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
Mesophotic coral reef Mesophotic coral reef A Mesophotic coral reef, from "meso" meaning middle and "photic" meaning light, is characterised by the presence of both light dependent coral and algae, and organisms that can be found in water with low light penetration. They normally grow between 30 to and up to in tropical and subtropical water. The most common species at the mesophotic level are corals, sponges and algae. The corals ranges can overlap with Deep-water coral but are distinguished by the presence of zooxanthellae and their requirement for light. They can also be thought of as part of shallow water coral ecosystems,