Diversity and distribution of phototrophic primary producers in saline lakes from Transylvania, Romania

Phototrophic primary producers are regarded as valuable indicators in aquatic habitats, since they are spread in a wide range of environmental conditions. However, the communities harbored by extreme ecosystems such as the saline lakes have been scarcely investigated with respect to their diversity and roles in the ecosystem functioning. The present study investigates the structure, diversity, and distribution of autotrophs from 19 lakes located in the Transylvanian Basin (Romania). Overall, 83 aquatic taxa were identified, belonging to Bacillariophyta (67), Cyanobacteria (10), Chlorophyta (4), Euglenophyta (1), and Xanthophyta (1). Standardized limnological methods were employed for sampling and analyses: measurements of morphometric, physical and chemical parameters, sampling techniques, optical microscopy identification of taxa and multivariate processing of data. Because saline lakes typically sustain undiversified biotic communities, usually well adapted to extreme conditions, we hypothesized that: (1) The main environmental driver of taxonomic diversity (expressed as species richness) would be the salinity; and (2) the same halophilic dominant taxa would occur in all hypersaline lakes (TDS > 50 g L −1 ). However, our results disproved both statements. Firstly, salinity was found to be an important driver of taxa diversity, but only subsequent to high habitat heterogeneity, lake area and nutrient concentrations. Secondly, high percentages of halotolerant, and not halophilic species were found, together with increased numbers of rare species (appearing in only one lake). Thus, the present study helps improve the current knowledge on the diversity of primary producers from saline lakes, opening new perspectives in understanding the functioning of such extreme environments.