Marine heatwaves: a death-sentence for corals in the Mediterranean

The latest data published by the Copernicus Climate Change Service warns against the devastating effects that marine heatwaves can have on marine ecosystems, particularly corals.

Corals are home to extremely high level of marine biodiversity. However, they are also fragile living beings, easily affected by both light and heat. According to the European Copernicus Service, August 2020 was characterised by several episodes of marine heatwaves. Such episodes can be fatal to corals, as well as to marine ecosystems more broadly.

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Cause of stress and illness

A marine heatwave is a short period of abnormally high temperatures in a sea or ocean.  Last month, in some areas of the Mediterranean, the water’s temperature was 2, 3, or even 4 degrees above average. Warmer water causes physiological stress and increases microbe virulence in corals, eventually leading to the animal’s death. A large number of species cannot survive in water above 25 degrees.

With global warming, marine heatwaves have become longer and more intense. According to a report by the World Meteorological Organisation, coral reefs are expected to shrink by 70-90% if the temperatures rise by 1.5 degrees, and by more than 99% if the temperatures rise by 2 degrees.