The world’s corals are bleaching. Here’s why and what it means for the ocean’s future.

Two prominent research organizations confirmed a few weeks ago what scientists had long thought: the world’s warm water coral reefs are bleaching en masse for the fourth time in 25 years.   Corals are collections of hundreds of thousands of tiny animals. Often a riot of colours, they turn a boney white when they are under stress, which can be a precursor to their death.  Scientists believe surging ocean temperatures, driven in ​​​​part by climate change, are responsible for the latest bleaching event, which has spanned from Panama to Australia – ​​and is getting worse.   Experts say corals are among the most vulnerable ecosystems on the planet to climate change. These undersea cities, which support ​​​​25 per cent of marine life, could virtually disappear by the end of this century.  “The loss of corals would be a true tragedy from a biodiversity and economic perspective,” says Leticia Carvalho, the Head of the Marine and Freshwater Branch of the United Nations Environment Programme (UNEP). “It would be devastating for one of the richest ecosystems on our blue planet and hundreds of millions of people around the world who depend on coastal fisheries.”  Here is a closer look at the global bleaching event and what it could mean for the future of the world’s corals.  Distribution of warm water corals. Credit: UNEP Corals can be found throughout the ocean, from the balmy waters of the Red Sea to the frigid depths of the North Atlantic. But perhaps the best known live in the warm, shallow waters of the tropics, where they form stunning, multi-coloured reefs.  At the heart of each individual coral is a polyp, a clear, tube-shaped animal with a ring of tentacles that it uses to catch prey. Some corals surround themselves with a limestone skeleton forged from calcium absorbed from sea water. Corals get their colour from thousands of plant-like organisms known as zooxanthellae, which live inside the corals and provide them with food. It is a symbiotic relationship that is fundamental to the health of reef ecosystems around the world.