In coastal environments and biomes, the
littoral zone extends from the
high water markOrdinary high water mark refers to the highest level reached by a body of water that has been maintained for a sufficient period of time to leave evidence on the landscape. It may be indicated by destruction of terrestrial vegetation, the presence of marks on trees or debris deposits...
, which is rarely inundated, to shoreline areas that are permanently submerged. It always includes the
intertidal zoneThe intertidal zone is the area that is exposed to the air at low tide and underwater at high tide . This area can include many different types of habitats, including steep rocky cliffs, sandy beaches, or wetlands...
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.
The word "littoral" is used both as a
nounIn linguistics, a noun is a member of a large, open lexical category whose members can occur as the main word in the subject of a clause, the object of a verb, or the object of a preposition....
and an
adjectiveIn grammar, an adjective is a word whose main syntactic role is to modify a noun or pronoun, giving more information about the noun or pronoun's referent...
. It derives from the Latin noun
litus, litoris, meaning "shore". (The doubled 't' is a late medieval innovation and the word is sometimes seen in the more classical-looking spelling 'litoral'.)
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 from one part of the world to another, and between different disciplines. For example, military commanders speak of the littoral in ways that are quite different from marine biologists.
Overview
The adjacency of water gives a number of distinctive characteristics to littoral regions. Water's
erosiveErosion is a gravity driven process that moves solids in the natural environment or their source and deposits them elsewhere...
power results in particular types of
landformIn the earth sciences and geology sub-fields, a landform or physical feature comprises a geomorphological unit, and is largely defined by its surface form and location in the landscape, as part of the terrain, and as such, is typically an element of topography...
s, such as sand dunes, and
estuariesAn estuary is a semi-enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries are thus subject to both marine influences, such as tides, waves, and the influx of saline water; and riverine influences, such as flows of...
. 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
humidityHumidity is the amount of water vapour in the air. In daily language the term "humidity" is normally taken to mean relative humidity. Relative humidity is defined as the ratio of the partial pressure of water vapour in a parcel of air to the saturated vapour pressure of water vapour at a prescribed...
due to evaporation usually creates a
microclimateA microclimate is a local atmospheric zone where the climate differs from the surrounding area. The term may refer to areas as small as a few square feet or as large as many square miles...
supporting unique types of organisms.
Lake definitions
In lakes, where tides are usually negligibly small, other definitions of "littoral" are used. The
MinnesotaMinnesota is a state in the Midwestern region of the United States. The twelfth largest state by area in the U.S., it is the twenty-first most populous, with 5.2 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the...
Department of Natural ResourcesMany sub-national governments have a Department of Natural Resources or similarly-named organization:Australia*Queensland Department of Natural Resources and MinesCanada*Natural Resources Canada*New Brunswick**New Brunswick Department of Natural Resources...
defines littoral as that portion of the lake that is less than 15 feet in depth. This zone is home to most of the aquatic plant life (both rooted and floating) in a pond or lake because the high amount of sunlight reaching it allows for significant
photosynthetic activityPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
.
Military definitions
For the purposes of naval operations, the
United States NavyThe United States Navy is the sea branch of the U.S. Armed Forces. It is one of the seven uniformed services of the United States. As of 31 December 2008, the U.S. Navy had about 331,682 personnel on active duty and 124,000 in the Navy Reserve. It operates 283 ships in active service and more than...
divides the littoral zone in a different way (see diagram above). The US Army Corps Engineers and EPA have their own definitions, and these have legal implications.
Other definitions
In
oceanographyOceanography , also called oceanology or marine science, is the branch of Earth science that studies the ocean...
and
marine biologyMarine biology is the scientific study of living organisms in the ocean or other marine or brackish bodies of water. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology classifies species based on the environment...
, the idea of the littoral zone is extended roughly to the edge of the continental shelf. Starting from the shoreline, the littoral zone begins at the spray region just above the high tide mark. From here, it moves to the intertidal region between the high and low water marks, and then out as far as the edge of the
continental shelfThe continental shelf is the extended perimeter of each continent and associated coastal plain, and was part of the continent during the glacial periods, but is undersea during interglacial periods such as the current epoch by relatively shallow seas and gulfs. The continental rise is below the...
