zooplankton
   HOME

TheInfoList



OR:

Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal'').
Plankton Plankton are the diverse collection of organisms found in water (or air) 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 cr ...
are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by currents in the
ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...
, or by currents in seas,
lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much lar ...
s or
river A river is a natural flowing watercourse, usually freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the ...
s. Zooplankton can be contrasted with phytoplankton, which are the plant component of the plankton community ("phyto" comes from the Greek word for ''plant''). Zooplankton are heterotrophic (other-feeding), whereas phytoplankton are autotrophic (self-feeding). This means zooplankton cannot manufacture their own food but must eat other plants or animals instead — in particular they eat phytoplankton. Zooplankton are generally larger than phytoplankton, most are microscopic, but some (such as
jellyfish Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella- ...
) are macroscopic and can be seen with the naked eye. Many protozoans (single-celled protists that prey on other microscopic life) are zooplankton, including
zooflagellate In some older systems of classification, Zoomastigophora is a phylum (more commonly known as zooflagellates) within the kingdom Protista. Organisms within this group have a spherical, elongated body with a single central nucleus. They are single-ce ...
s, foraminiferans, radiolarians, some dinoflagellates and marine microanimals. Macroscopic zooplankton include pelagic
cnidarian Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in Fresh water, freshwater and Marine habitats, marine environments, predominantly the latter. Their distinguishing feature is cnidocyt ...
s, ctenophores, molluscs,
arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...
s and
tunicate A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata (). It is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time ...
s, as well as planktonic arrow worms and bristle worms. The distinction between plants and animals often breaks down in very small organisms. Recent studies of marine microplankton have indicated over half of microscopic plankton are mixotrophs. A mixotroph is an organism that can behave sometimes as though it were a plant, and sometimes as though it were an animal, using a mix of autotrophy and heterotrophy. Many marine microzooplankton are mixotrophic, which means they could also be classified as phytoplankton.


Overview

Zooplankton (; ) are heterotrophic (sometimes detritivorous)
plankton Plankton are the diverse collection of organisms found in water (or air) 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 cr ...
. The word ''zooplankton'' is derived from the
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
''zoon'' (), meaning "animal", and ' (), meaning "wanderer" or "drifter". Zooplankton is a categorization spanning a range of
organism In biology, an organism () is any life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy (biology), taxonomy into groups such as Multicellular o ...
sizes including small protozoans and large metazoans. It includes holoplanktonic organisms whose complete life cycle lies within the plankton, as well as meroplanktonic organisms that spend part of their lives in the plankton before graduating to either the nekton or a sessile,
benthic 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 "t ...
existence. Although zooplankton are primarily transported by ambient water currents, many have locomotion, used to avoid predators (as in diel vertical migration) or to increase prey encounter rate. Just as any species can be limited within a geographical region, so are zooplankton. However, species of zooplankton are not dispersed uniformly or randomly within a region of the ocean. As with phytoplankton, ‘patches’ of zooplankton species exist throughout the ocean. Though few physical barriers exist above the mesopelagic, specific species of zooplankton are strictly restricted by salinity and temperature gradients; while other species can withstand wide temperature and salinity gradients. Zooplankton patchiness can also be influenced by biological factors, as well as other physical factors. Biological factors include breeding, predation, concentration of phytoplankton, and vertical migration. The physical factor that influences zooplankton distribution the most is mixing of the water column ( upwelling and downwelling along the coast and in the open ocean) that affects nutrient availability and, in turn, phytoplankton production. Through their consumption and processing of phytoplankton and other food sources, zooplankton play a role in aquatic
food web A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Another name for food web is consumer-resource system. Ecologists can broadly lump all life forms into one ...
s, as a resource for consumers on higher trophic levels (including fish), and as a conduit for packaging the organic material in the biological pump. Since they are typically small, zooplankton can respond rapidly to increases in phytoplankton abundance, for instance, during the spring bloom. Zooplankton are also a key link in the biomagnification of
pollutant A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like o ...
s such as mercury. File:Typical ocean models featuring zooplankton 2.jpg,

