Plankton are the diverse collection of organism
s found in water
) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucial source of food to many small and large aquatic organisms, such as bivalve
Marine plankton includes bacteria
and drifting or floating animal
s that inhabit the saltwater
s and the brackish
waters of estuaries
. Freshwater plankton are similar to marine plankton, but are found in the freshwater
s of lakes and rivers. Plankton are usually thought of as inhabiting water, but there are also airbourne versions, the aeroplankton
, that live part of their lives drifting in the atmosphere. These include plant spore
and wind-scattered seed
s, as well as microrganisms swept into the air from terrestrial dust storms and oceanic plankton swept into the air by sea spray
Though many planktonic species
in size, ''plankton'' includes organisms over a wide range of sizes, including large organisms such as jellyfish
. Plankton are defined by their ecological niche
and level of motility
rather than by any phylogenetic
classification. 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
The name ''plankton'' is derived from the Greek
adjective πλαγκτός (), meaning ''errant
'', and by extension, ''wanderer'' or ''drifter'', and was coined by Victor Hensen
in 1887. 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 current
s. This is in contrast to nekton
organisms, such as fish
and marine mammal
s, 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
s, and some jellyfish
). By contrast, meroplankton
are only planktic for part of their lives (usually the larva
l stage), and then graduate to either a nektic (swimming) or benthic
(sea floor) existence. Examples of meroplankton include the larvae of sea urchin
s, marine worm
s, and most fish
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.
Plankton are primarily divided into broad functional (or trophic level
(from Greek ''phyton'', or plant), are autotroph
or eukaryotic alga
e that live near the water surface where there is sufficient light
to support photosynthesis
. Among the more important groups are the diatom
s and coccolithophore
(from Greek ''zoon'', or animal), are small protozoa
ns or metazoa
ns (e.g. crustacean
s and other animal
s) that feed on other plankton. Some of the eggs
e of larger nektonic animals, such as fish, crustaceans, and annelid
s, are included here.
and fungus-like organisms
, which, like bacterioplankton, are also significant in remineralisation and nutrient cycling
, which play an important role in remineralising
organic material down the water column (note that prokaryotic phytoplankton are also bacterioplankton).
are viruses. Viruses are more abundant in the plankton than bacteria and archaea, though much smaller.
s. 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:
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 microorganism
s and operate at low Reynolds number
s, where the viscosity of water is more important than its mass or inertia.
Marine plankton includes bacteria, 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 in the freshwaters of lakes and rivers.
are tiny lifeforms that float and drift in the air, carried by the current
of the wind
; they are the atmospheric analogue
to oceanic plankton. Most of the living things that make up aeroplankton are very small to microscopic
in size, and many can be difficult to identify because of their tiny size. Scientists can collect them for study in traps and sweep nets from aircraft
, kites or balloons. Aeroplankton is made up of numerous microbes
, including virus
es, about 1000 different species of bacteria
, around 40,000 varieties of fungi
, and hundreds of species of protist
es and liverworts
that live some part of their life cycle as aeroplankton, often as spore
, and wind-scattered seed
s. Additionally, peripatetic microorganisms are swept into the air from terrestrial dust storms, and an even larger amount of airborne marine microorganisms are propelled high into the atmosphere in sea spray. Aeroplankton deposits hundreds of millions of airborne viruses and tens of millions of bacteria every day on every square meter around the planet.
Many animals live in terrestrial environments by thriving in transient often microscopic bodies of water and moisture, these include Rotifer
s and Gastrotrich
s 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 although 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 copepod
s 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
are fragile animals that live in the water column in the ocean. Their delicate bodies have no hard parts and are easily damaged or destroyed. Gelatinous zooplankton are often transparent. All jellyfish
are gelatinous zooplankton, but not all gelatinous zooplankton are jellyfish. The most commonly encountered organisms include ctenophore
, and Chaetognatha
in coastal waters. However, almost all marine phyla, including Annelida
, contain gelatinous species, but many of those odd species live in the open ocean and the deep sea and are less available to the casual ocean observer.
are the eggs
of fish. They are mostly found in the sunlit zone of the water column
, less than 200 metres deep, which is sometimes called the epipelagic
or photic zone
. Ichthyoplankton are planktonic
, meaning they cannot swim effectively under their own power, but must drift with the ocean currents. Fish eggs cannot swim at all, and are unambiguously planktonic. Early stage larvae swim poorly, but later stage larvae swim better and cease to be planktonic as they grow into juveniles
. Fish larvae are part of the zooplankton
that eat smaller plankton, while fish eggs carry their own food supply. Both eggs and larvae are themselves eaten by larger animals.
