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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Plankton | 3/7 | https://en.wikipedia.org/wiki/Plankton | reference | science, encyclopedia | 2026-05-05T07:36:10.175954+00:00 | kb-cron |
Plankton are also found at the ocean surface. Organisms that live at or just below the air-sea interface are called neuston. They float either on the water's surface (epineuston) or swim in the top few centimeters (hyponeuston). Many neuston qualify to be categorised as part of the broader plankton community, because they drift largely as currents or wind dictate, lacking strong enough swimming ability to counter them. Neustonic animals are primarily adapted to float upside-down on the ocean surface, similar to an inverted benthos, and form a unique subset of the zooplankton community, which plays a pivotal role in the functioning of marine ecosystems. Neustonic zooplankton are partially responsible for the active energy flux between superficial and deep layers of the ocean.Neustonic plankton is also a food source for marine zooplankton and fish migrating from the deep layers and seabirds.
==== In deep ocean ==== In 2025, researchers discovered microbial communities inhabiting the ocean conveyor belt, even at great depths in the ocean. Ocean currents are generated by surface wind and storms down to about 500 m (1,600 ft) below the surface. But the average depth of the ocean goes far below to 3.7 km (2.3 mi). At these greater depths, currents are driven by differences in water density, which in turn are controlled by differences in water temperature and salinity. This mechanism results in a circulation which behaves like a conveyor belt, carrying water and microorganisms to great depths and around the world. Water samples were taken along the full depth of the water column in the South Pacific Ocean, from Easter Island to Antarctica. They found marked increases in microbial diversity about 300 m (1,000 ft) deep, in a layer they call the prokaryotic phylocline. This zone, similar to the pycnocline, represents a shift from less diverse surface waters to abundant microbial ecosystems in the deep ocean. For instance, a group they called the Antarctic Bottom Water contains microbes suited to cold and high pressure, while another group they called the Ancient Water Group, located in slowly circulating water isolated from the surface for over a millennium, contains microbes with genes adapted to low oxygen.
== By taxon == Plankton contains representatives from all major divisions of life. This is because plankton are defined by habitat (water/air) and behaviour (drifting), and not by any phylogenetic or taxonomic considerations. So plankton are not a taxon, but they can be divided into broad taxonomic groups, as follows:
planktonic animals (metazoa) : – mostly predators (zooplankton) of smaller plankton. Examples are arrow worms, sea butterfly, ostracods, and salps. There are also planktonic microanimals typically smaller than one mm, such as copepods, water fleas, rotifers, and larval stages of various crustaceans and corals. planktonic protists: – single-celled eukaryote microorganisms, mostly invisible to the naked eye, such as diatoms, dinoflagellates, coccolithophores, foraminifera, radiolarians, and ciliates. Planktonic protists include algae (phytoplankton), protozoa (zooplankton), and many mixoplankton. planktonic fungi: – known also as mycoplankton, play important roles in remineralisation and nutrient cycling. For example, in the mycoloop, parasitic chytrids facilitate the transfer of nutrients from large, inedible phytoplankton to zooplankton. planktonic prokaryotes: planktonic bacteria and archaea known also as bacterioplankton and archaeoplankton. These play important roles as primary producers, or in remineralising organic material like mycoplankton down the water column. Photosynthetic cyanobacteria are important members of the phytoplankton. The unusually small Pelagibacter ubique, perhaps the most abundant bacterium on Earth, makes up about one third of microbial cells in the surface ocean, and plays important roles recycling nutrients in the microbial loop. The Roseobacter clade are significantly connected to phytoplankton. planktonic viruses: – known also as virioplankton, though not always classified as living organisms, are abundant in planktonic communities and influence microbial dynamics. Viruses are small infectious agents that can replicate only inside the living cells of a host organism, because they need the replication machinery of the host to do so. They are more abundant in the plankton than bacteria and archaea, though much smaller. Viruses can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea. In the viral shunt, viruses infect and break down (lyse) bacteria, releasing their nutrients and organic matter back into the water instead of allowing them to be consumed by larger organisms like zooplankton. This "shunts" nutrients away from higher trophic levels, keeping them in the microbial loop for reuse by other microorganisms.
== By size == 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 term microplankton is sometimes used more broadly to cover plankton that cannot really be seen without using a microscope, say plankton less than about one millimetre across. 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. It is the largely unseen microplankton that are the main drivers of the marine food web. Microplankton and smaller groups are microorganisms that operate at low Reynolds numbers, where the viscosity of water is more important than its mass or inertia.
== By trophic mode == Trophic mode describes the role of a planktonic organism in the food web based on how it obtains energy and nutrients to sustain its growth, reproduction, and survival. By trophic mode, plankton can be divided into four broad functional groups: phytoplankton, zooplankton, mixoplankton and decomposers.
=== Phytoplankton === Phytoplankton (from Greek phyton, or plant) are autotrophic prokaryotic or eukaryotic 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.