Plankton are the diverse collection of
Marine plankton include
Although plankton are usually thought of as inhabiting water, there are also airborne versions that live part of their lives drifting in the atmosphere. These
Though many planktonic species are microscopic in size, plankton includes organisms over a wide range of sizes, including large organisms such as jellyfish. This is because plankton are defined by their ecological niche and level of motility rather than by any phylogenetic or taxonomic classification. Technically, the term does not include organisms on the surface of the water, called neuston, or those that swim actively in the water, called nekton.
The name plankton was coined by German marine biologist Victor Hensen in 1887 from shortening the word halyplankton from Greek ᾰ̔́λς háls "sea" and πλανάω planáō to "drift" or "wander".: 1 While some forms are capable of independent movement and can swim hundreds of meters vertically in a single day (a behavior called diel vertical migration), their horizontal position is primarily determined by the surrounding water movement, and plankton typically flow with ocean currents. This is in contrast to nekton organisms, such as fish, squid and marine mammals, which can swim against the ambient flow and control their position in the environment.
Within the plankton, holoplankton spend their entire life cycle as plankton (e.g. most algae, copepods, salps, and some jellyfish). By contrast, meroplankton are only planktic for part of their lives (usually the larval stage), and then graduate to either a nektic (swimming) or benthic (sea floor) existence. Examples of meroplankton include the larvae of sea urchins, starfish, crustaceans, marine worms, and most fish.
The amount and distribution of plankton depends on available nutrients, the state of water and a large amount of other plankton.
The study of plankton is termed planktology and a planktonic individual is referred to as a plankter. The adjective planktonic is widely used in both the scientific and popular literature, and is a generally accepted term. However, from the standpoint of prescriptive grammar, the less-commonly used planktic is more strictly the correct adjective. When deriving English words from their Greek or Latin roots, the gender-specific ending (in this case, "-on" which indicates the word is neuter) is normally dropped, using only the root of the word in the derivation.
Some marine diatoms — a key phytoplankton group
The amphipod Hyperia macrocephala – part of the zooplankton
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Plankton are primarily divided into broad functional (or trophic level) groups:
- algae that live near the water surface where there is sufficient light to support photosynthesis. Among the more important groups are the diatoms, cyanobacteria, dinoflagellates and coccolithophores.
- nutrient cycling.
- bacteria and archaea, which play an important role in remineralisingorganic material down the water column (note that prokaryotic phytoplankton are also bacterioplankton).
- Mixotrophs. Plankton have traditionally been categorized as producer, consumer and recycler groups, but some plankton are able to benefit from more than just one trophic level. In this mixed trophic strategy—known as mixotrophy—organisms act as both producers and consumers, either at the same time or switching between modes of nutrition in response to ambient conditions. This makes it possible to use photosynthesis for growth when nutrients and light are abundant, but switching to eat phytoplankton, zooplankton or each other when growing conditions are poor. Mixotrophs are divided into two groups; constitutive mixotrophs, CMs, which are able to perform photosynthesis on their own, and non-constitutive mixotrophs, NCMs, which use phagocytosis to engulf phototrophic prey that are either kept alive inside the host cell which benefit from its photosynthesis, or they digest their prey except for the plastids which continues to perform photosynthesis (kleptoplasty).
Recognition of the importance of mixotrophy as an ecological strategy is increasing, as well as the wider role this may play in marine biogeochemistry. Studies have shown that mixotrophs are much more important for the marine ecology than previously assumed, and comprise more than half of all microscopic plankton. Their presence act as a buffer that prevents the collapse of ecosystems during times with little to no light.
Plankton are also often described in terms of size. Usually the following divisions are used: 
Group Size range
Examples Megaplankton > 20 cmCephalopoda; Amphipoda Macroplankton 2→20 cm Mesoplankton 0.2→20 mmTunicata Microplankton 20→200 µm large Nanoplankton 2→20 µm smallXanthophyta Picoplankton 0.2→2 µm smallbacteria; Chrysophyta Femtoplankton < 0.2 µmmarine viruses
However, some of these terms may be used with very different boundaries, especially on the larger end. 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.
The microplankton and smaller groups are microorganisms and operate at low Reynolds numbers, where the viscosity of water is more important than its mass or inertia. 
Marine plankton includes marine bacteria and archaea, algae, protozoa and drifting or floating animals that inhabit the saltwater of oceans and the brackish waters of estuaries.