Ecologically important protozoan zooplankton groups include the foraminiferans, radiolarians and dinoflagellates (the last of these are often mixotrophic). Important metazoan zooplankton include
cnidaria Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in Fresh water, freshwater and Marine habitats, marine environments, predominantly the latter. Their distinguishing feature is cnidocyt ...
ns such as
jellyfish Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella- ...
and the
Portuguese Man o' War The Portuguese man o' war (''Physalia physalis''), also known as the man-of-war, is a marine hydrozoan found in the Atlantic Ocean and the Indian Ocean. It is considered to be the same species as the Pacific man o' war or blue bottle, which is ...
; crustaceans such as cladocerans,
copepod Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat. Some species are planktonic (inhabiting sea waters), some are benthic (living on the ocean floor), a number of species have p ...
s, ostracods, isopods, amphipods, mysids and krill; chaetognaths (arrow worms); molluscs such as pteropods; and
chordate A chordate () is an animal of the phylum Chordata (). All chordates possess, at some point during their larval or adult stages, five synapomorphies, or primary physical characteristics, that distinguish them from all the other taxa. These five ...
s such as salps and juvenile fish. This wide phylogenetic range includes a similarly wide range in feeding behavior: filter feeding,
predation Predation is a biological interaction In ecology, a biological interaction is the effect that a pair of organisms living together in a community have on each other. They can be either of the same species (intraspecific interactions), or o ...
and symbiosis with autotrophic phytoplankton as seen in corals. Zooplankton feed on
bacterioplankton Bacterioplankton refers to the bacterial component of the plankton that drifts in the water column. The name comes from the Ancient Greek word ' ('), meaning "wanderer" or "drifter", and ', a Latin term coined in the 19th century by Christian G ...
, phytoplankton, other zooplankton (sometimes cannibalistically), detritus (or marine snow) and even nektonic organisms. As a result, zooplankton are primarily found in surface waters where food resources (phytoplankton or other zooplankton) are abundant. Zooplankton can also act as a
disease A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...
reservoir A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including control ...
. Crustacean zooplankton have been found to house the bacterium '' Vibrio cholerae'', which causes cholera, by allowing the cholera vibrios to attach to their chitinous exoskeletons. This symbiotic relationship enhances the bacterium's ability to survive in an aquatic environment, as the exoskeleton provides the bacterium with carbon and nitrogen.


Size classification

Body size has been defined as a "master trait" for plankton as it is a morphological characteristic shared by organisms across taxonomy that characterises the functions performed by organisms in ecosystems. It has a paramount effect on growth, reproduction, feeding strategies and mortality. One of the oldest manifestations of the biogeography of traits was proposed over 170 years ago, namely Bergmann's rule, in which field observations showed that larger species tend to be found at higher, colder latitudes. Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
In the oceans, size is critical in determining trophic links in planktonic ecosystems and is thus a critical factor in regulating the efficiency of the biological carbon pump. Body size is sensitive to changes in temperature due to the thermal dependence of physiological processes. The plankton is mainly composed of ectotherms which are organisms that do not generate sufficient metabolic heat to elevate their body temperature, so their metabolic processes depends on external temperature. Consequently, ectotherms grow more slowly and reach maturity at a larger body size in colder environments, which has long puzzled biologists because classic theories of life-history evolution predict smaller adult sizes in environments delaying growth. This pattern of body size variation, known as the temperature-size rule (TSR), has been observed for a wide range of ectotherms, including single-celled and multicellular species, invertebrates and vertebrates. The processes underlying the inverse relationship between body size and temperature remain to be identified. Despite temperature playing a major role in shaping latitudinal variations in organism size, these patterns may also rely on complex interactions between physical, chemical and biological factors. For instance, oxygen supply plays a central role in determining the magnitude of ectothermic temperature-size responses, but it is hard to disentangle the relative effects of oxygen and temperature from field data because these two variables are often strongly inter-related in the surface ocean. Zooplankton can be broken down into size classes which are diverse in their morphology, diet, feeding strategies, etc. both within classes and between classes:


