Lagoon (Back Reef)
The lagoon (aka back reef zone) of a coral reef ecosystem is, for linear reefs (barrier and fringing reefs), that portion that lies between the reef crest and the shoreline. In the case of circular reef systems (atolls), it is centrally located.
A coral reef lagoon is a comparatively sheltered environment that contains a number of productive and unique habitats.
The extent, depth, and habitat complexity of coral reef lagoons varies substantially with reef type and local sea floor topography.
Some parts of the lagoon may be exposed at low tide, and (compared to other coral reef zones) this area experiences comparatively large temperature and salinity variations, reduced water circulation, and considerable sediment accumulation.
NOTE ON TERMINOLOGY: Coral reef zone terminology differs among reef scientists. Thus, you occasionally may see the term “reef flat” used to denote the same zone we refer to here as the “lagoon” or “back reef”, particularly in discussions of fringing reefs.