Data on cyanobacterial toxins and the genes of their biosynthesis in the phytoplankton of the mesotrophic Lake Pleshcheyevo (Yaroslavl oblast) during the blooming period of cyanobacterium Gloeotrichia echinulata (Smith et Sowebry) Richter are given for the first time. In the phytoplankton of the lake, the presence of hepatotoxins of microcystins (MC) was recorded using chromatography–mass spectrometry; in DNA isolated from plankton, the mcyE gene for the biosynthesis of these cyanotoxins was detected using PCR. No other types of cyanotoxins (cylindrospermopsin, anatoxin-a, and saxitoxins) or the presence of genes for their synthesis in the phytoplankton are identified during the study period. MC biosynthesis genes mcyA and mcyE were absent in thirty colonies of Gloeotrichia echinulata isolated from the lake, which is consistent with their inability to produce cyanotoxin. Using molecular methods, the potential ability to biosynthesize MC in Microcystis aeruginosa and species of the genus Dolichospermum inhabiting in the lake is demonstrated. This paper discusses the toxicity of Gloeotrichia echinulata and the need for the further long-term monitoring of toxigenic cyanobacteria in Lake Pleshcheyevo.

Летом и осенью 2009–2013 гг. исследовали фитопланктон среднего течения р. Ко- стромы и ее притоков первого порядка Корёга и Тёбза. На основании анализа флористического и видового разнообразия, соотношения крупных таксономических групп (отделов), доминирующих видов, численности, биомассы и размерности клеток фитопланктона, а также содержания хлоро- филла а и сапробности вод обнаружены как сходства, так и различия фитопланктона рек и каче- ства их вод. Установлено, что разнообразие и обилие фитопланктона рек определяли зеленые, диатомовые водоросли и цианопрокариоты. Показано, что в притоках (малых реках) разнообра- зие и обилие фитопланктона, а также уровень трофии вод снижались. Последнее сопровожда- лось увеличением пропорции в потамопланктоне рек Корёга и Тёбза обилия миксотрофных фи- тофлагеллят. При этом размерность клеток водорослей в притоках увеличивалась. Сапробность вод во всех реках соответствовала β-мезосапробной зоне органического загрязнения. Оценка качества вод по различным индикаторным показателям фитопланктона показала, что реки от- носились к двум классам: чистым и водам удовлетворительной чистоты, причем более высоким качеством отличались воды притоков. This study was undertaken in the summer and fall of 2009–2013 to investigate phytoplankton in the middle reaches of the Kostroma River and its first-order Koryoga and Tyobza tributaries. Based on the analysis of floral and species diversity, the ratio of large taxonomic groups (divisions), dominant species, abundance, biomass and phytoplankton cell size, as well as chlorophyll а content and water saprobity, both similarities and differences were found in the phytoplankton of the rivers and the quality of their waters. It was also found that the diversity and abundance of the river phytoplankton was determined by green algae, diatoms and cyanoprokaryotes. It was shown that in the tributaries (small rivers) the diversity and abundance of phytoplankton, as well as the level of water trophy, decreased. The latter was accompanied by an increase in the proportion of mixotrophic phytoflagellates in the potamoplankton of the Koryoga and Tyobza rivers. At the same time, the algae cell size in the tributaries increased. The water saprobity in all the rivers corresponded to the β-mesosaprobic zone of organic pollution. The water quality assessment based on various indicator parameters of phytoplankton showed that the rivers under study belonged to two classes: clean and satisfactory clean, with higher water quality in the tributaries.

