1. General Discussion
Ciliated protozoa are ubiquitous unicellular eukaryotes that inhabit freshwater and marine aquatic environments, soils, and sediments. Ciliates are important organisms in the transfer and transformation of nutrients in ecological food chains.1,2 In the aquatic environment, ciliates are an integral part of the zooplankton and periphyton communities, feed predominantly on bacteria and small algae,3–5 and mediate the transfer of energy from the microbial food web to the larger metazoan.1 In soils and sediments, ciliates feed primarily on bacteria and organic detritus.6 The prevalence of ciliates and their importance in trophic processes make them particularly appropriate as organisms used to assess water quality.7
Recent advances in environmental toxicity assessments have focused on microscale testing, more rapid bioassessment techniques, and more sensitive indicators of water quality (i.e., sublethal versus lethal effects).8,9 The potential for using ciliates to evaluate water quality was recognized some time ago.10–12 More recently, investigators have focused increasingly on ciliates as test and indicator organisms for assessing eutrophic and contaminated media because they represent a neglected trophic level in most toxicity-test batteries and are sensitive to a broad range of toxicants in the natural environment.11,12 A comprehensive review of this field can be found elsewhere.13,14