The Copernicus Sentinel-2A satellite takes us over part of the Great Barrier Reef off Australia’s northeast coast on 1 April 2017.
Extending more than 2000 km and covering an area of some 350 000 sq km, it is the planet’s biggest single structure made by living organisms, called coral polyps.

Despite its name, it is not a single reef but contains nearly 3000 different reefs. The reef is home to over 1500 tropical fish species, 400 types of coral, more than 200 species of bird, 5000 species of mollusc, 500 species of seaweed and six species of sea turtle. It is also a breeding area for humpback whales.

In recognition of its significance, the reef was made a UNESCO World Heritage Site in 1981 and is the world’s most protected marine area.

Coral reefs worldwide are increasingly under threat from coral bleaching. This happens when algae living in the corals’ tissues, which capture the Sun’s energy and are essential to coral survival, are expelled owing to high water temperatures.

The whitening coral may die, with subsequent effects on the reef ecosystem, and thus fisheries, regional tourism and coastal protection.

The corals of the Great Barrier Reef have now suffered two bleaching events in successive years. Experts are very concerned about the capacity for reef survival under the increased frequency of these global warming-induced events.

Credit: contains modified Copernicus Sentinel data (2017), processed by ESA, CC BY-SA 3.0 IGO Larger image