Coral reefs are faced with many threats, among them increasing coastal developments and flourishing tourist destinations, destructive and unsustainable fishing practices, rampant pollution, the proliferation of invasive species and coral diseases. There are also the effects of climate change to contend with -- things like rising sea levels and increasingly acidic ocean waters -- that could be spurring problems such as coral bleaching.
It's no surprise that these fragile, yet incredibly complex, beautiful and resourceful ecosystems are failing at an alarming rate. It's estimated that 25 percent of coral reefs around the world already have disappeared and another 67 percent are at risk of disappearing [source: Planetary Coral Reef Foundation]. Coral reef diseases were first reported in the 1970s, and since then, coral has been increasingly plagued by little-understood threats like black band disease. Also since the 1970s, the number of crown of thorn starfish -- a nasty predator of coral that few marine species are willing to mess with -- has multiplied greatly. Up to 90 percent of the Florida Keys' coral reefs have lost their living covers [source: Planetary Coral Reef Foundation].
Overfishing and destructive fishing practices are the biggest threats to coral reefs, but people are contributing to other types of reef destruction. Global warming causes much more damage to these delicate ecosystems than people realize. Scientists don't yet know what the effects of coral bleaching will be, but they do know that 2010 was among the warmest years on record. Extreme bleaching events kill coral and less extreme ones weaken it, making a reef more vulnerable to other threats [source Burke]. By 2030, about half of the reefs around the world may be subjected to thermal stress, which is regular bleaching from warmer temperatures. Coral reefs can't recover from this type of chronic exposure.
Air pollution damages reefs because the increased CO2 settles in the oceans and alters the chemistry of the water, making it more acidic. Eventually, this affects the saturation level of aragonite, which corals need to build skeletons.
Only a little more than a quarter of the world's coral reefs lie inside marine protected areas, such as reserves and locally managed marine areas. That leaves nearly 75 percent of the reefs left unprotected. Coral reefs are important for more than their beauty. They are home to thousands of diverse plant and fish species, provide food for people in communities near the reefs and support many local economies. Coral reefs also provide ingredients for many medicines [source: Coral Reef Alliance].
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