New Hope for Coral
Scientists are hoping to preserve the Great Barrier Reef by spawning algae- boosted coral
By hand-rearing larvae, scientists are experimenting to save endangered reefs.
THE MAGIC MOMENT IS HERE.
A near-full moon casts its glow across the nighttime waters of the Great Barrier Reef off Cairns, in northern Queensland. Shadowy fields of coral are gently illuminated by dive lights as we fin through the darkness on scuba, ten metres below. Underwater it’s a balmy 27 degrees. Fish and a big moray eel watch us pass; white-tip and grey reef sharks ignore us, flying along sandy channels on their evening’s work.
But these are nightly marvels. We’re looking for magic that individual Barrier Reef sites see only yearly, usually for a few hours over a night or two between October and December in the week after a full moon. Ahead, it’s just beginning. A single patch of coral bubbles with white snowdrops that rise instead of fall.
Soon the waters fill with a snowstorm of tiny blobs, floating upwards to form a pinkish slick on the surface. This is the Great Barrier Reef’s annual mass coral spawning, when countless billions of coral polyps release their egg-and-sperm bundles together in a vast synchronised outburst.
It’s the moment James Cook University marine biologist Katie Chartrand has been waiting for. She hasn’t come for the spectacle, awesome as it is (and a tourism drawcard). She’s here to fight for the reef’s future with cutting-edge science. Her goal is to help corals better resist and recover from mass bleaching, a global warming effect posing a major threat to their existence.
“We’re trying to capture the egg and sperm that’s being released from corals that survived the 2016-17 bleaching events, corals that were able to get through that stressful warming event,” she says.
From their base at Marine World tourist pontoon at Moore Reef – 45 kilometres offshore from Cairns – Katie and her Larval Restoration Project colleagues are ready with floating capture pens that use boom arms to scoop portions of the spawn slick, aided by wind and current. Held in six fine-mesh inflatable pools, millions of coral egg-and-sperm bundles will spend the next few days fertilising and forming larvae.
“We’re hoping to help create that next generation of corals that potentially has inbuilt heat tolerance to survive into the future,” says Katie.
“We’re relying on healthy, beautiful reef systems to help feed in and
seed areas that have been damaged.”
The Larval Restoration Project has twin goals. One is the targeted settling of larvae from spawning corals to replenish bleached areas. The other – a world first here at the November 2019 spawning – is to give this larvae a ‘booster shot’ against future bleaching events.
The science behind the concept relies on how corals feed – and bleach. Virtually all corals keep zooxanthellae algae in their tissue, which supplies their colour and almost all their nutrients. Bleaching happens when corals expel their algae, which turns toxic when overheated. It’s not necessarily
fatal, depending on how soon conditions cool, but global warming has turned a natural process into a deadly threat by vastly increasing its incidence and severity.
Not all zooxanthellae is equal, though. Some species cope with heat better than others, so the idea is to boost bleach-resistance by arming corals with heat-hardy algae, mixing it with larvae caught in the floating pools.
“It’s been demonstrated time and time again to withstand some of these warming events,” Katie says of the algae in question.
One odd feature of bleaching is its patchiness; reefs often have mixtures of affected and unaffected corals. “We don’t know exactly why some patches of coral survived the bleaching event,” says Larval Restoration Project co-leader Professor Peter Harrison, of Southern Cross University. “But we do know most of them have got more temperature-tolerant algae, and that’s what we’re going to put in. We’re trying a combination of heat-tolerant larvae from surviving corals and heat-tolerant symbionts added in. It’s that combination we’re hoping will give a thermal tolerance lift of about two to three degrees.”
Katie and the team have lab-reared more than ten billion cells of the tougher algae. “We’ll be settling algae with larvae under five-by-six metre underwater mesh sheets that look sort
of like a wedding veil,” she says. “We’ll be pumping in the larvae that have the algae and comparing that with controls [such as] larvae without algae.”
An expert in seagrass ecology, American-born Katie has long-studied photosynthesis in marine organisms and has done coral conservation work in the Caribbean. Algal uptake, she adds, is not just for heat tolerance, but also to “boost the energy supply to these coral babies during that developmental phase. Trials have shown we can increase the number of coral larvae that settle and survive through those early months.”
