Reefs are disappearing.
Staghorn coral are one of the dominant building blocks of coral reefs all over the world, but now they're in trouble.
The most visible effect is bleaching. When water conditions get too stressful, corals lose the algae that give them their color. If it keeps up for too long, the corals die.
Recent surveys suggest 93 percent of corals in Australia's Great Barrier Reef are bleaching to some degree.
Researchers warn staghorn reefs near the mouth of the Amazon River are also at risk. Nearby oil drilling presents a "major environmental challenge."
But recovery is still possible. Scientists say tighter controls on runoff and dredging would give corals a better chance in today's warmer waters.
This video includes clips from the Australian Institute of Marine Science / CC BY 3.0, NOAA, lister wang / CC BY 3.0 and Moura et al., and images from P. Muir / Science Advances, Carden C. Wallace / Science Advances and the XL Catlin Seaview Survey. Music is from MADS / CC BY 3.0.