Mass bleaching of Barrier Reef could go global

Clone rangers: All of the tiny animals in a single reef colony are clones of one another. © Alamy

Are all the coral reefs going to disappear? The Great Barrier Reef has just suffered its third mass bleaching event in five years, causing huge loss in the world’s largest living structure.

Rising ocean temperatures may have pushed the world’s tropical coral reefs over a tipping point where they are hit by bleaching on a “near-annual” basis, according to the head of a US government agency programme that monitors the globe’s coral reefs.

Dr Mark Eakin, coordinator of Coral Reef Watch at the National Oceanic and Atmospheric Administration, said there was a risk that mass bleaching seen along the length of the Great Barrier Reef in 2020 could mark the start of another global-scale bleaching event.

Coral reefs are one of nature’s true wonders.

They are living organisms, colonies of tiny little animals that join together to form stunning marine edifices.

In terms of biodiversity, experts estimate that coral reefs rival rainforests in the huge variety of wildlife they support. They provide habitat for 25% of marine life – but cover only 1% of the ocean floor.

But these incredible ecosystems are under threat.

Experts say coral reefs are the poster child for the negative effects of climate crisis. They are the most visible example of how quickly warming temperatures can transform the environment.

Global warming is one important factor that leads to coral bleaching, an event that transforms multicoloured underwater landscapes into ghostly graveyards.

When the water gets too hot, corals kick out the algae that live with them. These algae provide all the kaleidoscopic colours that we associate with coral reefs, as well as 95% of the food that corals need to survive.

Corals cannot build their reefs without working with the algae. So when these are expelled, the coral turns white. The skeletons underneath the live coral, accumulated over generations, are cruelly exposed.

For instance, live growing coral on Caribbean reefs has declined to just 8% of the reefs’ composition, compared with 50% in 1970. Scientists have estimated that all the world’s coral could be dead by 2100.

This year, the Great Barrier Reef experienced its third major bleaching event in five years. A leading professor, Terry Hughes, described seeing the reef as feeling “like an art lover wandering through the Louvre... as it burns to the ground”.

After the devastating bleaching events in 2016 and 2017, many publications penned obituaries for the reef system, which covers a larger surface area than the UK.

But bleaching does not necessarily mean that the reef is dead. If temperatures return to normal after a particularly warm season, coral can recover – this is what scientists are working to achieve.

This is important because coral reefs are critical to 500 million people around the world, providing food, jobs and tourism. Reefs provide a nursery for many commercial fish species and contribute around $375bn (£328bn) a year to the global economy.

So, are all the coral reefs going to disappear?

Bleached by the beach

Quite possibly. Global temperatures are continuing to rise. Our actions over the last few centuries have profoundly affected the natural world. Nowhere is this more true than in the reefs, where subtle temperature changes can destroy entire ecosystems. With most of the damage already done, we now need to make sure that we do not lose other wondrous natural habitats.

Not necessarily. Some scientists hope that by slowing down the speed at which we are warming the planet, corals might be able to adapt to slightly warmer water. If temperatures stabilise or if unusually hot seasons remain unusual, much of the world’s coral reefs can survive. We all have to work hard at living sustainably to ensure that this becomes a reality.

You Decide

  1. There are many reasons why people like coral reefs and want to protect them. Which one do you think is the most important?
  2. Do you think that humanity can make the changes needed to ensure that natural wonders like the Great Barrier Reef can survive this century?


  1. Write down a list of the small things you can do every day to help stop coral bleaching. Make sure you do your research first!
  2. Teach someone in your home about corals. Draw them a diagram about how coral reefs work and explain the threat of coral bleaching.

Some People Say...

“For years, we thought the oceans were so vast and the inhabitants so infinitely numerous that nothing we could do could have an effect upon them. But now we know that was wrong.”

David Attenborough, English broadcaster and natural historian

What do you think?

Q & A

What do we know?
Bleached coral does not necessarily die. That said, coral left in warm water for too long, rarely survives. In 2010 in Florida, it was colder waters that contributed to coral bleaching. Corals can bleach due to pollution, low tides and overexposure to sunlight, as well as warming waters.
What do we not know?
We do not know how many bleaching events are likely to take place in the coming years. Predicting global temperatures is an imperfect science. This means that the demise of global coral reefs could happen a lot faster or slower than expected, regardless of the actions we take.

Word Watch

Buildings, structures (from the Latin for a “made dwelling”).
A measure of natural variation at the genetic, species and ecosystem level. The more different species there are in a single location, the higher that place’s biodiversity.
Home, the place where a species lives.
Biological communities made up of different, interacting organisms and their physical environment.
Poster child
A person or thing that best represents a specific idea or cause.
Plant-like living things that can make food from sunlight by photosynthesis. They are very important because they make much of Earth’s oxygen.
Complex patterns of colours; multicoloured.
The Louvre
The world’s largest art museum is in Paris.
Articles commemorating the life of someone who has died


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