The meromictic coastal water bodies have a specific vertical structure consisting of the layers with different hydrological, hydrochemical parameters and plankton communities that have been poorly investigated, especially the protist component. Here, we report the first data on the species richness and taxonomic composition of protists in the Arctic coastal meromictic Lake Trekhtzvetnoe (Kandalaksha Bay, White Sea). This lake is the second meromictic water body on the coast of the White Sea, where the protist communities have been comprehensively studied using light, transmission and scanning electron microscopy. A total of 189 species and forms of heterotrophic, mixotrophic and phototrophic protists assigned to different taxonomic groups have been recorded, including 50 species new for the White Sea region. The supergroup TSAR was the richest, with Stramenopliles and Alveolata showing the largest number of species. The taxonomic list and micrographs of cells for observed protists are provided. Most species of protists are characterized by a wide geographical distribution. Half of the found species are freshwater. Taxonomic composition of the protist communities varied in the main hydrological zones (myxolimnion, chemocline and monimolimnion) according to the vertical stratification of hydrological and hydrochemical parameters. The similarity and differences of protist communities have been compared with those of another Arctic meromictic Lake, Kislo-Sladkoe.

В прибрежных водоемах, образовавшихся путем отделения от Белого моря в ходе послеледникового под­нятия берега, в хемоклине – градиентной зоне между аэробной и сероводородной зонами – часто наблюдается окрашенная прослойка воды с массовым развитием фототрофных микроорганизмов. Спектры пропускания солнечного света, измеренные на разных горизонтах трех стратифицированных водоемов и в прибрежной морской акватории с помощью погружаемого волоконно-оптического зонда, сопоставлены со спектрами поглощения света водой на этих же горизонтах. Для слоев с массовым развитием аноксигенных фототрофов по спектрам поглощения определены концентрации бактериохлорофиллов. Согласно полученным данным диапазоны проходящего солнечного спектра в водной толще («цветовые экологические ниши») в значительной степени зависят от растворенных в воде гуминовых веществ. Их концентрация возрастает по мере изоляции водоема от моря, из-за чего фотическая зона сужается по глубине, хемоклин оказывается ближе к поверхности и наблюдается сдвиг спектра попадающего в хемоклин света в более длинноволновую сторону. В морской бухте до хемоклина доходит в основном свет с длиной волны 524–593 нм, в морской стратифицированной лагуне преобладают длины волн 526–597 нм, в водоемах с пресным поверхностным слоем воды солнечный спектр сдвинут в красную область (573–727 нм). Показано, что «цветовые экологические ниши» в различных водоемах заняты организмами, светособирающие антенны которых адаптированы к поглощению квантов света соответствующего спектрального диапазона. Этот факт может быть использован для предсказания таксономического состава различных слоев стратифицированного водоема. In coastal water bodies formed by separation from the White Sea during the post-glacial uplift of the coast, in the chemocline (the gradient zone between the aerobic and hydrogen sulfide zones), a colored layer of water with a development of phototrophic microorganisms is often observed. The solar light transmission spectra measured at different horizons under water in three stratified water bodies in the coastal marine area using a submersible fiber optic probe are compared with the absorption spectra of light by water from the same horizons. In the layers with massive development of anoxygenic phototrophs, the concentrations of bacteriochlorophylls were determined from the absorption spectra. According to the data obtained, the ranges of the transmitted solar spectrum in the water column (“color ecological niches”) are largely determined by humic substances dissolved in water. Their concentration increases as the water body is isolated from the sea, due to which the photic zone narrows with depth, the chemocline becomes closer to the surface, and a shift towards longer wavelengths appears in the spectrum of light entering the chemocline. In the marine bay, the 520– 600 nm part of the spectrum reaches the chemocline, in the marine stratified lagoon, wavelengths of 510–6700 nm predominate, in reservoirs with a fresh surface layer of water, the solar spectrum is shifted to the red region (520–7200 nm). It is shown that "color ecological niches" in various water bodies are occupied by organisms whose light-collecting antennas are adapted to absorb light quanta of the corresponding spectral range.