Freshwater plankton are similar to marine plankton, but are found inland in the freshwaters of lakes and rivers.
Sea spray containing marine microorganisms can be swept high into the atmosphere and may travel the globe as aeroplankton before falling back to earth.
Many animals live in terrestrial environments by thriving in transient often microscopic bodies of water and moisture, these include rotifers and gastrotrichs which lay resilient eggs capable of surviving years in dry environments, and some of which can go dormant themselves. Nematodes are usually microscopic with this lifestyle. Water bears, despite only having lifespans of a few months, famously can enter suspended animation during dry or hostile conditions and survive for decades. This allows them to be ubiquitous in terrestrial environments despite needing water to grow and reproduce. Many microscopic crustacean groups like copepods and amphipods (of which sandhoppers are members) and seed shrimp are known to go dormant when dry and live in transient bodies of water too
Tychoplankton are organisms, such as free-living or attached benthic organisms and other non-planktonic organisms, that are carried into the plankton through a disturbance of their benthic habitat, or by winds and currents. This can occur by direct turbulence or by disruption of the substrate and subsequent entrainment in the water column. Tychoplankton are, therefore, a primary subdivision for sorting planktonic organisms by duration of lifecycle spent in the plankton, as neither their entire lives nor particular reproductive portions are confined to planktonic existence. Tychoplankton are sometimes called accidental plankton.
The elaboratemarine radiolarians can eventually produce opal.
- Cliffs of Dover.
Planktonicalgae bloom of coccolithophoresoff the southern coast of England
- Great Pyramids.
Apart from aeroplankton, plankton inhabits oceans, seas, lakes and ponds. Local abundance varies horizontally, vertically and seasonally. The primary cause of this variability is the availability of light. All plankton ecosystems are driven by the input of solar energy (but see chemosynthesis), confining primary production to surface waters, and to geographical regions and seasons having abundant light.
A secondary variable is nutrient availability. Although large areas of the
While plankton are most abundant in surface waters, they live throughout the water column. At depths where no primary production occurs, zooplankton and bacterioplankton instead consume organic material sinking from more productive surface waters above. This flux of sinking material, so-called marine snow, can be especially high following the termination of spring blooms.
The local distribution of plankton can be affected by wind-driven Langmuir circulation and the biological effects of this physical process.
|The Secret Life of Plankton - YouTube|
Aside from representing the bottom few levels of a food chain that supports commercially important fisheries, plankton ecosystems play a role in the biogeochemical cycles of many important chemical elements, including the ocean's carbon cycle. Fish larvae mainly eat zooplankton, which in turn eat phytoplankton
Primarily by grazing on phytoplankton, zooplankton provide
It might be possible to increase the ocean's uptake of
Phytoplankton absorb energy from the Sun and nutrients from the water to produce their own nourishment or energy. In the process of photosynthesis, phytoplankton release molecular oxygen (O
2) into the water as a waste byproduct. It is estimated that about 50% of the world's oxygen is produced via phytoplankton photosynthesis. The rest is produced via photosynthesis on land by plants. Furthermore, phytoplankton photosynthesis has controlled the atmospheric CO
2 balance since the early Precambrian Eon.
The absorption efficiency (AE) of plankton is the proportion of food absorbed by the plankton that determines how available the consumed organic materials are in meeting the required physiological demands.
The growth of phytoplankton populations is dependent on light levels and nutrient availability. The chief factor limiting growth varies from region to region in the world's oceans. On a broad scale, growth of phytoplankton in the oligotrophic tropical and subtropical gyres is generally limited by nutrient supply, while light often limits phytoplankton growth in subarctic gyres. Environmental variability at multiple scales influences the nutrient and light available for phytoplankton, and as these organisms form the base of the marine food web, this variability in phytoplankton growth influences higher trophic levels. For example, at interannual scales phytoplankton levels temporarily plummet during El Niño periods, influencing populations of zooplankton, fishes, sea birds, and marine mammals.
The effects of anthropogenic warming on the global population of phytoplankton is an area of active research. Changes in the vertical stratification of the water column, the rate of temperature-dependent biological reactions, and the atmospheric supply of nutrients are expected to have important impacts on future phytoplankton productivity. Additionally, changes in the mortality of phytoplankton due to rates of zooplankton grazing may be significant.
