The science of saving the Barrier Reef
Over two weeks late last spring, the weather was unseasonably foul on the southern parts of the Great Barrier Reef. For the scientists and volunteers working there, intense winds made boat trips and diving challenging. Nonetheless, they persevered, buoyed by their belief the largest reef system in the world is worth saving.
A few months earlier, Deloitte Access Economics had valued the Barrier Reef at $56 billion, with an economic contribution of $6.4 billion a year. Some would argue you can’t put a price on a World Heritage-listed area spanning 3000 kilometres and home to more than 400 species of coral, 1500 species of fish and 200 species of birds.
In January, Malcolm Turnbull announced a nearly $60 million plan for protecting the reef, including $6 million for a Reef Restoration and Adaptation Program (RRAP) led by the Australian Institute of Marine Science (AIMS) and the CSIRO to explore ways to help the reef adapt to climate change. In April, the government announced a further $500 million pledge, including the controversial $444 million grant to the Great Barrier Reef Foundation, for reef restoration, adaptation and resilience-building projects. While it’s not yet clear how the latter money will be spent, the RRAP is under way.
The RRAP is currently in the concept feasibility phase of a 10-year plan. More than 60 scientists and engineers from 14 organisations have combined forces in efforts to “future proof” the reef. Climate change mitigation is key to protecting reef systems worldwide, says the program director, engineer David Mead. “But even if you follow the best-case scenario, then temperatures are still going to rise and stay elevated for quite a long period of time, and mass bleaching events are going to increase in likelihood,” he says.
Even if crown-of-thorns starfish management and water-quality targets are reached, “there’s a strong likelihood that additional tools are going to be required to help the system adapt and [to] restore damaged areas”.
The RRAP is exploring a suite of interventions that may be considered. Weighing up potential benefits against risks is crucial, Mead says, so the reef doesn’t end up as another “cane toad example”.
Some options involve “local scale geoengineering” as a preventive or restorative measure. One possibility is “brightening” clouds over the reef to deflect sunlight. Spraying fine droplets of salt water into clouds turns “big balls [of water vapour] into small balls – which reflect more sunlight – giving a higher degree of shading”, Mead says.
Another option is “sunscreen” for corals. Mead explains that bleaching is caused not only by water temperature, but also the number of light particles – or photons – that reach the coral. Scientists have been testing non-toxic materials that could form a film on the ocean’s surface and reduce corals’ exposure to photons.
Other work is examining ways to help reefs recover faster from damaging events, which usually takes 10 to 15 years. In a stable system, reefs die off and recover. However, “what we’ve been seeing on the Great Barrier Reef over the last 30 years is that those knockdown events are increasing in frequency, so the system doesn’t quite recover back to where it was each time,” Mead says.
One course of action is helping coral larvae settle and survive on existing reefs. Larvae don’t do well on unstable or algae-covered surfaces created by destructive events. By stabilising surfaces and reducing algal infestation, larvae could more easily repopulate damaged areas.
Another method is improving coral health before, during or after bleaching events. Mead explains that corals that survive bleaching are weakened due to loss of their zooxanthellae – the resident algae they need for survival. “It becomes a race against time,” he says. “Will they re-establish their algal cultures … quickly enough, or will they starve to death or die of coral disease?”
Developing probiotics or nutritional supplements for coral, or helping them re-establish their microbial communities, could help a higher proportion survive.
Another category is bioengineering. Scientists are looking at several “assisted evolution” approaches that could accelerate the development of coral qualities such as temperature tolerance, or growth or reproduction characteristics.
Assisted gene flow, for example, aims to spread naturally warm-adapted genes across the reef to protect corals in cooler sections against continued warming and bleaching. Another experiment involves hybridisation. Combining egg and sperm from different species – which sometimes occurs in nature – could create hybrids that are better adapted for survival in warmer water.
All these measures are at different stages of development, and a plan is due for delivery by the RRAP in 2019. Where possible, priority will be given to methods that help the reef help itself, rather than those requiring aggressive and ongoing interventions.
Few people know more about helping the reef than marine biologist Professor Peter Harrison, the founding director of the Marine Ecology Research Centre at Southern Cross University. Since being part of a team that discovered the mass coral spawning phenomenon in the early 1980s, Harrison’s research has focused on understanding when and how corals reproduce, and how humans and nature disrupt this process.
He believes that maintaining genetic diversity by utilising the reef’s sexual reproduction processes is crucial for its future, and has spent decades developing techniques to maximise fertilisation rates, rear coral larvae on a massive scale and optimise larval development, with a goal of getting them back onto damaged reef systems.
He started with pilot studies in the Philippines, on what had been “incredibly diverse, luxuriant reefs that produce large numbers of fish”, but were devastated by blast fishing, where explosives are used to stun fish. By adding larvae back onto degraded reefs, coral populations were re-established and they started breeding within three years. Although happy with the results, Harrison cautions “this is not a magical reef recovery in large-scale approach. It’s research to find out what is feasible and what’s possible.”
The next step was taking this work to the Barrier Reef. During the November 2016 coral spawning, Harrison and his team collected vast quantities of eggs and sperm from the slick of sexual soup around Heron Island. They reared more than a million coral larvae, which were delivered back onto reef patches in underwater mesh tents.
When the researchers returned for the mass spawning during the rough weather of November 2017, the surviving juvenile corals had successfully established themselves. “This experimentally proves that larvae density is really important in terms of showing how to potentially do this at a larger scale in future,” Harrison says.
“There’s the potential for this to become less experimentally constrained. Simply enabling hundreds of millions of coral larvae to be washed onto a reef system at the right time so they settle quickly is going to provide an effective means of stimulating coral recovery.”
The next step is scaling up the work to hectare-sized areas, followed by using surviving corals from the northern and central Barrier Reef systems that were heavily impacted by the mass bleaching events of 2016 and 2017. “Those survivors should have recovered sufficiently so that they will go through their normal sexual reproductive cycle in November and December this year,” Harrison says.
He hopes to “catch the genetic diversity that’s left in the surviving corals, which presumably are more likely to be adapted to higher temperatures than the ones that died. By maximising their fertilisation rates and larvae settlement success, we could stimulate the evolution of that population.”
His team will start in specific areas, because some reefs act like factories, producing larvae that are distributed onto other reefs down-current. “The plan would be not to try and do the impossible and suddenly do this on hundreds and hundreds of reefs, but to start the process on some identified key reef systems.”
In the future, Harrison hopes to upscale by capturing natural coral spawn slicks that will still happen in some areas, and protecting the embryos for the development period. “Instead of watching them disperse and potentially never finding a reef again, they will hopefully settle back onto key reef systems … and form more thermally resistant populations.” The hope is they will become “the foundation of the next generation of coral communities”.
Harrison and Mead agree that the future of the reef is perilous. While Harrison doesn’t believe all coraIs will die – except under a worst-case scenario – genetic diversity in surviving populations will probably continue to decrease. “It is likely that environmental conditions are going to get harder and therefore the numbers of adult breeding corals on these reef systems are likely to decline further. Therefore, intervening now … while we try and sort out the bigger problems of climate change at a global scale [is] important.”
Mead agrees that timing is crucial. “If you can do things early, you need to do less, you protect a broader part of the biodiversity, and it’s less interventionist … If we wait 10 years and then start, a number of options could be off the table by then.”
Still, he remains cautiously optimistic. “[The Great Barrier Reef] is battered and bruised,” he says, “but it’s not down and out yet.”
This article was first published in the print edition of The Saturday Paper on Oct 20, 2018 as "Coral support".
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