In the wild, coral larvae suffer huge natural die- off before survivors attach to surfaces and begin reef-building. Supplying algae early – well before corals naturally acquire it – turbo-charges larvae metabolism, helps speed growth and increases their overall chances, regardless of bleaching.
“In the lab we know it works,” Peter says. “If you put the algae and larvae together you do get uptake and an increased rate of settlement and survival. But this is the first time we’re doing it at scale on the reef system.”
Peter was part of the prize-winning Australian team that discovered coral spawning back in 1981. He’s even had a coral species named after him. After years developing and testing larval restoration here and in the Philippines, he’s excited about its potential for expansion into ever larger, more meaningful scales. But for now, it’s a matter of monitoring this spawning’s algae-boosted sample.
“When the larvae are ready to settle, after about five days, we’re going to distribute them in a range of ways. We’ll use divers and snorkellers to squirt larvae back onto the dead reef areas. We’re going to use an
“IT’S BEEN DEMONSTRATED TIME AND TIME AGAIN TO WITHSTAND SOME OF THESE WARMING EVENTS”
underwater drone called Larval Bot, designed to contain large numbers of larvae and use GPS tracking to put larvae back into designated parts of the reef. Then we can monitor every six months or year and see how many corals are growing and surviving.”
It may seem surprising to find reef experts so hopeful about making a difference. After all, the 201617 mass bleachings – two summers running, for the first time – sparked headlines worldwide proclaiming the Great Barrier Reef’s death, or doom. Panoramas of bone-white dead or dying coral told a tale of heartbreaking, total devastation.
But destruction was far from complete. The Reef – actually some 3000 separate reefs across an area the size of Italy – suffered an estimated 22 per cent coral mortality overall, almost all in the far north. For all the damage and loss, two-thirds of the Great Barrier Reef – including many of the most visited locales – saw little or no bleaching, and some sites, including Moore Reef, have been recovering well. The effect of another mass bleaching outbreak this year, which has hit the south too, remains to be seen.
“The reef is by no means dead,” says Katie. “It’s a nuanced story and one very difficult to tell. We have an amazing amount of biodiversity still out here that we rely on to have success in this project. So we’re harnessing those corals that are incredibly healthy and doing well out there.”
Moore Reef’s importance in reef recovery efforts, Katie reveals, goes beyond providing healthy spawn for larval experiments. “It has been identified as a source reef,” she says. “It has the potential to supply eggand-sperm bundles downstream for other reef systems.”
And of course, its Marine World makes an ideal base for the project, with full support from the pontoon’s tourism operators. Helping the Reef is everyone’s priority out here.
Mass spawning shows the Great Barrier Reef is still bursting with life – and where there’s life, there’s hope. There’s a big caveat, though. “None of this makes sense unless we’re trying to deal with climate change,” Peter says. “In high carbon-dioxide conditions with extreme temperatures, corals no longer survive on coral reefs. The fossil record shows that really clearly.”
Katie concurs. “There are areas that are incredibly degraded, and they’re not ever going to necessarily go back to where they were without significant action on climate change.”
Thankfully, those algae-boosted coral babies have more chance of resisting whatever raised temperatures come their way in a warming future.
On spawning night, a silver pinprick of light bubbles upwards in the sea’s darkness. It looks like a micro-sized astronomical object, but it’s coral spawn. It’s life – resilient, beautiful life – going about its vital business as always, no matter what.
For all the problems it faces, the Great Barrier Reef is very much alive, still growing and replenishing. Corals are still building their massive, magnificent structures that keep ocean life – and human economies – thriving. Snorkellers and scuba-divers still enjoy vibrant, colourful, fish-filled coral gardens along some 2000 ki lometres of Queensland coast. There’s no doubt man-made climate change has brought the Great Barrier Reef its greatest existential threat. Yet human ingenuity is bringing something else, too – hope that this threat might be better withstood while the wider struggle to limit global warming continues.
“FOR ALL THE PROBLEMS IT FACES, THE GREAT BARRIER REEF IS VERY MUCH ALIVE”