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The water vole (Arvicola amphibius) is widespread throughout Eurasia. In 2020, 17 specimens were collected from the islands of the White Sea during the field expedition of the Karelian Research Centre. It was the first record of this species for White Sea island fauna since the 1950s. Among the captured voles, there were two different colour variants of the animals: almost black and reddish-brown. We tend to classify the black type of colour as melanism. This type of colouration is new for the species in the region, according to data from long-term monitoring of continental populations of small mammals. All reddish-brown samples, with the exception of one juvenile male, presented white spots on various parts of the body. The white-spotting patterns of reddish-brown colouration were also first recorded for water voles in the region. Individuals with different colouration types inhabited islands separated by about 50 kms of water. [ABSTRACT FROM AUTHOR]

This paper presents the results of forecasts of the fields of hydrometeorological parameters using the coupled ocean–atmosphere system for the White Sea region for the period from June 2, 2015 to September 1, 2015. The coupled system included three models: atmospheric WRF-ARW, oceanic ROMS, and wave SWAN. The skills of sea surface temperature and 2 m air temperature forecasts have been estimated. The systematic overestimation of the computed sea surface temperature values relative to the OISST analysis data is 0.4°C. The forecast of the 2 m air temperature was generally more successful when using the coupled system than with the WRF-ARW model, and the improvement was observed mainly in the land areas immediately adjacent to the White Sea. Time intervals in which the influence of the sea on the forecast of 2 m air temperature was maximal and minimal are given. [ABSTRACT FROM AUTHOR]

A general overview of the landforms of the Baltic crystalline shield was made; geologic, tectonic and geomorphological processes which created the modern landscapes were analyzed. The Baltic crystalline shield, composed by Archaean and Proterozoic rocks, is among the most ancient massives on Earth. It has seen numerous periods of tectonic activation, folding and faulting since the Precambrian time, which left numerous veins and intrusions with extreme diversity of minerals. In the Neotectonic time, the existing faults were re-activated and new ones were set, resulting in intense movements of crustal blocks. During the Quaternary, the Baltic shield was covered by ice sheets for several times. The ice left numerous moraines, glacial striae and fluvioglacial landforms. The last glaciation ended by 10–11 ka, and uplift of the Earth's crust driven by glacioisostatic adjustment (GIA) started. The rates of this uplift exceeded the eustatic rise of the World Ocean from meltwater input. Because of this, the eastern part of the Russian territory within the Baltic Shield experience a relative sea level (RSL) fall in the Holocene. Although the general uplift of the Earth-s crust in the last millennia was GIA-driven, local tectonic block movements of the Earth's crust were imposed on this general uplift, creating scatter in the RSL data. Such movements along major faults left numerous traces of ancient earthquakes. The combination of ancient resistant intrusive and metamorphic rocks, long-term uplift, past glaciations and high tides of the White Sea created the unique landscapes of the Baltic Shield with its rocky benches, skerries and sheepback rocks, meromictic lakes in former sea gulf which will later become isolation basins, series of uplifted coastal bars of well-rounded boulders and large tidal flats with boulders displaced by sea ice. [ABSTRACT FROM AUTHOR]

With high-throughput sequencing of the variable region V3–V4 of the 16S rRNA gene, the study of the full phylogenetic composition of microbial communities developed on the surface of titanium plates exposed in the water column of the coastal zone of the Black and White Seas was carried out. The presence of potentially corrosive microorganisms from various physiological groups, such as sulfate-reducing bacteria, acidophilic iron-oxidizing bacteria and archaea, sulfur-oxidizing and nitrifying bacteria, was shown in the fouling. In the fouling of titanium plates exposed in the Black Sea, the most common microorganisms were uncultivated sulfate-reducing bacteria of the order Desulfotomaculales, which accounted for 8.13% of all 16S rRNA gene sequence reads, as well as acidophilic iron-oxidizing bacteria of the genera Acidiferrobacter (5.47%), Acidithiobacillus (4.52%), and Acidiphilium (2.55%). Acidophilic archaea accounted for up to 7.97% of all reads. In the fouling of titanium plates exposed in the White Sea, the most common were also acidophilic bacteria from the orders Acidiferrobacterales and Acidithiobacillales (7.68%), as well as acidophilic archaea from the order Thermoplasmatales (7.43%). Uncultivated sulfate-reducing bacteria of the order Desulfotomaculales were also represented in relatively high numbers (6.61% of all reads). [ABSTRACT FROM AUTHOR]

Activities of key enzymes of energy and carbohydrate metabolism (cytochrome c oxidase (COX), lactate dehydrogenase (LDH), aldolase, glucose 6-phosphate dehydrogenase (G6PDH), and 1-glycerophosphate dehydrogenase (1-GPDH)) were studied in pink salmon Oncorhynchus gorbuscha (Walb.) smolts from the White Sea in a cage experiment simulating the transition from a freshwater to a marine environment. A decrease in COX, G6PDH, and 1-GPDH activities and an increase in LDH and aldolase activities were observed in juveniles with an increase in water salinity. Based on the findings, a redistribution of energy substrates between the reactions of aerobic and anaerobic metabolism towards higher anaerobic ATP synthesis was assumed for pink salmon. This may indicate that adaptive mechanisms rearrange metabolism to provide energy for osmoregulation in pink salmon juveniles when the salinity changes in their habitat. [ABSTRACT FROM AUTHOR]

