View source for Earth:Littoral zone

{{Short description|Part of a sea, lake, or river that is close to the shore}}
{{Ocean habitat topics|image=[[File:Littoral Zones.jpg|250px]]|caption=Different disciplines and agencies divide the littoral zone into different subregions, according to how they want to view the zone.}}

The '''littoral zone''', also called '''litoral''' or '''nearshore''', is the part of a [[Earth:Sea|sea]], [[Earth:Lake|lake]], or [[Earth:River|river]] that is close to the [[Earth:Shore|shore]].<ref name=Seekell2021>{{Cite journal|last1=Seekell|first1=D.|last2=Cael|first2=B.|last3=Norman|first3=S.|last4=Byström|first4=P.|title=Patterns and variation of littoral habitat size among lakes|journal=Geophysical Research Letters|year=2021|volume=48|issue=20|language=en|pages=e2021GL095046|doi=10.1029/2021GL095046|bibcode=2021GeoRL..4895046S|s2cid=244253181|issn=1944-8007|doi-access=free}}</ref> In coastal ecology, the littoral zone includes the [[Earth:Intertidal zone|intertidal zone]] extending from the [[High water mark|high water mark]] (which is rarely inundated), to coastal areas that are permanently [[Earth:Underwater|submerged]] — known as the ''foreshore'' — and the terms are often used interchangeably. However, the geographical meaning of ''littoral zone'' extends well beyond the intertidal zone to include all neritic waters within the bounds of continental shelves.

==Etymology==
The word ''littoral'' may be used both as a noun and as an adjective. It derives from the [[Social:Latin language|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''.)<ref>{{OED|littoral}}</ref>

==Description==
The term has 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. For lakes, the littoral zone is the nearshore habitat where [[Biology:Photosynthetically active radiation|photosynthetically active radiation]] penetrates to the lake bottom in sufficient quantities to support photosynthesis.<ref name=Seekell2021 /> 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 the definition used by [[Biology:Marine biology|marine biologists]].

The adjacency of water gives a number of distinctive characteristics to littoral regions. The [[Earth:Erosion|erosive]] power of water results in particular types of [[Earth:Landform|landform]]s, such as sand dunes, and [[Earth:Estuary|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 particularly the formation of extensive wetlands. In addition, the additional local [[Physics:Humidity|humidity]] due to evaporation usually creates a [[Earth:Microclimate|microclimate]] supporting unique types of organisms.

==In oceanography and marine biology==
[[File:Olympic Coast National Marine Sanctuary.jpg|thumb|The littoral zone of an ocean is the area close to the shore and extending out to the edge of the continental shelf.]]
[[File:Portugal 20040711 027.jpg|thumb|right|The intertidal zone of a beach is also part of the littoral zone.]]
[[File:Klamath river estuary.jpg|thumb|right|[[Earth:Estuary|Estuaries]] are also in the littoral zone.]]

In [[Physics:Oceanography|oceanography]] and [[Biology:Marine biology|marine biology]], the idea of the littoral zone is extended roughly to the edge of the [[Earth:Continental shelf|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 [[Earth:Continental shelf|continental shelf]]. These three subregions are called, in order, the supralittoral zone, the eulittoral zone, and the sublittoral zone.

===Supralittoral zone===
{{main|Earth: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 that live here must cope with exposure to fresh water from rain, cold, heat, dryness and [[Earth:Predation|predation]] by land animals and seabirds. At the top of this area, patches of dark [[Biology:Lichen|lichen]]s can appear as crusts on rocks. Some types of [[Biology:Common periwinkle|periwinkles]], [[Biology:Neritidae|Neritidae]] and detritus feeding Isopoda commonly inhabit the lower supralittoral.<ref name="Yip and Madl">Yip and Madl</ref>

===Eulittoral zone===

The ''eulittoral zone'' (also called the ''midlittoral'' or ''mediolittoral zone'') is the ''intertidal zone'', known also as the ''foreshore''. It extends from the spring high tide line, which is rarely inundated, to the spring low tide line, which is rarely not inundated. It is alternately exposed and submerged once or twice daily. Organisms living here must be able to withstand the varying conditions of temperature, light, and salinity. Despite this, [[Earth:Productivity (ecology)|productivity]] is high in this zone. The wave action and turbulence of recurring tides shape and reform 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 [[Biology:Barnacle|barnacle]]s. Exposed sites show a wider extension and are often divided into further zones. For more on this, see [[Biology:Intertidal ecology|intertidal ecology]].

===Sublittoral zone===

The ''sublittoral zone'' starts immediately below the eulittoral zone. This zone is permanently covered with seawater and is approximately equivalent to the [[Earth:Neritic zone|neritic zone]].

