Microalgae or microphytes are microscopic algae, typically found in freshwater and marine systems, living in both the water column and sediment. they're unicellular species which exist individually, or chained or groups. counting on the species, their sizes can range from a couple of micrometers (μm) to a couple of hundred micrometers. Unlike higher plants, microalgae don't have roots, stems, or leaves. they're specially adapted to an environment dominated by viscous forces. Microalgae, capable of performing photosynthesis, are important for all times on earth; they produce approximately half the atmospheric oxygen and use simultaneously the greenhouse emission CO2 to grow photoautotrophically. Microalgae, along side bacteria, form the bottom of the food cycle and supply energy for all the trophic levels above them. Microalgae biomass is usually measured with chlorophyll concentrations and may provide a useful index of potential production. The standing stock of microphytes is closely associated with that of its predators. Without grazing pressures the standing stock of microphytes dramatically decreases.