Tufa deposition and periphyton overgrowth as factors affecting the ciliate community on travertine barriers in different current velocity conditions

Abstract

A characteristic of aquatic systems in karstic region is the formation of tufa – the product of calcium carbonate precipitation. Artificial substrata (glass slides) were used to investigate the influence of tufa deposits at two different current velocities (5 cm s−1 and 50 cm s−1) on the ciliate assemblages in periphyton. After two-month exposure periods, periphyton biomass and tufa deposit were c. three times greater at 50 cm s−1 than at 5 cm s−1. Ciliate population density was also higher on artificial substrata exposed in a lotic than in a lentic microhabitat (the overall mean number of ciliates at 5 cm s−1 was 122 ind. cm−2, and at 50 cm s−1 497 ind. cm−2). At each of the two observed current velocities, a Principal Components (PCA) ordination of the colonized ciliate associations showed a spatial separation of the associations that developed under two different conditions of tufa deposition. During the period of greater tufa deposit, associated with greater periphyton overgrowth rate, the ciliate communities had higher species diversity (a higher number of species and a lower number of individuals). Species diversity of ciliates had a positive nonlinear relation to tufa deposition rate. These results suggest that artificial surfaces covered by a rough tufa layer associated with greater periphyton biomass offer diverse conditions for colonization by ciliates.