Pleuston are the organisms that live in the thin surface layer existing at the air-water interface of a body of water as their habitat.[1] Examples include some cyanobacteria, some gastropods, the ferns Azolla and Salvinia and the seed plants Lemna, Wolffia, Pistia, Eichhornia crassipes and Hydrocharis. Some fungi and fungi-like protists may be also found.

Wasserläufer bei der Paarung crop
The water strider, a common pleuston


The term Neuston is used either:

  • As a synonym for Pleuston: hence, the collective term for the organisms that float on the top of water (epineuston) or live right under the surface (hyponeuston).
  • That subset of floating organisms that are microscopic[2] or those that rely on surface tension to float.[3] This is in comparison with the term pleuston, which is then its superset, including those organisms that float by buoyancy or are macroscopic.

Neustons, broadly defined, are made up of some species of fish (see flying fish[4]), beetles (see whirligig beetle), protozoans, bacteria and spiders (see fishing spider and diving bell spider). Springtails in the genera Podura and Sminthurides are almost exclusively neustonic, while Hypogastrura species often aggregate on pond surfaces. Water striders such as Gerris are common examples of insects that supports their weight on water's surface tension. By extension, the term may also refer to non-organismal floating aggregations (see, e.g., Great Pacific Garbage Patch).

Distinction versus other aquatic life

Plankton (organisms that float or drift within the water) are distinguished from nekton (organisms that swim, powerfully, in the water), and benthos (organisms on the bottom of a body of water).


  1. ^ "Pleuston". Merriam-Webster Online.
  2. ^ P. S. Liss, W. George N. Slinn (1983-07-31). Air-sea exchange of gases and particles. p. 148. ISBN 978-90-277-1610-1.
  3. ^ James H. Thorp, Alan P. Covich (2001-04-23). Ecology and classification of North American freshwater invertebrates. p. 34. ISBN 978-0-12-690647-9.
  4. ^ "The Sea Surface and Global Change by P. S. Liss, Robert A. Duce". Retrieved 9 June 2018.

External links

Aquatic animal

An aquatic animal is an animal, either vertebrate or invertebrate, which lives in the water for most or all of its lifetime. Many insects such as mosquitoes, mayflies, dragonflies and caddisflies have aquatic larvae, with winged adults. Aquatic animals may breathe air or extract oxygen that dissolved in water through specialised organs called gills, or directly through the skin. Natural environments and the animals that live in them can be categorized as aquatic (water) or terrestrial (land). This designation is paraphyletic.

Aquatic ecosystem

An aquatic ecosystem is an ecosystem in a body of water. Communities of organisms that are dependent on each other and on their environment live in aquatic ecosystems. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems.

Aquatic plant

Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes. A macrophyte is an aquatic plant that grows in or near water and is either emergent, submergent, or floating, and includes helophytes (a plant that grows in marsh, partly submerged in water, so that it regrows from buds below the water surface). In lakes and rivers macrophytes provide cover for fish and substrate for aquatic invertebrates, produce oxygen, and act as food for some fish and wildlife.Aquatic plants require special adaptations for living submerged in water, or at the water's surface. The most common adaptation is aerenchyma, but floating leaves and finely dissected leaves are also common. Aquatic plants can only grow in water or in soil that is permanently saturated with water. They are therefore a common component of wetlands.Fringing stands of tall vegetation by water basins and rivers may include helophytes. Examples include stands of Equisetum fluviatile, Glyceria maxima, Hippuris vulgaris, Sagittaria, Carex, Schoenoplectus, Sparganium, Acorus, yellow flag (Iris pseudacorus), Typha and Phragmites australis.


Benthos is the community of organisms that live on, in, or near the seabed, river, lake, or stream bottom, also known as the benthic zone. This community lives in or near marine or freshwater sedimentary environments, from tidal pools along the foreshore, out to the continental shelf, and then down to the abyssal depths.

Many organisms adapted to deep-water pressure cannot survive in the upperparts of the water column. The pressure difference can be very significant (approximately one atmosphere for each 10 metres of water depth).Because light is absorbed before it can reach deep ocean-water, the energy source for deep benthic ecosystems is often organic matter from higher up in the water column that drifts down to the depths. This dead and decaying matter sustains the benthic food chain; most organisms in the benthic zone are scavengers or detritivores.

The term benthos, coined by Haeckel in 1891, comes from the Greek noun βένθος "depth of the sea". Benthos is used in freshwater biology to refer to organisms at the bottom of freshwater bodies of water, such as lakes, rivers, and streams. There is also a redundant synonym, benthon.

Floodplain restoration

Floodplain restoration is the process of fully or partially restoring a river's floodplain to its original conditions before having been affected by the construction of levees (dikes) and the draining of wetlands and marshes.

The objectives of restoring floodplains include the reduction of the incidence of floods, the provision of habitats for aquatic species, the improvement of water quality and the increased recharge of groundwater.

