An ocean change that has alarmed scientists since the late 1990s is getting worse, with no signs that it'll end. Harmful bleaching of coral, blamed on warming seas, now affects 84 percent of tropical reefs worldwide, a partnership called the International Coral Reef Initiative announced recently. “Mass coral bleaching has been documented in at least 83 countries and territories,” says the group, which has U.S. representatives. The Pacific, Atlantic and Indian oceans are affected, along with seas such as the Mediterranean and Caribbean. "We're looking at something that's completely changing the face of our planet and the ability of our oceans to sustain lives and livelihoods," warns oceanographer Mark Eakin of Maryland, who retired from the National Oceanic and Atmospheric Administration (NOAA).

Bleaching happens when living coral turns white. Offshore reefs are bright and colorful because of microscopic algae (pronounced AL-gee), which are expelled when the ocean environment gets too hot and stresses the coral. If the temperature stays high, the coral won't let the algae back and will die. Entire reef ecosystems deteriorate. (Coral also may bleach because of extremely low tides, pollution, or too much sunlight.) Thousands of marine animals depend on coral, including some species of sea turtles, fish, crabs, shrimp, jellyfish, sea birds and starfish. Reefs provide shelter, spawning grounds and protection from predators. Reefs also absorb the force of waves and storm surges, keeping coastal communities safer. Additionally, reef tourism brings in billions of dollars each year and supports thousands of jobs on islands and shore communities.

Coral can recover if temperatures aren't too extreme. But only a global reduction in greenhouse gas emissions to limit ocean warming before too much longer will guarantee at least some coral survives, scientists say. "We need to learn from this to not do this to other ecosystems," says ecologist David Obura of Kenya, a country in east Africa on the Indian Ocean coast. Another ocean monitor, Melanie McField of the Smithsonian Institution in Washington, D.C., poetically describes how reefs are changing: "Bleaching is always eerie – as if a silent snowfall has descended on the reef. . . . There is usually an absence of fluttering fish and an absence of the vibrant colors on the reef. It's an ashen pallor and stillness in what should be a rowdy vibrant reefscape.”

Monitoring group says: "The ongoing global coral bleaching event is the biggest to date." – International Coral Reef Initiative

U.S. specialist says: "As the world's oceans continue to warm, coral bleaching is becoming more frequent and severe. When these events are sufficiently severe or prolonged, they can cause coral mortality, which hurts the people who depend on the coral reefs for their livelihoods." -- Derek Manzello of NOAA

Australian scientist says: "Seeing something like can be devastating. Ecological grief is real. People who spend a lot of time under the water see it changing before their eyes." -- Britta Schaffelke of the Australian Institute of Marine Science