Difference between revisions of "Plankton" - New World Encyclopedia

Latest revision as of 15:17, 15 February 2009

Photomontage of plankton organisms

An amphipod

Plankton is the collective name for certain organisms (mostly microscopic) that drift in the oceans, lakes, rivers, and other bodies of water. Plankton have a tremendous importance in the web of life on earth.

The name plankton is derived from the Greek word planktos, meaning "wanderer" or "drifter." While some forms of plankton can swim, they cannot do so strongly enough to avoid being carried along by the water current. This is in contrast to nekton organisms that can swim against the current and control their position (for instance fish, squid, and marine mammals). It is also in contrast to benthos organisms that live on the bottom of bodies of water (for instance coral, clams, and lobsters).

Within the plankton itself, holoplankton are those organisms that spend their entire life cycle as part of the plankton. By contrast, meroplankton are those organisms that are only planktonic for part of their lives, usually the larval stage of fish and other aquatic organisms.

Plankton exhibit both the harmony of life and the fragility of our systems. The harmony is reflected in the cycle of energy and carbon via plankton: through photosynthesis, certain plankton capture the sun's rays and carbon, which is then circulated through other plankton and consumers, which in turn passes to decomposing plankton, releasing nutrients back into the water column. Most of the oxygen we breath is produced by photosynthetic plankton in our oceans. However, given the central importance of plankton for energy, carbon, and oxygen cycles, were the delicate balance of the oceans to be irreparably harmed, our own lives could be significantly impacted.

The study of plankton is termed planktology. Individual plankton are referred to as plankters.

Functional groups

Plankton are primarily divided into broad functional (or trophic level) groups:

Phytoplankton (from Greek phyton, or plant), use photosynthesis to convert sunlight into chemical energy for life.
Zooplankton (from Greek zoon, or animal), feed on the phytoplankton or other zooplankton.
Bacterioplankton, mainly decompose the remains of other organisms.

This scheme divides the plankton community into broad producer, consumer, and recycler groups. In reality, even the trophic level of some plankton is not straightforward. For example, although most dinoflagellates are either photosynthetic producers or heterotrophic consumers, many species do both depending upon their circumstances.

Phytoplankton

NASA satellite image of the large phytoplankton bloom in the Bering Sea in 1998. The greenish color is caused by the high concentration of phytoplankton.

Some marine diatoms - a key phytoplankton group

Main article: Phytoplankton

Phytoplankton, like plants, obtain energy through photosynthesis, and so must live in the well-lit surface layer (the euphotic zone) of the ocean. They provide the energy for almost all life in the sea.

Cyanobacteria. Cyanobacteria, also called "blue-green algae," are bacteria. They are thought to be the first organisms on earth that developed photosynthesis. They are one of the few organisms that can take nitrogen from the air and "fix" it into organic molecules so it can be used by plants and animals.

Diatoms. Diatoms are protists. They are single-celled algae with protective cell walls made of silica. In favorable conditions, diatoms "bloom," reproducing rapidly so that they dominate an area. When conditions turn less favorable, for instance the coming of winter or a depletion of nutrients, they can turn dormant and sink to lower levels until currents return them to the surface and a new bloom can take place.

Dinoflagellates. Dinoflagellates are also protists. They differ from diatoms in having a whip-like tail that enables them to move in the water, mostly up and down in response to changing conditions. Dinoflagellates also bloom, which can create a "red tide" in which they release toxins that can kill fish and/or humans who eat shellfish in which the toxins have become concentrated. Those dinoflagellates that do not use photosynthesis but eat other organisms are considered zooplankton.

Seaweeds. Although the word "plankton" is most often used for microscopic, or at least very small organisms, seaweeds, which are multi-cellular algae, may be considered planktonic if they drift in the open ocean rather than are anchored to the bottom. Sargassum weed forms huge floating islands in the western Atlantic Ocean that provide a home for many unique animals.

Zooplankton

Krill

Zooplankton are animals or animal-like organisms. They mostly live in the surface waters since they feed on the phytoplankton and on other zooplankton.

