A coral reef is formed from the calcium carbonate skeletons of corals in the photic zone of marine
environemnts with high water quality.
It begins as a fringing reef on young islands, forming an offshore barrier reef as the island submerges, and eventually becoming an atoll with an inner lagoon.
Dinoflagellate algae live symbiotically within the tissues of coral animals. Red and green algae also contribute photosynthetic activity to this biome, making it the most productive of all the biomes. 1