Coral reefs are diverse underwater ecosystems often called "rainforests of the sea." They are habitats for a wide variety of marine life.
So it's good news for the fishing and tourism industries that widespread coral bleaching — a process that turns the reefs white, weak and vulnerable to breaking down — has stopped in all three ocean basins, according to the U.S. National Oceanic and Atmospheric Administration (NOAA).
The coral bleaching event of the last two years, triggered by high water temperatures, has had far-reaching effects, said Mark Eakin, NOAA research scientist and Coral Reef Program coordinator.
"There are islands in the central Pacific Ocean…where the entire coral reef has been bleached," he told VOA. The bleaching drove the fish away, and "the people who relied on fish for food or their businesses, their livelihood just disappeared."
He added that in many places, the bleaching began to kill and disintegrate the coral reefs, which protect shorelines from beach erosion and often draw tourists who don diving gear to see the reefs' unique underwater beauty.
"In many of those places, people are dependent on coral reefs for income, because they are popular tourist attractions," Eakin said. "If the bleaching happens, people don’t come to visit dead coral reefs."
High temps kill coral
Coral bleaching has been a recurring problem in recent decades, as water temperatures have risen worldwide, a result of global warming. One of the worst bleaching events began in late 2014. Since then, more than 70 percent of coral reefs around the world have experienced prolonged high temperatures.
The heat makes coral expel tiny organisms, called zooxanthellae, that provide the coral with its nutrients. If the organisms do not return, the coral can starve and die. In time, the coral skeletons crumble, causing the entire reef to collapse
The first global bleaching event noticed by scientists happened in 1998 during a strong El Nino — the phenomenon that makes Pacific ocean waters warmer than normal, often wreaking havoc on weather patterns.
The latest bleaching also coincided with a strong El Nino.
But “coral reef are not beyond help,” said Jennifer Koss, director of the NOAA Coral Reef Conservation Program.
She said scientists are taking steps to protect the reefs, in part by identifying coral species "that are more resilient to rising ocean temperatures and acidified waters."
According to the NOAA report, areas of the U.S. hit by severe bleaching are Florida, Hawaii, the Pacific territory of Guam and the Mariana Islands.
"And we have also seen bleaching all the way from the east coast of Africa all the way around and back again to the west coast of Africa," Eakin said.
For now, the bleaching has eased or stopped in most areas. "There may be some bleaching later this year in the north Pacific and in the Caribbean but its not as widespread as it had been," he said.
Long-term, scientists will be watching closely to see if the reefs regain their strength. If they don't, the oceans and those who depend on them for a living could be in trouble.