Diatomeen

Diatomeen, or diatoms, are a diverse group of algae comprising unicellular and colonial photosynthetic protists in the class Bacillariophyceae. They are characterized by their siliceous cell walls, known as frustules, which consist of two interlocking halves. The frustule exhibits intricate ornamentation and porosity that varies among species and fossilizes well, making diatomaceous deposits common in sediment records.

Diatoms inhabit nearly all aquatic environments, including oceans, rivers, lakes, and moist soils. They can be planktonic, drifting in the water column, or benthic, living on submerged substrates. As major primary producers, they contribute substantially to carbon fixation and are foundational to many aquatic food webs. Their pigments typically include chlorophylls a and c and the carotenoid fucoxanthin.

Life cycle and reproduction are notable features. Most diatoms reproduce asexually by mitosis, but with each division the average cell size decreases. When cells become very small, sexual reproduction occurs to restore cell size, often through the formation of an auxospore that re-establishes the maximum size.

Diatomaceous material has significant practical uses. Fossil diatoms form diatomaceous earth, which is used as a filtration medium, abrasive, filler, and polishing agent. In modern monitoring, diatom assemblages are used as bioindicators to assess water quality and past environmental conditions in paleolimnology and paleoceanography. Some species can produce toxins, such as domoic acid in certain Pseudo-nitzschia, with implications for seafood safety.