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The World's Largest Living Structure Is Facing Unprecedented Threats

028 Coral Bleaching at Heron Island

Extensive bleaching at Heron Island. Catlin Survey

Australia's Great Barrier Reef is experiencing coral bleaching and crown of thorns infestations that are having devastating effects. But, with much of the major damage localised to the far north, is there still hope that the reef can be saved from further decline? 

Tangled forests of branching coral, the bumpy brown and purple branches tipped with white, turquoise, mauve; cascading veils of encrusting coral; plate corals big enough for the BFG’s dinner; plump, soft corals swaying in the current; fish of every hue and shape flitting, hovering, lurking, chasing, fleeing. Hardy Reef, located beyond the Whitsunday Islands in the southern section of the Great Barrier Reef (GBR) is, by any measure, remarkable – a diverse, thriving underwater ecosystem. However, what was particularly remarkable when I dived it in July was that my expectations were confounded, something was missing: the stark white beacons of a bleak future – bleached coral. 

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Unexpected cloud cover in March last spared the southern section of the GBR from bleaching

Earlier this year, the GBR suffered its worst bleaching event in recorded history. More than 90 per cent of the individual reefs experienced some level of bleaching as an El Niño event brought unprecedented high water temperatures, causing the stressed corals to eject the photosynthetic algae that give them their characteristic colour – and provide them with 90 per cent of their energy.  

‘By early February we were starting to see some stress and low levels of bleaching,’ says Dr Lyle Vail, the director of the Australian Museum’s research station on Lizard Island in the northern section of the GBR, 270km north of Cairns. ‘By March it had picked up quite dramatically and likewise in April, and then we started to see some mortality in April and May.’

Around Lizard Island water temperatures in the shallows reached as high as 33ºC. ‘The corals around here are adapted to temperatures up to about 29.5 degrees Celsius,’ says Vail. ‘Once it starts getting over that for any length of weeks, they start stressing out. We were hitting those high temperatures in February and they stayed there into late April, May.’

Unsurprisingly, the reefs around Lizard suffered extensive damage. ‘In the shallow waters in the lagoon, the acroporas and staghorn corals are the ones that are really prone to bleaching and we’ve probably lost 80 or 90 per cent of the colonies,’ says Vail. ‘The hot water went down to at least 20m; in some places it was down to 30m. So we were seeing high levels of stress in corals in deeper water. The hot water was fairly uniform, both across the shelf and at depth, so there are very few places where you can go and say, “Gee, luckily this area escaped the bleaching” – it didn’t happen that way.’

By the time the event had run its course, 93 per cent of the individual reefs on the GBR had suffered some level of bleaching and almost a quarter, about 22 per cent, of the coral had died. But as bad as it was, the impact could have been significantly worse. ‘At Cairns, Townsville, the central section and especially the southern section, even though they bleached, there were relatively low levels of mortality,’ says Vail.

Overall, the reefs north of Cairns, and particularly north of Lizard Island were the worst hit. These reefs suffered severe bleaching and high levels of coral mortality, both hard and soft. Fish communities have suffered and many areas are already being overtaken by algae. ‘Once [the corals] die, the algae comes on them – a thin film of algae within a day or two after dying and then, within a week, they’re pretty well covered with algae,’ says Vail. South of Cairns, the reefs fared much better, and those located around the Whitsundays, including Hardy Reef, and further south escaped largely unscathed. 

'The local weather is largely what saved the southern two thirds of the GBR,’ says Dr Neal Cantin, a research scientist with the Australian Institute of Marine Science (AIMS). ‘The heat was in the system to bleach the entire reef the way that the north bleached, but ex-Cyclone Winston came through right at the peak of the warming in March and that provided extensive cloud cover from south of Cairns right through to Mackay. The cloud did two things: it slowed down the warming but it also shaded the reefs.’

It also brought rain, which helped to cool the water, prompting the bleached corals to take the photosynthetic algae back into their tissues. ‘The temperature dropped by two degrees Celsius, so ex-Cyclone Winston rescued the southern half of the reef,’ says Professor Terry Hughes, director of the Australian Research Council Centre of Excellence for Coral Reef Studies at James Cook University (JCU) in Townsville.

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GRIM UP NORTH 

Scientists had been aware for some time that a bleaching event was on the cards. ‘Even last year, they were saying that an El Niño event was on its way and that often causes bleaching,’ says Vail. ‘It’s not that the El Niño itself causes the bleaching, but it brings conditions such as clear skies. A bleaching event isn’t just about hot water, it’s also about the amount of UV radiation hitting the corals.’

026 Filming the Coral Bleaching at Lizard Island

Heron Island. Catlin Survey

In the months leading up to the event, Hughes convened the National Coral Bleaching Taskforce, drawing together more than 300 scientists from ten institutions around Australia to co-ordinate research efforts. The task force carried out extensive aerial surveys, scoring the bleaching severity at the peak of the event for about a third of the GBR – close to 1,200 reefs along the whole length and breadth of the reef, a process that Hughes describes as ‘very confronting’. 

