate-resistant corals.

On the quest for 'super corals'

Verena Schoepf of the University of Western Australia and the ARC Centre of Excellence for Coral Reef Studies is currently researching reefs in Western Australia, where unique coral strains are naturally heat-resistant.

Trying to understand the mechanism that has made this coral more tolerant to warm water could also be key to nurturing or even selectively breeding climate-resistant "super corals" in the future.

But Schoepf reserves some skepticism regarding the scale of coral recovery. "These restoration efforts, no matter how well they work or how good they are, are not going to be enough to save coral reefs on a global scale," she told DW.

 "At the same time, it's already worth something if we can save at least some of our reefs."