Vol 9, No 4 (2016)

The rotifer Ascomorpha ovalis (Bergendal, 1892) was found for the first time in Glubokoe Lake (Moscow Region) in June 2010. Long-term observations of zooplankton dating back to 1897, including our own studies starting in 2004 and carried out on a yearly basis, had never recorded this species before 2010. The density of the population was 25 ind./L in the 0–10 m water layer. In 2011–2012, the species did not disappear but was naturalized in the lake. A. ovalis is an indicator of oligotrophic conditions. The tendency for ongoing oligotrophication of the pelagial of Glubokoe Lake is supported by the penetration and naturalization of Ascomorpha ovalis during recent years and the presence of the oligotrophic rotifer Gastropus hyptopus (Ehrenberg, 1838) detected in the lake earlier.

In this study, a total of 27 species of dragonfly and damselfly larvae were identified, including 14 species from suborder Anisoptera and 13 from Zygoptera. The dominant species are Libellula quadrimaculata, Enallagma cyathigerum, and Erythromma najas. Frequently occurring species are Coenagrion hastulatum, C. lunulatum, C. pulchellum, Ischnura elegans, Platycnemis pennipes, Lestes virens, and Libellula depressa. Rare species are Lestes sponsa, Libellula fulva, Gomphus flavipes, Gomphus vulgatissimus, Sympetrum flaveolum, Aeshna viridis, Ae. cyanea, Ae. grandis, Ae. mixta, Calopteryx splendens, C. virgo, and Ophiogomphus cecilia.

Diatom species Aulacoseira pardata English & Potapova, new for the flora of Russia, has been found in the course of studying samples from Lake Frolikha (Transbaikal region) by scanning electron microscopy. Numerical morphological features of the species in the studied population differ from the type population, which indicates their greater variability. It is shown that A. pardata is distinguished from the similar species A. septentrionalis (Camburn & Charles) Genkal & Kulikovskiy by the shape of spines and shape and size of areolae on the valve mantle. Species A. septentrionalis, new for the lake, as well as for Cis-Baikal and Transbaikal regions, has also been recorded in Lake Frolikha.

Virioplankton and bacterioplankton abundance has been determined in the pelagic and littoral zones of the Rybinsk Reservoir during the ice-covered period. The role of viruses in heterotrophic bacterioplankton infection and mortality is assessed. At water temperatures between 0.3 and 0.9°C, the number of planktonic virus particles and planktonic bacteria varies from 37.1 × 10⁶ to 84.1 × 10⁶ particles/mL, (57.3 ± 2.1) × 10⁶ particles/mL on average and from 2.50 × 10⁶ to 6.11 × 10⁶ cells/mL, (3.66 ± 0.16) × 10⁶ cells/mL on average, respectively. The ratio of the virus number to the bacteria number varies from 8.8 to 27.9, being 16.5 ± 0.7 on average. Visually infected cells comprise 0.3–0.5% (1.5 ± 0.2% on average) of the total number of bacterioplankton. Infected bacterial cells contain from 5 to 107 (17 ± 4 on average) mature virus particles. The average virus-induced mortality of bacteria accounts for 13.0 ± 1.9% (variations range from 2 to 55%) of the daily bacterial production, indicating that viruses play an important role in the regulation of bacterioplankton production and abundance in the Rybinsk Reservoir during the ice-covered period.

Data on the hepato- and neurotoxigenic cyanobacteria in phytoplankton of the Rybinsk Reservoir have been obtained for the first time. Different methods for revealing toxigenic cyanobacteria (light microscopy, PCR analysis, and enzyme-linked immunosorbent assay) demonstrate the same results. Hepatotoxins microcystins and for the first time neurotoxins saxitoxins were detected in the reservoir, whereas cylindrospermopsin and anatoxin-a were not revealed. The presence of mcyE and stxA genes responsible for microcystin and saxitoxin biosynthesis in total phytoplanktonic DNA is demonstrated. The following three genera of cyanobacteria containing mcyE gene are identified: Microcystis (M. aeruginosa, M. viridis), Planktothrix (P. agardhii), and Dolichospermum (Anabaena). It is hypothesized that saxitoxin-producing cyanobacteria Dolichospermum (Anabaena) inhabit the Rybinsk Reservoir.

The impacts of fish and nutrient enrichment on the biomass of small and large cladoceran species were studied in mesocosms under eutrophic conditions. Fish shifted the ratio between small and large species to favour small cladocerans compared to control mesocosms, while nutrient enrichment favoured large cladocerans. Both fish vital activity and nutrient enrichment increased total and blue-green algae concentrations. While chlorophyll concentrations increased in response to fish and nutrient enrichment, there were no significant effects of fish on total cladoceran biomass and the relative proportion of large species due to high variability among replicates within treatments. However, fish and nutrient enrichment affected average total cladoceran biomass and the biomass of large species compared to control conditions.

Strontium (Sr) and calcium (Ca) contents and Sr/Ca ratios in otoliths of pikeperch Sander lucioperca have been studied by X-ray fluorescent microanalysis. A sample of 95 specimens from the Lower Volga region are studied. The fish were obtained in a section of the Akhtuba River at a distance of 250–279 km upstream from the Caspian Sea. Some specimens in the sample have low strontium content throughout the otolith. The other fish have increased both Sr content and Sr/Ca ratios in core zones of otolith or near its outer edge: the Sr/Ca ratio is over 6.00 × 10^–3, with a maximum at 10.02 × 10^–3. The fish with a low Sr/Ca ratio live in freshwater and demonstrate a resident life history strategy. Pikeperch that have increased ratios of Sr/Ca in outer zones of otolith demonstrate a migratory life history strategy. These fish leave the freshwater of the Volga and feed in brackish water of the Northern Caspian Sea. Some migratory fish migrate to the sea as underyearlings, stay in a brackish water for 1 year or less, and then return back to fresh water for the rest of its life. The other group migrates back and forth from freshwater to the sea several times during their life. Finally, some fish leave freshwater for 1–2 years, spending this time in the Northern Caspian Sea. The conclusion is that the pikeperch stock in the Lower Volga has a complicated composition and consists of freshwater (residents and rheodromic ones) and migratory (anadromous and semianadromous) fish.

The pH values are determined in the digestive tract of nine fish species in Lake Chany (West Siberia). Seasonal changes in pH values are found along the intestine of fish. Intestinal pH values decrease in summer as the temperature rises and increase during the cold season as the temperature drops. The hypothesis has been advanced that temperature-dependent pH changes in the intestine may serve as a regulatory mechanism that maintains the activity of hydrolytic enzymes at the level required for successful digestive processes due to some adaptive modifications of the medium where these enzymes operate.

The levels of metal content and toxicity have been determined in bottom sediments of water bodies in Central and South Vietnam. It is found that the concentration of metals (As, Cr, Cu, Hg, Ni, Pb, and Zn) exceed the value of the abundance of elements in the Earth’s crust, which may be associated with geochemical features of the province. Acute toxicity of water-extracted sediment elutriate for Ceriodaphnia and whole (native) sediments for chironomid larvae is not recorded in any investigated water bodies. An increase in the relative abundance of Chironomus riparius larvae with deformations of mouthpart structures compared to the control was observed for most of the water bodies. This index reaches the value in the Khe River (Cân Thơ city). Antenna anomalies prevailed in pathomorphological disorders.

data on the first find of stellate tadpole goby on August 2014 in the Volzhskii reach of the Rybinsk Reservoir is presented.