The influence of substratum age on patterns of protozoan assemblages in freshwater Aufwuchs : a case study

Artificial substrata (glass slides) were used to investigate the dynamics of Aufwuchs-protozoa (Testacea) in 5 bodies of water. A comparison of substrata exposed for only 4 weeks in contrast to others exposed for several months gave insight into some methodological requirements in the use of artificial substrata. The Testacea colonization of differently-aged substrata varied considerably. After 4 weeks, specimen numbers and biovolumes were much lower than on older substrata, and species composition also differed considerably in most samples. Short-term exposures of glass slides gave no reliable information on trends displayed by Testacea populations that had developed for longer time periods, especially during winter. It is recommended that, when using newly exposed substrata for bioindication or the analysis of ecological processes in Aufwuchs, the variables that affect the rate of colonization of different taxonomic groups should be considered carefully.