Stramenopiles and Cercozoa dominate the heterotrophic protist community of biological soil crusts irrespective of edaphic factors.

• We estimated the abundance and diversity of heterotrophic protists in biocrusts with the liquid aliquot method (LAM). • Amoebae, amoeboflagellates, and flagellates, from the phylum Cercozoa and Stramenopiles, dominated the protists community. • Measured environmental factors were not found to shape the community composition of heterotrophic protists significantly. • There was no distance-decay relationship between geographical distance and protists community dissimilarity. • For the most taxa, no clear co-occurrence pattern could be observed, it seemed they co-occurred randomly. Biological soil crusts (biocrusts) are terrestrial micro-habitats distributed in drylands and also in temperate coastal dunes. Biocrusts harbor phototrophic and heterotrophic microorganisms in the upper soil layer, which fulfil important ecological functions such as primary production and energy channelling via the microbial loop. Heterotrophic protists, although being an essential component of the microbial food web of biocrusts, have rarely been investigated. Therefore, in the present study, we used the liquid aliquot method (LAM) to assess the abundance and diversity of protists in biocrusts from coastal dunes at the Baltic Sea for the first time. The total abundance of protists ranged between 10 × 103 and 128 × 103 individuals g−1 dry weight. The community was dominated by naked amoebae (54 %) and flagellates (44 %). The most common taxa were Spumella -like flagellates (Stramenopiles), Paracercomonas -like amoeboflagellates, and Sandonidae-like glissomonads (both from the phylum Cercozoa) as well as heteroloboseans. Despite significant differences in the beta diversity of protist morphotypes, the measured environmental drivers, such as pH, total organic carbon, nitrogen, and phosphorus did not explain these differences. Also, the geographical distance could not predict the community dissimilarity, suggesting that the diversity of protists in biocrusts is controlled by biotic or other physicochemical parameters. [ABSTRACT FROM AUTHOR]