Picozooplankton

<2μm


Nanozooplankton

2-20μm


Microzooplankton

20-200μm ''Major grazers of the
plankton Plankton are the diverse collection of organisms found in water (or air) 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 cr ...
...'' Microzooplankton are defined as heterotrophic and mixotrophic plankton. They primarily consist of phagotrophic protists, including ciliates, dinoflagellates, and mesozooplankton nauplii. As the primary consumers of marine phytoplankton, microzooplankton consume ~ 59–75% daily of the marine primary production, much larger than mesozooplankton. That said, macrozooplankton can sometimes have greater consumption rates in eutrophic ecosystems because the larger phytoplankton can be dominant there. Microzooplankton are also pivotal regenerators of nutrients which fuel primary production and food sources for metazoans. Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License. Despite their ecological importance, microzooplankton remain understudied. Routine oceanographic observations seldom monitor microzooplankton biomass or herbivory rate, although the dilution technique, an elegant method of measuring microzooplankton herbivory rate, has been developed for almost four decades (Landry and Hassett 1982). The number of observations of microzooplankton herbivory rate is around 1600 globally, far less than that of primary productivity (> 50,000). This makes validating and optimizing the grazing function of microzooplankton difficult in ocean ecosystem models.


Mesozooplankton

0.2-20 millimeters Because plankton is rarely fished, it has been argued that mesoplankton abundance and species composition can be used to study marine ecosystems' response to climate change. This is because they have life cycles that generally last less than a year, meaning they respond to climate changes between years. Sparse, monthly sampling will still indicate vacillations.


Taxonomic groups


Protozoans

Protozoans are protists that feed on organic matter such as other
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
s or organic tissues and debris. Historically, the protozoa were regarded as "one-celled animals", because they often possess
animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
-like behaviours, such as
motility Motility is the ability of an organism to move independently, using metabolic energy. Definitions Motility, the ability of an organism to move independently, using metabolic energy, can be contrasted with sessility, the state of organisms th ...
and
predation Predation is a biological interaction In ecology, a biological interaction is the effect that a pair of organisms living together in a community have on each other. They can be either of the same species (intraspecific interactions), or o ...
, and lack a cell wall, as found in plants and many
algae Algae ( , ; : alga ) are any of a large and diverse group of photosynthetic, eukaryotic organisms. The name is an informal term for a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from ...
. Although the traditional practice of grouping protozoa with animals is no longer considered valid, the term continues to be used in a loose way to identify single-celled organisms that can move independently and feed by heterotrophy. Marine protozoans include
zooflagellate In some older systems of classification, Zoomastigophora is a phylum (more commonly known as zooflagellates) within the kingdom Protista. Organisms within this group have a spherical, elongated body with a single central nucleus. They are single-ce ...
s, foraminiferans, radiolarians and some dinoflagellates.


Radiolarians

Radiolarians are unicellular predatory protists encased in elaborate globular shells usually made of silica and pierced with holes. Their name comes from the Latin for "radius". They catch prey by extending parts of their body through the holes. As with the silica frustules of diatoms, radiolarian shells can sink to the ocean floor when radiolarians die and become preserved as part of the ocean sediment. These remains, as microfossils, provide valuable information about past oceanic conditions.Wassilieff, Maggy (2006
"Plankton - Animal plankton"
''Te Ara - the Encyclopedia of New Zealand''. Accessed: 2 November 2019.
File:Mikrofoto.de-Radiolarien 6.jpg, Like diatoms, radiolarians come in many shapes File:Podocyrtis papalis Ehrenberg - Radiolarian (30448963206).jpg, Also like diatoms, radiolarian shells are usually made of silicate File:Acantharian radiolarian Xiphacantha (Haeckel).jpg, However acantharian radiolarians have shells made from strontium sulfate crystals File:Spherical radiolarian 2.jpg, Cutaway schematic diagram of a spherical radiolarian shell