The article presents for the first time the data on cyanobacterial toxins and the genes of their biosynthesis in the phytoplankton of the mesotrophic Lake Pleshcheyevo Yaroslavl Region, during the period of cyanobacterium Gloeotrichia echinulata (Smith et Sowebry) Richter – bloom. In the phytoplankton of the lake, the presence of hepatotoxins microcystins was recorded using chromatography – mass spectrometry; in DNA isolated from plankton, the mcyE gene for the biosynthesis of these cyanotoxins was detected using PCR. During the study period, other types of cyanotoxins (cylindrospermopsin, anatoxin – a, saxitoxins) and the presence of genes for their synthesis in the phytoplankton were not identified. In thirty colonies of G. echinulata isolated from the lake, the microcystin biosynthesis genes mcyA and mcyE were absent, which is consistent with their inability to produce cyanotoxin. Using molecular methods, the potential ability to biosynthesize microcystins in Microcystis aeruginosa and species of the genus Dolichospermum inhabiting in the lake was demonstrated. The paper discusses the toxicity of Gloeotrichia echinulata and the need for further long-term monitoring of toxigenic cyanobacteria in Lake Pleshcheyevo.

Based on the data of complex environmental studies, which have been regularly carried out at six standard stations of the Rybinsk Reservoir since the middle of the 20th century, the orientation of changes in the elements of the reservoir ecosystem associated with global climatic events has been analyzed. During the period of climate warming, which began in 1977 and continues into the 21st century, the air temperature in the warm season increased by 0.9°C, the water temperature by 1.4°C, the average annual inflow by 7.5%, and the duration of the ice-free period by two weeks. An increase in electrical conductivity and color of water, a decrease in transparency were noted. With significant interannual variations in biological characteristics, in the XXI century, the number of bacterioplankton increased by 1.7 times, and bacterial production doubled. Chlorophyll content increased by 1.4 times and values 15 µg/L reflecting the eutrophic state of the reservoir began to be observed more often. In the biomass of phytoplankton, the proportion of small cell forms increased. The total abundance of phytoplankton increased due to the development of cyanobacteria, which form a long summer maximum in the seasonal dynamics of the community. The increase in water mineralization promoted the progressive spread of alien brackish-water algae. Biomass of zooplankton increased by 2.5 times. An increase in the abundance of crustaceans (Cladocerans, by 1.6 times; Copepods, by 1.9 times) caused a change in the structure of zooplankton and the formation of a strong late summer peak of biomass. The intensification of hydrobiological processes was clearly manifested after the abnormally hot 2010, the conditions of which not only stimulated the development of plankton communities, but also but also caused the formation of oxygen deficiency in the bottom layers. Warming has significantly transformed the ecosystem of the Rybinsk Reservoir, intensified eutrophication processes and worsened water quality. Changes in hydrometeorological characteristics have gone beyond the mild scenario of climate warming.

According to the saprobity index, estimated by the phytoplankton biomass, the degree of organic pollution of ecotone areas (the mouth of the Il’d River and the littoral of the Volga reach of the Rybinsk Reservoir) has been determined. The saprobity index in protected shallow waters was 1.83 in 2009 and 2.07 in 2010; in the pelagial, it was 2.14 and 2.13 in 2009 and 2010, respectively. In the river–reservoir system, the lowest average values of the saprobity index were noted in the mouth area of the Il’d River: in 2009 it was 1.94, in 2010 1.87, and in 2011 1.88. In the river and the reservoir, its values were higher: 2.05 and 2.07 in 2009, 1.96 and 2.08 in 2010, and 1.97 and 1.99 in 2011, respectively. The decrease in saprobity in shallow waters and at the mouth of the river, compared to the bordering water, indicates a higher intensity of self-purification processes, which can ensure the sustainability of the ecosystem of the reservoir as a whole. Abnormal weather phenomena, in particular, high summer water temperatures, can lead to the destabilization of the features of ecotone algocenoses and, as a result, to a violation in the process of self-purification of the reservoir.

The seasonal and interannual dynamics of phytoplankton in the mouth area and adjacent free flowing sections of the small river and in the pelagic area of the reservoir in 2009–2011 are presented. The increased species richness, abundance, and biomass of algae in the mouth area indicate that the edge effect is manifested in the tributary mouth area. A phytoplankton community is formed in the river mouth that is different from that in the adjacent areas. However, abnormal weather conditions can lead to disruption of the stability of ecotonic algocenoses.