Copepods. Copepods are small crustaceans, most about 1-2 millimeters long with some larger. They are unusual among animals in only having one eye. Most species feed on the single-celled phytoplankton and are in turn eaten by fish and other larger animals.

Krill. Krill are also crustaceans. Related to shrimp, they are larger than copepods, most being about 1-2 centimeters long. They are sometimes not considered true plankton since they can swim, although they are still carried along by the currents. Most species of krill come together in large "swarms" that contain billions of individuals. They are eaten by many other animals, including many species of whales. There is some commercial fishing of krill, mostly to feed fish in aquariums and aquaculture, but also for human consumption.

Eel lava

Jellyfish. Jellyfish are among the largest planktonic animals. Most feed on zooplankton and small fish. Some jellyfish can grow to as large as 2 meters in diameter, with the tentacles much longer. It is suspected that the world's jellyfish population is increasing as their competitors, the large fish, are removed by human fishing.

Larva. The larva of fish and other animals such as coral and marine worms are also included in the zooplankton. The larva of the common eel, Anguilla anguilla, looks so different from the adult that is was thought to be a separate species until the 1890s.

Bacterioplankton

Bacterioplankton are bacteria which mostly live by decomposing the remains of other organisms, although some are parasites. Cyanobacteria are also bacteria, but they are considered to be among the phytoplankton since they use photosynthesis. Bacterioplankton are found at all levels of the ocean, not just near the surface as are most other plankton. They serve an important purpose of breaking down the remains of other organisms so that their nutrients can be reused, and are also eaten by zooplankton. Some bacterioplankton live near volcanic vents on the ocean bottom where they feed off of chemicals the vent releases into the water. They support a community of other living things which is remarkable among the earth's ecosystems for not depending on sunlight for energy.

Size groups

Siphonophora – the "conveyor belt" of the developing larvae and the ovarium can be seen

Plankton are also often described in terms of size. Usually the following divisions are used:

Megaplankton, 2×10^-1→2×10⁰ m (20-200 cm)
Macroplankton, 2×10^-2→2×10^-1 m (2-20 cm)
Mesoplankton, 2×10^-4→2×10^-2 m (0.2 mm-2 cm)
Microplankton, 2×10^-5→2×10^-4 m (20-200 µm)
Nanoplankton, 2×10^-6→2×10^-5 m (2-20 µm)
Picoplankton, 2×10^-7→2×10^-6 m (0.2-2 µm), mostly bacteria
Femtoplankton, < 2×10^-7 m, (< 0.2 µm), consisting of marine viruses

However, some of these terms may be used with very different boundaries, especially on the larger end of the scale. The existence and importance of nano- and even smaller plankton was only discovered during the 1980s, but they are thought to make up the largest proportion of all plankton in number and diversity.

Distribution

Ceratium, a dinoflagellate phytoplankter

Plankton are found throughout the oceans, seas, and lakes of Earth. However, the local abundance of plankton varies horizontally, vertically, and seasonally. The primary source of this variability is the availability of light. Almost all plankton ecosystems are driven by the input of solar energy and this confines primary production to surface waters, and to geographical regions and seasons when light is abundant.

A secondary source of variability is that of nutrient availability. Although large areas of the tropical and sub-tropical oceans have abundant light, they experience relatively low primary production because of the poor availability of nutrients such as nitrate, phosphate, and silicate. This is a product of large-scale ocean circulation and stratification of the water column. In such regions, primary production still usually occurs at greater depth, although at a reduced level (because of reduced light).

Studies have shown that the mineral iron (but only in the proper amounts) leads to increased blooms of many (though not all) kinds of phytoplankton. Iron is primarily made available to oceanic phytoplankton through the deposition of atmospheric dust on the sea surface. Oceanic areas adjacent to arid parts of continents thus typically have abundant phytoplankton (e.g., the western Atlantic Ocean, where trade winds bring dust from the Sahara Desert in North Africa).