In [[Earth:Physical oceanography|physical oceanography]], the sublittoral zone refers to coastal regions with significant tidal flows and energy dissipation, including non-linear flows, [[Internal wave|internal wave]]s, river outflows and oceanic fronts. In practice, this typically extends to the edge of the [[Earth:Continental shelf|continental shelf]], with depths around 200 meters.

In marine biology, the sublittoral zone 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 [[Earth:Photic zone|photic zone]]. This results in high [[Earth:Primary production|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 [[Earth:Continental shelf|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. [[Biology:Coral|Coral]]s 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, which may extend to 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 animals such as [[Biology:Mussel|mussel]]s and [[Biology:Oyster|oyster]]s.

Shallower regions of the sublittoral zone, extending not far from the shore, are sometimes referred to as the '''subtidal zone'''.

== Habitats in littoral zones ==
Many vertebrates (e.g., mammals, waterfowl, reptiles) and invertebrates (insects, etc.) use both the littoral zone as well as the terrestrial ecosystem for food and habitat. Biota that are commonly assumed to reside in the [[Earth:Pelagic zone|pelagic zone]] often rely heavily on resources from the littoral zone.<ref name="sciencedirect.com">{{Cite web|title=Littoral Zone - an overview {{!}} ScienceDirect Topics|url=https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/littoral-zone|access-date=2021-04-06|website=www.sciencedirect.com}}</ref> Littoral areas of ponds and lakes are typically better oxygenated, structurally more complex, and afford more abundant and diverse food resources than do profundal sediments. All these factors lead to a high diversity of insects and very complex trophic interactions.<ref name="sciencedirect.com"/>

The great lakes of the world represent a global heritage of surface freshwater and aquatic biodiversity. Species lists for 14 of the world’s largest lakes reveal that 15% of the global diversity (the total number of species) of freshwater fishes, 9% of non-insect freshwater invertebrate diversity, and 2% of aquatic insect diversity live in this handful of lakes. The vast majority (more than 93%) of species inhabit the shallow, nearshore littoral zone, and 72% are completely restricted to the littoral zone, even though littoral habitats are a small fraction of total lake areas.<ref name=":0">{{cite web|last=Vadeboncoeur|first=Yvonne|date=July 2011|title=Borders of Biodiversity: Life at the Edge of the World's Large Lakes|url=https://www.researchgate.net/publication/232684079|access-date=6 April 2021}}</ref>

Because the littoral zone is important for many recreational and industrial purposes, it is often severely affected by many human activities that increase nutrient loading, spread invasive species, cause acidification and climate change, and produce increased fluctuations in water level.<ref name="sciencedirect.com"/> Littoral zones are both more negatively affected by human activity and less intensively studied than offshore waters. Conservation of the remarkable biodiversity and biotic integrity of large lakes will require better integration of littoral zones into our understanding of lake ecosystem functioning and focused efforts to alleviate human impacts along the shoreline.<ref name=":0" />

==In freshwater ecosystems==
[[File:Primary zones of a lake.png|thumb|upright=1.7| The three primary zones of a lake are the littoral zone, the open-water (also called the [[Earth:Photic zone|photic]] or limnetic) zone, and the deep-water (also called the aphotic or profundal) zone.]]
[[File:Moon Lake shoreline - Riding Mountain National Park.JPG|thumb|right|Shoreline of a lake with nearly unvegetated littoral zone]]

In freshwater situations, the littoral zone is the nearshore habitat where [[Biology:Photosynthetically active radiation|photosynthetically active radiation]] penetrates to the lake bottom in sufficient quantities to support photosynthesis.<ref name=Seekell2021 /> Sometimes other definitions are used. For example, the Minnesota Department of Natural Resources defines littoral as that portion of the lake that is less than 15 feet in depth.<ref>{{cite web|url=http://www.dnr.state.mn.us/lakefind/surveys.html#littoral|title=Fisheries lake surveys|website = Minnesota Department of Natural Resources}}</ref> Such fixed-depth definitions often do not accurately represent the true ecological zonation, but are sometimes used because they are simple measurements to make bathymetric maps or when there are no measurements of light penetration. The littoral zone comprises an estimated 78% of Earth's total lake area.<ref name=Seekell2021 />

