Ciliates (Alveolata, Ciliophora) as bioindicators of environmental pressure: A karstic river case

Ciliates are single celled eukaryotes recognized as key players in the microbial loop of aquatic ecosystems. The present study was carried out on Krka River (Croatia), a karst freshwater ecosystem characterized by tufa barriers, biomineralization and highly diverse communities. main aims were to investigate ciliate community structure biofilm (i.e. periphyton) samples collected from light- dark-exposed lithified tufa/stones. Furthermore, establishing links between patterns environmental parameters, we aimed assess bioindicator potential specific taxa for monitoring habitats. periphyton sampling performed at four representative sites river source, upstream, middle downstream sections. Ciliate investigated via traditional microscopy analyses DNA (eDNA) metabarcoding (Illumina sequencing hypervariable V9-region SSU rRNA gene). molecular approach recorded substantially higher number taxa, most which taxonomically belonging genera typically occurring barriers. results did not show any location. However, eDNA indicated significant differences among locations regarding structure. Thereby, hydrological parameters saprobiological classification structuring factors community. coupling with morphological provides robust, in-depth analytical system elucidating ciliated protists.