Inland Water Biology

Data on the composition and content of photosynthetic pigments in plankton of the Volga River reservoirs in summer period of 2015–2023 are under consideration. The determination of pigments was carried out using standard spectrophotometric methods. Chl a concentrations are close to those obtained in 1989–1991. The distribution of Chl a throughout the water area of reservoirs retains its long-term characteristics. The waters of tributaries, coastal waters, and shallow water areas are characterized by an increased abundance of phytoplankton. A negative relationship between reservoir-average Chl a concentrations and the total inflow volume (R² = 0.50) and a direct dependence on water temperature (R² = 0.35) were revealed. Based on the average Chl a concentrations over the years of observation, the current trophic status of the Ivankovo, Uglich, and Cheboksary reservoirs is assessed as eutrophic (29.5±1.9, 22.7±1.6 and 28.2±2.7 µg/L respectively), the Saratov and Volgograd reservoirs are mesotrophic (6.8±0.6 and 9.6±0.8 µg/L), Kuibyshev and Gorky reservoirs are moderately eutrophic (13.0±0.7 and 13.1±1.4 µg/L). The content of additional chlorophylls b and c, pheopigments, plant carotenoids and their ratio with chlorophyll a, as well as the composition of green pigments in the Volga River reservoirs are characterized by significant similarity and have not changed over the 30-year period.

In August 2015–2018, the phytoplankton of 15 reservoirs of the Volga, Kama, Don rivers, Volga-Don Canal, and the unregulated part of the Lower Volga was studied. A decrease in the species richness, diversity, cell size, total phytoplankton and phytoflagellates biomass in the Volga-Kama cascade was observed from the upper to the lower reaches of the regulated rivers. This reflected the zonation and hydrological continuity. The proportion of biomass of non-heterocystous cyanobacteria in the reservoirs increased with increasing salinity of their waters. The trophic state of the reservoirs was assessed based on the phytoplankton biomass value.

Summer (July–August) zooplankton in Kama and Votkinsk reservoirs is being studied for last decade (2014–2023). Species list also includes archive data from 2012 to 2013. There are 149 taxa in two studied bodies of water, four of them registered for the first time. Distribution of Caspian invader Cercopagis pengoi is shown and patterns of mass development of north american rotifer Kellicottia bostoniensis are detected. It is found that abundance is mostly provided by Rotifera (43%) and Copepoda (32%) while 73% of biomass formed by Cladocera in Kama reservoir. Rotifera are forming 53% of number in Votkinsk reservoir while Cladocera are forming 77% of biomass there. Mean abundance of summer zooplankton in Kama reservoir in studied period is 120±6 ind. thous./m³, it equals 115±8 ind. thous./m³ in Votkinsk reservoir. Pluriannual changes in species composition, structure, abundance, and peculiarities of spatial distribution of zooplankton are discussed.

In August 2023, a study of the plankton community of the sluice chambers of the Volga-Don shipping Canal named after V.I. Lenin and adjacent territories (the Volga River near Volgograd, between the locks and in the Tsimlyansk reservoir near Kalach-on-Don) was conducted. Alien species from various biogeographic complexes have been recorded in all its components (phyto-, proto- and metazooplankton). Skeletonema subsalsum (A. Cleve) Bethge, 1928 as part of the phytoplankton is from the Ponto-Caspian complex. The marine species Leprotintinnus pellucides (Cleve, 1899) is included as part of the ciliates. 9 species from various biogeographic complexes were found in zooplankton, namely: Heterocope caspia Sars G.O., 1897, Eurytemora caspica Sukhikh & Alekseev, 2013, Cercopagis (Cercopagis) pengoi (Ostroumov, 1891) from Ponto-Caspian; Cornigerius maeoticus (Pengo, 1879) from Ponto-Azov; Calanipeda aquaedulcis Krichagin, 1873 from the Mediterranean; Thermocyclops taihokuensis, Harada, 1931 from the East Asian; American Acanthocyclops americanus (Marsh, 1893) and Moina cf. micrura Kurz, 1875 with uncertain status. It has been established that, despite the intensive mixing of water in the sluice chambers, alien species are actively developing and entering the rank of dominant ones. The proportion of dead Copepoda individuals in sluice chambers is lower than that of Cladocera. However, the abundance of Cladocera is so large that even with high mortality, they are part of the dominant complex of species, while some zooplankter individuals were in an active reproductive state. Significant abiotic factors for alien species in the the Volga-Don shipping Canal were electrical conductivity (for Heterocope caspia, Moina cf. micrura and Acanthocyclops americanus) and temperature (for Skeletonema subsalsum). For crustaceans consuming detritus, bacteria, algae, ciliates and other zooplankters, reliable correlations with the listed food resources were noted.

