Coral reefs are bleaching as global waters warm
Frequency has risen fivefold in four decades
The world’s coral reefs are under siege from global warming, according to a new study in the journal Science.
Worldwide, the frequency of severe coral bleaching events has increased nearly fivefold in the past four decades, from once every 25 to 30 years in the early 1980s to once every six years in 2016, the study suggests.
Almost every coral reef on the planet has been affected by bleaching: “Our results show that 94% of tropical reefs have already bleached severely, by an average of three times, since 1980,” said study lead author Terry Hughes of the Australian Research Council’s Centre of Excellence for Coral Reef Studies. “The remaining 6% has also bleached, but less severely so far.”
Warmer, more acidic ocean water is the cause of the bleaching, Pieter Tans, chief greenhouse gas scientist for the National Oceanic andAtmospheric Administration, said last year. The bleaching occurs when algae that nourish coral wither from the warming waters and die, leaving behind white coral skeletons.
“Coral bleaching is a stress response caused by exposure of coral reefs to elevated ocean temperatures,” said study co- author Andrew Baird, also of the Centre of Excellence for Coral Reef Studies.
Hughes said that coral is the backbone of reefs as it provides an essential habitat for fish and many other species, adding that the decline of corals threatens the entire ecosystem.
Researchers measured the rate of coral bleaching at locations throughout the tropics over the past four decades.
They found a dramatic shortening of the gap between bleaching events, which not only harms the ecosystems but also livelihoods of many millions of people, the study published Thursday said.
Bleaching events are taking place regardless of naturalwarmer or cooler cycles such as El Niño or La Niña.
“Before the 1980s, mass bleaching of corals was unheard of, even during strong El Niño conditions, but nowrepeated bouts of regional- scale bleaching and mass mortality of corals has become the new normal around the world as temperatures continue to rise,” Hughes said.