While plankton are found in the greatest abundance in surface waters, they occur throughout the water column. At depths where no primary production occurs, zooplankton and bacterioplankton instead make use of organic material sinking from the more productive surface waters above. This flux of sinking material can be especially high following the termination of spring blooms.

Importance of Plankton

A copepod (Calanoida sp.) ca. 1-2 mm long

Plankton form the basis of almost all life in the sea. They convert the sun's energy into chemical energy, which is passed on up various food chains to support the great variety of ocean animals, including the fish and shellfish that are harvested by humans. Ninety percent of the world's photosynthesis is carried out in the oceans by microscopic phytoplankton, providing the energy for this process.

Phytoplankton, like plants, break down carbon dioxide releasing the oxygen and holding on to the carbon. If plankton sink to the bottom without being eaten by other organisms, this carbon is taken out of atmospheric circulation. Since carbon dioxide plays a role in the greenhouse effect, trapping the sun's heat and warming the atmosphere, this has an effect on the earth's climate. It has been suggested by some that the growth of phytoplankton could be encouraged by fertilizing the ocean with iron or other minerals as a way to counteract any global warming. (See article on the carbon cycle.)

References
ISBN links support NWE through referral fees

Omori, M., and T. Ikeda. 1992. Methods in Marine Zooplankton Ecology. Malabar, USA: Krieger Publishing Company.
Svarney, E. S., and P. Barnes-Svarney. 2000. The Handy Ocean Answer Book. Farmington, MA: Visible Ink Press.

