How the reef became blue again

The loss of the Great Barrier Reef is feared by some scientists but research shows coral are far more diverse and resilient than once believed

The loss of the 3000 prize reefs collectively known as the Great Barrier Reef is feared by some scientists but research shows their living coral are far more diverse and resilient than they've been given credit for

WE are skimming across an azure sea beneath a sky as big and blue as you could imagine. A gentle northeasterly breeze brushes the edge off the early summer heat in this idyllic corner of the Great Barrier Reef, where climate change and its implications for Australia's greatest natural wonder resonate with lacerating intensity.

Marine scientist Ray Berkelmans has been diving here in the Keppels, a scattering of tawny islands and coral outcrops 40 minutes by fast boat from the central Queensland coast, for 27 years.

In that time he has seen the corals bleach repeatedly and more lethally, reinforcing the belief that elevated ocean temperatures associated with longer, hotter and drier summers pose a desperate threat to the reef.

The crown of thorns starfish has come and gone, thankfully, never with the voracious weight of plagues elsewhere on the reef, while the population centres of Yeppoon and Rockhampton on the mainland continue to boom, imposing constant stress and strain on coral formations.

The Keppels are a microcosm of the challenges confronting the reef, which stretches northwards from this anchor point for more than 2200km to the tip of Cape York Peninsula.

The effect of tourism might be felt more keenly in Cairns, Port Douglas and the Whitsunday Islands, the big three jumping off points to the reef, but they resonate here, too, as debate rages over proposals to redevelop the mothballed resort on Great Keppel Island and to carve golf courses and a marina into the landscape.

Track along the Queensland coast, to the sugar bowl of the Burdekin, near Townsville, or to the thickly planted canefields to the north and south of Cairns, and similar concerns are voiced about runoff from the mighty Fitzroy River into the inshore waters lapping the Keppel reefs.

The volume of sediment washing on to the reef is said to have increased fivefold during the past 150 years.

Until recently this was rated as a prime threat to its existence.

Now it's climate change, front and centre. One way or another global warming will be the death of the reef, the alarmists say. On the more extreme predictions the reef could become history within the next quarter of a century.

In the Keppels, however, an inconvenient truth has emerged to puncture the gloom and doom.

After bleaching to an unprecedented extent in 2006 -- when an estimated 35 per cent of corals were killed, "like a white blanket was thrown over them", according to Berkelmans -- the Keppel reefs have bounced back to an extent that has stunned and delighted him, exciting hope that the reef as a whole may be more resilient to climate change than was thought.

"In 2006, we basically saw the [Keppel] corals acclimatise before our eyes," says Berkelmans, conducting Inquirer on a tour of what he calls his lab rat reefs. "About 95 per cent of the corals were affected, and we think just over a third died, which was a lot more than we had seen before.

"What surprised us -- stunned us, really -- is how strongly they have come back. It's not everywhere . . . we've still got reefs struggling. But, generally, you would have to say the coral cover is as good, if not better in places, [as] it was prior to bleaching in 2006, and that has caused us to do a lot of thinking and work on how the corals in the Keppels have coped with bleaching events."

As the climate change talks in Copenhagen enter their decisive phase with the arrival in the Danish capital of world leaders including Obama Barack, China's Wen Jiabao and Kevin Rudd, with his ring-side seat as a friend of the conference chair, the experience in the Keppels is cautionary and encouraging.

Berkelmans, 52, a senior research scientist with the Townsville-based Australian Institute of Marine Science, says there is no doubt that climate change has adversely affected the inshore reefs off Rockhampton and Yeppoon.

Like those elsewhere in the vast expanse of the GBR, the Keppel corals live in "an extremely narrow window of temperature tolerance", he says. They will stress and start to bleach if the water temperature falls below 18C or exceeds 28.5C; corals farther north on the reef, off Townsville, say, cheerfully cope with warm water that would kill their Keppel cousins.

Berkelmans says coral is one of the planet's perfect creations: its living heart, a polyp distantly related to jellyfish, is encased in a skeleton of calcium carbonate, which is the building block of the reef. Photosynthesising algae called zooxanthellae live within each coral, giving it colour and food from sunlight.

In return, the algae feast on nitrogen waste from the coral.

Unfortunately, this exquisite symbiosis can break down if coral comes under stress, as happens when water temperature moves outside the coral's tolerance range. Instead of producing life-sustaining sugars, the zooxanthellae excrete toxins. In a process scientists don't fully understand, the algae is expelled, turning the reef from a wonder world that glows with every colour of the rainbow under light to a wintry tract of white and dying coral.

