Littoral zone

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The littoral zone or nearshore is the part of a sea, lake, or river that is close to the shore. [1] In coastal ecology, the littoral zone includes the intertidal zone extending from the high water mark (which is rarely inundated) to coastal areas that are permanently 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.

Contents

Etymology

The word littoral may be used both as a noun and as an adjective. 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.) [2]

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 photosynthetically active radiation penetrates 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 by marine biologists.

The adjacency of water gives a number of distinctive characteristics to littoral regions. The erosive power of water 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 particularly the formation of extensive wetlands. In addition, the additional local humidity due to evaporation usually creates a microclimate supporting unique types of organisms.

In oceanography and marine biology

The littoral zone of an ocean is the area close to the shore and extending out to the edge of the continental shelf. Olympic Coast National Marine Sanctuary.jpg
The littoral zone of an ocean is the area close to the shore and extending out to the edge of the continental shelf.
The intertidal zone of a beach is also part of the littoral zone. Portugal 20040711 027.jpg
The intertidal zone of a beach is also part of the littoral zone.
Estuaries are also in the littoral zone. Klamath river estuary.jpg
Estuaries are also in the littoral zone.

In oceanography and marine biology, 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 shelf. 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 that live here must cope with exposure to fresh water from rain, cold, heat, dryness 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 supralittoral. [3]

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, 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 barnacles. Exposed sites show a wider extension and are often divided into further zones. For more on this, see 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 neritic zone.

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 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 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 following:

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 pelagic zone often 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. [5]

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. [6]

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. [6]

In freshwater ecosystems

The three primary zones of a lake are the littoral zone, the open-water (also called the photic or limnetic) zone, and the deep-water (also called the aphotic or profundal) zone. Primary zones of a lake.png
The three primary zones of a lake are the littoral zone, the open-water (also called the photic or limnetic) zone, and the deep-water (also called the aphotic or profundal) zone.
Shoreline of a lake with nearly unvegetated littoral zone Moon Lake shoreline - Riding Mountain National Park.JPG
Shoreline of a lake with nearly unvegetated littoral zone

In freshwater situations, the littoral zone is the nearshore habitat where photosynthetically active radiation penetrates to the lake bottom in sufficient quantities to support photosynthesis. [1] 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. [7] 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, marsh and aquatic vegetation. [8] 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; [9] in general, the area of wet meadows along lakes and rivers increases with natural water level fluctuations. [10] [11] 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. [9]

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. [12] 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. [13] [14] 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, [15] a definition which therefore includes a significant portion of land as well as water area.

See also

Related Research Articles

<span class="mw-page-title-main">Coast</span> Area where land meets the sea or ocean

The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the ocean or a lake. The Earth has around 620,000 kilometres (390,000 mi) of coastline. Coasts are important zones in natural ecosystems, often home to a wide range of biodiversity. On land, they harbor important ecosystems such as freshwater or estuarine wetlands, which are important for bird populations and other terrestrial animals. In wave-protected areas they harbor saltmarshes, mangroves or seagrasses, all of which can provide nursery habitat for finfish, shellfish, and other aquatic species. Rocky shores are usually found along exposed coasts and provide habitat for a wide range of sessile animals and various kinds of seaweeds. Along tropical coasts with clear, nutrient-poor water, coral reefs can often be found between depths of 1–50 meters.

<span class="mw-page-title-main">Estuary</span> Partially enclosed coastal body of brackish water

An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environments and are an example of an ecotone. Estuaries are subject both to marine influences such as tides, waves, and the influx of saline water, and to fluvial influences such as flows of freshwater and sediment. The mixing of seawater and freshwater provides high levels of nutrients both in the water column and in sediment, making estuaries among the most productive natural habitats in the world.