Естественное или искусственное отделение водоема от материнской акватории ведет к стратификации его водной толщи и развитию вертикальной последовательности планктонных сообществ. Данные по сукцессии водорослевых сообществ единичны. В работе представлено исследование сезонной изменчивости состава и обилия микроводорослей в разных слоях водной толщи полузамкнутой лагуны под названием «Озеро Кисло-Сладкое» в 2021 г. в период устойчивой стратификации с придонной аноксией. Определены видовой состав и углеродная биомасса на разной глубине, интегрированная биомасса фитопланктона (ФП) в водном столбе (Bint). Проведен анализ сходства структуры ФП для разных слоев воды. Выявлено 53 вида и/или рода с преобладанием морских форм и 11 таксонов более высокого ранга. В период ледостава большая часть водной толщи была анаэробной, подо льдом доминировала пресноводная цианобактерия Microcystis ichthyoblabe. После схода льда максимум углеродной биомассы переместился к границе сероводородной зоны. В мае – начале июня наибольшие значения Вint определяла зеленая водоросль Chlamydomonas sp., в июне – июле – диатомовая водоросль Cyclotella choctawhatcheeana. Тип питания ФП с преимущественно автотрофного в начале сезона (март – июль) сменился на преимущественно гетеротрофный (август – октябрь). Наибольшие значения Bint отмечены в июле–сентябре (149,8 мг С/м2) при доминировании хищной динофлагелляты Oxyrrhis marina. Проведено сравнение полученных результатов с данными по водоемам подобного типа.

Natural or artificial separation of a water body from its parent water area leads to stratification of its water column and the development of a vertical sequence of planktonic communities. Data on succession of algal communities are sparse. Seasonal variability in the composition and abundance of microalgae in different water layers of the semienclosed lagoon called Lake Kislo-Sladkoe in 2021 was studied during stable stratification and bottom anoxia. Species composition and carbon biomass at different depths, as well as the integrated phytoplankton biomass in the water column (Bint), were determined. An analysis of the similarity of the phytoplankton structure in different water layers was carried out. A total of 53 species and/or genera with a predominance of marine forms and 11 higher rank taxa were identified. During the ice-covered period, most of the water column was anaerobic, and the freshwater cyanobacterium Microcystis ichthyoblabe dominated under the ice. After ice thaw, the biomass maximum shifted towards the boundary of the sulfide zone (into the chemocline). In May–early June, the highest biomass was determined by green alga Chlamydomonas sp., while that in June-July was by the diatom Cyclotella choctawhatcheeana. The type of nutrition changed from predominantly autotrophic at the beginning of the season (March–July) to predominantly heterotrophic (August–October). The highest biomass values were recorded in July–September (149.8 mg С/m2) due to the dominance of the predatory dinoflagellate Oxyrrhis marina. A comparison was made with water bodies of a similar type.

Measurements of the spectral composition of light at the boundary of the photic zone in seven coastal reservoirs, which are isolated from the sea to varying degrees, as well as in the marine water area and in a freshwater lake showed that in marine and brackish reservoirs, mainly green light reaches it; in lakes with a fresh upper layer it is orange, red and far-red. In meromictic reservoirs, the photic zone was limited by a colored layer of water with a massive development of phototrophic microorganisms. Their pigment composition is in good agreement with the spectral composition of transmitted light. The marine bays and lagoons were dominated by taxa with red pigments: cryptophytic algae with phycoerythrin-545, purple sulfur bacteria with okenone carotenoid, brown green sulfur bacteria with isorenieratene and bacteriochlorophyll e. In lakes with fresh upper water, unicellular algae and green sulfur bacteria with chlorobactene and bacteriochlorophyll d developed. The spectral range can serve as a selective factor that determines the composition of a community of phototrophs with structurally different antennas and similar light absorption spectra.

