Diatomeas

Diatomeas, or diatoms, are a major group of algae within the class Bacillariophyceae, part of the larger stramenopile lineage. They are among the most abundant and diverse phytoplankton in oceans, freshwater, and damp soils. Diatoms are mostly unicellular, though many species form chains or colonies, and they are defined by their intricate siliceous cell walls, called frustules.

Diatom frustules come in two broad forms: centric diatoms, which are radially symmetrical, and pennate diatoms, which are bilaterally symmetric. Some pennate species possess a raphe, a slit that enables gliding motility. Their pigments include chlorophyll a and c, along with fucoxanthin, which gives a golden-brown color to many diatoms.

Ecologically, diatoms require dissolved silica for building their frustules and thus play a key role in the global silica cycle. They are primary producers in many aquatic ecosystems, contributing substantially to carbon fixation and forming the base of many food webs. Diatom populations respond to nutrient availability and can form blooms in nutrient-rich waters.

Reproduction is primarily asexual, with daughter cells inheriting a portion of the parent’s frustule. With successive divisions, cell size gradually declines until sexual reproduction occurs, restoring cell size through the formation of auxospores.

Fossil evidence of diatoms dates back to at least the Jurassic period. Diatomaceous earth, composed of accumulated fossilized frustules, has widespread industrial uses, including filtration, polishing, and insulation. In addition, contemporary diatom assemblages are used as bioindicators to assess water quality and environmental change.