‘We found a very strong north-south pattern,’ Hughes says. ‘The southern third is okay, the middle third was moderately bleached, at about the same intensity as the two previous mass-bleaching events in 1998 and 2002, and then the northern 800km or so, from Port Douglas up, were really, really badly damaged.’ 

In all, about 85 per cent of the coral mortality on the GBR occurred in the region north of Lizard Island, where about half of the coral died, compared with very little mortality in the southern section.

The task force also carried out in-water surveys of 145 reefs between Townsville and the Torres Strait, and as Vail observed at Lizard Island, it found that the bleaching occurred down to unprecedented depths. ‘We did most of our surveys in shallow water, but we did dive to 40 metres and we found bleaching all the way down,’ says Hughes. ‘There was some lessening of bleaching below about 20 metres, but even at 20, 30, 40 metres we saw substantial bleaching.’

The scientists also observed unexpected levels of coral mortality. ‘The conventional thinking about loss of corals from bleaching is that a coral that’s white is nutritionally compromised,’ says Hughes. ‘It has lost the microscopic algae that live inside its tissue. The algae photosynthesise and give energy to the coral host, and if they don’t come back quickly enough, the coral will slowly die. We’re seeing that now, but in addition, we’re seeing another kind of mortality that was much, much quicker. At the peak of the summer, the corals didn’t just slowly die of starvation, they died directly from heat stress. When we censused those reefs in March, in the northern part of the reef, 20 per cent had already died.’ 

The good news is that now that the sea temperatures have returned to normal, the reef is beginning to recuperate. ‘We’re already seeing recovery,’ Vail says. ‘I’m amazed at how quickly corals start to bounce back.      

Obviously, we haven’t had a spawning event since the bleaching, so it’s not recruitment; it’s the corals that didn’t die. Often it seems to be the very little ones; perhaps they were shaded by a plate coral so they didn’t get as much direct sunlight.’

GBR map

WIDER IMPACT

While the bleaching and death of the coral, both hard and soft, were the most visible impacts of the hot summer, as Professor Ove Hoegh-Guldberg, director of the Global Change Institute at the University of Queensland, points out, those impacts directly affect many of the other thousands of species that live in and around the GBR. ‘What you’re looking at is not only the loss of 25 per cent of the corals, but also a huge impact on a whole bunch of other creatures,’ he says. 

‘Corals are the architects of the reef, but if they’re significantly diminished, it has much broader impacts in the whole ecosystem,’ agrees Terry Hughes. ‘Just like the mix of corals is changing because some species cope
better than others, so too is the mix of fish. The most susceptible fish, such as butterflyfish, feed on corals. Then there are the other fish, little blennies and gobies, that are often very specific to which coral they like to live in.’ 

It’s these species that are already being impacted. ‘Here on Lizard, we have a whole bunch of gobies, roughly 13 species, half quite common before the bleaching,’ says Vail. ‘After the bleaching event, we can only find one or two, and they aren’t all that common.’ 

UNDER THREAT

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Run-off from the mainland (sometimes as a result of dredging for coal ports) brings sediment, which settles on coral polyps, and nutrients, which can cause algal blooms that can fuel outbreaks of crown of thorns (COT) starfish. COTs are currently the biggest source of coral mortality on the Great Barrier Reef.

POLITICAL COST

This year’s bleaching event took place against the backdrop of a federal election in Australia, during which the health of the reef became a significant campaign issue. The major parties all released policies, promising varying levels of funding to ‘save the reef’. The conservative Liberal-National coalition, which eventually won the election, committed to spending AU$1billion over ten years, but questions were quickly raised about the way in which those funds would be spent, and where they would come from – and whether it would be enough to do the job. 

Several groups have recently released estimates of the cost of solving the GBR’s water quality problems. Run-off from the mainland brings sediment, which makes the water cloudy and settles on coral polyps, and nutrients, which can cause algal blooms that, in turn, can fuel outbreaks of crown of thorns starfish (COTS). ‘There’s very strong evidence that elevated levels of nutrients increase the availability of food for the larvae of the COTS, contributing to population outbreaks,’ explains Dr Katharina Fabricius, a senior principal research scientist at AIMS. ‘And at this stage, COTS are the biggest source of coral mortality on the GBR.’ 

Scientists contend that improving water quality will increase the reef’s ability to bounce back from bleaching events, but significantly reducing the run-off will be costly. A recent paper in Estuarine, Coastal and Shelf Science by JCU academics Dr Jon Brodie and Professor Richard Pearson suggested that AU$10billion in funding would be required over ten years. Another study, produced by environmental consultancy Alluvium, put the cost at AU$8.2billion over the same time period.