<span class="mw-page-title-main">Marsh</span> Wetland that is dominated by herbaceous rather than woody plant species

A marsh is a wetland that is dominated by herbaceous rather than woody plant species. Marshes can often be found at the edges of lakes and streams, where they form a transition between the aquatic and terrestrial ecosystems. They are often dominated by grasses, rushes or reeds. If woody plants are present they tend to be low-growing shrubs, and the marsh is sometimes called a carr. This form of vegetation is what differentiates marshes from other types of wetland such as swamps, which are dominated by trees, and mires, which are wetlands that have accumulated deposits of acidic peat.

<span class="mw-page-title-main">Maritime geography</span> Collection of terms used by naval military units

Maritime geography is a collection of terms used by naval military units to loosely define three maritime regions: brown water, green water, and blue water.

<span class="mw-page-title-main">Benthic zone</span> Ecological region at the lowest level of a body of water

The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "the depths." Organisms living in this zone are called benthos and include microorganisms as well as larger invertebrates, such as crustaceans and polychaetes. Organisms here generally live in close relationship with the substrate and many are permanently attached to the bottom. The benthic boundary layer, which includes the bottom layer of water and the uppermost layer of sediment directly influenced by the overlying water, is an integral part of the benthic zone, as it greatly influences the biological activity that takes place there. Examples of contact soil layers include sand bottoms, rocky outcrops, coral, and bay mud.

<span class="mw-page-title-main">Tide pool</span> Rocky pool on a seashore, separated from the sea at low tide, filled with seawater

A tide pool or rock pool is a shallow pool of seawater that forms on the rocky intertidal shore. Many of these pools exist as separate bodies of water only at low tide.

<span class="mw-page-title-main">Tidal marsh</span> Marsh subject to tidal change in water

A tidal marsh is a marsh found along rivers, coasts and estuaries which floods and drains by the tidal movement of the adjacent estuary, sea or ocean. Tidal marshes experience many overlapping persistent cycles, including diurnal and semi-diurnal tides, day-night temperature fluctuations, spring-neap tides, seasonal vegetation growth and decay, upland runoff, decadal climate variations, and centennial to millennial trends in sea level and climate. Tidal marshes are formed in areas that are sheltered from waves, in upper slops of intertidal, and where water is fresh or saline. They are also impacted by transient disturbances such as hurricanes, floods, storms, and upland fires.

<span class="mw-page-title-main">Neritic zone</span> Relatively shallow part of the ocean above the drop-off of the continental shelf

The neritic zone is the relatively shallow part of the ocean above the drop-off of the continental shelf, approximately 200 meters (660 ft) in depth. From the point of view of marine biology it forms a relatively stable and well-illuminated environment for marine life, from plankton up to large fish and corals, while physical oceanography sees it as where the oceanic system interacts with the coast.

<span class="mw-page-title-main">Aquatic ecosystem</span> Ecosystem in a body of water

An aquatic ecosystem is an ecosystem formed by surrounding a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms that are dependent on each other and on their environment. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems. Freshwater ecosystems may be lentic ; lotic ; and wetlands.

<span class="mw-page-title-main">Intertidal zone</span> Area of coast exposed only at low tide

The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide. This area can include several types of habitats with various species of life, such as seastars, sea urchins, and many species of coral with regional differences in biodiversity. Sometimes it is referred to as the littoral zone or seashore, although those can be defined as a wider region.

<span class="mw-page-title-main">Rocky shore</span> Intertidal area of coast where solid rock predominates

A rocky shore is an intertidal area of seacoasts where solid rock predominates. Rocky shores are biologically rich environments, and are a useful "natural laboratory" for studying intertidal ecology and other biological processes. Due to their high accessibility, they have been well studied for a long time and their species are well known.