In August 2018–2023, the composition of copepods of the Kama River was studied within the Volga–Kama and Kama Reaches of the Kuibyshev Reservoir, as well as the Nizhnekamsk and Votkinsk reservoirs. It was established that the East Asian species T. taihokuensis (Harada, 1931) first recorded at the mouth of the Kama River in 2018, and by 2023 it had colonized the Volga–Kama reach. In 2022, the invader was first registered in the lower section of the Kamsky reach of the Kuibyshev Reservoir and the Nizhnekamsk Reservoir. The northern border of the invader's distribution is located near the mouth of the Belaya River (56° N) 320 km from the confluence of the Kama and Volga rivers.

Comparative analysis of taxonomic and trophic structures of benthic invertebrates’ communities had been carried out based on collections from riverine parts of Kama (2012), Votkinsk (2010) and Nizhnekamsk (2015) reservoirs. Species list is given, trends of changes in benthic fauna are shown. They are depauperization on specific and generic levels, decrease in ratio of mayflies, stoneflies and caddisflies, in absolute and relative species richness of chironomids, also in ratio of Tanitarsinae among chironomids, increase in mollusks and crustaceans’ species richness. Major trend of changes in quantitative aspect downstream among riverine parts of studied reservoirs is increase of absolute and relative biomass density in filterators and scrapers, which are gastropods and large bivalve mollusks.

The study of zoobenthos was conducted in July 2021 on small and medium-sized rivers of the Upper Volga from the village. Selizharovo to the Ivankovo reservoir in areas poorly affected by economic activity. The task was to study the features of river biocenoses in landscapes of different types. The western part of the territory under consideration is elevated (Valdai upland), the eastern part is low–lying (Upper Volga lowland); watercourses in these areas differ in flow velocity and type of bottom sediments. These two factors lead to differences in the composition of bottom biocenoses: in upland rivers, the number of species of mayflies, brooks, and spring wort is significantly higher than in watercourses of low-lying territories. There is a connection in the series: landscape – hydrological characteristics of rivers – bottom biocenoses. Water quality indicators – the Woodiwiss and BMWP indices indicate the uncontamination of watercourses. At the same time, the indicators themselves naturally change under the influence of landscape (and hydrological) parameters. Therefore, when conducting a biological indication of the Upper Volga watercourses, it is recommended to take into account the landscape features of the formation of bottom biocenoses.

Based on long-term studies, modern data on populations of Dreissena bugensis and D. polymorpha in the water area of the Kuibyshev Reservoir are presented. It is shown that the basic quantitative parameters in all considered reaches of the reservoir, identified types of sediments and depths were formed by D. bugensis. In the consortia of dreissenids, 146 taxa of benthic invertebrates were identified, of which 26 taxa were alien species. The abundance in such communities was mainly formed by crustaceans, and the biomass, by mollusks. The analysis of seasonal dynamics showed a decrease in the quantitative parameters of D. bugensis from May to October, while for D. polymorpha, on the contrary, there was an increase by autumn. An analysis of the interannual dynamics has revealed an increase in the abundance of D. polymorpha and a decrease in D. bugensis in recent years.

