Coral looks like rock. It feels like rock. But every piece of coral is actually a city of tiny animals called polyps - soft, jelly-like creatures related to jellyfish, each one no bigger than a pencil eraser.
Every polyp pulls minerals out of seawater and builds itself a hard little stone cup to live in. Over thousands and thousands of years, generations of polyps stack their cups on top of older cups, and the whole pile slowly grows into the giant rocky structures we call reefs.
Most reef-building corals don’t survive alone. They share their bodies with tiny algae called zooxanthellae, which live inside the polyps and make food from sunlight, sharing the energy with their coral hosts. That’s why coral needs clear, sunny water - and why warmer oceans are so dangerous: the algae get stressed and leave, and the coral turns white and starts to starve.
