Commonly, coral reefs are located in shallow subtropical and tropical waters between 30o N and 30o S of the equator. About 90% of the coral reef of the world happens in the region of Indo-West Pacific biography. The biggest coral reef in the world is the Great Barrier Reef that is located on the coast of Australia. The 2nd largest coral reef is located on the Caribbean coast of Belize and Mexico. Corals in the absence of zooxanthellae algae are also found in several oceans that are nearly 6000 metres or 20,000 feet deep. However, these deep-sea corals don’t get light for photosynthesizing. And so, they grow slowly.