This happened in the Keppels in 1998, when an estimated half of the Great Barrier Reef was hit by a worldwide coral bleaching event linked to an El Nino episode (during which much of the tropical Pacific becomes unusually warm). Another mass bleaching took place four years later, affecting more than 60 per cent of the reef, and killing perhaps 5 per cent of corals. The 2006 bleaching was largely localised to the reefs off central Queensland, but was by far the worst Berkelmans had seen.

In the doldrums of summer the ocean temperature hit 30C in the Keppels and stayed there day after day through late January and February 2006, with little cloud cover or wind to temper lethal heating of the reef shallows. About 95 per cent of the corals bleached, one-third of which died. "Everything was just so bone white, it was awful to see . . . just like someone had thrown a white blanket over the reef and smothered it," the researcher recalls.

Three years on, the picture couldn't be more different. True, the reef off North Keppel Island is a long way from recovered. Much of the coral that survived bleaching is stricken by disease or choked by brown algae. But this is an exception to the miracle that has taken place beneath these waters.

Parts of Miall Reef, 15 bone-jarring minutes by launch west of Great Keppel Island, have achieved 100 per cent coral cover. Blue and gold damsel fish dart between the thriving staghorn and plate corals; on the sandy bottom, fat parrot fish are too busy gobbling algae to worry about the presence of snorklers.

"We were tremendously surprised that the Keppels came back so well," Berkelmans says after we climb back into the boat. "To look at it, you wouldn't know that 2006 happened."

As it turns out, there is another crucial window for coral affected by bleaching. Those that expel their zooxanthellae have a narrow opening to recolonise with new, temperature-resistant algae before succumbing. In the Keppels in 2006, Berkelmans and his team noticed that the dominant strain of zooxanthellae changed from light and heat-sensitive type C2, to more robust types D and C1.

This, he believes, equipped the corals to face water temperatures up to 1.5 degrees higher than their usual tolerance. "It means the difference in being able to cope with a summer like 2006 or bleaching and dying," he says. "In fact, in 2006 we were noticing corals of the same species side by side; one was bleached bone white and the other was normally pigmented.

"One was stressed to the max and the other one was perfectly normally pigmented . . . for the corals that survived, the majority of them had basically expelled the less tolerant type of zooxanthellae and the remaining tolerant zooxanthellae multiplied and reoccupied the space in the coral tissues. It happened virtually before our eyes."

Could this process be repeated elsewhere on the reef? That is the question, Berkelmans agrees. In the past 60 years, the baseline water temperature has increased by 0.6 of a degree, the scientist says, with most of that happening in the time he has been studying the reef. If the doomsayers are to be believed, the reef as we know it will be gone by the time the cumulative temperature gain reaches one degree in 2050.

Yet contrary to popular belief, coral bleaching is episodic rather than chronic; hardly any would exist on the reef right now, Berkelmans says. That could change with breathtaking speed if conditions become conducive to another mass bleaching event, as is anticipated later this summer when a newly formed El Nino weather pattern intensifies, giving rise to more stifling doldrums days.

Scientists are already looking at the possibility of transplanting corals from heat-resistant colonies in the reef's north to more vulnerable reaches. Berkelmans says the Keppels experience shows the reef can adjust to climate change, but whether this was a local phenomenon or one with wider implications for the reef remains to be seen.

When pressed, he says he is more optimistic about the reef's medium-term prospects, especially in inshore areas such as the Keppels. "People say the reef is dying. Well, the Great Barrier Reef is 2000km long, with 3000 reefs. Are you telling me all of it is going to die? "I don't think so," Berkelmans says. "There are some areas that are naturally more resilient than others, there are some areas that see warmer temperatures less frequently because of favourable oceanography or other factors . . . we might lose species, and we might lose them at many reefs. The reef would look vastly different, but the reef would still be there. I don't think there is any doubt about that."

Great Barrier Reef Marine Park Authority chairman Russell Reichelt agrees the reef is generally in "robust good health". Without minimising the threat of climate change, he says it is no accident that the reef is in better condition than any other reef in the world.

"That's because it is largely offshore and there's no Manila or Jakarta sitting beside it," explains Reichelt, a marine scientist by training. "We don't have dynamite fishing, cyanide fishing, we have the resources of a developed country to put in place lines of protection . . . I suppose what I am saying is the reef has a lot going for it, despite the challenges ahead."

