The photo above shows Hanauma Bay Nature Preserve in Honolulu, Hawaii. The coral reefs at the popular tourist destination are threatened by coral bleaching triggered by warmer ocean waters.

(Courtesy of TripAdvisor)

At a Glance

Coral bleaching has threatened one of Hawaii's most popular reefs.Almost 50 percent of the Hanauma Bay Nature Preserve's coral reef was bleached between October 2015 and January 2016.

The colorful reefs inhabiting one of Hawaii’s most popular destinations face a major threat as coral bleaching begins to take its toll.

Between October 2015 and January 2016, andnearly 10 percent of the corals were killed, according to a recent study.

Bleaching occurs when corals are stressed by changes in their environment, leading them to discharge tiny photosynthetic algaeknown as zooxanthellae. over the past two years, leaving two-thirds of it completely bleached, according to a previous report.

While studyingHanauma Bay, the scientists separated it into four quadrants and recorded the water's temperature in 15-minute intervals, the study said. They also tracked the patterns of water circulation to get a better understanding of how ocean currents contributed to the bleaching.

They discoveredrecirculation of water played the largest role, and areas where the currents recirculated had the highest amount of bleaching and deaths.

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“Our results suggest circulation patterns facilitate localized heating and influence bleaching dynamics in HBNP,” wrote the researchers.

According to the study, incoming ocean water flows towardthe shore and the reef boundary before following a counterclockwise pattern west and exiting the bay. While the water movesover the shallow reef flat,it experiences significant heating.

Bleaching to this extent is relatively new for the Aloha State.

“,” study author Ku'ulei Rodgers told Popular Science. “Here in Hawaii, we only had a bleaching event in 1996, and then the corals recovered. Unlike many places in the world, here we did very well until 2014.”

In 2014 and 2015, 90 percent of the coral reefs in the Main Hawaiian Islands – the state's eight largest islands – were bleached, and that was more than 50 percent of resulting deaths in some areas, according to the study.

“Oceans will continue to absorb a significant amount of carbon even once emissions are reduced but we must slow the increase to begin addressing the impacts of climate change,” the researchers wrote. “Sound management strategies based on scientific research will increasingly play a more important role.”

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