Freshwater ecosystem

Freshwater ecosystems are a subset of Earth's aquatic ecosystems. They include lakes and ponds, rivers, streams, springs, bogs, and wetlands. They can be contrasted with marine ecosystems, which have a larger salt content. Freshwater habitats can be classified by different factors, including temperature, light penetration, nutrients, and vegetation.

Freshwater ecosystems can be divided into lentic ecosystems (still water) and lotic ecosystems (flowing water).Limnology (and its branch freshwater biology) is a study about freshwater ecosystems. It is a part of hydrobiology.

Original attempts to understand and monitor freshwater ecosystems were spurred on by threats to human health (ex. Cholera outbreaks due to sewage contamination). Early monitoring focused on chemical indicators, then bacteria, and finally algae, fungi and protozoa. A new type of monitoring involves quantifying differing groups of organisms (macroinvertebrates, macrophytes and fish) and measuring the stream conditions associated with them.


The Gerridae are a family of insects in the order Hemiptera, commonly known as water striders, water skeeters, water bugs, pond skaters, water skippers, or Jesus bugs. Consistent with the classification of the Gerridae as true bugs (i.e., suborder Heteroptera), gerrids have mouthparts evolved for piercing and sucking, and distinguish themselves by having the unusual ability to walk on water, making them pleuston (surface-living) animals. They are anatomically built to transfer their weight to be able to run on top of the water's surface. As a result, one could likely find water striders present in any pond, river, or lake. Over 1,700 species of gerrids have been described, 10% of them being marine.While 90% of the Gerridae are freshwater bugs, the oceanic Halobates makes the family quite exceptional among insects. The genus Halobates was first heavily studied between 1822 and 1883 when Buchanan-White collected several different species during the Challenger Expedition. Around this time, Eschscholtz discovered three species of the Gerridae, bringing attention to the species, though little of their biology was known. Since then, the Gerridae have been continuously studied due to their ability to walk on water and unique social characteristics. Small gerrids have frequently been confused with the other semiaquatic bugs, the Veliidae. The most consistent characteristic used to separate these two families are internal genitalia differences. Since internal genitalia require specific training and tools to identify, it is almost impossible to tell a member of the Gerridae apart from a member of the Veliidae by external visual cues. One must study their habitat and behaviors to properly differentiate the two without looking at their specific anatomy.


Limnology ( lim-NOL-ə-jee; from Greek λίμνη, limne, "lake" and λόγος, logos, "knowledge"), is the study of inland aquatic ecosystems.

The study of limnology includes aspects of the biological, chemical, physical, and geological characteristics and functions of inland waters (running and standing waters, fresh and saline, natural or man-made). This includes the study of lakes, reservoirs, ponds, rivers, springs, streams, wetlands, and groundwater. A more recent sub-discipline of limnology, termed landscape limnology, studies, manages, and seeks to conserve these ecosystems using a landscape perspective, by explicitly examining connections between an aquatic ecosystem and its watershed. Recently, the need to understand global inland waters as part of the Earth System created a sub-discipline called global limnology. This approach considers processes in inland waters on a global scale, like the role of inland aquatic ecosystems in global biogeochemical cycles.Limnology is closely related to aquatic ecology and hydrobiology, which study aquatic organisms and their interactions with the abiotic (non-living) environment. While limnology has substantial overlap with freshwater-focused disciplines (e.g., freshwater biology), it also includes the study of inland salt lakes.

List of watershed topics

This list embraces topographical watersheds and drainage basins and other topics focused on them.


Macrobenthos consists of the organisms that live at the bottom of a water column and are visible to the naked eye. In some classification schemes, these organisms are larger than 1 mm; in another, the smallest dimension must be at least 0.5 mm. They include polychaete worms, pelecypods, anthozoans, echinoderms, sponges, ascidians, crustaceans.

A visual examination of macroorganisms at the bottom of an aquatic ecosystem can be a good indicator of water quality.

Marine ecoregions

Marine ecoregions are ecoregions (ecological regions) of the oceans and seas identified and defined based on biogeographic characteristics.


Meiobenthos, also called meiofauna, are small benthic invertebrates that live in both marine and fresh water environments. The term meiofauna loosely defines a group of organisms by their size, larger than microfauna but smaller than macrofauna, rather than a taxonomic grouping. In practice, that is organisms that can pass through a 1 mm mesh but will be retained by a 45 μm mesh, but the exact dimensions will vary from researcher to researcher. Whether an organism will pass through a 1 mm mesh will also depend upon whether it is alive or dead at the time of sorting.

The term meiobenthos was first coined in 1942 by Mare, but organisms that would fit into the meiofauna category have been studied since the 18th century. A comprehensive text on meiofauna is Introduction to the study of meiofauna by Higgins and Thiel (1988).


