<P> Phytoplankton / ˌfaɪtoʊˈplæŋktən / are the autotrophic (self - feeding) components of the plankton community and a key part of oceans, seas and freshwater basin ecosystems . The name comes from the Greek words φυτόν (phyton), meaning "plant", and πλαγκτός (planktos), meaning "wanderer" or "drifter". 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 . </P> <P> Phytoplankton are photosynthesizing microscopic organisms that inhabit the upper sunlit layer of almost all oceans and bodies of fresh water on Earth . They are agents for "primary production," the creation of organic compounds from carbon dioxide dissolved in the water, a process that sustains the aquatic food web . </P>

Phytoplankton are heterotrophs which depend on autotrophs for nutrition