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Coral reefs are,in fact,a necessary part of our ecosystem and provide opportunities for human beings to gain a better understanding of the ocean.Unfortunately,they're also disappearing faster than ever.
According to a warning by the US National Oceanic and Atmospheric Administration(NOAA) on Oct.8,the world is in its third recorded global coral bleaching（白化）since 1998 and 2010.This means no place with coral has been spared,as coral reefs are coming into contact with increasingly warm seas,which is leading to them dying off in large numbers.
Coral bleaching is like human cancer.It happens when corals are under stress from changes in light,nutrients,or temperature.This causes the coral to drive away the symbiotic algae（共生藻类）,living within their tissues（组织）, which play an important role in providing food for coral while making it colorful.Without the algae,coral reefs become pale and weak.In some cases they are not able to recover and eventually die off.
The current coral bleaching event started back in late 2014 and continued into this year with no signs of stopping.The BBC reports that 35% of coral reefs in the world will likely be affected,and an estimated 4,633 square miles (about 120,000 square kilometers) of coral reefs could die.
The loss of coral reefs is no small matter.Although they only take up 0.1% of the ocean floor,coral is home to about 25% of marine life.This isn't just a problem for divers and fish,as Eakin pointed out.Coral reefs are important globally,he added,as they protect shorelines,produce money in tourism,and help provide food for 500 million people worldwide.So people cannot overlook the environmental,economic and social effects of the loss.
The NOAA warning about coral bleaching came just about two months before a global climate summit（峰会）in Paris,where hundreds of world leaders will attempt to work out a plan to fight climate change.
Oceans will be a key subject during the summit,and Eakin says there's an "absolutely urgent need" for action.
