Please explain: The ins and outs of coral bleaching

Posted on Posted in Marine, Please explain

Coral bleaching has been back in the headlines again recently – surely we’re all aware of it by now. With internationally renowned activists like David Attenborough campaigning for action to save the Great Barrier Reef (GBR), I think most would agree it’s become a global issue that warrants attention.


Often the media reports regarding the plight of the GBR, and coral bleaching in particular, can be confusing. The audience can be bombarded with overwhelming facts and figures, and sometimes alarming predictions or impassioned opinions. Aside from all of that, what are they actually talking about? What is coral bleaching?


A neat, simple diagram that sums up the basic process of coral bleaching. Source:


Admittedly, I’m no expert on the topic, but I did catch Australian Story last week, and it featured some of Australia’s experts on coral bleaching. I have been lucky enough to hear these guys talk about their research and they are brilliant. So, in their words, here’s a summary of the coral bleaching process:


“Corals have adapted to work within certain temperature thresholds, so they can’t get too cold for too long and they can’t get too hot for too long. Basically corals are these amazing animals that build their cities, their structures and they grow a plant-like cell (zooxanthellae) in their flesh and they use that to convert the energy of the sun into food. But when it gets too hot they have to expel that cell and what happens is they turn clear, you see their skeleton through the clear animal and it starves to death and that’s the process of coral bleaching.” RICHARD VEVERS, THE OCEAN AGENCY

“If (hot) conditions are mild or they don’t last for very long, those little tiny plants can come back and live in the tissues. And the coral can survive. There will have been impact. It won’t have grown during that period and so on. But it’s still living. But what we’re seeing more and more is that as sea temperatures increase these corals that go white tend to die.” PROFESSOR OVE HOEGH-GULDBERG

“And the flesh peels away and algae settles on the skeleton and you see these wispy bits of skeleton and it just looks revolting.” RICHARD VEVERS, THE OCEAN AGENCY


A close up of a bleached Brain coral (Diploria strigosa). Source:

The transition from healthy coral to dead coral can occur in a matter of weeks. For many of the worlds coral reefs already affected by bleaching, coupled with ocean acidification (I will visit this process in another post soon), this means there’s no going back. The reefs have no capacity to rebuild. The ramifications of losing coral reefs, and the GBR in particular, are incredibly far-reaching; think ecological, economic, social and cultural impacts.

If you want to read on, here are some good starting points:

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