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@@ Line 1: / Line 1: @@
-'''Steve, I added the articles from phytoplankton and bacterioplankton from Wikipedia. This is because in other articles, we often cite phytoplankton and zooplankton, and if they are a separate section, I can link right to those sections. But there was not any Wikipedia article on zooplankton, so please author a paragraph on them in the relevant section. Because I simply cut and pasted from the phytoplankton and bacterioplankton articles, there may  be some overlap with what is already in the article. Thanks.''' [[User:Rick Swarts|Rick Swarts]] 21:41, 30 May 2006 (UTC)
+{{Copyedited}}{{Paid}}{{Approved}}{{Images OK}}{{Submitted}}
-{{Contracted}}
 [[Image:plankton.jpg|thumb|right|250px|Photomontage of plankton organisms]]
+[[Image:Amphipodredkils.jpg|thumb|right|200px|An amphipod]]
+'''Plankton''' is the collective name for certain [[organism]]s (mostly microscopic) that drift in the oceans, lakes, rivers, and other bodies of water. Plankton have a tremendous importance in the web of life on earth.
-'''Plankton''' is the collective name for certain organisms (mostly microscopic) which drift in the water of the oceans, lakes, and other bodies of water.  Plankton have a tremendous importance in the web of life on earth.
+The name '''plankton''' is derived from the Greek word ''planktos'', meaning "wanderer" or "drifter." While some forms of plankton can swim, they cannot do so strongly enough to avoid being carried along by the water current. This is in contrast to '''nekton''' organisms that can swim against the current and control their position (for instance [[fish]], [[squid]], and marine [[mammal]]s). It is also in contrast to '''[[benthos]]''' organisms that live on the bottom of bodies of water (for instance [[coral]], [[clam]]s, and [[lobster]]s).
-==Definitions==
-[[Image:Amphipodredkils.jpg|thumb|right|200px|An [[amphipoda|amphipod]]]]
-The name '''plankton''' is derived from the Greek word ''planktos'', meaning "wanderer" or "drifter".  While some forms of plankton can swim, they can not do so strongly enough to avoid being carried along by the water current.   This is in contrast to '''nekton''' organisms that can swim against the current and control their position (e.g. [[fish]], [[squid]], and marine [[mammal]]s).  It is also in contrast to '''benthos''' organisms which live on the bottom.
-[[Image:Diatoms through the microscope.jpg|thumb|left|200px|Some marine [[diatom]]s - a key [[phytoplankton]] group]]
+Within the plankton itself, '''holoplankton''' are those organisms that spend their entire [[life cycle]] as part of the plankton. By contrast, '''meroplankton''' are those organisms that are only planktonic for part of their lives, usually the larval stage of [[fish]] and other aquatic organisms.
-Within the plankton itself, '''holoplankton''' are those organisms that spend their entire life cycle as part of the plankton (e.g. most algae, copepods, salps, and jellyfish). By contrast, '''meroplankton''' are those organisms that are only planktonic for part of their lives, usually the larval stage (e.g. the larvae of sea urchins, starfish, crustaceans, marine worms, and most fish.
+Plankton exhibit both the harmony of [[life]] and the fragility of our systems. The harmony is reflected in the cycle of [[energy]] and [[carbon]] via plankton: through photosynthesis, certain plankton capture the sun's rays and carbon, which is then circulated through other plankton and consumers, which in turn passes to decomposing plankton, releasing nutrients back into the water column. Most of the [[oxygen]] we breath is produced by photosynthetic plankton in our oceans. However, given the central importance of plankton for energy, carbon, and oxygen cycles, were the delicate balance of the oceans to be irreparably harmed, our own lives could be significantly impacted.
-The study of plankton is termed planktology.  Individual plankton are referred to as '''plankters'''.
+The study of plankton is termed planktology. Individual plankton are referred to as '''plankters'''.
 ==Functional groups==
+Plankton are primarily divided into broad functional (or trophic level) groups:
-[[Image:hyperia.jpg|thumb|right|200px|An [[amphipoda|amphipod]] (''Hyperia macrocephala'')]]
+*'''Phytoplankton''' (from Greek ''phyton'', or plant), use [[photosynthesis]] to convert sunlight into chemical energy for life.
-Plankton are primarily divided into broad functional (or [[trophic level]]) groups:
-*'''Phytoplankton''' (from Greek ''phyton'', or plant), use [[photosynthesis]] to convert sunlight into chemical energy for life.