Improving water quality on the reef is a high priority for the government. Last year, it convinced UNESCO to leave the reef off its list of endangered World Heritage Sites, thanks largely to its drafting the Reef 2050 Plan,
an ‘overarching framework for protecting and managing the reef until 2050’. However, in December 2016, the government has to report back to UNESCO about the implementation and adequate funding of the plan if it wants to keep the GBR off the ‘in danger’ list. 

FUTURE HOPES

‘Improving water quality is a very good idea,’ says Hughes. ‘The reef now needs all the help it can get to try to bounce back, but the elephant in the room remains climate change. We can’t climate-proof reefs by making them more resilient.’

With global temperatures set to continue to rise if carbon dioxide emissions aren’t reined in, the long-term future of the GBR looks bleak. There are still glimmers of hope, however. ‘The GBR is, thankfully, a very diverse ecosystem, with 250 to 300 different coral species,’ says Cantin of AIMS. ‘That lends itself to what’s known as functional redundancy – when you have more species in the system, you potentially have more species that can cope with and adapt to a changing environment.

Some of the reefs are still looking pretty spectacular,’ he continues. ‘For example, consider the reefs off Townsville – some of them bleached and some of them didn’t bleach very much at all. And some of them still have pretty high coral cover. To me, the fact that you still have such diverse and healthy systems after this event is a positive.

‘But we’re definitely seeing more frequent bleaching events, more severe bleaching events,’ he adds. ‘They’re only getting worse, so the future for coral reefs doesn’t look promising, but it’s a diverse system that can recover if it’s given the time.’ 

Fabricius is also quietly optimistic. ‘We still understand so little about acclimatisation and the ability of corals from the northern GBR, which are used to warm water, to move further south,’ she says. ‘In my mind, there’s still a pretty significant hope that the GBR will be able to move down the temperature gradient from north to south, but it needs to happen very rapidly.’ 

Based on the media reports and the shocking statistics, divers could be forgiven for thinking that the Great Barrier Reef is no longer a very attractive destination. ‘Quite a few people did ring up and ask whether it was still worth going out to the reef,’ says Paul Crocombe, owner of Adrenalin Snorkel & Dive in Townsville.

The good news, however, is that a remarkable amount of the reef escaped the bleaching event virtually unscathed. ‘We haven’t had to change any of our dive sites,’ Crocombe says. ‘We’ve been fortunate that there has been minimal bleaching on the reefs off Townsville. Where we regularly go, there are a few very small patches, maybe one or two per cent of the reef, that people would notice has been bleached. The corals out here, very few of them reached the point where they were going white, so we had very low mortality of the corals down here from the bleaching.’

The same is true further north. According to Trina Baker, sales and marketing manager with Cairns-based liveaboard operator Spirit of Freedom, the bleaching event has had little impact on their business. ‘There are a couple of sites that we’ve chosen not to go back to, but we’ve found other sites as replacements, so in terms of our actual operation, it hasn’t really affected us too much,’ she says. ‘The corals have made a great recovery, with all of the colour coming back over the winter.’

Baker recently returned from a recce trip up to the far northern sector of the reef, which suffered the worst bleaching and mortality. ‘We went specifically to the outer reef sites, not the inshore or the mid-shelf, and we were surprised at how good it was,’ she says. ‘It was much better than we could have hoped for. Probably the worst site we saw had around five per cent mortality, but at most of the sites it was less than one per cent. We found good, healthy coral everywhere we went.’  

THE GOOD NEWS FOR DIVERS

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Based on the media reports and the shocking statistics, divers could be forgiven for thinking that the Great Barrier Reef is no longer a very attractive destination. ‘Quite a few people did ring up and ask whether it was still worth going out to the reef,’ says Paul Crocombe, owner of Adrenalin Snorkel & Dive in Townsville.
 
The good news, however, is that a remarkable amount of the reef escaped the bleaching event virtually unscathed. ‘We haven’t had to change any of our dive sites,’ Crocombe says. ‘We’ve been fortunate that there has been minimal bleaching on the reefs off Townsville. Where we regularly go, there are a few very small patches, maybe one or two per cent of the reef, that people would notice has been bleached. The corals out here, very few of them reached the point where they were going white, so we had very low mortality of the corals down here from the bleaching.’

The same is true further north. According to Trina Baker, sales and marketing manager with Cairns-based liveaboard operator Spirit of Freedom, the bleaching event has had little impact on their business. ‘There are a couple of sites that we’ve chosen not to go back to, but we’ve found other sites as replacements, so in terms of our actual operation, it hasn’t really affected us too much,’ she says. ‘The corals have made a great recovery, with all of the colour coming back over the winter.’

Baker recently returned from a recce trip up to the far northern sector of the reef, which suffered the worst bleaching and mortality. ‘We went specifically to the outer reef sites, not the inshore or the mid-shelf, and we were surprised at how good it was,’ she says. ‘It was much better than we could have hoped for. Probably the worst site we saw had around five per cent mortality, but at most of the sites it was less than one per cent. We found good, healthy coral everywhere we went.’ 

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