FRESHWATER INVERTEBRATES OF LAKE ZAISAN

In this article, freshwater invertebrates are studied. Lake Zaisan is considered as an object. The article updates the list of invertebrate fauna of Lake Zaisan, which is currently relevant. The article presents steps for collecting invertebrates and determining their species composition. According to the results of the study, the species composition of thirty-nine invertebrates was determined. The author notes that the species composition of invertebrates is higher on the coast than in the lake environment, that is, the number of planktonic invertebrates is higher than that of benthos invertebrates. The author notes that the Reed thickets and kelp areas along the Lake Shore are a favorable environment for the growth of benthos organisms, that is, the predominance of benthos invertebrates, and on the sandy shores of the lake there are no invertebrates. In the course of the study, it was found that the lake is dominated by OAR-footed Scorpions, oligochetes, chironomid larvae, ashamurt Scorpions, slug worms. High-altitude Scorpions, leeches, leeches, and water mites are rare. The article considers the problem of reducing the water level of Lake Zaisan from one hundred to five hundred meters over the past year. It is worth noting that the number of benthos organisms has also decreased, as the areas of coastal reeds and algae have dried up. In addition, it is concluded that the ichthyofauna of the lake has also decreased. The result of this research work can be applied to the standard curriculum of the discipline zoology. The information contained in the article can be used by students studying at biological faculties of higher educational institutions, biology teachers in secondary schools. It will be interesting for secondary schools near Lake zaisan to use the identified invertebrates and their photos as a local component.

Warming Decreases Bioconversion of Polyunsaturated Fatty Acids in Chironomid Larvae Maintained on Cyanobacterium Microcystis

Cyanobacteria dominance and warming have been suggested to decrease the production of polyunsaturated fatty acids (PUFA) in freshwater ecosystems. Physiological adaptations of poikilothermic animals to higher temperatures may further decrease PUFA levels in aquatic food webs. We conducted diet manipulation experiments to investigate the combined effects of dietary PUFA and warming on the proportions of eicosapentaenoic acid (EPA) and arachidonic acid (ARA) in Chironomus riparius. The experimental diet consisted of a nontoxic cyanobacterium Microcystis, which contained C20 PUFA: 20:3n-3, 20:4n-3, and 20:3n-6, but no EPA or ARA. Additionally, we used TetraMin® fish flakes as a control treatment. A temperature increase from 20 °C to 25 °C decreased the proportion of n-3 C20 PUFA and the n-3/n-6 ratio in Microcystis. Diet manipulation experiments indicated that Chironomus desaturated dietary C20 precursors to EPA and ARA, but warming decreased this bioconversion and resulted in lower levels of EPA and ARA in Chironomus. Warming did not alter the proportions of EPA and ARA in Chironomus larvae if these PUFA were readily available in the diet (TetraMin® control treatment). In conclusion, warming and cyanobacteria dominance may decrease the production and trophic transfer of physiologically important PUFA in freshwaters by (1) decreasing the n-3/n-6 ratio and the abundance of n-3 C20 precursors in Microcystis, and (2) decreasing the bioconversion of n-3 and n-6 C20 precursors to EPA and ARA in chironomids. These changes may have cascading effects throughout the food web and decrease the content of EPA in fish, potentially affecting its availability to humans.

Effects of Macrofaunal Recolonization on Biogeochemical Processes and Microbiota—A Mesocosm Study

Macroinvertebrates are widespread in lake sediments and alter sedimentary properties through their activity (bioturbation). Understanding the interactions between bioturbation and sediment properties is important given that lakes are important sinks and sources of carbon and nutrients. We studied the biogeochemical impact of macrofauna on surface sediments in 3-month-long mesocosm experiments conducted using sediment cores from a hypoxic, macrofauna-free lake basin. Experimental units consisted of hypoxic controls, oxic treatments, and oxic treatments that were experimentally colonized with chironomid larvae or tubificid worms. Overall, the presence of O2 in bottom water had the strongest geochemical effect and led to oxidation of sediments down to 2 cm depth. Relative to macrofauna-free oxic treatments, chironomid larvae increased sediment pore water concentrations of nitrate and sulfate and lowered porewater concentrations of reduced metals (Fe2+, Mn2+), presumably by burrow ventilation, whereas tubificid worms increased the redox potential, possibly through sediment reworking. Microbial communities were very similar across oxic treatments; however, the fractions of α-, β-, and γ-Proteobacteria and Sphingobacteriia increased, whereas those of Actinobacteria, Planctomycetes, and Omnitrophica decreased compared to hypoxic controls. Sediment microbial communities were, moreover, distinct from those of macrofaunal tubes or feces. We suggest that, under the conditions studied, bottom water oxygenation has a stronger biogeochemical impact on lacustrine surface sediments than macrofaunal bioturbation.