. These three subregions are called, in order, the supralittoral zone, the eulittoral zone and the sublittoral zone.
Supralittoral zone
The
supralittoral zone (also called the
splash,
spray, or
supratidal zone) is the area above the spring high tide line that is regularly splashed, but not submerged by ocean water. Seawater penetrates these elevated areas only during storms with high tides.
Organisms here must cope also with exposure to air, fresh water from rain, cold, heat and
predationIn ecology, predation describes a biological interaction where a predator feeds on its prey, . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of the prey...
by land animals and seabirds. At the top of this area, patches of dark
lichenLichens are composite organisms consisting of a symbiotic association of a fungus with a photosynthetic partner , usually either a green alga or cyanobacterium...
s can appear as crusts on rocks. Some types of
periwinklesThe common periwinkle, winkle, or Littorina littorea, is a small edible species marine gastropod with gills and an operculum in the family Littorinidae, the winkles.- Shell :...
,
NeritidaeNeritidae, known as the nerites, are a taxonomic family of small to medium-sized saltwater and freshwater snails which have a gill and a distinctive operculum...
and detritus feeding Isopoda commonly inhabit the lower supralitoral.
Eulittoral zone
The
eulittoral zone (also called the
midlittoral or
mediolittoral zone) is the
intertidal zone, also known as the
foreshore. It extends from the spring high tide line, which is rarely inundated, to the neap low tide line, which is rarely not inundated. The wave action and turbulence of recurring tides shapes and reforms cliffs, gaps, and caves, offering a huge range of habitats for sedentary organisms. Protected rocky shorelines usually show a narrow almost homogenous eulittoral strip, often marked by the presence of
barnacleA barnacle is a type of arthropod belonging to infraclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings. They are sessile suspension feeders, and have...
s. Exposed sites show a wider extension and are often divided into further zones. For more on this, see
intertidal ecologyIntertidal ecology is the study of intertidal ecosystems, where organisms live between the low and high tide lines. At low tide, the intertidal is exposed whereas at high tide, the intertidal is underwater...
.
Sublittoral zone
The
sublittoral zone, also called the
neritic zone, starts immediately below the eulittoral zone. This zone is permanently covered with seawater.
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 shelfThe continental shelf is the extended perimeter of each continent and associated coastal plain, and was part of the continent during the glacial periods, but is undersea during interglacial periods such as the current epoch by relatively shallow seas and gulfs. The continental rise is below the...
, 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 zoneThe photic zone or euphotic zone is the depth of the water in a lake or ocean, that is exposed to sufficient sunlight for photosynthesis to occur...
. This results in high
primary production400px|thumb|Global oceanic and terrestrial photoautotroph abundance, from September [[1997]] to August 2000. As an estimate of autotroph biomass, it is only a rough indicator of primary production potential, and not an actual estimate of it...
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 shelfThe continental shelf is the extended perimeter of each continent and associated coastal plain, and was part of the continent during the glacial periods, but is undersea during interglacial periods such as the current epoch by relatively shallow seas and gulfs. The continental rise is below the...
. 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 following:
- The infralittoral zone is the algal dominated zone to maybe five metres below the low water mark.
- The circalittoral zone is the region beyond the infralittoral, that is, below the algal zone and dominated by sessile
In limnology, sessility is that quality of an organism which rests unsupported directly on a base, either attached or unattached to a substrate. It is a characteristic of vegetation which is anchored to the benthic environment. There are two families of sessile rotifers: Flosculariidae and...
animals such as oysterThe word oyster is used as a common name for a number of distinct groups of bivalve molluscs which live in marine or brackish habitats. The valves are highly calcified....
s.
Shallower region of the sublittoral zone, extending not far from the shore, are sometimes referred to as the
subtidal zone.