About twenty-five percent of all marine fish species reside in coral reefs, according to The Nature Conservancy; and about 500 million people are estimated by the International Union for the Conservation of Nature (IUCN) to be dependent on coral reefs for livelihoods. Hence, the death of coral reefs due to coral bleaching would largely affect the entire marine ecosystem.
An international group of researchers has recently measured the rate at which coral bleaching has been occurring over the past four decades throughout the tropics. The study published in the journal Science found out that there is a drastic decrease in time intervals between bleaching events, or in short, bleaching events are accelerating.
“The time between bleaching events at each location has diminished five-fold in the past 3-4 decades, from once every 25-30 years in the early 1980’s to an average of just once every six years since 2010,” explains lead author Terry Hughes, who is also the director of ARC Center of Excellence for Coral Reef Studies.
What is coral bleaching and how it happens? “Coral bleaching is a stress response caused by exposure of coral reefs to elevated ocean temperatures,” explains co-author Andrew Baird. As a response to stresses, such as heat and infection, corals are forced to eject the symbiotic algae that they are dependent upon for survival. “When bleaching is severe and prolonged, many of the corals die. It takes at least a decade to replace even the fastest-growing species,” continues Baird.
The researchers have attributed the increasing rate of coral bleaching with time is to earth warming. They have demonstrated in the study that the current ocean temperatures are higher than four decades ago. “The climate has warmed rapidly in the past 50 years, first making El Ninos dangerous for corals, and now we’re seeing the emergence of bleaching in every hot summer,” explains coauthor Mark Eakin.
The study involved 100 various coral reefs scattered around the globe were surveyed. Around 94 percent of these, according to the study, experienced severe bleaching since the 1980’s.
“It is clear that we’re going to lose most of the world’s coral reefs,” says coauthor Mark Eakin, who is also the coordinator of the National Oceanic and Atmospheric Administration’s Coral Reef Watch program. He also warned that it is expected for the ocean temperatures to sufficiently increase such that a massively 90 percent of the world’s coral reefs will undergo bleaching annually.