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The Latest Bleaching Event May Be Over, But Reefs Are Still in Danger

Places like Guam and Hawaii could soon face more hot water

Though some reefs may soon get reprieve, not all are in the clear. (USFWS - Flickr/Creative Commons)
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After years of the worst bleaching event in recorded history, the world’s coral reefs could use a break. So when experts announced earlier this month that the devastating bleach is likely at an end, it seemed cause for celebration. But that excitement may be somewhat premature. As USA Today’s Kyla P. Mora reports, some reefs are still in trouble.

When water temperatures rise too high, coral reefs get stressed and kick out the symbiotic algae that lives inside their tissues, feed them and give them their vibrant colors. This makes them appear as if they are "bleached." Though these events don't always kill coral, they can weaken them. And the longer the bleaching event is, the more deadly it becomes.

Since the late 1990s, three serious bleaching events laid waste to corals in the Great Barrier Reef and elsewhere. The most recent began in 2015 and became the longest, most damaging such event on record. Now, it seems be reaching an end, but as Mora reports, that doesn’t mean every reef is in the clear. Though the National Oceanic Atmospheric and Atmospheric Administration declared the event over in the Atlantic, Indian and Pacific Oceans, NOAA’s Coral Reef Watch still predicts conditions that could lead to bleaching in places like Guam and Hawaii. 

Guam has already been hit hard by coral bleaching. The region’s diverse coral ecosystem was recently barraged by warm waters for four years straight. Coral ecologist Laurie Raymundo told the Washington Post’s Chelsea Harvey last summer that about 85 percent of Guam’s reefs are thought to have bleached. Now, reports the Guam Daily Post, satellite images and climate models show another bleaching event is headed for Guam, with the island’s waters facing likely bleaching within five to eight weeks as water temperatures rise. In a press release, NOAA predicts ongoing risk for coral reefs in Hawaii, too.

Rising sea temperatures happen in part due to El Niño events, which are caused by natural climate fluctuations. But people also play a role. According to the United States Environmental Protection Agency, sea surface temperatures have risen at an average of 0.13°F per decade since the beginning of the 20th century—a shift largely driven by greenhouse gas emissions. And some studies indicate that climate change could intensify El Niño conditions, which could bleach even more reefs in the future.

The current bleaching outlook is consistent with other sobering data. New research suggests America’s main reefs, from Florida to Puerto Rico, Guam to Hawaii, are particularly fragile. As The Guardian’s Oliver Milman reports, NOAA scientists warn that reefs already devastated from the latest bleaching event could disappear entirely in the next 20 or 30 years. Things may be cooling for some of the world’s reefs, but other precious coral landscapes are still in hot water.

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