Drained of colour, becoming ghost-like. This is what is happening to the world’s corals. The bright and beautiful are being ‘bleached’, from thermal stress. A great coral die-off is here.
The highest thermal stress we've ever seen...
Vulnerable at the best of times, conditions have combined to create a global mass bleaching of coral. The world could lose 5% of its corals this year — more than 12,000 square kilometers.
Combination picture of a healthy coral and a bleached coral
Temperature rise is among the main reasons. This causes stress to corals, breaking down the partnership they have with algae, a symbiosis by which they feed and which adorns them with their colour.
What corals are
Corals are marine invertebrates, animals, not plants. They typically live in colonies. They can be soft or stony. Some need sunlight so they thrive no deeper than 60 metres. Other corals can live as deep as 3,000 metres, where no sunlight penetrates. Corals are found not only in tropical and subtropical waters such as off Australia, therefore, but also as far north as Alaska. Highly diverse ecosystems form where there are corals. Reefs live in less than one percent of the surface area of the seas and oceans, but are the habitat of 25 percent of all marine fish species.
As the oceans absorb atmospheric heat and this is increasing, coral bleaching is a sign of climate change — the proverbial canary in the coal mine.
Combination picture of the sea surface temperature in 1997 and 2015 by the NOAA