Coral reef islands and atolls. The reef face is the zone above the reef floor or the reef drop-off. This zone is often the reef's most diverse area. Coral and calcareous algae provide complex habitats and areas that offer protection, such as cracks and crevices. Invertebrates and epiphytic algae provide much of the food for other organisms. A common feature on this forereef zone is spur and groove formations that serve to transport sediment downslope. The reef flat is the sandy-bottomed flat, which can be behind the main reef, containing chunks of coral. This zone may border a lagoon and serve as
Open brain coral Open brain coral The open brain coral ("Trachyphyllia geoffroyi") is a brightly colored free-living coral species in the family Merulinidae. It is the only species in the monotypic genus Trachyphyllia and can be found throughout the Indo-Pacific. Open brain corals can be solitary or colonial. They are small corals, rarely reaching over 20 cm in diameter. They are free-living and exhibit a flabello-meandroid growth form, meaning they have distinct valley regions separated by walls. In colonial forms, the valley regions can contain multiple individual polyps. Complexity of valley regions can range; some are hourglass shaped while other cans be highly