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The Formation of Coral Reefs

Coral reefs are often called the "rainforests of the sea" due to their incredible biodiversity. These underwater ecosystems are built by colonies of tiny animals called coral polyps. A coral polyp is a soft-bodied organism that attaches itself to a rock on the seafloor and secretes a hard, protective limestone skeleton, or calicle. Over thousands of years, as colonies of polyps live, grow, and die, their accumulated skeletons build up to form the massive structures we know as coral reefs.

The formation and survival of coral reefs depend on a delicate set of environmental conditions. Most reef-building corals have a symbiotic relationship with microscopic algae called zooxanthellae, which live within the coral's tissues. The algae provide the coral with food and oxygen through photosynthesis, and in return, the coral gives the algae a protected environment. This relationship is also what gives corals their vibrant colors. Reefs therefore require clear, warm, shallow water to ensure the algae receive enough sunlight.

These specific requirements make coral reefs highly vulnerable to environmental changes. Pollution that clouds the water can block sunlight, while rising sea temperatures can cause corals to expel their symbiotic algae, a phenomenon known as coral bleaching. This process turns the corals white and, if prolonged, can lead to their death. The preservation of these vital ecosystems depends on maintaining the fragile balance of conditions that allowed them to form in the first place.