<span class="mw-page-title-main">Marine ecosystem</span> Ecosystem in saltwater environment

Marine ecosystems are the largest of Earth's aquatic ecosystems and exist in waters that have a high salt content. These systems contrast with freshwater ecosystems, which have a lower salt content. Marine waters cover more than 70% of the surface of the Earth and account for more than 97% of Earth's water supply and 90% of habitable space on Earth. Seawater has an average salinity of 35 parts per thousand of water. Actual salinity varies among different marine ecosystems. Marine ecosystems can be divided into many zones depending upon water depth and shoreline features. The oceanic zone is the vast open part of the ocean where animals such as whales, sharks, and tuna live. The benthic zone consists of substrates below water where many invertebrates live. The intertidal zone is the area between high and low tides. Other near-shore (neritic) zones can include mudflats, seagrass meadows, mangroves, rocky intertidal systems, salt marshes, coral reefs, lagoons. In the deep water, hydrothermal vents may occur where chemosynthetic sulfur bacteria form the base of the food web.

The supralittoral zone, also known as the splash zone, spray zone or the supratidal zone, sometimes also referred to as the white zone, is the area above the spring high tide line, on coastlines and estuaries, that is regularly splashed, but not submerged by ocean water. Seawater penetrates these elevated areas only during storms with high tides.

<i>Lobelia dortmanna</i> Species of aquatic plant

Lobelia dortmanna, Dortmann's cardinalflower or water lobelia, is a species of flowering plant in the bellflower family Campanulaceae. This stoloniferous herbaceous perennial aquatic plant with basal leaf-rosettes and flower stalks grows to 0.7–2 m (2.3–6.6 ft) tall. The flowers are 1–2 cm long, with a five-lobed white to pale pink or pale blue corolla, produced in groups of one to ten on an erect raceme held above the water surface. The fruit is a capsule 5–10 mm long and 3–5 mm wide, containing numerous small seeds.

<span class="mw-page-title-main">Wrack zone</span> Coastal area where organic material is deposited at high tide

The wrack zone or wrack line is a coastal feature where organic material and other debris is deposited at high tide. This zone acts as a natural input of marine resources into a terrestrial system, providing food and habitat for a variety of coastal organisms.

<span class="mw-page-title-main">Pond</span> Relatively small body of standing water

A pond is an area filled with water, either natural or artificial, that is smaller than a lake. Defining them to be less than 5 hectares in area, less than 5 meters (16 ft) deep, and with less than 30% emergent vegetation helps in distinguishing their ecology from that of lakes and wetlands. Ponds can be created by a wide variety of natural processes, or they can simply be isolated depressions filled by runoff, groundwater, or precipitation, or all three of these. They can be further divided into four zones: vegetation zone, open water, bottom mud and surface film. The size and depth of ponds often varies greatly with the time of year; many ponds are produced by spring flooding from rivers. Ponds may be freshwater or brackish in nature. 'Ponds' with saltwater, with a direct connection to the sea that maintains full salinity, would normally be regarded as part of the marine environment because they would not support fresh or brackish water organisms, so not really within the realm of freshwater science.

This is a glossary of terms used in fisheries, fisheries management and fisheries science.

<span class="mw-page-title-main">Coastal fish</span> Fish that inhabit the sea between the shoreline and the edge of the continental shelf

Coastal fish, also called inshore fish or neritic fish, inhabit the sea between the shoreline and the edge of the continental shelf. Since the continental shelf is usually less than 200 metres (660 ft) deep, it follows that pelagic coastal fish are generally epipelagic fish, inhabiting the sunlit epipelagic zone. Coastal fish can be contrasted with oceanic fish or offshore fish, which inhabit the deep seas beyond the continental shelves.

<span class="mw-page-title-main">Marine habitats</span> Habitat that supports marine life

Marine habitats are habitats that support marine life. Marine life depends in some way on the saltwater that is in the sea. A habitat is an ecological or environmental area inhabited by one or more living species. The marine environment supports many kinds of these habitats. Marine habitats can be divided into coastal and open ocean habitats. Coastal habitats are found in the area that extends from as far as the tide comes in on the shoreline out to the edge of the continental shelf. Most marine life is found in coastal habitats, even though the shelf area occupies only seven percent of the total ocean area. Open ocean habitats are found in the deep ocean beyond the edge of the continental shelf.

References

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