Littoral refers to the coast of an ocean or sea, or to the banks of a river, lake or estuary. In coastal environments, the littoral zone extends from the high water mark, which is rarely inundated, to shoreline areas that are permanently submerged. It always includes the intertidal zone and is often used to mean the same as the intertidal zone. However, the meaning of "littoral zone" can extend well beyond the intertidal zone.
There is no single definition. What is regarded as the full extent of the littoral zone, and the way the littoral zone is divided into subregions, varies in different contexts (lakes and rivers have their own definitions). The use of the term also varies between different parts of the world, and between different disciplines that use the term. Military commanders speak of the littoral in ways that are different from marine biologists.
The word "littoral" is used both as a noun and an adjective. It derives from the Latin noun litus, litoris, meaning "shore". (The doubled 't' is a late mediaeval innovation and the word is sometimes seen in the more classical-looking spelling 'litoral'.)
The adjacency of water gives a number of distinctive characteristics to littoral regions. Water's erosive power results in particular types of landforms, such as sand dunes, and estuaries. The natural movement of the littoral along the coast is called the littoral drift. Biologically, the ready availability of water enables a greater variety of plant and animal life, and the additional local humidity due to evaporation usually creates a microclimate supporting unique types of organisms.
Organisms here must cope also with exposure to air, fresh water from rain, cold, heat and predation by land animals and seabirds. At the top of this area, patches of dark lichens can appear as crusts on rocks. Some types of periwinkles, neritidae and detritus feeding isopoda commonly inhabit the lower supralitoral.
In physical oceanography, the sublittoral zone refers to coastal regions with significant tidal flows and energy dissipation, including non-linear flows, internal waves, river outflows and oceanic fronts. In practice, this typically extends to the edge of the continental shelf, with depths around 200 metres.
In marine biology, the sublittoral refers to the areas where sunlight reaches the ocean floor, that is, where the water is never so deep as to take it out of the photic zone. This results in high primary production and makes the sublittoral zone the location of the majority of sea life. As in physical oceanography, this zone typically extends to the edge of the continental shelf. The benthic zone in the sublittoral is much more stable than in the intertidal zone; temperature, water pressure, and the amount of sunlight remain fairly constant. Sublittoral corals do not have to deal with as much change as intertidal corals. Corals can live in both zones, but they are more common in the sublittoral zone.
Within the sublittoral, marine biologists also identify the
Shallower region of the sublittoral zone, extending not far from the shore, are sometimes referred to as the subtidal zone.