Nekton or necton refers to the aggregate of actively swimming aquatic organisms in a body of water. The term was proposed by German biologist Ernst Haeckel to differentiate between the active swimmers in a body of water, and the passive organisms that were carried along by the current, the plankton. As a guideline, nektonic organisms have a high Reynolds number (greater than 1000) and planktonic organisms a low one (less than 10). However, some organisms can begin life as plankton and transition to nekton later on in life, sometimes making distinction difficult when attempting to classify certain plankton-to-nekton species as one or the other. For this reason, some biologists choose not to use this term.

Particle (ecology)

In marine and freshwater ecology, a particle is a small object. Particles can remain in suspension in the ocean or freshwater. However, they eventually settle (rate determined by Stokes' law) and accumulate as sediment. Some can enter the atmosphere through wave action where they can act as cloud condensation nuclei (CCN). Many organisms filter particles out of the water with unique filtration mechanisms (filter feeders). Particles are often associated with high loads of toxins which attach to the surface. As these toxins are passed up the food chain they accumulate in fatty tissue and become increasingly concentrated in predators (see bioaccumulation). Very little is known about the dynamics of particles, especially when they are re-suspended by dredging. They can remain floating in the water and drift over long distances. The decomposition of some particles by bacteria consumes a lot of oxygen and can cause the water to become hypoxic.

Photic zone

The photic zone, euphotic zone (Greek for "well lit": εὖ "well" + φῶς "light"), or sunlight (or sunlit) zone is the uppermost layer of water in a lake or ocean that is exposed to intense sunlight. It corresponds roughly to the layer above the compensation point, i.e. depth where the rate of carbon dioxide uptake, or equivalently, the rate of photosynthetic oxygen production, is equal to the rate of carbon dioxide production, equivalent to the rate of respiratory oxygen consumption, i.e. the depth where net carbon dioxide assimilation is zero.

It extends from the surface down to a depth where light intensity falls to one percent of that at the surface, called the euphotic depth. Accordingly, its thickness depends on the extent of light attenuation in the water column. Typical euphotic depths vary from only a few centimetres in highly turbid eutrophic lakes, to around 200 meters in the open ocean. It also varies with seasonal changes in turbidity.

Since the photic zone is where almost all of the photosynthesis occurs, the depth of the photic zone is generally proportional to the level of primary production that occurs in that area of the ocean. About 90% of all marine life lives in the photic zone. A small amount of primary production is generated deep in the abyssal zone around the hydrothermal vents which exist along some mid-oceanic ridges.

The zone which extends from the base of the euphotic zone to about 200 metres is sometimes called the disphotic zone. While there is some light, it is insufficient for photosynthesis, or at least insufficient for photosynthesis at a rate greater than respiration. The euphotic zone together with the disphotic zone coincides with the epipelagic zone. The bottommost zone, below the euphotic zone, is called the aphotic zone. Most deep ocean waters belong to this zone.

The transparency of the water, which determines the depth of the photic zone, is measured simply with a Secchi disk. It may also be measured with a photometer lowered into the water.


Plankton are the diverse collection of organisms that live in large bodies of water and are unable to swim against a current. The individual organisms constituting plankton are called plankters. They provide a crucial source of food to many large aquatic organisms, such as fish and whales.

These organisms include bacteria, archaea, algae, protozoa and drifting or floating animals that inhabit—for example—the pelagic zone of oceans, seas, or bodies of fresh water. Essentially, plankton are defined by their ecological niche rather than any phylogenetic or taxonomic classification.

Though many planktonic species are microscopic in size, plankton includes organisms over a wide range of sizes, including large organisms such as jellyfish.

Technically the term does not include organisms on the surface of the water, which are called pleuston—or those that swim actively in the water, which are called nekton.

Ramsar site

A Ramsar site is a wetland site designated to be of international importance under the Ramsar Convention.The Convention on Wetlands, known as the Ramsar Convention, is an intergovernmental environmental treaty established in 1971 by UNESCO, which came into force in 1975. It provides for national action and international cooperation regarding the conservation of wetlands, and wise sustainable use of their resources.Ramsar identifies wetlands of international importance, especially those providing waterfowl habitat.

As of 2016, there were 2,231 Ramsar sites, protecting 214,936,005 hectares (531,118,440 acres), and 169 national governments are currently participating.


Seston are the organisms (bioseston) and non-living matter (abioseston or tripton) swimming or floating in a water body. Bioseston can be often regarded as plankton, although it includes nekton as well. Abioseston comprises detritus as well.


Veliidae is a gregarious family of predatory insects in the suborder Heteroptera. They are commonly known as riffle bugs, small water striders, or broad-shouldered water striders because the segment immediately behind the head is wider than the rest of the abdomen. The genus Rhagovelia is also referred to as a ripple bug.

Veliidae have a specialized body plan that allows them to walk on water and are pleuston. Gerridae is another closely related group that is also pleuston and both are in the superfamily Gerroidea. Veliide are smaller however, between 1.5 and 6 mm. They can be found on ponds, near lake shores, and in rivers worldwide. Some species can also be found on plants near water, in salt water or in mud flats.

Aquatic ecosystems

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