Pikeperch Sander lucioperca is a valuable fish species whose reproductive biology and efficiency of natural reproduction, as well as the factors determining them, are poorly studied. Based on the materials collected in 2018–2023, the results of the study of sexual maturation, gonadosomatic index (GSI), absolute (AF) and relative fecundity (RF) of pikeperch from five areas of the Kama reservoir, located on the northeastern border of the natural range of the species, are presented. Population fecundity of pikeperch and efficiency of species natural reproduction based on egg to adult survival coefficients were estimated. Latitudinal variability of pikeperch sexual maturity rates within the reservoir was revealed. A decrease in generative metabolism relative to somatic metabolism was found with the age of fish after they reached the length of 55–60 cm and 11+ age, which is manifested by stabilization of the values of RF and GSI in larger and older fish. The maximum values of GSI, AF and RF were observed for pikeperch in the lower part of the Kama reservoir, which may be related to more favorable feeding conditions for the species. The lowest values of AF and RF were characteristic for the headwaters of the Kama reservoir with highest water flow. At the same time, pikeperch in the upper part of the reservoir were characterized by the highest survival rate from eggs to adult individuals. The lowest efficiency of natural reproduction was found in the central part of the reservoir, characterized by maximum width, presence of large bays and predominant distribution of shallow water habitats.

The Black and Caspian Sea Sprat, or Tyulka (Kilka or Sardelka) Clupeonella cultriventris (Nordmann, 1840) (Actinopterygii: Clupeiformes) is a small pelagic species, the most abundant nonindigenous fish species of the Volga-Kama basin playing an important role as one of the key elements of food webs in freshwater ecosystems. In this paper, we characterize the complete mitochondrial genome of Tulka from an unambiguously adventive population of the Upper Volga (58.38861 N, 38.32694 E). Voucher identification was performed both by morphological characters and a DNA sequence blast against the GenBank international database. For sequencing of the complete mitochondrial genome, a classical Sanger sequencing was applied with the PCR product from a set of 48 primer pairs giving a complete overlapping and unambiguous reading of each nucleotide in at least two replications. Annotated full mitogenome of C. cultriventris with length of 16650 bp has a gene arrangement characteristic of (and conservative) Clupeiformes contains 22 transport RNAs, 13 protein-coding genes, two ribosomal RNAs, and a single noncoding region. This mitochondrial genome demonstrates a 98.7% similarity to the previously studied one from the Black Sea. Based on these data, there are no sufficient reasons to separate the freshwater Sprat of the Volga-Kama region into a separate taxon.

The analysis of long-term data (2010–2023) on the assessment of the toxicity of native bottom sediments (BS) the Gorky reservoir by biotesting using larvae of the Chironomus riparius mosquito. The results obtained indicate that the situation with pollution of BS, as well as their uneven integral toxicity in the water area of the reservoir, generally persists. The average values of linear sizes of chironomid larvae in most cases were significantly lower than the control values. Significant differences in mortality of chironomid larvae during biotesting to reservoir sites were noted in 2016 and 2017, linear sizes – in 2017 and 2021. In general, the average values of the toxicity index were lower than the control values, which indicates the toxicity of BS. The maximum values of the toxicity index were observed in 2011, the lowest in 2010 and 2017. The content of the common forms Cr, Mn, Zn, As, Cd and Pb in the BS of the reservoir significantly exceeded their clarks in the Earth's crust, which indirectly indicates additional anthropogenic pollution. Concentrations of the studied elements increased downstream and reached maximum values in the dam section of the reservoir (Chkalovsk station). The values of the geoaccumulation index and the pollution coefficient indicate an insignificant intake of priority heavy metals (Cr, Ni, Cu, Zn, Cd, Pb) of anthropogenic origin into the Gorky reservoir. The highest values of the geoaccumulation index were recorded for the lake section of the reservoir. The values of the pollution coefficient indicate moderate Cd contamination of the BS of the Kostroma extension and the lake site of the storage facility. According to the correlation analysis, the mortality of chironomid larvae was influenced by P, Mn, Fe, Co, Zn, As and Bi, but a significant regression model was obtained only for Mn (R² = 0.513).