By Alex Dobuzinskis
(Reuters) - A survey of coral reefs off the Hawaiian island of Oahu has shown warm ocean waters recently contributed to a higher rate of coral bleaching than the state has seen in decades, sparking concerns about the ecosystem, a state official said on Tuesday.
The findings from dives last week by researchers with the Hawaii Division of Aquatic Resources follows federal warnings of a possible large decline in coral cover in the archipelago this century due to climate change and warming oceans.
Coral underpins the region's aquatic ecosystem by providing shelter to countless species of fish, and Hawaii's varied marine life supports the local economy by attracting visitors from around the world.
"People come to Hawaii to see corals, they come to Hawaii to use our oceans," said Frazer McGilvray, administrator of the Division of Aquatic Resources. "If our corals die, it could potentially take a long, long time for them to recover."
He said that when ocean waters warm, it distresses coral and leads the organism to expel the algae that is vital to its survival, which in turn causes bleaching of the coral.
As water temperatures cool, coral can recover its color, and it remains unclear how much of the coral has died as it has bleached white, McGilvray said. The survey did not produce forecasts for how much of the coral may die from the bleaching.
He said his agency had received reports of coral bleaching throughout the archipelago so it sent divers to investigate in the waters of Waimanalo, Lanikai and Kaneohe Bay, all sites around the Hawaiian island of Oahu.
The survey found 75 percent of major reef-building coral at those sites was showing signs of bleaching, McGilvray said, adding that the last time researchers saw a similar rate of bleaching in Hawaii's ocean waters was in 1996, and even then it was less severe.
"It's pretty alarming," McGilvray said. "That's a high, high percentage of corals to be bleaching."
The bleaching comes as Hawaii has experienced a recent warm spell. Divers with the Division of Aquatic Resources have measured ocean temperatures of around 85 degrees Fahrenheit (29.4 Celsius), which is higher than the normal range of 72 degrees to 78 degrees (22.2 to 25.5 C), McGilvray said.
(Reporting by Alex Dobuzinskis in Los Angeles; Editing by Sandra Maler)