Why the Great Barrier Reef isn’t magically ‘blue again’

The Australian newspaper published a contentious article titled ‘How the reef became blue again‘ last weekend, discussing the ‘resilience’ of the Great Barrier Reef to climate change. On a whole the article did a pretty good job in getting the scientific facts correct, but the debate and ensuing discussion is full of rhetoric deliberately misleading.

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.

True. We (Guillermo Diaz-Pullido and a group of scientists from the University of Queensland, James Cook University, the Great Barrier Reef Marine Park Authority and the Australian Institute of Marine Science) published a paper in the journal PLoS ONE titled “Doom and Boom on a Resilient Reef: Climate Change, Algal Overgrowth and Coral Recovery” (read it here, the journal is open access). In this we concluded “Our study provides a key example of the doom and boom of a highly resilient reef, and new insights into the variability and mechanisms of reef resilience under rapid climate change”

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.

False. The whole “until recently…” is deliberately misleading and makes scientists sound flippant. Sediment run-off is still a prime threat to the inshore reef. Studies have shown that there has been an 8-10 fold increase in sediment loading since European settlement of the QLD coastline in the late 19th century, and recent increases in nutrients and herbicides are a considerable cause for concern. Whilst the impacts of climate change are more recent, this doesn’t make the impact of anthropogenic runoff any less of a ‘prime threat’. Indeed, recent research suggests that by actively improving water quality through better management of the reef and catchments at a regional scale, we can actually increase the survival of inshore reefs to coral bleaching events.

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

Inconvenient to whom? If you asked ANY marine biologist, this is great news. This is exactly how the media (especially The Australian newspaper) make deliberate efforts to portray scientists as being ‘gloom mongers’, and by calling this an ‘inconvenient truth’ pretends that there is a GREAT CONTROVERSY, when in reality there isn’t that much disagreement at all. Never let the truth get in the way of journalistic creativity.

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.”

It surprised me and many other scientists, too. A few people at the time tried to call foul on Ove Hoegh-Guldberg on HOW HE GOT IT ALL WRONG without actually noticing he was a co-author on the Keppells PLoS ONE paper with Ray Berklemens. So far, no objections.

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.

So far, so good. It’s a little misleading to suggest that scientists don’t ‘fully understand’ bleaching – we have a pretty good grip on the mechanisms and the causes.

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.

Calling this a ‘miracle’ is possibly stretching the truth a little, but still – so far, so good.

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.

Calling scientists “doomsayers” is simply poor journalism. Ray Berkelmans and a group of scientists have done some great work in the Keppells documenting shifts in coral community structure and symbiont shuffling during bleaching events. His research shows some local scale acclimation to increased temperatures, which is great. Whether the Keppells are an exception being such a low latitutude and low diversity inshore reef system is the question – how applicable are these findings to other reef areas?

Either way, you would be hard pushed to find a scientist who doesn’t perceive this as great news – the Australian is trying it’s best to create controversy out of thin air.

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.

So far, the controversy is kept to a minimum and the science surprisingly accurate. Adaption is a good thing, but as Ove pointed out before, the degree to which corals can adapt is critical:

Ove Hoegh-Guldberg, a leading coral biologist at the University of Queensland, Brisbane, says the findings are very interesting, in that they demonstrate a way in which corals can acclimatise to warmer temperatures – to an extent. However, he is cautious about what the results might mean in the long run, as type D provides the coral with only about an extra 1 to 1.5 °C of heat tolerance.

“After changing to D, corals don’t really have any other options – and the benefits of D will eventually be overwhelmed by climate warming,” he says.

So – how to make this article more more sensational and sell more newspapers? Here goes:

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.”

It seems that people have picked up on “Are you telling me all of it is going to die? I don’t think so” and ignored every other work in the paragraph:  “The reef would look vastly different, but the reef would still be there. I don’t think there is any doubt about that“. To an extent I agree – the entire Great Barrier Reef won’t disappear overnight, but impact of losing entire reefs, species and biodiversity due to climate change will be huge. Here is a figure from Hoegh-Guldberg et al (2007) showing extant examples of reefs from the Great Barrier Reef that are used as analogs for the ecological structures anticipated for 375ppm, 450-500ppm and >500ppm:

To me, the debate isn’t whether the reef will “die entirely”, but that the entire reef will look vastly different under projected climate change – the reef isn’t magically going to become blue again. It’s hard to disagree with the conclusions of Hoegh-Guldberg et al (2007), who state that: “Climate change also exacerbates local stresses from declining water quality and overexploitation of key species, driving reefs increasingly toward the tipping point for functional collapse”

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.”