 *'''Zooplankton''' (from Greek ''zoon'', or animal), feed on the phytoplankton or other zooplankton.
 *'''Bacterioplankton''', mainly decompose the remains of other organisms.
-This scheme divides the plankton community into broad '''producer''', '''consumer''' and '''recycler''' groups.  In reality, even the trophic level of some plankton is not straightforward.  For example, although most dinoflagellates are either photosynthetic producers or heterotrophic consumers, many species do both depending upon their circumstances.
+This scheme divides the plankton community into broad '''producer''', '''consumer''', and '''recycler''' groups. In reality, even the trophic level of some plankton is not straightforward. For example, although most dinoflagellates are either photosynthetic producers or heterotrophic consumers, many species do both depending upon their circumstances.
 ==Phytoplankton==
-[[image:phytopla.gif|thumb|Diagrams of some typical phytoplankton]]
+[[Image:Coccolithophore bloom.jpg|left|thumb|150px|NASA satellite image of the large phytoplankton bloom in the Bering Sea in 1998. The greenish color is caused by the high concentration of phytoplankton.]]
-Most phytoplankton are too small to be individually seen with the unaided eye.  However, when present in high numbers, their presence may appear as discoloration of the water (the color of which may vary with the phytoplankton present).
+[[Image:Diatoms through the microscope.jpg|thumb|right|200px|Some marine [[diatom]]s - a key phytoplankton group]]
+{{main|Phytoplankton}}
+Phytoplankton, like plants, obtain energy through [[photosynthesis]], and so must live in the well-lit surface layer (the euphotic zone) of the ocean. They provide the [[energy]] for almost all life in the sea.
-Phytoplankton, like plants, obtain energy through a process called [[photosynthesis]], and so must live in the well-lit surface layer (termed the [[euphotic zone]]) of an [[ocean]], [[sea]], or [[lake]]. Through photosynthesis, phytoplankton (and [[terrestrial]] plants) are responsible for much of the [[oxygen]] present in the [[Earth's atmosphere]].  Their cumulative energy fixation in carbon compounds ([[primary production]]) is the basis for the vast majority of oceanic and some freshwater [[food chain]]s ([[chemosynthesis]] is a notable exception). As a side note, one of the more remarkable food-chains in the ocean&mdash;remarkable because of the small number of links&mdash;is that of phytoplankton fed on by [[krill]] (a type of shrimp) fed on by [[baleen]] [[whale]]s.
+'''Cyanobacteria'''. [[Cyanobacteria]], also called "blue-green algae," are [[bacteria]]. They are thought to be the first organisms on earth that developed photosynthesis. They are one of the few organisms that can take [[nitrogen]] from the air and "fix" it into organic molecules so it can be used by [[plant]]s and [[animal]]s.
-While almost all phytoplankton species are obligate photoautotrophs, there are some that are [[mixotrophic]] and other, non-pigmented species that are actually [[heterotroph|heterotrophic]] (the latter are often viewed as [[zooplankton]]).  Of these, the best known are [[dinoflagellate]] [[genus|genera]] such as ''[[Noctiluca]]'' and ''[[Dinophyceae|Dinophysis]]'', that obtain organic carbon by [[ingestion|ingesting]] other organisms or [[detritus (biology)|detrital]] material.
+'''Diatoms'''. [[Diatom]]s are [[protist]]s. They are single-celled algae with protective cell walls made of silica. In favorable conditions, diatoms "bloom," reproducing rapidly so that they dominate an area. When conditions turn less favorable, for instance the coming of winter or a depletion of nutrients, they can turn dormant and sink to lower levels until currents return them to the surface and a new bloom can take place.
-In terms of numbers, the most important groups of phytoplankton include the [[diatom]]s, [[cyanobacteria]] and [[dinoflagellate]]s, although many other groups of [[alga]]e are represented.  One group, the [[coccolithophore|coccolithophorids]], is responsible (in part) for the release of significant amounts of [[dimethyl sulfide]] (DMS) into the [[Earth's atmosphere|atmosphere]].  DMS is converted to sulfate and these sulfate molecules act as [[cloud condensation nuclei]], increasing general cloud cover.
+'''Dinoflagellates'''. [[Dinoflagellate]]s are also protists. They differ from diatoms in having a whip-like tail that enables them to move in the water, mostly up and down in response to changing conditions. Dinoflagellates also bloom, which can create a "red tide" in which they release toxins that can kill [[fish]] and/or [[human]]s who eat shellfish in which the toxins have become concentrated. Those dinoflagellates that do not use photosynthesis but eat other organisms are considered zooplankton.
