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The Biology of Coral Reef Formation

Coral reefs are among the most biodiverse ecosystems on Earth, often referred to as "rainforests of the sea." These complex underwater structures are built by colonies of tiny animals called coral polyps. A single polyp is a soft-bodied organism related to sea anemones and jellyfish. To protect their soft bodies, they secrete a hard exoskeleton made of calcium carbonate. Over countless generations, the accumulated skeletons of these polyps build up to form the massive structures we know as coral reefs.

The growth of coral reefs depends on a vital symbiotic relationship. Living within the tissues of the coral polyps are microscopic algae called zooxanthellae. The algae perform photosynthesis, converting sunlight into energy. They provide the coral with essential nutrients and oxygen, which helps the polyps secrete their skeletons more quickly. In return, the coral provides the algae with a protected environment and the compounds necessary for photosynthesis. This relationship is also responsible for the vibrant colors seen in many corals.

Most reef-building corals thrive in warm, shallow, clear, and sunlit tropical waters. These specific conditions are necessary for the photosynthetic algae to survive. The health of coral reefs is a sensitive indicator of ocean conditions. Factors such as rising sea temperatures and ocean acidification can disrupt the symbiotic relationship between corals and their algae, leading to a phenomenon known as coral bleaching, where the corals expel the algae and turn white, threatening the entire reef ecosystem.