Whilst Reichelt is correct in saying that there is no dynamite or cyanide fishing, the science doesn’t seem to support his observations of the reef being in “robust good health”. Comparing the GBR to the Phillipines and suggesting that we are managing our reefs better than they are is possibly misleading: a paper published in PLoS ONE by John Bruno and Elizbeth Selig found quite the opposite:

“…in 2003, coral cover on the Great Barrier Reef, considered the “best-managed” and “one of the most ‘pristine’ coral reefs in the world”, was not significantly greater than on reefs in the Philippines and other subregions that are often thought to be highly threatened and poorly managed”

Indeed, judging by the declines in coral cover over a 20 year period (see the graph below), combined with with the GBR-wide decline in coral growth reported last year, it’s hard to suggest that the GBR is in ‘robust good health’.

Percent coral cover in the GBR between 1980-1983 and 2000-2003 during different periods (Bruno & Selig 2007)

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.

At this point it’s wise to say that this isn’t really an ‘opposing view’ rather than a consensus view.

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.

Australia ‘loves the underdog‘, so to speak. The problem with Peter Ridd’s attempt to ‘defy scientific orthodoxy’ is that he doesn’t have much science to back up his opinion or ‘general view’.

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.

Whilst Ridd has some impressive publications, there is nothing there that shows that the effect of sediment and nutrient run-off from the land on nearshore coral reefs is ‘overstated’.

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.

The science doesn’t support Ridd’s opinion – the “Corals like it hot” meme has been debunked before (see here, here and here for more discussion)

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.

Nobody has said that ‘bleaching will be the end of the world’ – besides which, Ridd is yet to provide any evidence that this 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.”

As far as I see it, from this article, two things make it difficult for the public to have confidence: first, here is a scientist who is attempting to ‘defy the scientific orthodoxy’ based upon opinions rather than any actual evidence. Second, here is an article that is deliberately trying to push this into a bipartisan issue of ‘doomsayers’ vs ‘iconoclasts’ – which couldn’t be any further from the truth.

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.

It’s hard to argue against rhetoric like this – the author may find this hard to believe, but it doesn’t mean that the proposition is in any way less reasonable because of this.

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.”

And so continues the Australian newspaper’s war against science

4 thoughts on “Why the Great Barrier Reef isn’t magically ‘blue again’

  1. I guess Ridd aspires to be the Plimer of Marine Biology, and similarly become the darling of the corporate media. Great that he can have “a spirited banter on what climate change means for the reef” though, I mean, nothing hinges on the answer.

    As I have remarked before, there is a special section of hell reserved for climate change deniers – it’s called Australia.

  2. Peter Ridd is science advisor for the Australian Environment Foundation (AEF), which just happens to share its place of business with the right-wing think tank Institute of Public Affairs. The head of the AEF admitted on Triple J’s Hack program that the group was basically set up to protect the interests of the timber industry.

    Doesn’t mean that his comments are wrong, but that they probably come with an agenda.

  3. Hey Jimmy,

    The Triple J audio is in the archives – click here for a link. The problem with Peter Ridd isn’t his advisory position (no matter how much agenda they come with), it’s that his comments have little scientific grounding…

  4. The story for this article was principally about Peter Ridd’s views and The Australian newspaper has an editorial stance of promoting skeptical views as though they had come from the same knowledge base as scientific views. No wonder the public debate is so polarizing.

    Conducting a scientific exchange through the filter of a journalist is fraught with problems. Being taken out of context is a comment event. In closely dissecting the journalist’s writing and quotes, you run the same risk of error in ascribing views to interviewees – whether it be me, Ray or even Peter for that matter.

    Where you discuss comments I made about ‘robust good health’ you write as though the journalist’s extracts were all I had to say on the matter. As I said to the journalist there have been signficant, negative changes on the Reef since European settlement, and I’ve seen significant loss of inshore reefs since 1968 when I first snorkelled on the Reef. The “good health” comments were in the context of comparison with many coral reefs in other parts of the world.

    For interest, I put a comment explaining my position on climate change risks to the Great Barrier Reef on the web at http://www.gbrmpa.gov.au — see the section on media updates). I’ve read this blog with interest, and have also been enjoying http://www.skepticalscience.com.


Leave a Reply

Your email address will not be published. Required fields are marked *