Foraminiferans

Like radiolarians, foraminiferans (''forams'' for short) are single-celled predatory protists, also protected with shells that have holes in them. Their name comes from the Latin for "hole bearers". Their shells, often called
tests Test(s), testing, or TEST may refer to: * Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities Arts and entertainment * ''Test'' (2013 film), an American film * ''Test'' (2014 film), ...
, are chambered (forams add more chambers as they grow). The shells are usually made of calcite, but are sometimes made of agglutinated sediment particles or
chiton Chitons () are marine molluscs of varying size in the class Polyplacophora (), formerly known as Amphineura. About 940 extant and 430 fossil species are recognized. They are also sometimes known as gumboots or sea cradles or coat-of-mail sh ...
, and (rarely) of silica. Most forams are benthic, but about 40 species are planktic. They are widely researched with well established fossil records which allow scientists to infer a lot about past environments and climates. File:EB1911 Foraminifera - Section of Rotalia beccarii.jpg, section showing chambers of a spiral foram File:Live Ammonia tepida.jpg, Live '' Ammonia tepida'' streaming granular ectoplasm for catching food File:Planktic Foraminifera of the northern Gulf of Mexico.jpg, Group of planktonic forams File:All Gizah Pyramids.jpg, The Egyptian pyramids were constructed from limestone that contained nummulites.


Amoeba

File:Amoeba proteus 2.jpg, Naked amoeba sketch showing food vacuoles and ingested diatom File:Arcella sp.jpg, Shell or test of a testate amoeba, '' Arcella'' sp. File:Collection Penard MHNG Specimen 533-2-1 Pamphagus granulatus.tif,
Xenogenic A xenobiotic is a chemical substance found within an organism that is not naturally produced or expected to be present within the organism. It can also cover substances that are present in much higher concentrations than are usual. Natural compo ...
testate amoeba covered in diatoms


Ciliates

File:Stylonychia putrina - 160x - II (13215594964).jpg, '' Stylonychia putrina'' File:Holophyra ovum - 400x (9836710085).jpg, ''Holophyra'' ovum File:Mikrofoto.de-Blepharisma japonicum 15.jpg, ''
Blepharisma japonicum ''Blepharisma japonicum'' is a species of protozoan that can be found either in water or soil in Japan. Description The body of an organism is elongated and ovoided. It has a curved anterior apex that is over the peristome. It has a cytostome ...
'' File:The ciliate Frontonia sp.jpg, This ciliate is digesting cyanobacteria. The mouth is at the bottom right.


Dinoflagellates

Dinoflagellates are a phylum of unicellular flagellates with about 2,000 marine species. Some dinoflagellates are predatory, and thus belong to the zooplankton community. Their name comes from the Greek "dinos" meaning ''whirling'' and the Latin "flagellum" meaning a ''whip'' or ''lash''. This refers to the two whip-like attachments (flagella) used for forward movement. Most dinoflagellates are protected with red-brown, cellulose armour.
Excavates Excavation may refer to: * Excavation (archaeology) * Excavation (medicine) * ''Excavation'' (The Haxan Cloak album), 2013 * ''Excavation'' (Ben Monder album), 2000 * ''Excavation'' (novel), a 2000 novel by James Rollins * '' Excavation: A Memo ...
may be the most basal flagellate lineage. File:Gyrodinium dinoflagellate.jpg, '' Gyrodinium'', one of the few naked dinoflagellates which lack armour File:Protoperidinium dinoflagellate.jpg, The dinoflagellate ''Protoperidinium'' extrudes a large feeding veil to capture prey File:Radiolarian - Podocyrtis (Lampterium) mitra Ehrenberg - 160x.jpg,
Nassellarian Nassellaria is an order of Rhizaria belonging to the class Radiolaria. The organisms of this order are characterized by a skeleton cross link with a cone or ring. Introduction Nassellaria is an order of Radiolaria under the class Polycystina. ...
radiolarians can be in symbiosis with dinoflagellates
Dinoflagellates often live in symbiosis with other organisms. Many
nassellarian Nassellaria is an order of Rhizaria belonging to the class Radiolaria. The organisms of this order are characterized by a skeleton cross link with a cone or ring. Introduction Nassellaria is an order of Radiolaria under the class Polycystina. ...
radiolarians house dinoflagellate
symbionts Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...
within their tests. The nassellarian provides ammonium and
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
for the dinoflagellate, while the dinoflagellate provides the nassellarian with a mucous membrane useful for hunting and protection against harmful invaders. There is evidence from DNA analysis that dinoflagellate symbiosis with radiolarians evolved independently from other dinoflagellate symbioses, such as with foraminifera. File:Ceratium tripos.jpg, ''Tripos muelleri'' is recognisable by its U-shaped horns File:Archives de zoologie expérimentale et générale (1920) (20299351186).jpg, '' Oodinium'', a genus of parasitic dinoflagellates, causes velvet disease in fish File:Karenia brevis.jpg, '' Karenia brevis'' produces red tides highly toxic to humans File:Algal bloom(akasio) by Noctiluca in Nagasaki.jpg,
Red tide A harmful algal bloom (HAB) (or excessive algae growth) is an algal bloom that causes negative impacts to other organisms by production of natural phycotoxin, algae-produced toxins, mechanical damage to other organisms, or by other means. HABs are ...


