Reef crest dominated by robust branching corals and coralline algae, Great Barrief Reef © WWF / James Morgan

Reef crest dominated by robust branching corals and coralline algae, Great Barrief Reef © WWF / James Morgan

What an underwater heatwave means for the Great Barrier Reef

17 Jul 2022

Keywords
  • great barrier reef
  • climate change
  • coral
  • marine protected areas
  • marine species
  • renewable energy
  • fight for the reef
  • coral bleaching

Our oceans need urgent protection.
Get involved and show your support for action to safeguard nature and set it on the path to recovery by 2030.

 

ADD YOUR VOICE

 

Australia is feeling the brunt of climate change. From more frequent and severe droughts and bushfires to cyclones and floods, climate change is impacting our people, our ecosystems and our economy in profound ways.

Not even the magnificent Great Barrier Reef is immune. In fact, this natural wonder and its network of marine sanctuaries is at the very forefront of climate change.

When underwater heatwaves hit, the impacts on the Reef can be devastating. Coral bleaching turns these verdant and vibrant underwater forests a ghostly white, during a transformation as graphic as it is heartbreaking.

What is coral bleaching and what causes it?

More than 600 species of coral live on the Great Barrier Reef, creating the colour and beauty for which this World Heritage Area is prized.

Like trees, coral acts as food and habitat for millions of other creatures that call the Reef home.

 

WWF’s Chris Hof beside a green turtle at Heron Island © WWF-Australia / Jacinta Shackleton

 

Coral is actually made up of colonies of very small creatures known as polyps, which are closely related to jellyfish. In one of the marine kingdom’s many splendid relationships, the polyps allow beneficial algae called zooxanthellae to live within their tissues. In return for the safe home, the algae provide the building blocks for the coral’s outer limestone skeleton, as well as its vibrant colour.

 

The last decade was the hottest in recorded history and, since 1910, the surface temperature of seas surrounding Australia has increased by over 1°C.

Warmer water temperatures, especially when they persist for eight weeks or more, are catastrophic for corals. It causes them to expel their resident zooxanthellae and the corals begin to die.

A series of underwater heatwaves in recent years has accelerated this devastating process, leaving the corals colourless (bleached) and the polyps vulnerable to disease and starvation. Coral mortality has increased with each subsequent underwater heatwave.

The deadly toll

Underwater heatwaves caused by rising temperatures threaten marine ecosystems around the world. Over the past 40 years, about half of all coral reefs are estimated to have been lost. Much of the living coral reef in the Great Barrier Reef Marine Park has now been damaged. In some sections, up to 90% of corals have been affected.

 

The last five years have been particularly brutal, with the Great Barrier Reef suffering widespread coral bleaching in 2016, 2017, 2020, and again in 2022. Occurring during a La Nina weather system, when the weather is typically cooler, cloudier and wetter, the bleaching event of early 2022 heralds a worrying new trend.

In the summer of 2016, the Reef experienced its worst coral bleaching ever, with an area roughly 1,100 kilometres long affected. A year later, a second severe bleaching occurred. Early research indicates that almost half of all coral in the 345,000-square-kilometre Great Barrier Reef Marine Park may have died in these two events. But the worst was yet to come.

 

Coral bleaching before after on March and May 2017, Lizard Island © XL Catlin Seaview Survey

 

In 2020, the Reef experienced its most widespread bleaching on record. Around 2,300 kilometres of coastal reefs were severely impacted - from the Torres Strait in the north, down to the Reef’s southern boundary. This third mass bleaching event in five years impacted parts of the southern Reef for the first time.

The very existence of this, the largest living structure on the planet, is now threatened. And along with it, the delicate web of marine life that depends on the Reef, including fish and turtles.

 

What can we do?

As climate change continues to heat our planet, coral bleaching is expected to become more severe and more frequent.

Should global temperatures rise between 1.5 and 2°C above pre-industrial levels, the frequency of underwater heatwaves will increase. If the planet should warm by 2°C, heatwaves will rise four times this and we will lose the Great Barrier Reef altogether.

But there is hope. The good news is that bleached coral is not dead coral. Stressed coral can recover if water temperatures cool down in time and the coral is not subject to repeated underwater heatwaves.

There is hope for our planet and for our Reef if Australia acts now to limit global temperatures to 1.5°C.

 

A green sea turtle (Chelonia mydas) swimming off Heron Island Research Station, Queensland © WWF / James Morgan

 

We can do this, right now, by transitioning our economy away from coal and gas, instead, making Australia a Renewable Energy Superpower. In driving down our greenhouse gas emissions, we can create well-paying jobs, providing economic opportunities with significant environmental returns as we protect our Reef from further temperature rises.

Given time, the Great Barrier Reef can recover if we turn to renewable energy sources and slow the rate of climate change.

But we cannot delay, not if we’re serious about protecting this international treasure. We must act now.

Learn more about how we're working to protect the Great Barrier Reef.

 

FIND OUT MORE

 

Recommended reading

Bottlenose dolphins swimming in the ocean © Tahlia Cohen / Unsplash

Oceans | Climate

What effect is global warming having on our oceans?

Our oceans are fundamental to life on Earth, but rising sea temperatures are threatening the future for people and our livelihoods, marine habitats an ...

Read more

Reef crest dominated by robust branching corals and coralline algae, Great Barrief Reef © WWF / James Morgan

Climate | Oceans

What an underwater heatwave means for the Great Barrier Reef

When underwater heatwaves hit, the impacts on the Great Barrier Reef can be devastating. In fact, this natural wonder and its network of marine sanctu ...

Read more

Get involved

{{thankYouPopup.firstname}} {{thankYouPopup.lastname}}

Thank you for your {{thankYouPopup.isMonthly ? 'monthtly' : ''}} donation of ${{ thankYouPopup.amount }}

Please check your email for confirmation

{{thankYouPopup.certificatename}}

If you have any questions about your donation, please do not hesitate to contact our friendly Supporter Services team either by email: enquiries@wwf.org.au or call 1800 032 551

Share this page with your friends and family to help endangered animals even more.