Where can free-living protozoans be found besides ponds and oceans?

Free-living protozoans are highly adaptable organisms that inhabit a wide range of environments beyond ponds and oceans. They are found in diverse terrestrial and aquatic habitats, including:

• Soils: Protozoans thrive in the moisture films surrounding soil particles. They are essential to soil health, where they regulate bacterial populations and contribute to nutrient cycling.12
• Bogs: These wetland environments support complex microbial communities that include protozoans.1
• Lakes and Estuaries: Like the ocean, these bodies of water host significant planktonic protozoan populations.1
• Wastewater Treatment Systems: Protozoans are actively utilized in wastewater treatment plants, such as activated sludge and percolating filter systems, to consume organic waste and bacteria.2
• Extreme Climates: They have successfully colonized habitats ranging from the Arctic to the Antarctic, as well as equatorial zones.1

Because many free-living protozoans rely on moisture films, they are considered aquatic organisms even when living in terrestrial environments. When conditions become unfavorable—such as during desiccation or freezing—many species survive by encysting, entering a dormant state until the environment becomes hospitable again.13