Spotting coral bleaching from space

A world-first space-based coral reef monitoring project has just got off the ground – literally. The Allen Coral Atlas project is now using high-resolution satellites to scan nearly a quarter of a million reefs across the globe – from space – to monitor coral-killing bleaching events in real-time.

“The current prognosis for the world’s coral reefs is bleak,” says remote sensing expert Chris Roelfsema from the University of Queensland (UQ). “With ever-warming, more polluted and acidic oceans, models predict that 70 per cent to 90 per cent of coral reefs will be lost by 2050. Until now, there hasn’t been a global system in place to monitor coral reefs under the stresses that may lead to their deaths.”

Previously, scientists and policymakers had to piece together separate datasets and maps. But this new tool can create comprehensive global maps to gain a bigger picture of the health of global reef systems through time.

“This monitoring capability will help us to see, for the first time, where and to what extent coral reef bleaching is likely to be occurring as well as where it isn’t bleaching so we can identify resilient reefs,” explains Paulina Gerstner, the Allen Coral Atlas Program Director.

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Bleached corals in Hawaii. Credit: Greg Asner

The project began in 2018, when next-gen CubeSats operated by Planet created a mosaic image of the world’s coral reefs, with a resolution of four metres per pixel. Researchers then took the data and built maps capturing details such as reef depth and water colour, and even to distinguish between coral, algae and microalgae, land, rock, sand and rubble.

Now the system has expanded to a global monitoring system to scan over 230,000 coral reefs on a biweekly basis. It relies on satellite imagery with a resolution of 4–10 metres to detect differences in reef brightness, coupled with an algorithm that analyses how severely a reef is under stress.

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Atlas Bleaching Data for Madagascar on April 26, 2021

“The Allen Coral Atlas will allow us to offer critically important information to scientists, decision and policymakers, something that’s urgently needed for rapid response and conservation,” says Roelfsema.

“Once we know where this is happening, governments and NGOs on the ground can swoop in to take action sooner, rather than later.”

But anyone can view the Atlas, scientist or not – it’s free to use online and can be accessed here.

The project is an international collaboration between ecologists, remote sensing scientists and software engineers from institutions such as UQ, Carnegie Institute for Science, and Hawaii Institute of Marine Biology.

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