The diatom communities from Apuseni Mountains: a first approach on crenic diatom flora

The unique geomorphological and hydrological characteristics along with the stable abiotic parameters have shaped springs into suitable aquatic habitats for a high number of microorganisms. Increasing anthropogenic impact, such as groundwater pollution, alteration or destruction of the eucrenal spring area and high demand for pristine water, are affecting the crenic biodiversity. The present study is the first to focus on taxa belonging to the Bacillariophyta phylum and includes diatom samples taken from 30 karstic springs located in the Apuseni Mountains, Romania. Because diatoms often display distinct preferences for specific substrates, 15 samples were collected from each spring: five from each of the three substrate types (bryophytes, stones, and fine sediments) within the eucrenal area. For qualitative assessment, three mixed samples were subsequently prepared for each substrate type, resulting in a total of 99 analysed samples. A total of 216 taxa were identified in the analysed samples, with 16% found only on bryophytes and 15% occurring only on sand. Two groups of frequent taxa, distinguished by their preferred substrate type and present in at least 25 springs have been observed: Caloneis fontinalis (Grunow) A. Cleve, Cocconeis lineata Ehrenberg and Meridion circulare (Greville) C. Agardh in epibryon, followed by Gomphonema parvulum (Kützing) Kützing and Planothidium dubium (Grunow) Round & Bukhtiyarova in epipsammon; three taxa Achnanthidium minutissimum (Kützing) Czarnecki, Amphora pediculus (Kützing) Grunow and Cocconeis placentula Ehrenberg stand out as a dominant group across all three types of substrates. Moreover, in the epilithon these were the only taxa present in all samples. Microhabitat-specific richness was shaped primarily by light conditions and canopy cover, with oxygen availability contributing as a secondary factor. Gomphonema elegantissimum E. Reichardt & Lange-Bertalot and Caloneis fontinalis, along with other 13 taxa have been identified for the first time in Romania. Keywords: Bacillariophyta, Carpathian Mountains, epibryon, epilithon, epipsammon.