Mixotrophs

A mixotroph is an organism that can use a mix of different sources of energy and carbon, instead of having a single trophic mode on the continuum from complete autotrophy at one end to heterotrophy at the other. It is estimated that mixotrophs comprise more than half of all microscopic plankton. There are two types of eukaryotic mixotrophs: those with their own
chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it ...
s, and those with
endosymbiont An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship. (The term endosymbiosis is from the Greek: ἔνδον ''endon'' "withi ...
s—and others that acquire them through kleptoplasty or by enslaving the entire phototrophic cell. The distinction between plants and animals often breaks down in very small organisms. Possible combinations are photo- and
chemotroph A Chemotroph is an organism that obtains energy by the oxidation of electron donors in their environments. These molecules can be organic molecule, organic (chemoorganotrophs) or inorganic compound, inorganic (chemolithotrophs). The chemotroph de ...
y, litho- and organotrophy, auto- and heterotrophy or other combinations of these. Mixotrophs can be either eukaryotic or prokaryotic. They can take advantage of different environmental conditions. Many marine microzooplankton are mixotrophic, which means they could also be classified as phytoplankton. Recent studies of marine microzooplankton found 30–45% of the ciliate abundance was mixotrophic, and up to 65% of the amoeboid, foram and radiolarian
biomass Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms biom ...
was mixotrophic. ''Phaeocystis'' species are endosymbionts to acantharian radiolarians. '' Phaeocystis'' is an important algal genus found as part of the marine phytoplankton around the world. It has a polymorphic life cycle, ranging from free-living cells to large colonies. It has the ability to form floating colonies, where hundreds of cells are embedded in a gel matrix, which can increase massively in size during blooms. As a result, ''Phaeocystis'' is an important contributor to the marine
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...
and sulfur cycles. File:Tintinnid ciliate Favella.jpg, Tintinnid ciliate ''Favella'' File:Euglena mutabilis - 400x - 1 (10388739803) (cropped).jpg, '' Euglena mutabilis'', a photosynthetic flagellate File:Stichotricha secunda - 400x (14974779356).jpg, Zoochlorellae (green) living inside the ciliate ''Stichotricha secunda'' File:Dinophysis acuta.jpg, The dinoflagellate ''Dinophysis acuta'' A number of forams are mixotrophic. These have unicellular
algae Algae ( , ; : alga ) are any of a large and diverse group of photosynthetic, eukaryotic organisms. The name is an informal term for a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from ...
as
endosymbiont An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship. (The term endosymbiosis is from the Greek: ἔνδον ''endon'' "withi ...
s, from diverse lineages such as the green algae, red algae, golden algae, diatoms, and dinoflagellates. Mixotrophic foraminifers are particularly common in nutrient-poor oceanic waters. Some forams are kleptoplastic, retaining
chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it ...
s from ingested algae to conduct photosynthesis. By trophic orientation dinoflagellates are all over the place. Some dinoflagellates are known to be photosynthetic, but a large fraction of these are in fact mixotrophic, combining photosynthesis with ingestion of prey ( phagotrophy). Some species are
endosymbiont An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship. (The term endosymbiosis is from the Greek: ἔνδον ''endon'' "withi ...
s of marine animals and other protists, and play an important part in the biology of
coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups. C ...
s. Others predate other protozoa, and a few forms are parasitic. Many dinoflagellates are mixotrophic and could also be classified as phytoplankton. The toxic dinoflagellate '' Dinophysis acuta'' acquire chloroplasts from its prey. "It cannot catch the cryptophytes by itself, and instead relies on ingesting ciliates such as the red ''
Myrionecta rubra ''Mesodinium rubrum'' (or ''Myrionecta rubra'') is a species of ciliates. It constitutes a plankton community and is found throughout the year, most abundantly in spring and fall, in coastal areas. Although discovered in 1908, its scientific im ...
'', which sequester their chloroplasts from a specific cryptophyte clade (Geminigera/Plagioselmis/Teleaulax)".