[What are Ichthyoplankton?]
Southwest Fisheries Science Center, NOAA. Modified 3 September 2007. Retrieved 22 July 2011.
Fish can produce high numbers of eggs which are often released into the open water column. Fish eggs typically have a diameter of about . The newly hatched young of oviparous fish are called larva
e. They are usually poorly formed, carry a large yolk sac
(for nourishment) and are very different in appearance from juvenile and adult specimens. The larval period in oviparous fish is relatively short (usually only several weeks), and larvae rapidly grow and change appearance and structure (a process termed metamorphosis
) to become juveniles. During this transition larvae must switch from their yolk sac to feeding on zooplankton
prey, a process which depends on typically inadequate zooplankton density, starving many larvae. In time fish larvae become able to swim against currents, at which point they cease to be plankton and become juvenile fish
are organisms that are planktic for their entire life cycle. Holoplankton can be contrasted with meroplankton
, which are planktic organisms that spend part of their life cycle in the benthic zone
. Examples of holoplankton include some diatom
s, some dinoflagellate
s, and salp
s, as well as some gastropod
mollusk species. Holoplankton dwell in the pelagic zone
as opposed to the benthic zone
Holoplankton include both phytoplankton
and vary in size. The most common plankton are protist
are a wide variety of aquatic organisms which have both planktonic and benthic
stages in their life cycles. Much of the meroplankton consists of larva
l stages of larger organism.
Meroplankton can be contrasted with holoplankton
, which are planktonic organisms that stay in the pelagic zone
as plankton throughout their entire life cycle. After a period of time in the plankton, many meroplankton graduate to the nekton
or adopt a benthic
) lifestyle on the seafloor
. The larval stages of benthic invertebrate
s make up a significant proportion of planktonic communities. The planktonic larval stage is particularly crucial to many benthic invertebrate in order to disperse
their young. Depending on the particular species and the environmental conditions, larval or juvenile-stage meroplankton may remain in the pelagic zone for durations ranging from hour to months.
are organisms that attach themselves to planktonic organisms or other floating objects, such as drifting wood, buoyant
shells of organisms such as ''Spirula
'', or man-made flotsam
. Examples include goose barnacle
s and the bryozoan ''Jellyella
''. By themselves these animals cannot float
, which contrasts them with true planktonic organisms, such as ''Velella
'' and the Portuguese Man o' War
, which are buoyant. Pseudoplankton are often found in the guts of filtering zooplankters
are organisms, such as free-living or attached benthic organism
s 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''.
File:Diatom Helipelta metil.jpg|Diatoms have glass shells (frustules) and also produce much of the worlds oxygen
File:Haeckel Spumellaria detail.png| The elaborate silicon shells of microscopic marine radiolarians can eventually produce opal
File:Coccolithus pelagicus.jpg| Coccolithophores have chalk plates called coccoliths, and produced the Cliffs of Dover
File:Cwall99 lg.jpg| Planktonic algae bloom of coccolithophores off the southern coast of England
File:Planktic Foraminifera of the northern Gulf of Mexico.jpg| Foraminiferans have calcious shells and produced the limestone in the 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 tropical and sub-tropical oceans have abundant light, they experience relatively low primary production because they offer limited nutrients such as nitrate, phosphate and silicate. This results from large-scale ocean circulation and water column stratification. In such regions, primary production usually occurs at greater depth, although at a reduced level (because of reduced light).
Despite significant macronutrient concentrations, some ocean regions are unproductive (so-called HNLC regions). The micronutrient iron is deficient in these regions, and adding it can lead to the formation of phytoplankton algal blooms. Iron primarily reaches the ocean through the deposition of dust on the sea surface. Paradoxically, oceanic areas adjacent to unproductive, arid land thus typically have abundant phytoplankton (e.g., the eastern Atlantic Ocean, where trade winds bring dust from the Sahara Desert in north Africa).
