THE DEEP BLUE — Warming waters are hurting the world's coral reefs almost five times more than they did 30 years ago.

New research, published in the journal Science, says that hotter waters caused by global has impaired reefs by causing them to bleach more frequently than they did in the 1980s.

The study looked at 100 coral reefs and found that the frequency of bleaching had gone from once every few decades, to once every six years.

According to the U.S. National Ocean Service, coral reefs are sessile animals fixed in place. Bleaching occurs when the reef reacts to stressful changes in temperature, light, nutrients and other conditions. This makes the animal eject the symbiotic algae in their tissue and turn pale white.

Corals can survive and even recover, but continued bleaching eventually leads to death.

Corals reefs are critical to the world's fish population and are important for tourism, coast protection against heavy storms, typhoons and even tsunamis. According to the World Wildlife, corals account for almost US$30 billion each in goods and services