Corals are dying in ocean reefs worldwide, the victims of abnormally hot waters warmed by El Niño and climate change.

Scientists have long known that higher ocean temperatures set off a biological reaction called bleaching. Heat-stressed corals expel the colorful symbiotic algae that provide them with food, and in doing so, the corals turn bone white and face potential starvation.

Now, Australian scientists have captured these death throes on video—and it’s horrible to behold.

The researchers placed specimens of the coral Heliofungia actiniformis into aquatic tanks that simulate their natural environment, and then they turned up the heat.

The footage reveals that the corals eject the algae through a process called pulsed inflation. They expand their bodies to as much