The article presents the results of hydrochemical studies of waterbodies with varying degrees of development of anaerobic conditions (up to the appearance of meromixia with sulfide anoxia) in the Porya Guba Bay (Kandalaksha Bay, White Sea, Kandalaksha State Nature Reserve). It is shown that these waterbodies, which are at different stages of isolation from the sea, have a unique hydrological and hydrochemical structure, formed at a certain stage of their evolution. The vertical stratification of water, with the development of all phenomena accompanying stagnation, is more pronounced in the most distant parts of their water area from the sea, where elevated contents of hydrogen sulfide (up to 16.5 mg/L), phosphates, silicon, nitrite, and ammonium nitrogen are noted in bottom anaerobic water. However, the concentrations of all major ions are comparable to those in seawater and hardly chance at all vertically. Analysis of the distribution of the hydrochemical parameters of the distant reaches of Ozerki Lagoon made it possible to conclude that, due to changes that have occurred with this waterbody over the past 90 years, it can now most likely be classified as meromictic.

In coastal basins separated from the White Sea due to post-glacial uplift, the spectrum of light at the boundary of the photic zone gradually shifts towards long waves: from predominantly green (in marine area and in bucket bays) to green-orange-red in lagoons, then to yellow-orange-red in meromictic lakes with fresh mixolimnion and orange-red in fresh lakes. This is due to increase of concentration of humic substances (CDOM, «yellow substance»). They attenuate short-wavelength light and reduce the photic zone. The light spectra are consistent with the color of photosynthetic microorganisms that dominate in the chemocline zone. Under green light, microorganisms with red pigments in the photosynthetic antennae receive an advantage, and under orange-red light, cells with a green color are advantageous. The relationship between the concentration of humic substances in surface waters and the pigment composition of microorganisms opens up the opportunity of assessing the stage of isolation and salinity of the mixolimnion, as well as influx of humic waters from the catchment area based on the remains of pigments in columns of anaerobic sediments.

The relic Lake Mogilnoe, separated from the Barents Sea by a sand and pebble dam, is located in the high Arctic on the Kildin island (Murmansk region). This lake is a classic example of a meromictic basin of marine origin. The data obtained during the 2018 expedition showed changes in the hydrochemical regime of the lake that have occurred over the past 20 years. Sulfide concentration in the monimolimnion of the lake was as high as 140 mg/L. A tendency for salinization of the surface waters to 7 g/L has been noted. The Lake Mogilnoe is characterized by a discrepancy between the halocline and thermocline levels. The chemocline zone in the lake is below the halocline level. In a narrow oxygen-containing layer between 3 and 7.5 m, aerobic microflora of the marine type and marine fauna were present. The bacterial plate was formed at the boundary of the sulfide layer at 8 m and mainly consisted of green sulfur bacteria (GSB). Brown-colored GSB species containing bacteriochlorophyll e were predominant. The previously formed concept of anaerobic phototrophic bacteria (APB) biodiversity based on morphological characteristics was modified using metagenomic data obtained by analyzing DNA from two samples of lake water in the chemocline zone, and was also supplemented by identifying new GSB species. Molecular diagnostic data confirmed the absolute dominance of the brackish species of GSB Chlorobium phaeovibrioides. This is the first isolation and identification of brown- and green-colored Prosthecochloris aestuarii morphotypes from Lake Mogilnoe, as well as of bacteriochlorophyll c-containing Prosthecochloris sp. The taxonomic position of Pelodyction phaem, which was constantly present in the Lake Mogilnoe, is discussed in detail. Despite the partial isolation of the ecosystem of Lake Mogilnoe from the Barents Sea, the main properties of the dominant GSB species and Prosthecochlori aestuarii turned out to be similar to those of the phylotypes living in lakes on the White Sea coast.

