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The Formation of Coral Reefs

Coral reefs are often referred to as the "rainforests of the sea" due to their incredible biodiversity. These underwater structures are built by colonies of tiny animals called coral polyps. A single coral polyp is a soft-bodied organism that attaches itself to a rock on the seafloor and then secretes a hard, protective limestone skeleton, or calicle. Over thousands of years, as colonies grow and expand, these skeletons build up, creating the massive structures we know as coral reefs. They are one of the oldest and most diverse ecosystems on Earth.

The growth of coral reefs is highly dependent on specific environmental conditions. Most reef-building corals have a symbiotic relationship with microscopic algae called zooxanthellae, which live within the coral's tissues. The algae perform photosynthesis, providing the coral with essential nutrients and energy to grow and build its skeleton. In return, the coral provides the algae with a protected environment and the compounds they need for photosynthesis. This relationship necessitates that coral reefs are found in clear, shallow, warm waters where sunlight can penetrate, typically between the latitudes of 30°N and 30°S.

Coral reefs can be categorized into three main types based on their formation. Fringing reefs grow near the coastline around islands and continents, separated from the shore by a narrow, shallow lagoon. Barrier reefs, such as the Great Barrier Reef in Australia, also parallel the coastline but are separated by a much deeper and wider lagoon. Atolls are rings of coral that create a protected lagoon and are usually located in the middle of the sea. Charles Darwin first theorized that these three reef types represent a sequence of development, where a fringing reef around a volcanic island becomes a barrier reef and then an atoll as the island subsides.