What do coral reefs need to survive?

Coral reefs need several things to survive, such as warm tropical waters, sunlight, clear water with low levels of nutrients and pollution, and a variety of marine life to support their ecosystem. They also require calcium carbonate to build their hard skeletons, which is extracted from seawater by tiny polyps that make up the coral. Without these essential conditions, coral reefs can become stressed and ultimately die off, resulting in devastating effects on marine biodiversity and the many human communities that depend on these ecosystems for their livelihoods.