- Pelagibacter ubique, the most common bacteria in the ocean, plays a major role in global carbon cycles
The tinycyanobacterium Prochlorococcusis a major contributor to atmospheric oxygen
The sea sparkle dinoflagellate glows in the night to produce the milky seas effect
Copepod from Antarctica, a translucent ovoid animal with two long antennae
Herring larva imaged with the remains of the yolk and the long gut visible in the transparent animal
Icefish larvae from Antarctica have no haemoglobin
Thectenophore has a transient anus which forms only when it needs to defecate
Eel larva drifting with the gulf stream
Antarctic krill, probably the largest biomass of a single species on the planet
Microzooplankton are major grazers of the plankton: two dinoflagellates and a tintinnid ciliate.
Sargassum seaweed drifts with currents using air bladders to stay afloat
Planktonic sea foam bubbles with image of photographer
Macroplankton: a Janthina janthina snail (with bubble float) cast up onto a beach in Maui
Fish & plankton
Zooplankton are the initial prey item for almost all
It's been shown that plankton can be patchy in marine environments where there aren't significant fish populations and additionally, where fish are abundant, zooplankton dynamics are influenced by the fish predation rate in their environment. Depending on the predation rate, they could express regular or chaotic behavior.
A negative effect that fish larvae can have on planktonic algal blooms is that the larvae will prolong the blooming event by diminishing available zooplankton numbers; this in turn permits excessive phytoplankton growth allowing the bloom to flourish .
The importance of both phytoplankton and zooplankton is also well-recognized in extensive and semi-intensive pond fish farming. Plankton population-based pond management strategies for fish rearing have been practiced by traditional fish farmers for decades, illustrating the importance of plankton even in man-made environments.
Whales & plankton
Of all animal fecal matter, it is whale feces that is the 'trophy' in terms of increasing nutrient availability. Phytoplankton are the powerhouse of open ocean primary production and they can acquire many nutrients from whale feces. In the marine food web, phytoplankton are at the base of the food web and are consumed by zooplankton & krill, which are preyed upon by larger and larger marine organisms, including whales, so it can be said that whale poop fuels the entire food web.
Humans & plankton
Plankton have many direct and indirect effects on humans.
Around 70% of the oxygen in the atmosphere is produced in the oceans from phytoplankton performing photosynthesis, meaning that the majority of the oxygen available for us and other organisms that respire aerobically is produced by plankton.
Plankton also make up the base of the marine food web, providing food for all the trophic levels above. Recent studies have analyzed the marine food web to see if the system runs on a top-down or bottom-up approach. Essentially, this research is focused on understanding whether changes in the food web are driven by nutrients at the bottom of the food web or predators at the top. The general conclusion is that the bottom-up approach seemed to be more predictive of food web behavior. This indicates that plankton have more sway in determining the success of the primary consumer species that prey on them than do the secondary consumers that prey on the primary consumers.
In some cases, plankton act as an intermediate host for deadly parasites in humans. One such case is that of cholera, an infection caused by several strains of Vibrio cholerae. These species have been shown to have a symbiotic relationship with chitinous zooplankton species like copepods. These bacteria benefit not only from the food provided by the chiton from the zooplankton, but also from the protection from acidic environments. Once the copepods have been ingested by a human host, the chitinous exterior protects the bacteria from the stomach acids in the stomach and proceed to the intestines. Once there, the bacteria bind with the surface of the small intestine and the host will start developing symptoms, including extreme diarrhea, within five days.
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- Ocean Drifters – Short film narrated by David Attenborough about the varied roles of plankton
- Plankton Chronicles Archived 2020-07-28 at the Wayback Machine – Short documentary films and photos
- COPEPOD: The Global Plankton Database – Global coverage database of zooplankton biomass and abundance data
- Plankton*Net – Taxonomic database of images of plankton species
- Guide to the marine zooplankton of south eastern Australia – Tasmanian Aquaculture and Fisheries Institute
- Sir Alister Hardy Foundation for Ocean Science – Continuous Plankton Recorder Survey
- Australian Continuous Plankton Recorder Project – Integrated Marine Observing System
- Sea Drifters – BBC Audio slideshow
-  – Images of planktonic microorganisms
- Plankton, planktic, planktonic – Essays on nomenclature
- Journal of Plankton Research[dead link] – Scientific periodical devoted to plankton