+'''Seaweeds'''. Although the word "plankton" is most often used for microscopic, or at least very small organisms, [[seaweed]]s, which are multi-cellular [[algae]], may be considered planktonic if they drift in the open ocean rather than are anchored to the bottom. Sargassum weed forms huge floating islands in the western Atlantic Ocean that provide a home for many unique animals.
 ==Zooplankton==
-needs some elaboration
+[[Image:Meganyctiphanes norvegica2.jpg|thumb|right|200px|Krill]]
-==Bacterioplankton==
+Zooplankton are [[animal]]s or animal-like organisms. They mostly live in the surface waters since they feed on the phytoplankton and on other zooplankton.
-'''Bacterioplankton''' refers to the [[bacterium|bacteria]]l component of the [[plankton]] that drifts in the water column. The name comes from the [[Greek language|Greek]] term, ''πλαγκτον'', meaning "wanderer" or "drifter", and ''bacterium'', a word coined in the [[19th century]] by [[Christian Gottfried Ehrenberg]]. They are found in both seawater and freshwater.
+'''Copepods'''. [[Copepod]]s are small [[crustacean]]s, most about 1-2 millimeters long with some larger. They are unusual among animals in only having one eye. Most species feed on the single-celled phytoplankton and are in turn eaten by fish and other larger animals.
+'''Krill'''. [[Krill]] are also crustaceans. Related to shrimp, they are larger than copepods, most being about 1-2 centimeters long. They are sometimes not considered true plankton since they can swim, although they are still carried along by the currents. Most species of krill come together in large "swarms" that contain billions of individuals. They are eaten by many other animals, including many species of [[whale]]s. There is some commercial fishing of krill, mostly to feed fish in aquariums and [[aquaculture]], but also for human consumption.
-Most bacterioplankton (for instance, ''Bacillus'' and ''Nitrosomonas'') obtain their energy through [[decomposition]] of other organisms, which largely renders them dependent on the [[phytoplankton]] for the production of dissolved organic matter as their main food source. A few species of bacterioplankton are capable of [[photosynthesis]] and [[chemosynthesis]]. Bacterio- and phytoplankton can regulate each others' numbers through mutual dependence and competition for resources such as [[phosphorus]]. They are preyed upon by [[protozoa]] and some [[cladocera]], as well as [[phage]]s.
+[[Image:Leptouk.jpg|thumb|right|200px|Eel lava]]
+'''Jellyfish'''. [[Jellyfish]] are among the largest planktonic animals. Most feed on zooplankton and small fish. Some jellyfish can grow to as large as 2 meters in diameter, with the tentacles much longer. It is suspected that the world's jellyfish population is increasing as their competitors, the large fish, are removed by human fishing.
+'''Larva'''. The [[larva]] of fish and other animals such as coral and marine worms are also included in the zooplankton. The larva of the common eel, ''Anguilla anguilla'', looks so different from the adult that is was thought to be a separate species until the 1890s.
+==Bacterioplankton==
+Bacterioplankton are [[bacteria]] which mostly live by decomposing the remains of other organisms, although some are parasites. [[Cyanobacteria]] are also bacteria, but they are considered to be among the phytoplankton since they use photosynthesis. Bacterioplankton are found at all levels of the ocean, not just near the surface as are most other plankton. They serve an important purpose of breaking down the remains of other organisms so that their nutrients can be reused, and are also eaten by zooplankton. Some bacterioplankton live near volcanic vents on the ocean bottom where they feed off of chemicals the vent releases into the water. They support a community of other living things which is remarkable among the earth's [[ecosystem]]s for not depending on sunlight for energy.
 ==Size groups==
-[[Image:Ctenophora.jpg|thumb|200px|[[Siphonophora]] &ndash; the "conveyor belt" of the upgrowing larvae and the ovarium can be seen]]
+[[Image:Ctenophora.jpg|thumb|200px|Siphonophora – the "conveyor belt" of the developing larvae and the ovarium can be seen]]
-Plankton are also often described in terms of size.  Usually the following divisions are used:
+Plankton are also often described in terms of size. Usually the following divisions are used:
-*Megaplankton, 2&times;10<sup>-1</sup>&rarr;2&times;10<sup>0</sup> m (20-200 cm)
+*Megaplankton, 2×10<sup>-1</sup>→2×10<sup>0</sup> m (20-200 cm)
-*Macroplankton, 2&times;10<sup>-2</sup>&rarr;2&times;10<sup>-1</sup> m (2-20 cm)