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.
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.
Primarily by grazing on phytoplankton, zooplankton provide carbon to the planktic foodweb, either respiring it to provide metabolic energy, or upon death as biomass or detritus. Organic material tends to be denser than seawater, so it sinks into open ocean ecosystems away from the coastlines, transporting carbon along with it. This process, called the biological pump, is one reason that oceans constitute the largest carbon sink on Earth. However, it has been shown to be influenced by increments of temperature. In 2019, a study indicated that at ongoing rates of seawater acidification, Antarctic phytoplanktons could become smaller and less effective at storing carbon before the end of the century.
It might be possible to increase the ocean's uptake of carbon dioxide () generated through human activities by increasing plankton production through iron fertilization – introducing amounts of iron into the ocean. However, this technique may not be practical at a large scale. Ocean oxygen depletion and resultant methane production (caused by the excess production remineralising at depth) is one potential drawback.
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 () 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 / balance since the early Precambrian Eon.
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.
File:Pelagibacter.jpg| ''Pelagibacter ubique'', the most common bacteria in the ocean, plays a major role in global carbon cycles
File:Prochlorococcus marinus (cropped).jpg| The tiny cyanobacterium ''Prochlorococcus'' is a major contributor to atmospheric oxygen
File:Noctiluca scintillans varias.jpg| The sea sparkle dinoflagellate glows in the night to produce the milky seas effect
File:Copepodkils.jpg| Copepod from Antarctica, a translucent ovoid animal with two long antennae
File:Clupeaharenguslarvaeinsitukils.jpg|Herring larva imaged with the remains of the yolk and the long gut visible in the transparent animal
File:Icefishuk.jpg|Icefish larvae from Antarctica have no haemoglobin
File:Mnemiopsis leidyi 2.jpg| The sea walnut ctenophore has a transient anus which forms only when it needs to defecate
File:LeptocephalusConger.jpg|Eel larva drifting with the gulf stream
File:Krill666.jpg|Antarctic krill, probably the largest biomass of a single species on the planet
File:Dinoflagellates and a tintinnid ciliate.jpg| Microzooplankton are major grazers of the plankton: two dinoflagellates and a tintinnid ciliate).
File:Sargassum on the beach, Cuba.JPG| Sargassum seaweed drifts with currents using air bladders to stay afloat
File:Plankton creates sea foam 2.jpg| Planktonic sea foam bubbles with image of photographer
File:Janthina.jpg| Macroplankton: a ''Janthina janthina'' snail (with bubble float) cast up onto a beach in Maui
Importance to fish
Zooplankton are the initial prey item for almost all fish larvae as they switch from their yolk sacs to external feeding. Fish rely on the density and distribution of zooplankton to match that of new larvae, which can otherwise starve. Natural factors (e.g., current variations) and man-made factors (e.g. river dams, ocean acidification, rising temperatures) can strongly affect zooplankton, which can in turn strongly affect larval survival, and therefore breeding success.
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 practised by traditional fish farmers for decades, illustrating the importance of plankton even in man-made environments.
* Gelatinous zooplankton
* Paradox of the plankton
*Kirby, Richard R. (2010). ''Ocean Drifters: A Secret World Beneath the Waves''. Studio Cactus Ltd, UK. .
*Dusenbery, David B. (2009). ''Living at Micro Scale: The Unexpected Physics of Being Small''. Harvard University Press, Cambridge, Massachusetts .
*Kiørboe, Thomas (2008). ''A Mechanistic Approach to Plankton Ecology''. Princeton University Press, Princeton, N.J. .
*Dolan, J.R., Agatha, S., Coats, D.W., Montagnes, D.J.S., Stocker, D.K., eds. (2013).''Biology and Ecology of Tintinnid Ciliates: Models for Marine Plankton''. Wiley-Blackwell, Oxford, UK .
– Short film narrated by David Attenborough about the varied roles of plankton
– Short documentary films and photos
COPEPOD: The Global Plankton Database
– Global coverage database of zooplankton biomass and abundance data
– 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
– Integrated Marine Observing System
– BBC Audio slideshow
– Images of planktonic microorganisms
Plankton, planktic, planktonic
– Essays on nomenclature
Journal of Plankton Research
– Scientific periodical devoted to plankton