Experimental determination of the temperature dependence of oxygen-isotope fractionation between water and chitinous head capsules of chironomid larvae

Oxygen-isotope values of invertebrate cuticle preserved in lake sediments have been used in palaeoenvironmental reconstructions, generally with the assumption that fractionation of oxygen isotopes between cuticle and water ($$\upalpha_{\text{cuticle}-\text{H}_{2}\text{O}}$$ α cuticle - H 2 O ) is independent of temperature. We cultured chironomid larvae in the laboratory with labelled oxygen-isotope water and across a range of closely controlled temperatures from 5 to 25 °C in order to test the hypothesis that fractionation of oxygen isotopes between chironomid head capsules and water ($$\upalpha_{\text{chironomid}-\text{H}_{2}\text{O}}$$ α chironomid - H 2 O ) is independent of temperature. Results indicate that the hypothesis can be rejected, and that $$\upalpha_{\text{chironomid}-\text{H}_{2}\text{O}}$$ α chironomid - H 2 O decreases with increasing temperature. The scatter in the data suggests that further experiments are needed to verify the relationship. However, these results indicate that temperature-dependence of $$\upalpha_{\text{chironomid}-\text{H}_{2}\text{O}}$$ α chironomid - H 2 O should be considered when chironomid δ18O is used as a paleoenvironmental proxy, especially in cases where data from chironomids are combined with oxygen-isotope values from other materials for which fractionation is temperature dependent, such as calcite, in order to derive reconstructions of past water temperature.

Results of zoobentos research in river Sotka, PINEZHSKY STATE RESERVE (Arkhangelsk region, Russia)

В статье рассмотрен качественный состав (видовое и таксономическое разнообразие) и количественные показатели (встречаемость, численность и биомасса) зообентоса р. Сотка в пространственном аспекте. Выявлены участки реки с минимальной и максимальной численностью и биомассой. Определены доминирующие группы донных животных по численности (личинки хирономид и малощетинковые черви) и биомассе (двукрылые, олигохеты и двустворчатые моллюски). На основе кластерного анализа (по видовому сходству) станции отбора бентосных проб объединены в 2 группы. Качество вод оценено как условно чистое - слабо загрязненное. Проведенные исследования зообентоса в уникальной реке на территории заповедника Пинежский будут использованы при ведении комплексного мониторинга качества вод и биотической части ее экосистемы (фито- и зоопланктон, зообентос, ихтиофауна), включая и приточную систему. The article considers the qualitative composition (species and taxonomic diversity) and quantitative indicators (occurrence, number and biomass) of zoobenthos of river Sotka in the spatial aspect. The sections of the river with the minimum and maximum abundance and biomass were identified. The dominant groups of benthic animals were determined by their numbers (chironomid larvae and small-bristle worms) and biomass (dipterans, oligochaetes and bivalve mollusks). Comparison of quantitative indicators in the annual aspect revealed a significant increase in biomass and relative stability of abundance over a 20-year period at the Filippovskoye site, as well as a decrease in numbers and biomass at the Moiseev Nos site. Based on cluster analysis (by species similarity), benthic sampling stations are combined into 2 groups. Water quality is assessed as conditionally pure, slightly polluted. Studies of zoobenthos in a unique river on the territory of the Pinezhsky reserve will be used to conduct a comprehensive monitoring of water quality and the biotic part of its ecosystem (phyto- and zooplankton, zoobenthos, ichthyofauna), including the inflow system.

Biodiversity Assessment of Chironomids (Diptera: Chironomidae) in Rajsamand Lake (Rajsamand, Rajasthan, India)

Present study was performed for taxonomic identification, assemblage, richness, spatial distribution and abundance analysis of chironomid larvae in the benthic and lentic shoreline habitat of Rajsamand Lake, India. Chironomids play an important role in shallow water aquatic ecosystems, so this study will give an idea about ecology of this area. Topographical and environmental factors are strongly correlated with the composition of chironomid communities. No information is available regarding these organisms in this defined area, so this study would provide data for comparison with chironomid community present in nearby and other ar ea, where study on chironomids is already done or will be done. This study on chironomids was conducted for the first time in Rajsamand Lake, India. Specimens were collected at seven sampling sites along shoreline of the Lake. A total of four genera (viz. Chironomus, Cryptochironomus, Einfeldia and Polypedilum) were reported. Polypedilum was the most dominant genus reported followed by Chironomus, Einfeldia and Cryptochironomus. Genus Cryptochironomus was reported for the first time in Rajasthan.