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For the first time, an assessment of the taxonomic and quantitative structure of the phytobenthos of seven saline rivers in the basin of the hypersaline Lake Elton (Volgograd region) is presented. The main types of algal communities developing on substrates were revealed: 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 in their species composition. The structure of algal communities is determined by Bacillariophyta (with the predominance of species of g. Navicula) and Cyanoprokaryota (of the gg. Phormidium, Leptolyngbya, and Geitlerinema). The abundance and biomass values vary widely, reaching their highest values (109 834–417 472 million cells/m2 and 523.6–567.6 g/m2) in cyanobacterial communities of mesohaline rivers at a water salinity reaching 16–19 g/L. Mineralization as a factor influencing the structure of communities most rigidly acts in the mouth 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 g. Dunaliella) and picoplankton were revealed. [ABSTRACT FROM AUTHOR]

For the first time, an assessment of the taxonomic and quantitative structure of the phytobenthos of seven saline rivers in the basin of the hypersaline Lake Elton (Volgograd region) is presented. The main types of algal communities developing on substrates were revealed: 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 in their species composition. The structure of algal communities is determined by Bacillariophyta (with the predominance of species of g. Navicula) and Cyanoprokaryota (of the gg. Phormidium, Leptolyngbya, and Geitlerinema). The abundance and biomass values vary widely, reaching their highest values (109 834–417 472 million cells/m2 and 523.6–567.6 g/m2) in cyanobacterial communities of mesohaline rivers at a water salinity reaching 16–19 g/L. Mineralization as a factor influencing the structure of communities most rigidly acts in the mouth 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 g. Dunaliella) and picoplankton were revealed. [ABSTRACT FROM AUTHOR]

This paper presents results of comprehensive studies of saline rivers in the arid Elton Lake region based on hydrobiological surveys of planktonic and bottom communities. Two tables representing the species structure of communities and produced on the basis of survey data collected on 13 river sites in 2013 and 2018, including data on the abundance of hydrobionts belonging to 94 different taxonomic groups of macrozoobenthos, meiobenthos, and zooplankton, have been compared. The co-inertia analysis has identified a high statistical consistency of the data matrices determined by objective spatial distribution patterns of aquatic organisms. A randomization test was applied to the Procrustean correlation coefficient, and it showed that the conjugacy of the two species structures in the space of latent variables is statistically significant (p = 0.00026). Concurrently, a change trend was noted for the taxonomic composition of some surveyed communities affected by dynamic abiotic factors. The relationship between the taxonomic structure of hydrobionts and the combination of 30 abiotic environmental factors measured in the course of the hydrobiological and hydrochemical monitoring of the studied river sites was analyzed. Using canonical correlation analysis and the technique of projection to latent structures, a complex of ordination diagrams has been produced permitting the identification of specific "environmental niches" for each species group, including certain sets of biotope characteristics. A significant mutual correlation between the planktonic and bottom communities has been established. This correlation indicates close interrelations between these communities determined both by biotic interactions and by mutually consistent reactions to changes in aquatic environmental factors. [ABSTRACT FROM AUTHOR]

The statistical background for the relationship between the taxonomic diversity of macrozoobenthos and water mineralization is presented in the example of the benthic communities of plain rivers in the Lower Volga River basin. Significant differences have been found for a complex of 35 indices of species and phylogenetic α- and β-diversity in the tributaries of the Saratov and Volgograd reservoirs compared to the saline rivers of the Elton Lake basin. The hypothesis of phylogenetic niche conservatism [5] is confirmed by a significant effect of phylogenetic overdispersion at low and medium salinity of watercourses and phylogenetic clustering at high water salinity. Mean salinity tolerance has been assessed for each of the 356 species considered; this index was interpreted as the statistical probability of inhabiting the waters of certain mineralization by particular species. A statistically significant phylogenetic signal corresponding to the species traits was revealed by Pagel's lambda and Bloomberg's K tests. Mean salinity tolerance for taxa of various systematic levels has been presented as a cladistic tree. [ABSTRACT FROM AUTHOR]

Abstract—A comparative analysis of the variability of the species structure of macrozoobenthos communities in small and medium rivers of the Middle and Lower Volga river basin has been carried out. The statistically significant influence of the natural climatic zone, where the watercourse is located, and manifestation of the latitudinal gradient of biodiversity are shown. A list of indicator species has been made for each geographical zone identified using different criteria of biotopical distribution. Based on the analysis, the indicator value (IndVal) index, which takes into account the zonal distribution of both the occurrence frequencies of a species and its abundance ratios, was recognized as the most adequate. Association rules that contain combinations of species that most frequently occur together in hydrobiological tests have been formulated using the Apriory algorithm. [ABSTRACT FROM AUTHOR]