Red Sea corals. Coral reefs are extensive and diverse marine ecosystems found in warm shallow waters. Corals are tiny animals that live in colonies. Some form hard calcium mineral structures, while others are soft and flexible. Different corals form a wide range of shapes. The resulting reef provides a home to numerous different marine organisms, such as fish, sponges, starfish, molluscs and crustaceans. Threats to coral reefs include sea pollution and bleaching, thought to be caused by heatwaves and prolonged warming due to global warming. Filmed in the Red Sea.