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 reef communities, and are more often found on sandy reef slopes, around continental islands, and lagoons. Open brain corals can often be found near other free-living corals. Large colonies of open brain corals are uncommon, and are typically only observed in marine protected areas. The IUCN lists open brain corals as "near threatened" due to habitat loss and over-harvesting for the aquarium trade. The biggest exporter of open brain coral is Indonesia. In 2005, Indonesia exported over 60,000 open brain corals for use in the aquarium trade. Other threats to open brain corals include disease, acidification, and severe storms. Open