Diatoms (microalgae) are ecologically common single-celled algae that can be found in nearly all habitats (marine, freshwater, terrestrial). They are often an important component of the phytoplankton and form diverse benthic communities in the shallow-water zones of seas. Diatoms use photosynthesis to convert soluble carbon dioxide into organic substances and play a pivotal part in the global carbon cycle. They are the most important producers of biomass and oxygen in the ocean and freshwater bodies alike. Diatoms make up the majority of marine phytoplankton and are the chief primary producers of organic materials; accordingly, they are an essential part of the food pyramid.
Due to their specific ecological preferences, their biodiversity and how often their opaline skeletons are well preserved in (marine) sediments, diatoms are also excellent paleoecological indicators. For further information see here.