University of Queensland's Associate Professor Sophie Dove tests coral survival in warmer, acidified water in March 2013. The coral has not survived and algae has taken over. Photo: Sophie Dove

By Graham Readfearn
15 April 2013

(ABC Environment) – 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.

The World Heritage-listed Great Barrier Reef is already under stress from natural and man-made hazards. There's climate change and ocean acidification, both driven by burning fossil fuels; run-off from farmland; attacks by crown-of-thorns starfish; cyclones; fishing; and shipping.

A study led by the Australian Institute for Marine Sciences found that since 1985 the reef has lost more than half its coral cover, with two thirds of that loss occurring since 1998.

Dove's experiment aims to find out what the future may hold for the reef. All the tanks have inside a near-identical mini-ecosystem with specimens taken from a reef slope next to Heron Island. Each tank is filled with sediments, rocks, 11 different types of coral, two types of snails and various other species such as sea cucumbers, small crabs and blenny fish.

There are three 'control' tanks where temperature and carbon dioxide (CO2) levels change every two hours in line with measurements taken by a sensor on the reef slope.

Conditions in three 'pre-industrial' tanks are treated to temperatures about 1°C less than today and CO2 levels at 100 parts per million below current levels in the atmosphere, a reduction of around 25 per cent.

Then there are the future tanks. One future scenario presumes the world will do something on emissions so that as we approach the end of this century temperatures are about 2°C warmer and CO2 levels rise a further 220 ppm.

The ecosystems in three 'do nothing' tanks undergo temperatures about 4.5°C above today with CO2 levels raised 600ppm.

All of the different scenario tanks move in tandem with the control tanks, meaning they undergo the normal daily and seasonal changes that happen on the reef.

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." [more]

The slippery slope to slime

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