Lake Kislo-Sladkoe is a stratified water body partly isolated from the White Sea. Perennial meromixis in the lake irregularly alternates with mixing events. Taking into account that the protists of Arctic coastal stratified water bodies are understudied, we evaluated for the first time the vertical structure, species richness, and diversity of protists assigned to different taxonomic groups in Lake Kislo-Sladkoe using light, luminescent, and scanning electron microscopy. To test the research hypothesis that a mixing event affects the vertical stratification and species composition of protists in a stratified lake, we compared the protist communities of Lake Kislo-Sladkoe in two extremely different states: strong meromixis vs. full vertical mixing. A total of 97 morphologically distinct phototrophic, heterotrophic, and mixotrophic protists were revealed with the most diverse supertaxa SAR (59), Obazoa (9), and Excavates (14). The hidden diversity of protists (43 species) was a bit less than the active diversity (54 species). A taxonomic list and micrographs of cells for the observed protists are provided. The majority of species revealed are cosmopolitan or widespread in the northern sea waters. The vertical patterns of protist communities were absolutely different in 2018 and 2021. In July 2018, clearly distinct protist communities inhabited different layers of the lake. Bloom of cryptophyte Rhodomonas cf. baltica was detected in chemocline, whereas the maximum density of its grazers was observed in adjacent layers, mainly dinoflagellates Gymnodinium sp. and Scrippsiella trochoidea, as well as a ciliate Prorodon sp. In 2021 due to the recent mixing of lake and seawater, there were no distinct communities in the water column except the superficial 0–1 m layer of fresh water.

The optical properties of chromophoric dissolved organic matter (CDOM) of natural water have been studied by fluorescence spectroscopy and absorption spectroscopy. Samples of natural water from various depths from the meromictic lakes Trekhtzvetnoe and Elovoe were taken. The dependences of the quantum yield and the maximum of fluorescence emission on the excitation wavelength in a wide range of excitation wavelength variation (250...500 nm) for different horizons of stratified reservoirs are obtained. It is shown that the dependences of the maximum of the fluorescence emission on the excitation wavelength and the dependences of fluorescence quantum yield on the excitation wavelength in both lakes and at all depths studied are similar. On the other hand, the absolute value of the quantum yield differs in different layers of water. For example, the values of the fluorescence quantum yield took values from 1.4% to 2.4% at an excitation wavelength of 340 nm. The similar nature of the dependence of the fluorescence intensity on the excitation wavelength is explained by the common origin of DOM fluorophores in the studied horizons of stratified lakes. The different values of the fluorescence quantum yield are due to the difference in the proportion of aromatic compounds in the composition of the CDOM and are associated with differences in the hydrochemical characteristics of water at different horizons.

The composition and structure of the anoxygenic phototrophic bacterial (APB) community in the water column of meromictic Lake Bol’shie Khruslomeny during winter were investigated. The community developed at the depth of 4.25 m, and its activity in the ice-cover period was very low (6.2 µmol C L–1 day–1). The water in the zone of highest development of phototrophic bacteria was of an unusual lemon-yellow color, probably due to the production and accumulation of polysulfides. The near-bottom water was also of lemon-yellow color and was resistant to oxidation by the air oxygen. In the zone of peak APB development the content of BChl d from green-colored green sulfur bacteria was considerably higher than that of BChl e from brown-colored green sulfur bacteria: 77 and 23

