Coral Experiment Shows CO2 Deadly to Reefs

April 19, 2013

Graham Readfern for ABC:

ON A LARGE WOODEN deck on a coral cay island in the middle of the Great Barrier Reef, research assistant Aaron Chai removes the lid from one of 12 circular white water tanks.

“This is the ‘do nothing’ tank,” he says, peering inside at a careful arrangement of dead, slimy, algae-covered and bleached-white corals.

In July last year, this small reef ecosystem looked very different – corals of vivid purples and blues beside the bright greens of turtle weeds. Since then the levels of carbon dioxide and temperature in the bowl-shaped tank have been changed to the kind of conditions expected by the end of this century if the world ‘does nothing’ about climate change and its fossil fuel use.

“It’s the slippery slope to slime,” says the University of Queensland’s Associate Professor Sophie Dove, who is running this experiment on the university’s research station on Heron Island, about 80 kilometres off Gladstone in central Queensland.


Coral in Tank 4 in July 2012. This tank imitated contemporary conditions on the reef.


Coral in Tank 4 in March 2013. The coral has developed as expected.

In the ‘do nothing’ tanks all but one of the corals has died and is being slowly covered in algae. Some of the coral skeletons have actually started to dissolve in the increased acidity of the water.

“If you look at those reefs in those future tanks now, they are really not all that attractive to tourists,” says Dove. “It’s not something that people would want to go and see. It is becoming more of a mono-culture and that stuff probably isn’t that palatable to the fish. That slippery slope to slime looks to be coming true.”

As humans have pumped more carbon dioxide into the atmosphere from burning fossil fuels, oceans have absorbed about a third of this extra CO2. This makes the water slightly more acidic and in theory makes it harder for corals to maintain their skeletons.


Coral in Tank 3 in July 2012. Conditions in this tank mimicked those expected in around 100 years if the world does nothing to kerb its fossil fuel use, with higher temperatures and acidity.


Coral in Tank 3 in March 2013. The coral has not survived and algae has taken over.

5 Responses to “Coral Experiment Shows CO2 Deadly to Reefs”

  1. […] Graham Readfern for ABC: ON A LARGE WOODEN deck on a coral cay island in the middle of the Great Barrier Reef, research assistant Aaron Chai removes the lid from one of 12 circular white water tank…  […]

  2. I have been saying for some time now that this issue is the “C” in CAGW. If coral reef communities collapse, the effects on the ecosystem will be absoutely catastrophic.

    It’s not just no pretty coral to look at – its a collapse in fishing industries around the world, on which hundreds of millions of people rely for their food and livelihoods.

    • astrostevo Says:

      @ ^ Mike Swinbourne : And also erosion – coral reefs dissipate the force of storms and protect sandy beaches and even rocky cliffs from increased erosion.

  3. … if anything You should be cited, just the greatest – with the highest achievements:

    Gattuso (2010., :

    “Surface ocean pH is estimated to have decreased from approximately 8.25 to 8.14 between 1751 and 2004 and may reach 7.85 in 2100.”
    “Although changes in the carbonate chemistry are well known, the biological and biogeochemical consequences are much less well constrained for several reasons. First, very few processes and organisms have been investigated so far (research in this area only began in the late 1990s). Second, most experiments were carried out in the short-term (hours to weeks), effectively neglecting potential acclimation and adaptation by organisms. Third, the interaction between pCO 2 and other parameters poised to change, such as temperature , concentration of nutrients and light, are essentially UNKNOWN.
    It is not anticipated that oceanic primary production will be directly affected by these changes in carbonate chemistry […] because most primary producers use carbon concentrating mechanisms that rely on CO 2. Note, however, that primary production of some species is likely to be stimulated.”
    “Note, however, that some calcifiers either do not show any response to increasing pCO 2 or exhibit a bell-shaped response curve with an optimum rate of calcification at pCO 2 values close to current ones and rates that decrease at pCO 2 values below and above the current values.”

    Suggett & Smith (2010,

    “Observations of non and sublethal bleaching (and subsequent recovery) are arguably not as readily reported as those of lethal bleaching since (1) the convenient tools used to quantify bleaching yield major ambiguity (and hence high potential for misidentification) as to the severity of bleaching; and (2) lethal bleaching events inevitably receive higher profile (media) attention and so are more readily reported.”
    “While this synonymous association has undoubtedly been key in raising public support, it carries unfair representation: nonlethal bleaching is, and always has been, a phenomenon that effectively occurs regularly in nature as corals acclimatize to regular periodic changes in growth environment (days, seasons etc).”
    “While bleaching induced coral mortality must remain our key concern it must be better placed within the context of bleaching signs that do not result in a long-term loss of reef viability. […]”

    … but first from the scope of basic knowledge (

    “… however, it is not unusual to see a fair amount of pH variation on coral reefs over the course of 24 hrs. During the daytime photosynthesis removes CO2, raising pH in the water overlying the reef.”
    “Daytime pH may rise to 8.3-8.6, resulting in Ωarag as high as 5-7. At night the production of CO2 from respiration can reduce reef pH as low as 8.1-7.8, causing Ωarag to fall as low as 1.5-2.5.”

  4. […] 2013/04/19: PSinclair: Coral Experiment Shows CO2 Deadly to Reefs […]

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