Water mites of the genus Hygrobates are widely distributed in all biogeographic regions except the Antarctic. Palaearctic Hygrobates species with reticulated soft integument generally have been considered as representatives of one common and widely distributed species, Hygrobates fluviatilis Strøm, 1768. Based on partial COI sequences (DNA-barcodes) and statistical analysis of morphological data, we show that these mites belong to six distinct lineages. Two of them are widely distributed in Central Europe: Hygrobates fluviatilis here redescribed based on a neotype designated from the type locality in Norway, and a species new to science, H. arenarius Smit & Pešić. The four remaining lineages represent additional species new to science that appear to have more restricted distributions: H. corsicus Pešić & Smit (Corsica, Sardinia), H. marezaensis Pešić & Dabert (Montenegro, Albania, Croatia), H. turcicus Pešić, Esen & Dabert (Turkey), and H. persicus Pešić & Asadi (Iran, E Turkey). Statistical morphometric analysis reveals that the latter two species cannot be separated on morphological characters and should be considered true cryptic species. We provide data concerning biology and geographical distributions together with a key to all species of the complex.

Summary Ursu Lake is located in the Middle Miocene salt deposit of Central Romania. It is stratified, and the water column has three distinct water masses: an upper freshwater‐to‐moderately saline stratum (0–3 m), an intermediate stratum exhibiting a steep halocline (3–3.5 m), and a lower hypersaline stratum (4 m and below) that is euxinic (i.e. anoxic and sulphidic). Recent studies have characterized the lake's microbial taxonomy and given rise to intriguing ecological questions. Here, we explore whether the communities are dynamic or stable in relation to taxonomic composition, geochemistry, biophysics, and ecophysiological functions during the annual cycle. We found: (i) seasonally fluctuating, light‐dependent communities in the upper layer (≥0.987–0.990 water‐activity), a stable but phylogenetically diverse population of heterotrophs in the hypersaline stratum (water activities down to 0.762) and a persistent plate of green sulphur bacteria that connects these two (0.958–0.956 water activity) at 3–3.5 to 4 m; (ii) communities that might be involved in carbon‐ and sulphur‐cycling between and within the lake's three main water masses; (iii) uncultured lineages including Acetothermia (OP1), Cloacimonetes (WWE1), Marinimicrobia (SAR406), Omnitrophicaeota (OP3), Parcubacteria (OD1) and other Candidate Phyla Radiation bacteria, and SR1 in the hypersaline stratum (likely involved in the anaerobic steps of carbon‐ and sulphur‐cycling); and (iv) that species richness and habitat stability are associated with high redox‐potentials. Ursu Lake has a unique and complex ecology, at the same time exhibiting dynamic fluctuations and stability, and can be used as a modern analogue for ancient euxinic water bodies and comparator system for other stratified hypersaline systems.

Geography, babeş-bolyai university, 5-7 clinicilor str., 400006 cluj-napoca, romania; 2 national institute of research and development for biological sciences (nirdbs), institute of biological research, 48 republicii str., 400015 cluj-napoca, romania; 3 department of Aquatic Microbial ecology, institute of Hydrobiology, biology center of the Academy of sciences of the czech republic, na sádkách 7, 370 05 České budějovice, czech republic; 4 department of Molecular biology and biotechnology, Faculty of biology and Geology, babeş-bolyai university, 5-7 clinicilor str., 400006 cluj-napoca, romania; 5 5department of taxonomy and ecology, Faculty of biology and Geology, babeş-bolyai university, 5-7 clinicilor str., 400006 cluj-napoca, romania; 6 electron Microscopy center, babeș-bolyai university, 5-7 clinicilor street, clujnapoca, romania; 7 center for systems biology, biodiversity, and bioresources, babes-bolyai university, 5-7 clinicilor str., 400006 cluj-napoca, romania *corresponding author: gheorghe.serban@ubbcluj.ro ABSTRACTin the present work, we review the current knowledge on genesis, limnology and biodiversity of salt lakes distributed around the inner contour of eastern carpathian arc (transylvanian basin, central romania). transylvanian salt lakes formed on ancient halite (nacl) deposits following natural processes or quarrying activities. Most of these lakes are located in eastern (sovata area), southern (ocna sibiului), and western (turda-cojocna) parts of the transylvanian basin, have small surfaces (0.1-4 ha), variable depths (2-100 m), are hypersaline (>10%, w/v, total salts, mainly nacl) and permanently stratified. As consequence of steady salinity/density gradient, heat entrapment below surface layer (i.e., heliothermy) develops in several transylvanian lakes. the physical and chemical water stratification is mirrored in the partition of plankton diversity. lakes with less saline (2-10% salinity) water layers appear to harbor halotolerant representatives of phyto-(e.g., marine native Picochlorum spp. and Synechococcus spp.), zoo-(e.g., Moina salina), and bacterioplankton (e.g., Actinobacteria, Verrucomicobia), whereas halophilic plankton communities (e.g., green algae Dunaliella sp., brine shrimp Artemia sp., and members of Halobacteria class) dominate in the oxic surface of hypersaline (>10% salinity) lakes. Molecular approaches (e.g., Pcr-dGGe, 16s rrnA gene-based clone libraries, and dnA metabarcoding) showed that the o 2 -depleted bottom brines of deep meromictic transylvanian lakes are inhabited by known extremely halophilic anaerobes (e.g. sulfate-reducing delta-Proteobacteria, fermenting clostridia, methanogenic and polymer-degrading archaea) in addition to representatives of uncultured/unclassified prokaryotic lineages. overall, the plankton communities thriving in saline transylvanian lakes seem to drive full biogeochemical cycling of main elements. However, the trophic interactions (i.e., food web structure and energy flow) as well as impact of human activities and predicted climate chang...

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The purpose of this study was to examine the sensitivity, in a field situation, of the hyporheic fauna to pollution by heavy metals and also to test the use of oxidative stress enzymes produced by this fauna as a sensitive indicator of oxidative stress generated by chemical contamination. This was done by surveying the patterns of distribution, structure, and composition of hyporheic invertebrate communities in one of the most polluted rivers in Romania. Twelve permanent sampling stations with differing water qualities were established along a 180 km transect of the Arieş River. Data on hyporheic invertebrate abundance and richness, chemistry of the surface and hyporheic water and interstitial suspended particles were analyzed via multifactorial analyses. In the downstream, more polluted stations, epigean species were less abundant and hyporheic communities, especially macrocrustaceans and oligochetes, became dominant. The higher levels of hyporheic invertebrate biodiversity in the moderately polluted stations compared to highly polluted, and the increase of the number of some hyporheos (especially macrocrustaceans) in the moderately polluted stations, suggested that the hyporheic fauna was more tolerant of heavy metal pollution than the surface water fauna of the area. However, the different richness and abundance of hyporheic fauna in sites of similar water chemistry suggested that additional factors, such as sediment structure are shaping the spatial distribution of hyporheic fauna. Strong correlations between superoxide dismutase (SOD) activity in pooled tissues extracts and some chemical parameters suggest that oxidative stress enzymes may prove to be sensitive indicators of chemical pollution in hyporheic zones.