microalgae

Microalgae are photosynthetic microorganisms that inhabit freshwater, marine, and damp terrestrial environments. Most are unicellular, though some form colonies or filaments. The group includes green algae (Chlorophyta), diatoms (Bacillariophyta), dinoflagellates, and coccolithophores. Cyanobacteria are photosynthetic but bacteria, not algae, and are sometimes called blue-green algae in older literature.

They use chlorophyll and accessory pigments to capture light and fix carbon dioxide into organic matter. They are major primary producers in aquatic ecosystems and contribute significantly to global oxygen production. Diatoms have silica cell walls; coccolithophores form calcium carbonate plates. Growth depends on light, nutrients, temperature, and mixing.

Most reproduce mainly by asexual division, enabling rapid population growth; some taxa undergo sexual reproduction under stress.

Applications include food supplements such as spirulina and chlorella, animal feed, cosmetics, and nutraceuticals. They are explored for biofuels, bioplastics, and pharmaceuticals, and are used in wastewater treatment and carbon capture.

Cultivation uses open ponds or closed photobioreactors. Key challenges are maintaining culture purity, optimizing light and gas exchange, and balancing inputs for sustainability. Some taxa can form harmful blooms or toxins; environmental risk arises if non-native strains are released.