In a saline semi-isolated lagoon on Cape Zeleny (White Sea), the annual dynamics of the vertical hydrological structure and the seasonal dynamics of phytoplankton were traced. Species composition, vertical distribution, abundance, nutrition type, and biomass were analyzed. In total, 293 species and supraspecific taxa of algae and cyanobacteria were found. Most of the identified species are marine, and 38 species are freshwater. Taxonomic composition changed in the lagoon throughout the year. Dinoflagellates dominated in winter and early June; unidentified cocci and flagellates in July; diatoms, dinoflagellates, and unidentified cells in August; dinoflagellates in September; and unidentified cocci and flagellates in October–November. The abundance of algae also changed in the lagoon throughout the year. The integrated biomass in the water column varied from 0.01 g C/m2 in January to 0.78 g C/m2 in early September. According to the environmental parameters, the water column of the lagoon was subdivided into several zones with different environmental conditions and corresponding phytoplankton communities. The similarity between the communities of different horizons was 32–46% in summer and 7% in winter. The chemocline layer was the most populous. It contained a maximum of phytoplankton biomass, 1–2 orders of magnitude higher than that in the overlying horizons. Despite the connection to the sea, the phytoplankton structure in the surface water layer in the lagoon and in the sea differed significantly in composition, quantitative parameters, and seasonal dynamics. The similarity between the communities never exceeded 50%. In terms of biomass dynamics, the lagoon lagged behind the sea until mid-summer, but, starting from August, it outnumbered it, and the phytoplankton development in the lagoon lasted longer, until late autumn. According to sequential tests DistLM, the phytoplankton structure and dynamics in the lagoon and in the sea were related to the daylength, water salinity, oxygen content, and pH by 24.5%. At the same time, the PhP structure did not depend on water temperature, underwater illuminance, or depth. Oxygen content and pH were defined by PhP activity. Salinity serves as a vector of the vertical sequence of ecological niches. The day length seems to be the crucial factor of the seasonal PhP dynamics in the semi-isolated coastal stratified lakes and lagoons.

Chlorosomal bacteriochlorophylls are the main photosynthetic pigments of green sulfur bacteria – anoxygenic phototrophic microorganisms. The spectral properties of chlorophylls of higher plants, algae and cyanobacteria are well studied, however, the spectral-luminescent properties of their related compounds, bacteriochlorophylls, which participate in anoxigenic photosynthesis, are practically not described in the scientific literature. The polarity of the solvent and the environment have a significant effect on the emission spectra (bacterio)chlorophylls, which is expressed in the spectral shift of the absorption and fluorescence maxima, as well as changes in the fluorescence intensity. The spectral characteristics of bacteriochlorophylls d and e were obtained in organic solvents such as acetone, methanol, ethanol and isopropanol, as well as in acetone-ethanol (7:2) and acetone-methanol (7:2) mixtures. These solvents are most often used for the extraction of bacteriochlorophylls from bacterial cells, so the work will be useful for the development of methods for the quantitative determination of chlorosomal bacteriochlorophylls in bacterial cells or in samples of natural water.

Fiard coasts are common on the periphery of the areas previously covered by ice sheets. The conditions in such areas are favorable for separation of bays and straits from the sea. As a result of the glacial isostatic adjustment of the area the fiards would be transformed into coastal lakes. To discover the regularities of evolution of such water bodies, we studied topography, sea and lake sediments, hydrology and diatom associations of meromictic Lake Kislo-Sladkoe at the Karelian Coast of the Kandalaksha Bay, the White Sea, Russia (66°32′54″N, 33°08′05″E). Detailed geomorphological, geodetic, bathymetric, and aerial imagery field works have been completed on the coastal area. We built a Digital Elevation Model (DEM) of the coast and seabed. Radioisotope dating (210Pb, 14С), grain size distribution, loss on ignition, Corg/Norg ratio and diatom analysis have been completed for the entire 1.5-m sequence of the Lake's sediments. Currently, the Lake Kislo-Sladkoe communicates with the sea through a rising sill. We have established that the water body is meromictic due to its upper water layer being of variable salinity, middle layer comprising of aerated salty water, and the near-bottom water layer being anaerobic. However, several-year-long periods of water stratification alternate there with occasional late-autumn or early-winter flushes. The water body evolution falls into four stages: (1) a strait with an active hydrodynamic environment (prior to 1500–1560s), (2) a strait with a variable hydrodynamic environment (1500–1560s to 1850–1890s), (3) a semi-isolated lagoon with a quiet hydrodynamic environment (1850–1890s to early 1950s), and (4) a meromictic lake at an early stage of separation from the sea (early 1950s to present). We show how coastal processes on fiard coasts change the mode and duration of isolation of coastal water bodies from the sea. Based on the assessment of the rate of the post-glacial rebound and hydrological conditions of the coastal area we propose an approach to estimating the duration of transitional phase between a marine bay or strait and freshwater lake, including its meromictic stage. We predict that the meromictic stage of the lake will be completed no earlier than c. 100–200 years after the sill rises above the tidal zone.