A novel variety of dinophyte algae Unruhdinium penardii var. robustum (Qi Zhang, G.X. Liu & Z.Y. Hu) Gottschling in Gottschling & al., 2017 (= Peridiniopsis penardii var. robusta Qi Zhang, G.X. Liu & Z.Y. Hu) has been detected for the first time in Russia. It was found in two reservoirs of the Lower Volga, Saratov and Volgograd, in late August–early September 2020. Its abundance varied from 500 to 4500 cells/L; biomass was from 0.008 to 0.071 mg/L. The length of cells varied from 29 to 40 µm, and the width varied from 24 to 31 µm.

This chapter contains a comprehensive description of the Volga River, the largest river in Europe, and its main tributaries, the Kama, Oka, Sheksna. It starts with a review of human history and biogeographical setting including paleogeography of the basin, as well as description of physiography and climate, and features of hydrological and biogeochemical regime in the past and present. Problems of the management, conservation, and economic importance of the basin are also under consideration. Much attention is paid to aquatic and riparian biodiversity. These sections include description of the species composition of macrophytes, algae, aquatic invertebrates, and fish with an assessment of the abundance, seasonal, and long-term dynamics of biological communities. Data on invasive species from Ponto-Caspian and Boreal-Arctic complex are given. Molecular studies performed during the last 10 years significantly clarified fauna composition as well as phylogeographic patterns.

Cyanobacterial blooms make significant changes in the functioning of aquatic ecosystems and may be harmful to their biotas. Vascular plants, including Elodea canadensis, can reduce cyanobacteria due to competition for resources and allelopathy. The present study examined the changes in abundance and reproductive variables of planktonic and benthic crustaceans under the influence of cyanobacteria and E. canadensis. We tested the hypothesis that the negative effects of cyanobacteria on crustaceans can be reduced by Elodea. Separate and joint effects of cyanobacteria and E. canadensis beds on the structure of zooplankton and embryo health of the amphipod Gmelinoides fasciatus were investigated using experimental ecosystems (i.e., microcosms). Elodea and cyanobacteria, which produce a small amount of toxins, had a positive effect on the total number of zooplankton, which increased over time. The abundance of Daphnia longispina and cyclopoids, as well as the frequency of dead amphipod embryos, were associated with the presence of cyanobacteria. The biomass of cyanobacteria was reduced in the microcosms with E. canadensis. The joint action of elodea and cyanobacteria resulted in a decrease in the number of Daphnia juveniles and an increase in the frequency of unhealthy and dead amphipod embryos, which suggests a decrease in the abundance of their population in the context of future biological invasions of E. canadensis and more frequent cyanobacterial blooms.

The changes in the ratio of species representing different morpho-functional groups, identified by physiological, morphological and ecological parameters [29] were analyzed based on the study on phytoplankton in different reaches of the Rybinsk Reservoir in 2000–2005. Water quality was assessed by the Q index of communities, developed taking into account the proportions of these groups. This assessment was compared with the evaluation using the values of Pantle–Buck saprobity index and phytoplankton biomass.

Cyanobacterial blooms are regarded as a global environmental problem. The role of cyanobacteria in the food web of water bodies is still unclear. We have carried out an experimental study of invertebrate trophic relationships during the bloom of the cyanobacterium Aphanizomenon flos-aquae. The key links of the food web—plankton, microperiphyton, detritus, and benthic invertebrates—were collected for stable isotope analysis of carbon (δ13C) and nitrogen (δ15N) after 20-day exposure in mesocosms simulating the conditions of the near-shore biotope of the Rybinsk Reservoir without cyanobacteria (variant I) and with high abundance of cyanobacteria (variant II). Statistically significant differences in the δ15N values for crustaceans (Cladocera, Copepoda, Asellus aquaticus and Gmelinoides fasciatus), and mayfly larvae have been revealed between the variants: these values were 1–4‰ lower in the variant with cyanobacteria than in the variant without them. The cyanobacteria-induced shifts in the δ15N value for consumers indicate an assimilation of diazotrophic nitrogen and incorporation of cyanobacterial nutrients into their food chains.

