RESPONSE OF CILIATE POPULATIONS TO CHANGING ENVIRONMENTAL-CONDITIONS ALONG A FRESH-WATER RESERVOIR

In this paper we present the results of a study carried out on populations of ciliates in a reservoir over a 13 month period. Seven physico-chemical parameters (temperature, pH, dissolved oxygen, BOD5, alkalinity conductivity and aerobic bacteria) were measured. A total of 52 species of protozoan ciliates were identified. The results from cluster and nodal analysis show that when Lemna gibba is present on the water surface, a ciliate biotope appears. This biotope is more similar to ciliates found on the sediments than those found in the absence of this plant. This similarity is caused by the provision of a substrate and exposure to anoxia. BOD5 and the biotope are the most significant factors influencing the diversity of ciliates. The analysis of the diversity index shows that ciliate diversity increases from surface samples without Lemna to surface samples with Lemna. Surface (neustonic) samples were more diverse then sediment samples, which showed an increase in diversity up to 30 ppm BOD5, then a levelling off, and an eventual decrease in species diversity.