Littoral zone
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Thelittoral zone,also calledlitoralornearshore,is the part of asea,lake,orriverthat is close to theshore.[1]Incoastal ecology,the littoral zone includes theintertidal zoneextending from thehigh water mark(which is rarely inundated), to coastal areas that are permanentlysubmerged— known as theforeshore— and the terms are often used interchangeably. However, the geographical meaning oflittoral zoneextends well beyond the intertidal zone to include allneriticwaters within the bounds ofcontinental shelves.
Etymology
[edit]The wordlittoralmay be used both as anounand as anadjective.It derives from theLatinnounlitus, litoris,meaning "shore". (The doubledtis a late-medieval innovation, and the word is sometimes seen in the more classical-looking spellinglitoral.)[2]
Description
[edit]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 wherephotosynthetically active radiationpenetrates to the lake bottom in sufficient quantities to support photosynthesis.[1]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 bymarine biologists.
The adjacency of water gives a number of distinctive characteristics to littoral regions. Theerosivepower of water results in particular types oflandforms,such assand dunes,andestuaries.The natural movement of the littoral along the coast is called thelittoral drift.Biologically, the ready availability of water enables a greater variety of plant and animal life, and particularly the formation of extensivewetlands.In addition, the additional localhumiditydue to evaporation usually creates amicroclimatesupporting unique types of organisms.
In oceanography and marine biology
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Inoceanographyandmarine biology,the idea of the littoral zone is extended roughly to the edge of thecontinental 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 thecontinental shelf.These three subregions are called, in order, thesupralittoral zone,theeulittoral zone,and thesublittoral zone.
Supralittoral zone
[edit]Thesupralittoral zone(also called thesplash,sprayorsupratidal 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 andpredationby land animals and seabirds. At the top of this area, patches of darklichenscan appear as crusts on rocks. Some types ofperiwinkles,Neritidaeand detritus feedingIsopodacommonly inhabit the lower supralittoral.[3]
Eulittoral zone
[edit]Theeulittoral zone(also called themidlittoralormediolittoral zone) is theintertidal zone,known also as theforeshore.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,productivityis 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 ofbarnacles.Exposed sites show a wider extension and are often divided into further zones. For more on this, seeintertidal ecology.
Sublittoral zone
[edit]Thesublittoral zonestarts immediately below the eulittoral zone. This zone is permanently covered with seawater and is approximately equivalent to theneritic zone.
Inphysical 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 thecontinental 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 thephotic zone.This results in highprimary productionand makes the sublittoral zone the location of the majority of sea life. As in physical oceanography, this zone typically extends to the edge of thecontinental 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.Coralscan live in both zones, but they are more common in the sublittoral zone.
Within the sublittoral, marine biologists also identify the following:
- Theinfralittoral zoneis the algal dominated zone, which may extend to five metres below the low water mark.
- Thecircalittoral zoneis the region beyond the infralittoral, that is, below the algal zone and dominated bysessileanimals such asmusselsandoysters.
Shallower regions of the sublittoral zone, extending not far from the shore, are sometimes referred to as thesubtidal zone.
Habitats in littoral zones
[edit]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 thepelagic zoneoften rely heavily on resources from the littoral zone.[4]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.[4]
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.[5]
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.[4]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.[5]
In freshwater ecosystems
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In freshwater situations, the littoral zone is the nearshore habitat wherephotosynthetically active radiationpenetrates to the lake bottom in sufficient quantities to support photosynthesis.[1]Sometimes other definitions are used. For example, theMinnesota Department of Natural Resourcesdefines littoral as that portion of the lake that is less than 15feetin depth.[6]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.[1]
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,wet meadow,marshandaquatic vegetation.[7]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;[8]in general, the area of wet meadows along lakes and rivers increases with natural water level fluctuations.[9][10]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.[8]
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.[11]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.[12][13]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
[edit]For the purposes of naval operations, theUS Navydivides the littoral zone in the ways shown on the diagram at the top of this article. TheUS Army Corps of Engineersand theUS Environmental Protection Agencyhave their own definitions, which have legal implications.
TheUKMinistry of Defencedefines the littoral asthose land areas (and their adjacent areas and associated air space) that are susceptible to engagement and influence from the sea.[14]
See also
[edit]- Ballantine scale– Marine biology measurement scale
- Benthic zone– Ecological region at the lowest level of a body of water
- Coastal fish– Fish that inhabit the sea between the shoreline and the edge of the continental shelf
- Foreshore– Area of coast exposed only at low tide
- Intertidal zone– Area of coast exposed only at low tide
- Limnetic zone– Photic zone above the benthic zone in a freestanding body of water
- Littoral combat ship– Ship designed for operations near shore
- Littoral series– Shoreline where the land descends gradually into the sea
- Littoral warfare– Military operations in coastal waters
- Longshore drift– Sediment moved by the longshore current
- Marine debris– Human-created solid waste in the sea or ocean
- Neritic zone– Relatively shallow part of the ocean above the drop-off of the continental shelf
- Pelagic zone– Unobstructed water in the body of the sea that is neither close to the surface nor to the sea floor
- Profundal zone– deep zone of an inland body of freestanding water, such as a lake or pond, located below the range of effective light penetration
- Shingle beach– Beach which is armoured with pebbles or small- to medium-sized cobbles
References
[edit]- ^abcdSeekell, D.; Cael, B.; Norman, S.; Byström, P. (2021)."Patterns and variation of littoral habitat size among lakes".Geophysical Research Letters.48(20): e2021GL095046.Bibcode:2021GeoRL..4895046S.doi:10.1029/2021GL095046.ISSN1944-8007.S2CID244253181.
- ^"littoral".Oxford English Dictionary(Online ed.).Oxford University Press.(Subscription orparticipating institution membershiprequired.)
- ^Yip and Madl
- ^abc"Littoral Zone - an overview | ScienceDirect Topics".sciencedirect.Retrieved2021-04-06.
- ^abVadeboncoeur, Yvonne (July 2011)."Borders of Biodiversity: Life at the Edge of the World's Large Lakes".Retrieved6 April2021.
- ^"Fisheries lake surveys".Minnesota Department of Natural Resources.
- ^Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. Chapter 2.
- ^abKeddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK.
- ^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.
- ^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.
- ^Houlahan, J. E.; Keddy, P. A.; Makkay, K.; Findlay, C. S. (2006). "The effects of adjacent land use on wetland species richness and community composition".Wetlands.26(1): 79–96.doi:10.1672/0277-5212(2006)26[79:TEOALU]2.0.CO;2.S2CID8050261.
- ^Middleton, B. A., ed. (2002).Flood Pulsing in Wetlands: Restoring the Natural Hydrological Balance.New York: John Wiley.
- ^Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497. Chapter 2.
- ^"Joint Doctrine Publication 0-10, UK Maritime Power"(PDF)(Fifth ed.). Ministry of Defense. October 2017.
Sources
[edit]- Haslett, Simon K (2001)Coastal Systems.Routledge.ISBN978-0-415-21302-8
- Mann, Kenneth Henry (2000)Ecology of Coastal WatersBlackwell Publishing.ISBN978-0-86542-550-7
- Yip, Maricela and Madl, Pierre (1999)LittoralUniversity of Salzburg.