Metazoa (animals)

Copepod Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat. Some species are planktonic (inhabiting sea waters), some are benthic (living on the ocean floor), a number of species have p ...
s are typically 1 to 2 mm long with a teardrop-shaped bodies. Like all crustaceans, their bodies are divided into three sections: head, thorax, and abdomen, with two pairs of antennae; the first pair is often long and prominent. They have a tough exoskeleton made of calcium carbonate and usually have a single red eye in the centre of their transparent head. About 13,000 species of copepods are known, of which about 10,200 are marine. They are usually among the more dominant members of the zooplankton. Metazoan zooplankton" style="float:left"> File:Copepod 2 with eggs.jpg,
Copepod Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat. Some species are planktonic (inhabiting sea waters), some are benthic (living on the ocean floor), a number of species have p ...
with eggs File:Tomopteriskils.jpg,
Segmented worm The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecol ...
File:Hyperia.jpg, Amphipod File:Krill666.jpg, Krill File:Glaucus atlanticus 1 cropped.jpg, Blue ocean slug


Holoplankton and meroplankton


Ichthyoplankton

Ichthyoplankton are the eggs and larvae of fish ("ichthyo" comes from the Greek word for ''fish''). They are planktonic because 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 juvenile fish. 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. File:Squidu.jpg, Juvenile planktonic squid File:Molalavdj.jpg, Ocean sunfish larvae (2.7mm) File:FMIB 47039 Ostracion hoops.jpeg, Boxfish larva


