engleski

Periphytic ciliate colonization in two tufa- depositing systems

Tufa is a freshwater calcium-carbonate deposit, creating a myriad of microhabitats for periphyton. While increasing habitat heterogeneity, it also generates a certain stress for periphytic biota. Periphyton development was studied using glass slides in two tufa-depositing environments characterised by barrage lakes: National park Krka and National park Plitvice Lakes (Croatia). NP Krka is under the influence of Mediterranean climate, whereas NP Plitvice Lakes has continental climate. The slide carriers were seasonally exposed on tufa barriers between barrage lakes during a one month period. The seasonal differences were pronounced for tufa deposition and chlorophyll a accrual, especially within NP Plitvice Lakes. During one year, 72 ciliate morphospecies were determined in NP Krka, and 71 were found in NP Plitvice Lakes. Ciliate assemblages were mostly influenced by the position within the lake system. Peritrichs and suctorians strongly dominated in assemblages on tufa barriers below lakes. Both groups probably prospered from the overflowing plankton-rich water. Flow velocity likely structured periphyton, as there was a clear relationship between ciliate biomass and taxa frequency within certain velocity range. Microhabitats with slow flow supported up to 50% more diverse ciliate assemblages than fast flowing microhabitats. In both hydrosystems, folliculinids Lagotia dinaridica, endemic to Dinaric hydrosystems, and Ascobius lentus colonized substrates under slow flow conditions. High tufa deposition during summer had negative influence on ciliate diversity, probably due to strong sedimentation. High discharge events mostly led to flushing of the attached taxa, whereas few taxa resisted the hydrological stress. Our findings suggest that the seasonal and microhabitat variations of tufa deposition processes, productivity and flow conditions likely play a dominant role in generating distributional patterns of periphyton community assemblages within karst and tufa-precipitating hydrosystems.

tufa barriers ; chlorophyll a ; flow velocity ; taxa richness

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