Phytoplankton (ˌfaɪtoʊˈplæŋktən) are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words φυτόν (phyton), meaning 'plant', and πλαγκτός (planktos), meaning 'wanderer' or 'drifter'.
Phytoplankton obtain their energy through photosynthesis, as do trees and other plants on land. This means phytoplankton must have light from the sun, so they live in the well-lit surface layers (euphotic zone) of oceans and lakes. In comparison with terrestrial plants, phytoplankton are distributed over a larger surface area, are exposed to less seasonal variation and have markedly faster turnover rates than trees (days versus decades). As a result, phytoplankton respond rapidly on a global scale to climate variations.
Phytoplankton form the base of marine and freshwater food webs and are key players in the global carbon cycle. They account for about half of global photosynthetic activity and at least half of the oxygen production, despite amounting to only about 1% of the global plant biomass. Phytoplankton are very diverse, varying from photosynthesizing bacteria to plant-like algae to armour-plated coccolithophores. Important groups of phytoplankton include the diatoms, cyanobacteria and dinoflagellates, although many other groups are represented.
Most phytoplankton are too small to be individually seen with the unaided eye. However, when present in high enough numbers, some varieties may be noticeable as colored patches on the water surface due to the presence of chlorophyll within their cells and accessory pigments (such as phycobiliproteins or xanthophylls) in some species.
[[File:Phytoplankton types.jpg|thumb|upright=3.3| center|Some types of phytoplankton (not to scale)'Left to right: cyanobacteria, diatom, dinoflagellate, green algae and coccolithophore]]
Phytoplankton are photosynthesizing microscopic protists and bacteria that inhabit the upper sunlit layer of marine and fresh water bodies of water on Earth.
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Cyanobacteria (saɪˌænoʊbækˈtɪəri.ə), also called Cyanobacteriota or Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name cyanobacteria refers to their color (), which similarly forms the basis of cyanobacteria's common name, blue-green algae, although they are not usually scientifically classified as algae. They appear to have originated in a freshwater or terrestrial environment.
The photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological processes that supply nutrients into the upper water column. The photic zone is home to the majority of aquatic life due to the activity (primary production) of the phytoplankton. In the photic zone, the photosynthesis rate exceeds the respiration rate.
Biomass is the mass of living biological organisms in a given area or ecosystem at a given time. Biomass can refer to species biomass, which is the mass of one or more species, or to community biomass, which is the mass of all species in the community. It can include microorganisms, plants or animals. The mass can be expressed as the average mass per unit area, or as the total mass in the community. How biomass is measured depends on why it is being measured. Sometimes, the biomass is regarded as the natural mass of organisms in situ, just as they are.
Focus is on lakes, rivers and reservoirs as aquatic systems. Specific is the quantitative analyse (incl. exercises) of physical, biogeochemical and sedimentological processes / interactions. The goal
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