Species composition of freshwater lichens in temperate mountain streams: the effect of site, habitat and local spatial isolation

Lichens associated with aquatic and semi-aquatic habitats are a specific ecological group of symbiotic organisms. Distribution patterns, especially those of freshwater lichens and factors determining their occurrence, are poorly recognized. The species richness and composition of lichens were studied in the splash and submerged zones of Carpathian mountain streams. Habitat parameters, including pH, water conductivity, dissolved oxygen content, silting and light intensity at sampling sites, were used in the analysis. The streams differed greatly in terms of the species composition; only three lichens (Thelidium minutulum, Verrucaria hydrophila and V. praetermissa) of the entire pool of 29 recorded species were found in all streams. This fact does not directly relate to the habitat parameters measured either at the level of individual streams or considering all the streams studied. Instead, the differences in the species composition of lichens increased with the geographical distance between streams, even locally. This means that the occurrence of lichens in mountain streams is strongly site-dependent and the variability in the habitat is of less importance for species presence. Presumably lack of effective natural vectors and weak dispersal ability are strong limiting factors for freshwater lichens. Nevertheless, increased ion concentration in water can considerably promote the development of the thalli of some species of lichens, as in the case of Verrucaria praetermissa, while it can be a limiting factor for others, as in the case of V. hydrophila.