Coral bleaching had caused unprecedented damage to Australia's Great Barrier Reef and the rest of the coral ecosystem worldwide last year.
It's not yet time to write the obituary for the coral reefs.
A study published in the journal Nature on March 15 ended with a call that to save the coral reefs from dying, it needs "urgent and rapid action to reduce global warming."
Other ways to save the coral reefs have little effects against bleaching due to warmer sea temperatures.
The Lucky Few
During last year's bleaching of the Great Barrier Reef, researchers have discovered that 8.9 percent of over a thousand reefs survived without bleaching. The giant reef suffered another bleaching event this year.
This number was smaller when compared to the 1998 and 2002 bleaching events where 40 percent of the corals survived the attack unscathed.
"It's confronting to go from a reef which is colorful, which is swarming with life, to a reef that's covered in dead corals and corals that are covered in a slimy green algae," Mia Hoogenboom, one of the authors of the study from James Cook University, said.
Bleaching Did Not Make Coral Resilient
The massive bleaching events had hit areas that overlapped, giving the researchers the opportunity to discover that bleaching did not make the coral more heat-resistant.
The researchers found out that the severity of the bleaching is almost the same "on reefs that had previously been bleached than on reefs that hadn't bleached before in that event last year."
Hoogenboom said previous bleaching events "didn't confer any resistance to bleaching in the most recent bleaching event."
Warming water does the killing as researchers found out that the reefs in areas with warmer sea temperatures are the most affected, Mark Eakin, a co-author of the study and coordinator of NOAA's Coral Reef Watch, said.
Even a few degrees Fahrenheit rise of sea temperatures for over many weeks would result in as many as 90 percent of the corals being bleached.
"If you think about it, on a really hot day ... it's not a big deal. But when it goes on and on through time, that's when people without air conditioning start dying," he explained.
The analogy applies to coral reefs when exposed to warmer sea temperatures over time, he said.
Other protective measures such as prohibiting overfishing and reducing pollution are of help to mitigate bleaching. Hoogenboom said improved water flow would minimize the damage to the reefs.
These measures, however, are ad-hoc in nature if sea temperatures continue to rise.
"Temperature is really the main driver of these mass coral bleaching events," she pointed out.
These findings made the team call for urgent global action to address climate change.