Soil diatoms, Coloured scanning electron micrograph (SEM). Although most diatom species occur in aquatic habitats, specific diatom communities occur in soil where they grow with other microalgae and cyanobacteria. In the soil food web, algae serve as food for soil protozoa and micro- and meio-fauna such as nematodes or collembolans. Magnification: x1600 when printed 10 centimetres wide.