Biological Soil Crust (IMAGE) Arizona State University Caption Biological soil crusts -- or communities of microorganisms that grow on the surface of the soil when there is no plant cover -- are key in protecting the soil from erosion and providing an environment where other microbes can thrive. Credit Estelle Couradeau Usage Restrictions Only with photo credit License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.