Along the shoreline of the White Sea, due to the post-glacial uplift of the coast, some water bodies with stable stratification have been formed. They have been classified as meromictic as they are at different stages of isolation from the Sea. As separation progresses, significant changes occur in the water column, including the composition of chromophoric dissolved organic matter (CDOM) and the structure of the aquatic microbial community. In this work, we searched for optical proxies of euxinia (anoxic conditions with accumulated hydrogen sulfide) in the water column of the meromictic lagoon on Zeleny Cape. The lagoon is separated from the White Sea basin by a shallow threshold that completely isolates the lagoon during low tide, but marine water enters the lagoon during high tide. The ecosystem in the lagoon is characterized by the marine salinity of water and a high organic matter content in the bottom water and sediments. In this study, spectral methods were used to obtain the depth distribution of CDOM, chlorophyll, and bacteriochlorophyll in the lagoon with strong water stratification and euxinic conditions in the bottom water. The measured optical CDOM characteristics were compared with hydrochemical data (water salinity, Eh, pH, dissolved oxygen), phytoplankton (oxygenic phototrophs), and green sulfur bacteria (anoxygenic phototrophs) distribution along the water column. The spectroscopic methods showed to have the advantages of not requiring water sample pre-treatment and allowing rapid sensing of CDOM and photosynthetic pigments at each horizon.

Meromictic lakes of the marine coast, quite widely distributed in the northern hemisphere, are the result of climate changes and glacier retreat. The bottom sediments of these lakes serve as a geological chronicle of the history of marine basin’s development with the geochemical occurrence forms of elements indicate various processes of their accumulation. This paper presents research results concerning the occurrence of forms of heavy metals in lake sediments along the coast of the White Sea. These results are based on a sequential seven step leaching procedure, followed by ICP-MS analysis and subsequent statistical data processing. To determine differences among the examined geochemical parameters, Pearson’s correlation analysis and Ward’s cluster analysis were utilized. The total content of Cr, Mn, Fe, Co, Ni, Zn, V, and Pb in the sediments did not exhibit significant differences based on their degree of isolation from the sea. The major contribution to deposition of these metals in sediments of the meromictic lakes studied is the residual form, encompassing the mineral matrix of the sediment. At the same time, the elevation of mobile forms for all the metals examined corresponds to an increase in the isolation of lakes from the White Sea. In the meromictic lake sediments, concentrations of Cu, Mo, and U demonstrated significant increases in forms tightly bound to organic matter, while Cd exhibited an association with Fe-Mn oxyhydroxides. Notably, a significant difference in the occurrence forms of Cu, Cd, Mo, and U was evident in the reduced sediments of meromictic lakes when compared to those of open sea bays. The meromictic lakes along the White Sea coast, positioned at various stages of isolation, hold promise for investigating the migration of metals in response to environmental changes.

