coralOn Tuesday, scientists reported that mass coral bleaching had occurred around the Lisianski atoll, 1,000 miles northwest of Honolulu. 

Less severe bleaching has also been confirmed at the Midway, Pearl and Hermes atolls.

Courtney Couch, a researcher at the Hawaii Institute of Marine Biology, estimates that 35 percent of the coral sites observed at Lisianski have been bleached, with one shallow area exhibiting 90 percent bleaching.

“It’s a pretty big deal,” she told reporters. “Especially after looking at the forecasts for thermal stress over the next month. It’s pretty much predicted to stay at this point for the next month and then peter off at the end of October.”

Coral bleaching occurs when ocean water becomes too warm (it can occur when water becomes too cold, but this is less often the case). The warm water causes corals to expel the algae (zooxanthellae) that lives in their tissues, which causes them to look white (hence, “bleached”).

According to the National Oceanic and Atmospheric Administration, the U.S. lost half its Caribbean coral reefs in 2005 due to a thermal stress event that was more severe than the previous 20 years combined.

Coral without their algae can live on, but their health is significantly compromised.

It’s possible for algae to return to their corals, but in such cases corals often remain weakened and more vulnerable to disease. Couch told the Associated Press that without their algae, corals have about an eight-week deadline before they succumb to heat-induced stress and die.

The Lisianski corals have been bleached for about 10 weeks. The three other atolls have been bleached for seven.

This is the third mass bleaching event recorded in the protected archipelago of the Papahanaumokuakea Marine National Monument. Couch says that El Nino is to blame for this latest event.

“The largest body of warm waters is literally sitting right over Lisianski right now, and it’s moving northward as the summer progresses,” she said.

Randall Kosaki is the monument’s deputy superintendent and chief scientist. “We’re working in one of the most protected marine areas on Earth,” he said. “And yet we’re not immune to human impacts that originate many thousands of miles away, leading to things like marine debris or in this case, global warming and climate change.”

There is evidence that oceans are warming all over the world in response to climate change. In 2013, Masahiro Watanabe led a team of scientists in a study that explored the apparent slow-down in global-mean surface air temperature. Their models found that between 2001 and 2010, the ocean became more efficient at absorbing global heat, leading to a slowdown in surface temperatures and an increase in ocean temperatures.

That’s no cause for celebration. Watanbe’s team concluded that as the planet continues to warm, ocean heat uptake efficiency will decrease over time and act to “accelerate surface warming in coming decades.”

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