+*Macroplankton, 2×10<sup>-2</sup>→2×10<sup>-1</sup> m (2-20 cm)
-*Mesoplankton, 2&times;10<sup>-4</sup>&rarr;2&times;10<sup>-2</sup> m (0.2 mm-2 cm)
+*Mesoplankton, 2×10<sup>-4</sup>→2×10<sup>-2</sup> m (0.2 mm-2 cm)
-*Microplankton, 2&times;10<sup>-5</sup>&rarr;2&times;10<sup>-4</sup> m (20-200 µm)
+*Microplankton, 2×10<sup>-5</sup>→2×10<sup>-4</sup> m (20-200 µm)
-*Nanoplankton, 2&times;10<sup>-6</sup>&rarr;2&times;10<sup>-5</sup> m (2-20 µm)
+*Nanoplankton, 2×10<sup>-6</sup>→2×10<sup>-5</sup> m (2-20 µm)
-*Picoplankton, 2&times;10<sup>-7</sup>&rarr;2&times;10<sup>-6</sup> m (0.2-2 µm), mostly [[bacterium|bacteria]]
+*Picoplankton, 2×10<sup>-7</sup>→2×10<sup>-6</sup> m (0.2-2 µm), mostly [[bacteria]]
-*Femtoplankton, &lt; 2&times;10<sup>-7</sup> m, (&lt; 0.2 µm), consisting of marine [[virus]]es
+*Femtoplankton, < 2×10<sup>-7</sup> m, (< 0.2 µm), consisting of marine [[virus]]es
-However, some of these terms may be used with very different boundaries, especially on the larger end of the scale.  The existence and importance of nano- and even smaller plankton was only discovered during the [[1980]]s, but they are thought to make up the largest proportion of all plankton in number and diversity.
+However, some of these terms may be used with very different boundaries, especially on the larger end of the scale. The existence and importance of nano- and even smaller plankton was only discovered during the 1980s, but they are thought to make up the largest proportion of all plankton in number and diversity.
 ==Distribution==
-[[Image:Ceratium hirundinella.jpg|thumb|right|200px|''Ceratium'', a [[dinoflagellate]] phytoplankter]]
+[[Image:Ceratium hirundinella.jpg|thumb|right|200px|''Ceratium'', a dinoflagellate phytoplankter]]
-Plankton are found throughout the oceans, seas and lakes of Earth.  However, the local abundance of plankton varies horizontally, vertically and seasonally.  The primary source of this variability is the availability of light.  All plankton ecosystems are driven by the input of solar energy (but see [[chemosynthesis]]), and this confines primary production to surface waters, and to geographical regions and seasons when light is abundant.
-A secondary source of variability is that of nutrient availability.  Although large areas of the [[tropics|tropical]] and [[sub-tropical]] oceans have abundant light, they experience relatively low primary production because of the poor availability of nutrients such as [[nitrate]], [[phosphate]] and [[silicate]].  This is a product of large-scale [[ocean current|ocean circulation]] and [[stratification]] of the water column.  In such regions, primary production, still usually occurs at greater depth, although at a reduced level (because of reduced light).
-Studies have shown{{citation needed}} that the mineral iron (but only in the proper amounts) leads to increased blooms of many (though not all) kinds of phytoplankton. Iron is primarily made available to oceanic phytoplankton through the deposition of atmospheric dust on the sea surface. Oceanic areas adjacent to arid parts of continents thus typically have abundant phytoplankton (e.g., the western Atlantic ocean, where trade winds bring dust from the Sahara Desert in north Africa). It seems a paradox that arid land areas may actually contribute to increased plant life proliferation in the world's oceans. It has been theorized (but never actually attempted) that large-scale 'seeding' of the world's oceans with iron would generate such massive blooms of phytoplankton so as to draw enough carbon dioxide out of the atmosphere to counteract the Greenhouse Effect (or global warming).{{citation needed}}
-While plankton are found in the greatest abundance in surface waters, they occur throughout the water column.  At depths where no primary production occurs, zooplankton and bacterioplankton instead make use of organic material sinking from the more productive surface waters above.  This flux of sinking material can be especially high following the termination of [[spring bloom]]s.
+Plankton are found throughout the oceans, seas, and lakes of Earth. However, the local abundance of plankton varies horizontally, vertically, and seasonally. The primary source of this variability is the availability of [[light]]. Almost all plankton ecosystems are driven by the input of solar energy and this confines primary production to surface waters, and to geographical regions and seasons when light is abundant.
-==Biogeochemical significance==