Gelatinous zooplankton

Gelatinous zooplankton Gelatinous zooplankton 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 zoopla ...
include ctenophores, medusae, salps, and Chaetognatha in coastal waters. Jellyfish are slow swimmers, and most species form part of the plankton. Traditionally jellyfish have been viewed as trophic dead ends, minor players in the marine food web, gelatinous organisms with a body plan largely based on water that offers little nutritional value or interest for other organisms apart from a few specialised predators such as the ocean sunfish and the leatherback sea turtle.Hamilton, G. (2016
"The secret lives of jellyfish: long regarded as minor players in ocean ecology, jellyfish are actually important parts of the marine food web"
''Nature'', 531(7595): 432-435.
Hays, G.C., Doyle, T.K. and Houghton, J.D. (2018) "A paradigm shift in the trophic importance of jellyfish?" ''Trends in ecology & evolution'', 33(11): 874-884. That view has recently been challenged. Jellyfish, and more gelatinous zooplankton in general, which include salps and ctenophores, are very diverse, fragile with no hard parts, difficult to see and monitor, subject to rapid population swings and often live inconveniently far from shore or deep in the ocean. It is difficult for scientists to detect and analyse jellyfish in the guts of predators, since they turn to mush when eaten and are rapidly digested. But jellyfish bloom in vast numbers, and it has been shown they form major components in the diets of
tuna A tuna is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae ( mackerel) family. The Thunnini comprise 15 species across five genera, the sizes of which vary greatly, ranging from the bullet tuna (max le ...
, spearfish and swordfish as well as various birds and invertebrates such as octopus, sea cucumbers, crabs and amphipods. "Despite their low energy density, the contribution of jellyfish to the energy budgets of predators may be much greater than assumed because of rapid digestion, low capture costs, availability, and selective feeding on the more energy-rich components. Feeding on jellyfish may make marine predators susceptible to ingestion of plastics." According to a 2017 study, narcomedusae consume the greatest diversity of mesopelagic prey, followed by physonect siphonophores, ctenophores and cephalopods. File:Parumbrosa polylobata 01.jpg,
Jellyfish Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella- ...
File:Ctenophora-Comb-jelly-Euplokamis-sp.-02.jpg, Bioluminescent ctenophore (comb jelly) File:Tunicate off Atauro island.jpg, This free-floating pyrosome is made up of hundreds of individual bioluminescent tunicates File:23 salpchain frierson odfw (8253212250).jpg, Salp chain
The importance of the so-called "jelly web" is only beginning to be understood, but it seems medusae, ctenophores and siphonophores can be key predators in deep pelagic food webs with ecological impacts similar to predator fish and squid. Traditionally gelatinous predators were thought ineffectual providers of marine trophic pathways, but they appear to have substantial and integral roles in deep pelagic food webs.Choy, C.A., Haddock, S.H. and Robison, B.H. (2017) "Deep pelagic food web structure as revealed by ''in situ'' feeding observations". ''Proceedings of the Royal Society B: Biological Sciences'', 284(1868): 20172116. . Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License


Role in food webs

Grazing by single-celled zooplankton accounts for the majority of organic carbon loss from marine primary production. Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
However, zooplankton grazing remains one of the key unknowns in global predictive models of carbon flux, the marine food web structure and ecosystem characteristics, because empirical grazing measurements are sparse, resulting in poor parameterisation of grazing functions. To overcome this critical knowledge gap, it has been suggested that a focused effort be placed on the development of instrumentation that can link changes in phytoplankton biomass or optical properties with grazing. Grazing is a central, rate-setting process in ocean ecosystems and a driver of
marine biogeochemical cycling Marine biogeochemical cycles are biogeochemical cycles that occur within marine environments, that is, in the saltwater of seas or oceans or the brackish water of coastal estuaries. These biogeochemical cycles are the pathways chemical substan ...
. In all ocean ecosystems, grazing by heterotrophic protists constitutes the single largest loss factor of marine primary production and alters particle size distributions. Grazing affects all pathways of export production, rendering grazing important both for surface and deep carbon processes. Predicting central paradigms of ocean ecosystem function, including responses to environmental change requires accurate representation of grazing in global biogeochemical, ecosystem and cross-biome-comparison models. Several large-scale analyses have concluded that phytoplankton losses, which are dominated by grazing are the putative explanation for annual cycles in phytoplankton biomass, accumulation rates and export production. File:Export Processes in the Ocean from Remote Sensing.jpg,
Pelagic food web Compared to terrestrial environments, marine environments have biomass pyramids which are inverted at the base. In particular, the biomass of consumers (copepods, krill, shrimp, forage fish) is larger than the biomass of primary producers. Thi ...
and the biological pump. Links among the ocean's biological pump and pelagic food web and the ability to sample these components remotely from ships, satellites, and autonomous vehicles. Light blue waters are the euphotic zone, while the darker blue waters represent the twilight zone.


Role in biogeochemistry

In addition to linking primary producers to higher trophic levels in marine food webs, zooplankton also play an important role as “recyclers” of carbon and other nutrients that significantly impact marine biogeochemical cycles, including the biological pump. This is particularly important in the oligotrophic waters of the open ocean. Through sloppy feeding, excretion, egestion, and leaching of fecal pellets, zooplankton release dissolved organic matter (DOM) which controls DOM cycling and supports the microbial loop. Absorption efficiency, respiration, and prey size all further complicate how zooplankton are able to transform and deliver carbon to the deep ocean.


