If you’ve ever snorkeled near a reef, you understand that these underwater structures are part of a sensitive ecosystem. Coral reefs provide food, shelter and breeding grounds for fish and marine invertebrates. The reefs constantly change; new polyps grow on the reef’s surface, while animals and storms grind the oldest parts into sand. Even the coral itself is symbiotic. Though classified as an animal, microscopic plants live within the coral’s tissues and trade nutrients with their hosts. Gazilliions of coral are needed to form a reef, especially the biggest ones.