'Devastating' hidden detail in image of Great Barrier Reef

Looking underwater it's possible to witness the decay first-hand.

Aerial images appear to show a healthy Great Barrier Reef but look a little closer and you’ll notice a number of mystery diseases eating away at it.

“Devastating” is how UNSW PhD candidate Samantha Burke describes the impact of just one troubling pathogen — black-band disease. “As the disease progresses it’s like watching an infantry moving across the coral. One side is live and on the other side of the decay it’s dead,” she told Yahoo News Australia.

In the past 25 years, disease coverage on coral has tripled to 9.92 per cent globally. By the end of the century, her modelling predicts 80 per cent of the world’s corals could be infected.

An aerial shot of the GBR with two boats on it.
While they are hard to see from above, disease is clearly destroying the world's reefs. Pictured is a file image showing the Great Barrier Reef from the air. Source: Getty

Warming waters are thought to be driving the spread because they weaken the coral’s immunity, but plastics and human activity are also thought to be contributors. Disturbingly the decline is likely to worsen even if temperature rises are conservative.

“What is clear is that coral disease prevalence is climbing across the globe, and without urgent action to address warming temperatures, more coral will become diseased,” Ms Burke said after releasing her study in the journal Ecology Letters.

Even if we were to stop and go carbon zero right now, there are still some effects that are expected to continue.Samantha Burke

Are the diseases bacterial or viral?

Surprisingly little is known about coral diseases. While some of them have names, researchers are yet to determine whether they’re viral or bacterial.

Coral underwater.
It's only when you look at coral underwater that it's possible to see infection. Source: Man Lim Ho

What’s clear are the symptoms and these have allowed scientists to group them into a number of categories. These are the current diseases being researched on the Great Barrier Reef:

  • White diseases that look similar to bleaching

  • Stony coral tissue loss disease

  • Black-band disease that is associated with vibrio bacteria

  • Brown-band disease.

  • Atramentous necrosis.

“The naming convention currently for coral diseases in general is just what it looks like, because we don’t have any particular pathogen that we’ve yet associated with any specific disease,” Ms Burke said.

“We have seen evidence of certain bacteria being present with particular diseases, but we don't know if that's just because those bacteria happened to be there, or if it’s causing the disease.”

Black-band disease in close up.
Black-band disease is one of several illnesses impacting the world's coral. This example was photographed in the Caribbean Sea. Source: Getty

Why has the Great Barrier Reef been singled out?

Modelling found the Pacific Ocean, where the Great Barrier Reef lies, is expected to experience a greater increase at a faster rate, if waters continue to warm. It’s unknown why the Pacific is particularly suffering.

Ms Burke said more knowledge is needed to better understand the diseases so scientists can work to slow down infection rates.

She also believes every effort must be made to slow global warming to mitigate the impact of disease.

“The rising temperatures are a considerable factor, so if we’re looking for a place to start… then lowering them would be a great avenue to pursue.”

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