PREMISE:The sporoderm of seed-plant pollen grains typically has apertures in which the outer sporopollenin-bearing layer is relatively sparse. The apertures allow regulation of the internal volume of the pollen grain during desiccation and rehydration (harmomegathy) and also serve as sites of pollen germination. A small fraction of angiosperms undergo pollination in water or at the water surface, where desiccation is unlikely. Their pollen grains commonly lack apertures, though with some notable exceptions. We tested a hypothesis that in some angiosperm aquatics that inhabit water of unstable salinity, the pollen apertures accommodate osmotic effects that occur during pollination in such conditions.METHODS:Pollen grains of the tepaloid clade of the monocot order Alismatales, which contains ecologically diverse aquatic and marshy plants, were examined using light microscopy and scanning electron microscopy. We used Ruppia as a model to test pollen grain response in water of various salinities. Pollen aperture evolution was also analyzed using molecular tree topologies.RESULTS:Phylogenetic optimizations demonstrated an evolutionary loss and two subsequent regains of the aperturate condition in the tepaloid clade of Alismatales. Both of the taxa that have reverted to aperturate pollen (Ruppia, Ruppiaceae; Althenia, Potamogetonaceae) are adapted to changeable water salinity. Direct experiments with Ruppia showed that the pollen apertures have a role in a harmomegathic response to differences in water salinity.CONCLUSIONS:Our results showed that the inferred regain of pollen apertures represents an adaptation to changeable water salinity. We invoke a loss-and-regain scenario, prompting questions that are testable using developmental genetics and plant physiology.

The article presents data on the composition and abundance of algal flora in the coastal stratified Kislo-Sladkoe Lake (the Karelian coast of the White Sea) after its flushing with seawater in autumn. The seasonal dynamics and vertical structure of the phytoplankton were monitored from March 17 to October 3, 2019. We also studied ice flora on March 17 and April 1. The largest carbon biomass of ice algae (0.79 g C/m(3)) dominated by Nitzschia frigida was recorded in April. The integrated biomass of phytoplankton in the water column varied from 0.01 g C/m(2) in March to 5.83 g C/m(2) during spring bloom in late May (when it was dominated by Chaetoceros invisibilis) and remained at the level of 0.07 to 0.29 g C/m(2) until October; heterotrophic forms replaced autotrophic algae during this period. A regression analysis has shown that the structure of the phytoplankton was influenced by length of daylight, water temperature, dissolved oxygen level, depth, pH, salinity, and illuminance.

Despite surprisingly a small number of protein-coding gene in mammalian genomes, a large variety of different RNAs is being produced. These RNAs are amazingly different in their number, size, cell localization, and mechanism of actions. Although new classes of short RNAs (sRNAs) are being continuously discovered, it is not yet obvious how many of the sRNAs are originated. Altogether, the research in the recent few years has identified an unexpectedly rich variety of mechanisms by which noncoding RNAs act, suggesting that we have identified probably only few of the many potential functional mechanism and more investigation will be needed to comprehensively understand the complex nature and biology of mammalian RNAome. Here, we focus on various aspects of the diversity of the biological role of these nonprotein-coding RNAs (ncRNAs), with emphasis, on functional mechanisms recently elucidated.

Optical characteristics of water in stratified lakes can be used to study the pigment composition of various groups of photosynthetic organisms, its depth distribution and changes in different seasons. In the Arctic zone it is especially important to explore the evolution of natural water bodies under the influence of climate change and urbanization processes. Several water bodies on the coast of the Kandalaksha Bay of the White Sea are known as being at different stage of isolation from the Sea. In some of them the colored water layers in their chemocline zone resulted from the massive development of anoxygenic phototrophic bacteria were observed. The most numerous inhabitants of the chemocline zone are green sulfur bacteria. Besides green sulfur bacteria and purple sulfur bacteria, there were found cyanobacteria above and inside the chemocline zone. To access the pigment concentration, we measured fluorescence spectra of acetone extractions prepared from water sampled from various depths within chemocline of the lake Trekhtzvetnoe in March 2021. To increase the sensitivity of fluorescence measurements to certain pigments we acquired synchronous spectra of luminescence spectrometer performing scanning with a constant wavelength offset of 30 nm. This paper presents for the first time depth distribution of photosynthetic pigments BChl d (from green sulfur bacteria) accompanied with phycobilins (from cyanobacteria) derived from synchronous fluorescence spectra of acetone extractions prepared from water from various depths. This type of spectral measurements allowed us to receive depth distribution of cyanobacteria within the bacterial plate of green sulfur bacteria with very high depth resolution.