Algal and cyanobacterial diversity in saline rivers of the Elton Lake Basin (Russia) studied via light microscopy and next-generation sequencing

Naturally saline rivers are known in various regions of the world. Saline rivers with a salinity gradient from the source to the mouth are particularly interesting, because the range of salinity is the structure-forming factor of the hydrobiont assemblage. Such rivers are represented by saline rivers of the Elton Lake Basin in Volgograd region of Russia (the Bolshaya Samoroda River and the Malaya Samoroda River). Herein, we analyzed taxonomic structure and species diversity of microalgae and Cyanobacteria of the saline rivers flowing into the Elton Lake by light microscopy and next-generation sequencing. The differences and possible causes of inconsistencies in the results obtained by these methods are discussed. In total, 91 taxa of microorganisms were identified by integrated approach in the assemblages of microalgae and Cyanobacteria in the middle course of the Bolshaya Samoroda River, and 60 taxa – in the river mouth. The species diversity of those assemblages in the hypersaline Malaya Samoroda River was lower: 27 taxa from the middle course and 23 taxa from the mouth. Next-generation sequencing allowed us to refine and expand the list of microalgae taxa in the studied saline rivers due to detection of species which were hard to identify, low-abundance taxa, as well as extremely small-cell forms. Some discrepancies between the data obtained by light microscopy and next-generation sequencing indicate the advantage of simultaneous use of both methods for study of the algae communities. Such a comprehensive approach provides the most accurate and correct list of taxa added with the morphological descriptions and 18S rRNA and 16S rRNA partial sequences. Generally, 18 taxa have been recorded for the first time in the Bolshaya Samoroda River, belonging to the phyla Chlorophyta (Borodinellopsis sp., Chlorochytrium lemnae Cohn, Caespitella sp., Halochlorococcum sp., Tetraselmis cordiformis (H. J. Carter) F. Stein), Ochrophyta (Pseudocharaciopsis ovalis (Chodat) D. J. Hibberd, Characiopsis sp., Poterioochromonas stipitata Scherffel, Chrysolepidomonas sp.), Euglenozoa (Euglena bucharica I. Kisselev, Lepocinclis tripteris (Dujardin) B. Marin & Melkonian, Phacus orbicularis K. Hübner, P. parvulus G. A. Klebs), Cryptophyta (Hemiselmis cryptochromatica C. E. Lane & J. M. Archibald, Rhodomonas sp., Hanusia phi J. A. Deane), Haptophyta (Pavlova sp.), Cyanobacteria (Johanseninema constrictum (Szafer) Hasler, Dvorák & Poulícková). Seven taxa have been detected for the first time in the algal and cyanobacterial assemblages of the Malaya Samoroda River from the phyla Chlorophyta (Tetraselmis cordiformis, T. arnoldii (Proschkina-Lavrenko) R. E. Norris, Hori & Chihara, T. tetrathele (West) Butcher, Pyrobotrys elongatus Korshikov), Cryptophyta (Hanusia phi), and Cyanobacteria (Synechococcus elongatus (Nägeli) Nägeli, Oscillatoria simplicissima Gomont).

Benthos Algae Communities of Saline Rivers in the Lake Elton Basin: Taxonomic and Quantitative Structure

For the first time, an assessment was given of the taxonomic and quantitative structure of the phytobenthos of seven saline rivers in the basin of the hypersaline lake Elton (Volgograd Region). Main types of algacenoses developing on substrates were revealed, namely: diatom phytobenthos, communities of diatoms with cyanoprokaryotes, cyanobacterial films and mats, and epiphyton. The phytobenthos consists of local, mosaic-distributed communities with a small similarity of their species composition. The algacenosis structure is determined by Bacillariophyta (with the predominance of species of the genus Navicula) and Cyanoprokaryota (of the genera Phormidium, Leptolyngbya, and Geitlerinema). The abundance and biomass values vary widely, reaching their highest values (109,834–417,472 mln cells/m2 and 523.6–567.6 g/m2 ) in cyanobacterial communities of mesohaline rivers with their salinity up to 16–19 g/L. Mineralization as a factor influencing the structure of communities, most rigidly acts in the estuarine sections of rivers, by controlling the composition of the dominant species. For critical salinity values (> 70 g/L), characteristic structural transformations of communities by the type of replacement of planktonic and benthic Bacillariophyta and Cyanoprokaryota by planktonic Chlorophyta (of the Dunaliella genus) and picoplankton were established.

Impact of secondary salinisation on the structure and diversity of oligochaete communities

Secondary salinisation has become one of the most important factors responsible for changes in the aquatic biota. Earlier research has focused on macroinvertebrates including oligochaetes in anthropogenically saline rivers and streams, but studies on oligochaetes in anthropogenically saline stagnant waters remain scarce. Therefore, this study was conducted to assess changes in the species composition as well as the abundance and biomass of oligochaete communities along a large salinity gradient in the anthropogenic inland water bodies located in the Upper Silesian Coal Basin (Southern Poland), which is one of the largest coal basins in Europe. Herein, a total of 27 oligochaete species including five alien species were assessed, namely, Potamothrix bavaricus, Potamothrix hammoniensis, Potamothrix moldaviensis, Psammoryctides albicola, and Psammoryctides barbatus. The results confirmed that the freshwater oligochaetes could tolerate elevated water salinity and showed highest densities and taxa richness in intermediate salinity. Moreover, the waters with the highest salinity had an extremely low number of oligochaete species. A salinity level above 2800 mg L−1 led to significant loss of diversity of the oligochaetes, and consequently, these habitats were colonized by halotolerant species, especially Paranais litoralis, whose abundance increased with increasing salinity gradient.

Biological aspects of the associations of biting midges (Diptera: Ceratopogonidae) in two saline rivers of the Elton Lake Basin, Russia

We studied species composition, density, biomass and production of larvae of the family Ceratopogonidae in two saline rivers (Volgograd region, Russia). Ceratopoponids make up an important part of macroinvertebrate community in these rivers. Average monthly production (dry weight) of ceratopogonid larvae in the rivers was 3.5–4.8gm–2 month–1 in May and ~0.9gm–2 month–1 in August. For the first time, feeding spectra of ceratopogonid larvae, Palpomyia schmidti Goetghebuer, 1934, was studied using fatty acid analyses. The larvae of P. schmidti appeared to selectively consume diatoms and other algae and to avoid bacteria and decomposed dead organic matter (detritus) of low nutritive quality.