Environmental degradation and contaminants directly affect aquatic communities and their species composition, and in particular protozoan species assemblages due to their rapid doubling times and high turnover rates. These fast responses combined with being susceptible to different forms of environmental and ecological changes mean that protozoan communities reorganize rapidly and, consequently, allow frequent biomonitoring1. In contrast to physicochemical approaches that depict a contamination just at the point and time of sampling, the abundances of ciliate and certain amoebozoan indicator species give detailed information about past and present degradation and pollution processes.
Protozoans (ciliates, amoebae) are ideal biological indicator species as these groups are composed of species with largely cosmopolitan distribution. Thus, the cause-effect system of these indicator species has a world-wide applicability. Particularly, ciliates are early predictors of organic pollution and other contaminants. Thus, they can be used as bioindicators that depict the intensity of human impact causing changes in an aquatic ecosystem. Because ciliate species assemblages differ among different ecosystem states, they also serve as system state indicators. Furthermore, ciliate assemblages can influence the functional status of a system, reflecting environmental problems such as the degradation of water quality. Consequently, the composition of indicator species serves as a measure to achieve the necessary reduction in contaminants as well as ecological restoration targets1. The species composition of ciliates can be used to assess the saprobic index of water quality. Due to their large genetic and phenotypic diversity, ciliates and testate amoebae display a wide spatial distribution, ranging from soil and wetland habitats to deep interstitial habitats in riverbed sediments2,3.