The littoral zone may form a narrow or broad fringing wetland, with extensive areas of aquatic plants sorted by their tolerance to different water depths. Typically, four zones are recognized, from higher to lower on the shore: wooded wetland, [[Earth:Wet meadow|wet meadow]], [[Earth:Marsh|marsh]] and aquatic vegetation.<ref name = keddy2>Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. Chapter 2.</ref> The relative areas of these four types depends not only on the profile of the shoreline, but upon past water levels. The area of wet meadow is particularly dependent upon past water levels;<ref name="Keddy, P.A 2010">Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK.</ref> in general, the area of wet meadows along lakes and rivers increases with natural water level fluctuations.<ref>Wilcox, D.A, Thompson, T.A., Booth, R.K. and Nicholas, J.R. 2007. Lake-level variability and water availability in the Great Lakes. USGS Circular 1311. 25 p.</ref><ref>Hughes, F.M.R. (ed.). 2003. The Flooded Forest: Guidance for policy makers and river managers in Europe on the restoration of floodplain forests. FLOBAR2, Department of Geography, University of Cambridge, Cambridge, UK. 96 p.</ref> Many of the animals in lakes and rivers are dependent upon the wetlands of littoral zones, since the rooted plants provide habitat and food. Hence, a large and productive littoral zone is considered an important characteristic of a healthy lake or river.<ref name="Keddy, P.A 2010"/>

Littoral zones are at particular risk for two reasons. First, human settlement is often attracted to shorelines, and settlement often disrupts breeding habitats for littoral zone species. For example, many turtles are killed on roads when they leave the water to lay their eggs in upland sites. Fish can be negatively affected by docks and retaining walls which remove breeding habitat in shallow water. Some shoreline communities even deliberately try to remove wetlands since they may interfere with activities like swimming. Overall, the presence of human settlement has a demonstrated negative impact upon adjoining wetlands.<ref>{{cite journal|last1=Houlahan |first1=J. E.|last2=Keddy|first2=P. A.|last3=Makkay|first3=K.|last4=Findlay|first4=C. S.|title=The effects of adjacent land use on wetland species richness and community composition|journal=Wetlands|date=2006|volume=26|issue=1|pages=79–96|doi=10.1672/0277-5212(2006)26[79:TEOALU]2.0.CO;2|s2cid=8050261 }}</ref> An equally serious problem is the tendency to stabilize lake or river levels with dams. Dams removed the spring flood, which carries nutrients into littoral zones and reduces the natural fluctuation of water levels upon which many wetland plants and animals depend.<ref>{{cite book|editor-last =Middleton|editor-first= B. A. |date = 2002|title = Flood Pulsing in Wetlands: Restoring the Natural Hydrological Balance|publisher= John Wiley|location = New York}}</ref><ref>Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497. Chapter 2.</ref> Hence, over time, dams can reduce the area of wetland from a broad littoral zone to a narrow band of vegetation. Marshes and wet meadows are at particular risk.

==Other definitions==
For the purposes of naval operations, the US Navy divides the littoral zone in the ways shown on the diagram at the top of this article. The US Army Corps of Engineers and the US Environmental Protection Agency have their own definitions, which have legal implications.

The UK Ministry of Defence defines the littoral as ''those land areas (and their adjacent areas and associated air space) that are susceptible to engagement and influence from the sea''.<ref>{{cite web|title =Joint Doctrine Publication 0-10, UK Maritime Power |date =October 2017|url = https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/662000/doctrine_uk_maritime_power_jdp_0_10.pdf |publisher = Ministry of Defense|edition = Fifth}}</ref>

==See also==
{{div col}}
* {{annotated link|Biology:Ballantine scale}}
* {{annotated link|Earth:Benthic zone}}
* {{annotated link|Earth:Intertidal zone}}
* {{annotated link|Engineering:Littoral combat ship}}
* {{annotated link|Social:Littoral warfare}}
* {{annotated link|Earth:Longshore drift}}
* {{annotated link|Earth:Marine debris}}
* {{annotated link|Earth:Neritic zone}}
* {{annotated link|Earth:Pelagic zone}}
* {{annotated link|Biology:Profundal zone}}
* {{annotated link|Earth:Shingle beach}}
{{div col end}}

==References==
{{Reflist|30em}}

=== Sources ===
{{Refbegin}}
* Haslett, Simon K (2001) ''Coastal Systems.'' Routledge. {{ISBN|978-0-415-21302-8}}
* Mann, Kenneth Henry (2000) [https://books.google.com/books?id=y4OIojDxtzsC&pg=PA179 ''Ecology of Coastal Waters''] Blackwell Publishing. {{ISBN|978-0-86542-550-7}}
* Yip, Maricela and Madl, Pierre (1999) [http://biophysics.sbg.ac.at/rovigno/rovigno3.htm ''Littoral''] University of Salzburg.
{{Refend}}

{{physical oceanography|expanded=other}}
{{coastal geography}}
{{Biomes}}

{{DEFAULTSORT:Littoral Zone}}
[[Category:Marine biology]]
[[Category:Aquatic ecology]]
[[Category:Habitats]]
[[Category:Coastal geography]]
[[Category:Oceanographical terminology]]
[[Category:Oceanography]]

{{Sourceattribution|Littoral zone}}