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White reefs – Nature’s cry for action on climate change

The newcomer became a keen student of the reef, soaking up its many nuances. In the summers he noticed that small patches of coral would turn totally white. “I didn’t really pay much attention to it because in a few weeks they would return to normal,” he said.

That changed forever in 1998. For the first time researchers recorded severe bleaching events on coral reefs in every region of the world. Scientists declared it the first global coral bleaching event.

Half the reefs on the Great Barrier Reef were impacted. “For the first time there was coral that just didn’t come back. It died, was covered in algae, and that was that. “Even back then people said it was climate change. You start to think ‘what’s going to happen next summer?’”

That same year Paul Marshall was at James Cook University. He and a fellow PhD student heard about the bleaching and headed out onto the reef to do some research. “The Great Barrier Reef had always seemed so magnificent and large and unassailable that we thought it was somewhat immune from bleaching. But seeing huge amounts of coral die was the kick in the guts that made me realise the reef actually wasn’t immune from the effects of human activities.

In the years ahead Dr Marshall went on to become founder and director of the Climate Change Program at the Great Barrier Reef Marine Park Authority (GBRMPA). “The bleaching was so widespread and dramatic you could actually survey for bleaching by looking out the window of a plane and picking the white reef,” said Marshall. “We saw bleaching that spanned two thousand kilometres north to south.”

The first mass coral bleaching event ever recorded for Western Australia occurred during the 2010-11 summer. Reefs from the Montebello and Barrow Islands in the north to Rottnest Island in the south were hit by an underwater heatwave peaking at up to five degrees Celsius above long-term averages. For the first time significant bleaching was recorded at the World Heritage-listed Ningaloo Reef. In one section of Ningaloo, live coral cover crashed from 80 per cent to 6 per cent.

Corals are actually tiny animals called polyps. They live in colonies of hundreds, thousands or even millions of individuals. Hard corals extract chemicals from seawater to create the limestone cups in which they live. Over decades these limestone cups build up to create a reef.

Millions of years ago coral polyps started allowing microscopic algae called zooxanthellae to live inside their cells. It was a development that enabled corals to thrive. The algae turn sunlight into energy and up to 95 per cent of the nutrients they make are leaked to the coral.

However, when the water is warmer than normal for weeks on end and there is bright sunshine, the algae go into overdrive and can produce toxic levels of oxygen.

As a self-defence mechanism the corals shed the algae. Coral polyps are actually clear; it is the zooxanthellae that give coral its beautiful colour. Without their zooxanthellae, corals no longer receive enough food. When bleaching is prolonged, they can die.

As Ove Hoegh-Guldberg, Director of the Global Change Institute, wrote in The Conversation: “Climate change has been driving up sea temperatures.

“When natural variability adds to this trend, such as during El Niño, temperatures now exceed the threshold for mass coral bleaching and death.”

The Intergovernmental Panel on Climate Change, the leading international body for the assessment of climate change, states that mass bleaching and coral death “is the most widespread and conspicuous impact of climate change”.

By February 2016, the National Oceanic and Atmospheric Administration’s Coral Reef Watch Coordinator Mark Eakin said: “We are currently experiencing the longest global coral bleaching event ever observed. We may be looking at a 2-to-2½-year-long event. Some areas have already seen bleaching two years in a row.”

And that’s the biggest concern for Dr Terry Done, formerly the Senior Principal Research Scientist at the Australian Institute of Marine Science. “Coral communities have a good capacity to bounce back but they need a decade or more between severe impacts. If they get clobbered too frequently it’s not just the corals in trouble; it’s all the other species which live in, on and among the corals,” Done said.

Aside from their natural beauty, coral reefs are extremely valuable ecosystems. Coral reefs account for up to 12 per cent of the fish caught in tropical countries, and up to 25 per cent of the fish caught by developing nations. They protect shorelines from storm surges and cyclones, and more than 100 countries benefit from the tourism and recreational value of their coral reefs.

While there is now wide acceptance that climate change is causing bleaching that wasn’t the case when Paul Marshall started at GBRMPA. “It was really hard to talk about bleaching and climate change because politicians don’t want to hear about problems. But you can’t really talk about coral bleaching without talking about causes and the biggest cause is climate change. So it’s been really interesting to see a shift in the willingness of government staff to talk about the importance of dealing with climate change.”

One of the turning points was the emergence of a new concept: improving the resilience of the reef. “Resilience was a way of understanding that there’s stuff we can do to help the reef cope with climate change. There was science to back it up. We now know that corals exposed to poor water quality, particularly elevated nutrients, will bleach at a lower temperature,” said Dr Marshall.

“These excess nutrients, mostly from agriculture, wash off the land and also cause crown of thorns starfish outbreaks which destroy coral. Sediments, made worse by clearing in reef catchments, inhibit the recovery of coral communities.

“Every person can take action to help coral reefs cope with climate change. It could be personal action to reduce your own greenhouse gas emissions. It might be having a strong voice in the public and political debate about the need to transition to renewable energy. Or if you’re a farmer or fisher or someone who lives on the coast you might be able to reduce pollution flowing to the reef,” Marshall said.

As for Tony Fontes, he hopes to be a 90 year old diving on the reef.

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