Nature's perfect match is breaking down and the Great Barrier Reef is in peril

Updated

Peel back the veneer and nature is a teeming war zone of many flashpoints. Species compete with their own kind and others for limited resources. In a dog-eat-dog world built upon Darwinian principles and food chain hierarchies, only the fittest survive — and the winners take all.



But oases of harmony do exist, where evolution has played matchmaker and engineered pockets of peaceful coexistence. Take, for instance, a relationship formed more than 210 million years ago around the time dinosaurs first appeared on earth.



Until recently, this remarkable and visually brilliant partnership was still going gangbusters.

This is a close-up of a healthy coral polyp — a relative of both jellyfish and anemones.

The tiny creature, which can be as small as a millimetre in diameter, forms the base of coral reefs around the world.

But it doesn't do it alone — it gets a bit of help from microscopic algae known as zooxanthellae.

Like their land-based plant relatives, zooxanthellae perform photosynthesis — a process that converts sunlight, water and carbon dioxide into by-products including oxygen and glucose.

Not only do the algae provide the coral with its vibrant colours, but about 90 per cent of what they produce is passed on to the host. In turn, the coral polyps secrete the calcium that forms the rigid structure of a coral reef colony.

"The very, very essential thing about corals is that they build their own place to live. Nothing else does that," said former chief scientist at the Australian Institute of Marine Science, Charlie Veron — a man dubbed "the godfather of coral".

And in return for this, the algae gets to hunker down in the coral's tiny crevices and avoid becoming easy fodder for the teeming marine life which congregates in a healthy reef environment.

Fuelled by this harmonious relationship, the polyps reproduce, or clone, again and again. A perfect partnership in a turbid world of borderline anarchy.

Over tens of thousands of years, these colonies spread to form the impressive underwater reef structures that we know today.

None more spectacular than Australia's very own Great Barrier Reef.

"So corals have got together with algae to build things that nothing else on earth can possibly rival. That's how they live. And I reckon that's as fascinating as biology can get," said Veron, a septuagenarian who has been diving in the waters around the Great Barrier Reef for half a century.

To put its size in perspective, the third biggest coral reef in the world is the Florida Reef stretching about 270 kilometres to the south of Florida.

The second biggest, according to UNESCO, is the Belize Barrier Reef at more than 300 kilometres.

The Great Barrier Reef is more than 2300 kilometres covering almost 350,000 square kilometres.

And size is important. Though coral reefs cover only 1 per cent of the world's land mass and 2 per cent of its ocean floors, they provide a home to almost a quarter of all marine life.

But the symbiotic relationship between coral and algae, that has survived since the late Triassic period, is breaking down.

Most reef-building corals require a "Goldilocks zone" to prosper. They can only thrive in an environment where water temperatures range between 18 and 29 degrees Celsius. Places where sunlight can penetrate, where the water is salty and the seas are not too rough.

The delicate reef ecosystem now finds itself challenged by the same human-induced factors which scientists say are responsible for climate change: rising temperatures and increasing levels of carbon dioxide in the atmosphere.

In 1998, the Great Barrier Reef experienced its most destructive bleaching event to date.

Algae, responding to the environmental changes, were increasing the production of oxygen to levels their corals host found toxic. Eventually, the coral began expelling its housemate in an act of self-defence.

Half the reef's corals were damaged. The southern and central regions were hardest hit.

Four years later, it happened again.

The southern and central portions of the reef were again hit hard.

But then came 2016. A spike in water temperatures killed off about a third of all shallow corals across the entire reef.

Half the corals north of Port Douglas died in the space of eight months.

The event was so intense researchers said it was as though parts of the reef to the north had been "cooked".

It wasn't over though.

The very next year a further 20 per cent of the corals were affected — the first back-to-back bleaching events ever recorded.

Zooxanthallae

Great Barrier Reef

Florida reef 270km

Belize Barrier Reef 300km

<1 1-10 10-30 30-60 >60 % Bleached 1998

<1 1-10 10-30 30-60 >60 % Bleached 2002

<1 1-10 10-30 30-60 >60 % Bleached 2016

Zooxanthallae Algae

Port Douglas Cairns Townsville Queensland

1mm Coral polyp

Great Barrier Reef

Florida reef 270km Great barrier reef 2300km Belize Barrier Reef 300km

An unprecedented succession of coral bleaching events has left reefs around the world in a catatonic state. Almost half the Great Barrier Reef has been reduced to a coral graveyard, with coral cover at its lowest point since monitoring began.

Under the right conditions, corals can regroup with algae and regrow and this has occurred across many areas of the reef. But even for the fastest growing corals that can take a decade.

"The problem with a 10-year window that's required for a decent recovery is that the chances of us having a fifth bleaching event in that time period is actually very high because of global warming," said director of the ARC Centre for Excellence for Coral Studies at James Cook University, Terry Hughes.

"I dread to think that it might be as soon as next year."

While he can't predict when the next big bleach will happen, Professor Hughes is confident in saying the reef of the future will never look like the one of old.

The heat-susceptible corals are dying off in greater numbers than tougher corals that are harder to bleach and better equipped to recover.

The reef is transforming — but to what extent largely depends on how countries respond to climate change, according to Professor Hughes.

To get a better sense of what the reef will look like under various scenarios of global warming, the US National Oceanic and Atmospheric Administration science agency created these models.

The map "emissions increase unabated" predicts when sections of the reef will next experience two bleaching events in a decade, if nothing is done to reduce global carbon emissions.

This shows that by 2025 and 2030 many parts of the reef will start to experience bleaching events twice per decade, with almost the entire reef bleached by 2065.

The other map shows a scenario in which emissions peak in 2040 but decline thereafter. By 2040, sections all down the reef will start to experience bleaching events twice per decade, with more sections experiencing it by 2065 and 2085.

Although Charlie Veron insists he's a realist, his views lean towards the pessimistic end of the spectrum.

"I see what lies ahead and I'm terrified of it. I'm terrified for my family, my children, and I'm doing all I can to buffer my family against what's coming," the marine scientist said.

Veron, who became a coral expert by accident after he fell in love with the intensity of life he found under water, has now quit his research into corals to become a full-time, self-appointed advocate.

When climate change was first mooted in the 1980s, Veron was highly sceptical, recalling his first exposure to the polarising debate about the world's changing weather patterns.

But rather than dismiss it as bunkum, Veron jumped into the academic literature and studied the data.

His epiphany was as sudden as it was shocking. "Oh my God, this is correct," he recalls telling himself as he realised the consequences of rising carbon dioxide emissions.

Unchecked, these emissions would change the chemistry of the oceans — the "lungs of the Earth" — wiping out coral colonies and triggering an environmental chain reaction.

The result is a term that no one should use lightly: mass extinction. That would be the Earth's sixth in the past 500 million years, but the first since humans arrived.

"At the rate we're going we're going to become an alien species on our own planet, because we're going to destroy everything else."

"That will be the end of humanity."

Veron is not a climate scientist and it's fair to say that his views are not universally endorsed by his peers. But his conviction is absolute.

The scenario he described is not hypothetical, he insists. There are precedents. When ocean habitats have collapsed in the past, they've "stayed collapsed for millions of years".

Watch 7.30 tonight for the first of three special pieces on the state of the reef from reporter Peter Greste and producer Amy Donaldson.

Credits

Research and interviews: Amy Donaldson and Peter Greste

Development: Ri Liu and Nathanael Scott

Design: Alex Palmer

Notes about this story

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Topics: great-barrier-reef, oceans-and-reefs, environment, climate-change, qld, australia

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