Environmental scientists are troubled by dramatic, sudden changes under the oceans. Brightly colored coral reefs are turning pale as they suffer from a phenomenon called bleaching, caused by warmer sea temperatures and possibly by chemical changes in the water. In just a few months, an underwater rainbow can turn a bright, ghostly white. If bleaching lasts too long, coral can starve to death. Underwater forests from Hawaii to Australia’s Great Barrier Reef are endangered, as are reefs off Florida, in the Caribbean and American Samoa in the South Pacific.

Global warming and a strong El Nino tropical weather system are believed to be key factors behind this mass bleaching, which began in the Pacific in the summer of 2014 and is expected to continue at least through 2016. It's only the third such occurrence on record and possibly the worst ever. More than a third of Earth's coral reefs are endangered, scientists say, and many may never recover. Oceans worldwide are by far the warmest on record. "It's really worrisome," says Vera Trainer at the Northwest Fisheries Science Center in Seattle, a federal research site. "If this is a single event that then goes away and we can forget about it down the road, it's OK. If it's a window into the future, it's not a good future."

Divers with high-definition cameras that capture 360-degree panoramas are documenting the condition of tropical reefs in a global survey project for research and public awareness. In addition, scientists at the Hawaii Institute of Marine Biology are trying to breed so-called super corals that can survive in warming oceans. They're taken off a reef and trained to withstand warmer, more acidic conditions without bleaching. The idea is that what doesn't kill coral makes it stronger.

Reefs cover less than 1 percent of the ocean floor, but are home to 25 percent of marine life. They're crucial incubators of the ocean’s ecosystem. Billions of fish, mollusks and other creatures rely on reefs for food and shelter. They also generate tourism dollars and act as natural barriers that provide storm surge protection for coastal residents. But they're vulnerable to pollution, higher ocean acid levels, overfishing and climate change.

U.S. impact: Ninety-five percent of U.S. corals, mostly off Hawaii and Florida, face potential bleaching in 2016.

Federal specialist says: "Hawaii is getting hit with the worst coral bleaching they have ever seen, right now. It's severe. It's extensive. And it's on all the islands." – Mark Eakin, National Oceanic and Atmospheric Administration (NOAA)

Environmentalist says: "This is a huge, looming planetary crisis, and we are sticking our heads in the sand about it." -- Justin Marshall, director of CoralWatch at Australia’s University of Queensland