The results of a study of phytoplankton in Taganrog Bay in the Sea of Azov and the downstream reaches of the Don River carried out in January–November 2017 are presented. A total of 210 species of eukaryotic algae and cyanoprokaryotes are identified. An analysis of the taxonomic, ecological, and geographical composition of the plankton algal flora and seasonal dynamics of biomass of phytoplankton taxonomic and size structures has revealed no changes in the ratio of large taxonomic and ecological–geographic groups in the algal flora when compared with previous years (1980s to early 2000s). However, the proportion of myxotrophic phytophagellates, cyanoprokaryotes from the planktotrichet complex, and small species increased in algal communities. It is shown that the water salinity is the main factor influencing the formation of species richness and total biomass and structure of phytoplankton. The maximum diversity and biomass of phytoplankton are recorded in the horohalinicum zone.

Human activity has disturbed the functioning of river ecosystems all around the globe. The current global climatic fluctuations and local anthropogenic impact lead to rearrangement in the structure and functioning of aquatic communities. One of the most important components of aquatic ecosystems is phytoplankton as the main primary producer of the organic matter, the basis for trophic relations and indicator of changes in the environment. This article presents the first results of a study concerning the peculiarities of quantitative distribution of biomass and species composition of phytoplankton in the delta of the Mekong River at the beginning of the dry season (December of 2018). Diatoms dominated according to biomass practically in all the stations of selection of samples. The total biomass of phytoplankton on average accounted for 0.049 ± 0.007 mg/L at the abundance of 40 ± 7 103 ind./L. In practically all the studied plots, according to biomass, the dominating diatoms were first of all Aulacoseira granulata, A. islandica, Cyclotella meneghiniana, Cyclotella spp., and Oxyneis binalis. Among Chlorophyta, most often we found Chlorella sp. and Scenedesmus quadricauda, but their biomass was insignificant. We determined statistically significant correlation relationships between biomass of phytoplankton and hydrological parameters. Based on the Spearman’s rank correlation coefficient, we determined negative relations between the total biomass of phytoplankton with salinity and pH. Positive correlation was seen between the biomass of diatoms and turbidity, and also between the temperature and the biomass of chlorophytes and Dinophyta. The biomass of golden algae (Chrysophyceae) and Dinophyta positively correlated with the mineralization. Quantitative regression analysis confirmed the close relationship between the total biomass of phytoplankton, hydrophysical and hydrochemical parameters. Besides the importance of scientific data on biological diversity and ecology of plankton algae, the results we obtained are necessary for organizing biological monitoring in the delta of the Mekong River in the future.

We studied the distribution of cyanotoxins and potential producers, as well as the variability of microcystin to biomass parameters (chlorophyll-a; MC/Chl-a; and biovolume; MC/BV) in 12 drinking water reservoirs of the world's largest reservoir system, the Volga-Kama-Don cascade (European part of Russia) during the summers of 2016 and 2018. MC concentrations varied from below 0.1 mu g L-1 in June up to 16.4 mu g L-1 in August and exceeded 1 mu g L-1 in 25 % of the samples. This MC variability was associated to changes in the abundance of widespread bloom formers such as Microcystis spp., Dolichospermum spp. and Planktothrix agardhii. Ratios of MC/Chl-a and MC/BVcyano ranged up to 0.88 mu g mu g(-1) and 4.5 mu g mm(-3), respectively. Together with microcystin profiles MC/BV eya ,, o ratios characterized cyanobacterial populations along the reservoir cascade and they indicated a potential toxin hazard better than MC/Chl-a. The neurotoxin anatoxin-a was observed only in the most southern and hypereutrophic Tsimlyansk Reservoir (maximum 0.01 mu g L-1). Toxin gene analysis revealed that MC mostly originated from Microcystis and Dolichospermum. During their co-existence up to 14 MC congeners cooccurred. Cuspidothrix issatschenkoi cf. Rcuphidiopsis mediterranea was identified as possible neurotoxin producers.