In reservoirs, protozoa are the basis of plankton, which feeds larger animals. Protozoa serve as food for intestinal, some worms, small crustaceans, fish fry. For many small animals and their larval stages, protozoa are often the only type of food.
After the death, the protozoa sink settle to the bottom of the reservoirs. For many millennia, sedimentary rocks have been formed from it under pressure. As a result of mountain building processes, the created rocks – limestone, chalk, tripoli – are brought to the surface. Of the foraminiferous limestones, the Pyrenees and the Alps, the mountains of North Africa, the Caucasus, Central and Central Asia are composed. Man makes extensive use of calcareous rocks for construction.
Protozoa play an important role in the soil formation process. They populate all types of soils. As reducers, they are active participants in the biological cycle of substances in the biosphere.
The simplest ones (rhizopods, flagella and infusoria) secrete biologically active substances that stimulate the growth of plant roots, increase seed germination, inhibit the activity of fungi harmful to plants, and also serve as food for many other organisms. They also carry out biological purification of water from pollution, that is, they play the role of orderlies in natural reservoirs.
The simplest are used for the production of dairy products and in the chemical industry, they are used to produce antibiotics, vitamins, hormones, enzymes. They spoil food (rotting bacteria), cause diseases of animal plants (tonsillitis, potato scab).