+A secondary source of variability is that of nutrient availability. Although large areas of the tropical and sub-tropical oceans have abundant light, they experience relatively low primary production because of the poor availability of nutrients such as [[nitrate]], [[phosphate]], and [[silicate]]. This is a product of large-scale ocean circulation and stratification of the water column. In such regions, primary production still usually occurs at greater depth, although at a reduced level (because of reduced light).
-[[Image:Copepodkils.jpg|thumb|right|200px|A [[copepod]] (''Calanoida'' sp.) ca. [[1_E-3_m|1-2 mm]] long]]
+Studies have shown that the mineral [[iron]] (but only in the proper amounts) leads to increased blooms of many (though not all) kinds of phytoplankton. Iron is primarily made available to oceanic phytoplankton through the deposition of atmospheric dust on the sea surface. Oceanic areas adjacent to arid parts of continents thus typically have abundant phytoplankton (e.g., the western Atlantic Ocean, where trade winds bring dust from the Sahara Desert in North Africa).
-Aside from representing the bottom few levels of a [[food chain]] that leads up to [[Commerce|commercially]] important [[Fishery|fisheries]], plankton [[ecosystem]]s play a role in the [[biogeochemical cycle]]s of many important [[Chemical element|elements]].  Of particular contemporary significance is their role in the ocean's [[carbon cycle]].
+While plankton are found in the greatest abundance in surface waters, they occur throughout the water column. At depths where no primary production occurs, zooplankton and bacterioplankton instead make use of organic material sinking from the more productive surface waters above. This flux of sinking material can be especially high following the termination of spring blooms.
-As stated, phytoplankton fix [[carbon]] in sunlit surface waters via photosynthesis.  Through (primarily) zooplankton grazing, this carbon enters the planktonic foodweb, where it is either [[Cellular respiration|respired]] to provide [[metabolism|metabolic]] energy, or accumulates as [[biomass]] or [[detritus]].  As living or dead organic material is typically more [[density|dense]] than [[seawater]] it tends to sink, and in open ocean ecosystems away from the [[coast]]s this leads to the transport of carbon from surface waters to the deep.  This process is known as the '''[[biological pump]]''', and is one of the reasons that the oceans constitute the largest (active) pool of carbon on [[Earth science|Earth]].
+==Importance of Plankton==
+[[Image:Copepodkils.jpg|thumb|right|200px|A copepod (''Calanoida'' sp.) ca. 1-2 mm long]]
+Plankton form the basis of almost all life in the sea. They convert the sun's energy into chemical energy, which is passed on up various [[food chain]]s to support the great variety of ocean animals, including the fish and shellfish that are harvested by humans. Ninety percent of the world's [[photosynthesis]] is carried out in the oceans by microscopic phytoplankton, providing the energy for this process.
-Some researchers have even proposed that it might be possible to increase the ocean's uptake of [[carbon dioxide#atmosphere|carbon dioxide]] generated through [[anthropogenic|human activities]] by increasing the production of plankton through [[fertilization]], primarily with the [[micronutrient]] [[iron]].  However, it is debatable whether this technique is practical at a large scale, and some researchers have drawn attention to possible drawbacks such as ocean [[oxygen depletion|anoxia]] and resultant [[methanogen|methanogenesis]] (caused by the excess production [[remineralisation|remineralising]] at depth).{{citation needed}}
+Phytoplankton, like plants, break down [[carbon dioxide]] releasing the [[oxygen]] and holding on to the [[carbon]]. If plankton sink to the bottom without being eaten by other organisms, this carbon is taken out of atmospheric circulation. Since carbon dioxide plays a role in the greenhouse effect, trapping the sun's heat and warming the atmosphere, this has an effect on the earth's climate. It has been suggested by some that the growth of phytoplankton could be encouraged by fertilizing the ocean with iron or other minerals as a way to counteract any global warming. (See article on the [[carbon cycle]].)
 ==References==
-*Omori, M. and Ikeda, T. (1992).  ''Methods in Marine Zooplankton Ecology'', Krieger Publishing Company, Malabar, USA.
+* Omori, M., and T. Ikeda. 1992. ''Methods in Marine Zooplankton Ecology''. Malabar, USA: Krieger Publishing Company.
+* Svarney, E. S., and P. Barnes-Svarney. 2000. ''The Handy Ocean Answer Book''. Farmington, MA: Visible Ink Press.
 {{credit3|Plankton|55921506|Phytoplankton|54393169|Bacterioplankton|38198468}}
 [[Category:Life sciences]]
+[[Category:Microbiology]]
+[[Category:Plants]]