Sloppy feeding and release of DOM

Excretion and sloppy feeding (the physical breakdown of food source) make up 80% and 20% of crustacean zooplankton-mediated DOM release respectively. In the same study, fecal pellet leaching was found to be an insignificant contributor. For protozoan grazers, DOM is released primarily through excretion and egestion and gelatinous zooplankton can also release DOM through the production of mucus. Leaching of fecal pellets can extend from hours to days after initial egestion and its effects can vary depending on food concentration and quality. Various factors can affect how much DOM is released from zooplankton individuals or populations. Absorption efficiency (AE) is the proportion of food absorbed by plankton that determines how available the consumed organic materials are in meeting the required physiological demands. Depending on the feeding rate and prey composition, variations in AE may lead to variations in fecal pellet production, and thus regulates how much organic material is recycled back to the marine environment. Low feeding rates typically lead to high AE and small, dense pellets, while high feeding rates typically lead to low AE and larger pellets with more organic content. Another contributing factor to DOM release is respiration rate. Physical factors such as oxygen availability, pH, and light conditions may affect overall oxygen consumption and how much carbon is loss from zooplankton in the form of respired CO2. The relative sizes of zooplankton and prey also mediate how much carbon is released via sloppy feeding. Smaller prey are ingested whole, whereas larger prey may be fed on more “sloppily”, that is more biomatter is released through inefficient consumption. There is also evidence that diet composition can impact nutrient release, with carnivorous diets releasing more dissolved organic carbon (DOC) and ammonium than omnivorous diets.


Carbon export

Zooplankton play a critical role in supporting the ocean's biological pump through various forms of
carbon export The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is the main component of biological compounds as well as a major compo ...
, including the production of fecal pellets, mucous feeding webs, molts, and carcasses.
Fecal pellets Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...
are estimated to be a large contributor to this export, with copepod size rather than abundance expected to determine how much carbon actually reaches the ocean floor. The importance of fecal pellets can vary both by time and location. For example, zooplankton bloom events can produce larger quantities of fecal pellets, resulting in greater measures of carbon export. Additionally, as fecal pellets sink, they are reworked by microbes in the water column, which can thus alter the carbon composition of the pellet. This affects how much carbon is recycled in the euphotic zone and how much reaches depth. Fecal pellet contribution to carbon export is likely underestimated; however, new advances in quantifying this production are currently being developed, including the use of isotopic signatures of amino acids to characterize how much carbon is being exported via zooplankton fecal pellet production. Carcasses are also gaining recognition as being important contributors to carbon export.
Jelly fall Jelly-falls are marine carbon cycling events whereby gelatinous zooplankton, primarily cnidarians, sink to the seafloor and enhance carbon and nitrogen fluxes via rapidly sinking particulate organic matter. These events provide nutrition to benth ...
s – the mass sinking of gelatinous zooplankton carcasses – occur across the world as a result of large blooms. Because of their large size, these gelatinous zooplankton are expected to hold a larger carbon content, making their sinking carcasses a potentially important source of food for
benthic organisms Benthos (), also known as benthon, is the community of organisms that live on, in, or near the bottom of a sea, river, lake, or stream, also known as the benthic zone.Census of Marine Zooplankton The Census of Marine Zooplankton is a field project of the Census of Marine Life that has aimed to produce a global assessment of the species diversity, biomass, biogeographic distribution, and genetic diversity of more than 7,000 described specie ...
* Diel vertical migration * Ocean acidification * Primary production * Thin layers (oceanography)


References


External links


SAHFOS
Sir Alister Hardy Foundation for Ocean Science
Ocean Drifters
Short film narrated by David Attenborough about the varied roles of plankton
Sea Drifters
BBC Audio slideshow
Plankton Chronicles
Short documentary films & photos
COPEPOD: The global plankton database
A global coverage database of zooplankton biomass and abundance data.
Guide to the marine zooplankton of south eastern AustraliaTasmanian Aquaculture and Fisheries Institute




{{Authority control Aquatic animals Biological oceanography Planktology Oceanographical terminology de:Plankton#Zooplankton