Corals are complex creatures that form enduring colonies, and just like other animals they need oxygen to live. Corals aren’t fortunate enough to have a consistent supply of oxygen, and they can’t change location to seek it out. During the day, the tiny polyps that make up a coral colony get plenty of oxygen from the symbiotic algae that photosynthesize within their tissues. But at night that process stops, and a coral polyp’s only source of oxygen is the water around it. Warmer water naturally carries less oxygen, which prompts corals to move their cilia faster and faster, as if gasping for breath.