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
Deep-water coral off Africa’s west coast. In addition to ocean bottoms, scientists find "Lophelia" colonies on North Sea oil installations, although oil and gas production may introduce noxious substances into the local environment. The world's largest known deep-water "Lophelia" coral complex is the Røst Reef. It lies between deep, west of Røst island in the Lofoten archipelago, in Norway, inside the Arctic Circle. Discovered during a routine survey in May 2002, the reef is still largely intact. It is approximately long by wide. Some further south is the Sula Reef, located on the Sula Ridge, west of Trondheim on the mid-Norwegian Shelf,