The opposing scientific view is bleak. Before leaving for Copenhagen, Queensland University's Ove Hoegh-Guldberg renewed his warning that existing generations of Australians would be the last to experience the reef in all its glory: the one to two degree water temperature rise forecast by the end of the century, in the absence of big cuts to greenhouse gas emissions, sounded the death knell for most corals, he said.

His concern is echoed by Charlie Veron, a former chief scientist with Australian Institute of Marine Science. Veron worked on the latest Reef Outlook Report for the marine park authority, which found that atmospheric carbon dioxide will have to be held under 400 parts per million if important animal species and corals on the reef are to have a fighting chance against climate change. The latest measured level of CO2 in the atmosphere is about 387ppm.

Were it to hit 450ppm, an emissions target publicly supported on several occasions by Rudd, then it's all over for the reef, according to the September Reef Outlook Report. "The result will be widespread destruction of coral communities, with a few persisting in shaded, turbid waters or at depth," it found. Vernon has said emissions will reach that level by 2035 unless something drastic is done. Coral reefs would become "the world's first global ecosystem to collapse", he told London newspaper The Times earlier this year. In July, the Zoological Society of London, the Royal Society and International Program on the State of the Ocean issued a joint statement warning that a mid-century extinction of coral reefs was inevitable.

How times change. Hoegh-Guldberg was howled down in the late 1990s when he started to talk about the risk of the reef being lost. Now it's the turn of Peter Ridd, a professor of physics at Townsville's James Cook University, to defy the scientific orthodoxy and question whether coral bleaching is all it is cracked up to be. "My general view is that the threats and supposed damage to the reef are greatly exaggerated," he says.

Ridd works in JCU's Marine Geographical Laboratory and has done extensive work on the effect on the reef of sediment and nutrient-packed run-off from the mainland, which he also rates as overstated. He accepts the baseline water temperature has increased on the reef and this is a result of climate change, but not necessarily that it is human-induced.

As for coral bleaching, Ridd points to Berkelmans's research. "It's difficult to see why such a small increase in temperature, given that these corals grow in much higher temperatures elsewhere, is going to make that much difference," he says.

Ocean acidification is another matter, however. This lesser-known product of climate change is a greater danger to the reef by Ridd's assessment. It happens as the ocean absorbs CO2 from the atmosphere, altering its pH value. Although surface sea temperatures are rising fastest in tropical regions, the threat of acidification comes from the higher latitudes, where the colder water takes in CO2 more easily.

The theory is that when atmospheric CO2 reaches between 480ppm and 500ppm, the warmer water lapping coral reefs will cease to be a barrier to acidification: even a small change is thought to spell trouble for calcifying organisms such as corals, making it more difficult for them to make the skeleton structures that in turn build reefs.

"Ten years ago, I was told that the coral was going to die from sediment, and we have proved that is complete rubbish," Ridd says. "They are saying that pesticides are a problem, but when you look at the latest data that is a load of rubbish. They are saying that bleaching is the end of the world, but when you look into it, that is a highly dubious proposition.

"So when something comes along like the calcification problem, you are sort of left with this wolf story . . . they are crying wolf all the time . . . and it is very difficult for the public to have confidence in what they are saying."

Ridd and Berkelmans cross paths in Townsville from time to time and maintain a spirited banter on what climate change means for the reef.

On a glorious day such as this in the Keppels, with a breeze on your face and the sun out, the water cool and sparkling, the coral beneath the sea dense and teeming with fish, it is certainly difficult to believe that so much beauty could readily be destroyed.

Berkelmans cautions, however, the doldrums days are never far away. The increase in the baseline water temperature of reef waters, confirmed by maritime records dating back to the 1870s and separately by coral core sampling, means the difference between a regulation summer and a bleaching season is narrowing, increasing the likelihood of another mass coral kill. It was forecast to happen last summer until a heavy wet season intervened, followed by only the second category five cyclone recorded on the reef. For now, the signs are ominous for a bleaching event in late January or February next year.

Berkelmans says there are signs the long-term Pacific Decadal Oscillation weather pattern is entering a cooling phase, and he hopes that will help when the crunch comes. But the reef cannot be expected to stay lucky forever. "If we get a few more weeks of this, then there will be trouble this summer," he warns. "Theoretically we could avoid another bleaching event . . . for the next few years, but the chances are we won't. The baseline is rising. Even if the variability stays the same, unfortunately we are going to see bleaching more and more frequently."