A coral reef is a diverse underwater ecosystem made up of coral polyps, which are small marine animals. These reefs are primarily found in warm, shallow waters of tropical oceans. Coral reefs provide habitat and shelter for many marine species, making them one of the most productive ecosystems on Earth. Coral reefs are often referred to as the "rainforests of the sea" due to their rich biodiversity. They are formed from calcium carbonate structures created by the coral polyps over thousands of years. Unfortunately, coral reefs face threats from climate change, pollution, and overfishing, leading to their decline in many regions.