Microalgae or microphytes are microscopic algae, usually found in freshwater and marine systems, both in the living column and in the water column. These are single-celled species that exist individually, or in chains or in groups. Depending on the species, their sizes can range from a few micrometers (μm) to a few hundred micrometers. Unlike higher plants, microalgae do not have roots, stems or leaves. They are specially adapted to an environment dominated by viscous forces. Microalgae, capable of carrying out photosynthesis, are important for life on earth; They produce about half of atmospheric oxygen and simultaneously use carbon dioxide from greenhouse gases to grow photoautotrophically. Microalgae and bacteria form the basis of the food web and provide energy at all levels of food. Microalgae biomass is often measured with chlorophyll a concentrations and can provide a useful clue to potential production. The growing microphytes of the stock are closely linked to those of its predators. Without grazing pressure, the stock's growing microphytes decreases considerably. The microalgae biomass is often measured with chlorophyll a concentrations and can provide a useful index of potential production.

The chemical composition of microalgae is not an intrinsic constant factor but a wide range over varies, both depending on the species and the growing conditions. Certain microalgae have the capacity to acclimatize to changes in environmental conditions by modifying their chemical composition in response to environmental variability. A more spectacular example is their ability to replace phosphorus-free membrane lipids with phosphorus-depleted environments. It is possible to accumulate the desired products in microalgae by a wide range of modifying environmental factors such as temperature, lighting, pH, CO2 supply, salt and nutrients. Microphytes also produce chemical signals that aid in the selection, defense and avoidance of prey. These chemical signals affect large-scale tropical structures such as algal blooms, but are propagated by simple diffusion and laminar advective flow. Microalgae such as microphytes are the staple food of many aquaculture species, especially filtering bivalves.