COMPOSITION AND SPECIES RICHNESS OF MOLLUSCAN COMMUNITIES IN RELATION TO VEGETATION AND WATER CHEMISTRY IN THE WESTERN CARPATHIAN SPRING FENS: THE POOR–RICH GRADIENT

Abstract

Molluscs, vegetation and water chemistry were investigated at 48 spring fens situated in the borderland between the Czech Republic and Slovakia in 1997–2000. The purpose of this study was to test whether the gradient from mineral-poor to mineral-rich fens is reflected in the composition and species richness of mollusc communities, and to determine the importance of vegetation in predicting the mollusc community composition. A cluster analysis of mollusc communities separated the fens studied into five basic clusters which accord well with the results of detrended correspondence analysis (DCA). These clusters are arranged along the first DCA axis following the poor–rich trophic gradient. Ca, Mg, Fe, K, pH and conductivity are strongly correlated with the first DCA axis of the mollusc data. Similarly, Ca, Mg, Fe, pH and conductivity explain a substantial part of species-data variation, as verified by separated canonical correspondence analyses (CCAs) with a single variable. When sites with Sphagnum spp. were excluded, no significant correlations with K, pH and conductivity were found, whereas the significance of correlation with Fe increased markedly. Site classifications based on mollusc data are applicable to vegetation data and vice versa. Vegetation composition is a more important factor for explaining the variation in mollusc species than water chemistry when both are included in two separated CCAs as constraining variables. We found a linear correlation between mollusc species richness and water calcium concentration in the poor fens. In the rich fens, such a correlation was not found, and species richness was dependent on other abiotic and biotic factors, namely the Fe concentration and the water regime.