Planktonic unicellular cyanobacteria are the dominant biomass producers and carbon fixers in the global ocean ecosystem, but they are not abundant in polar seawater. The interseasonal dynamics of picocyanobacterial (PC) abundance, picophytoplankton primary production, and phylogenetic diversity of PC Synechococcus were studied in the sub-Arctic White Sea. The PC abundance varied from 0.2–0.3 × 106 cells/L in February to 5.2–16.7 × 106 cells/L in July. Picophytoplankton primary production ranged from 0.22 mg C/m3 per day in winter to 11.32 mg C/m3 per day in summer. Synechococcus abundance positively correlated with water temperature and river discharge that increased in recent years in the White Sea. Phylogenetic analysis of the 16S rRNA gene and ITS region clone libraries from the White Sea and Barents Sea eDNA revealed picocyanobacterial sequences related to marine Synechococcus subclusters 5.1-I, 5.I-IV, 5.2, and 5.3. All Synechococcus S5.1-I were common in the White and Barents seas and were consistently present in the picophytoplankton composition throughout the year. Synechococcus S5.2 and S5.3 appear in the PC community in summer, suggesting their river origin, and Synechococcus S5.1-IV inhabits only the Barents Sea and was not detected in the White Sea. A unique Synechococcus phylotype was revealed. It is expected that the increase in the abundance of PC and their increasing role in ecosystem functioning, as well as the enrichment of the species composition with new phylotypes in the semi-enclosed sub-Arctic White Sea, which is vulnerable to the effects of climate change, will be characteristic of all Arctic seas in general. [ABSTRACT FROM AUTHOR]

We present new data of White Sea Coast dynamics within NE of the Gorlo Strait that were generated by satellite images, geomorphological and ground penetrating radar (GPR) profiling, aerial photography, and topographic surveys of coastal terraces and dunes. Our paleogeomorphological studies, supported by laboratory findings (diatom analysis and 14C dating), allowed us to reconstruct the morphodynamics of coastal and aeolian landforms. The obtained reconstruction enabled the evaluation of relative sea level (RSL) changes and the evolution of coastal landforms over the past ~ 3.7 cal ka BP. According to our research, sand was supplied to coastal zone and coastal dunes through scarp erosion (0.5–3.7 m/year) as well as from the shoreface, while the role of alluvial runoff is insignificant. The largest dune massifs were formed in the areas of longshore drift (from NE to SW) discharge. At the mouth of the Maida River, the barrier spit and foredune plain have been evolving from the end of the Holocene transgression (∼3.7–2.3 cal ka BP). The mean high water at this time was slightly higher (up to ∼2.5 m a.s.l.), and coastal processes were significantly more intense than current ones. Then, against a decrease in sea level and weakening sediment flows, the growth of the spit slowed. The ancient foredunes were stabilized by vegetation. Aeolian processes were activated ∼2.1 and after ∼0.8–0.7 cal ka BP. [ABSTRACT FROM AUTHOR]

The report provides new data on Vaucheria vipera Blum, one of the rarest collected marine species. In 2023, V. vipera was discovered in the littoral zone of the Unskaya Inlet of the White Sea. The record is considered first in Russia and the Arctic Ocean. The study of the morphology of specimens from the White Sea allowed to expand the morphological range of the species in terms of the maximum dimensions of oogonia, oospores, and antheridia. The work also pays attention to the basal septa that separate short branches bearing the gametangia. Based on the morphology of the gametangia, it is proposed to transfer this species to the section Woroninia. [ABSTRACT FROM AUTHOR]

Oligochaetes play a significant role in aquatic ecosystems, and studying their development can contribute to a deeper understanding of the evolutionary features of embryonic development in the phylum Annelida. In this paper, we initially explored a littoral oligochaete species from the White Sea, which is abundant in the vicinity of the White Sea Biological Station MSU and reproduces in the early summer. A molecular phylogenetic analysis utilizing COI and 18S markers confirmed that the species under investigation belongs to the genus Lumbricillus, family Enchytridae. The early stages of embryonic development were described in detail, and the timing of the onset of key stages was established. The specifics of the cellular patterns observed in the early embryo were elucidated using the fluorescence staining and confocal microscopy. The embryonic development of Lumbricillus sp. exhibits characteristics that are consistent with the typical development of oligochaetes. Additionally, it displays specific characteristics that are typical of representatives of the Enchytriidae family, including equal size of the 2d and 2D blastomeres and a small size of the 4D blastomere in comparison to the large 4d blastomere. The combination of synchrony and low developmental variability, coupled with the accessibility of the object, ease of maintenance and manipulation, makes Lumbricillus sp. a highly promising object for the study of embryonic development of annelids. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study of the macroalgal flora in Unskaya Inlet (White Sea) that was carried out in 2022–2023. The checklist of macrophytes, summarized from original and literature data, comprises 94 species: Chlorophyta, 26; Rhodophyta, 34; Phaeophyceae, 30; Xanthophyceae, 2; Charophyceae, 1; and Cyanophyta, 1. Of these, 46 species are new to the region, 4 are new to the White Sea, and 2 are new to the flora of Russia. From the offshore part to the head of Unskaya Inlet, the coastal surface runoff leads to significant freshening and increased turbidity of water, thus causing a sharp depletion of the species composition of algae. [ABSTRACT FROM AUTHOR]

Tidal estuaries play a crucial role, serving as major hubs for economic activities while also contributing to the preservation of natural diversity and bioproductivity. In Russia, these estuaries are primarily located in remote regions of the European North and the Far East, making them vital for energy and transportation usage as they essentially form the ‘cores’ of territorial development along the Northern Sea Route. To facilitate the development of energy and navigation infrastructure in tidal estuaries, as well as to plan and implement environmental protection measures, it is essential to have a comprehensive understanding of their hydrological regime. Unlike regular river flow, tidal estuaries exhibit more complex hydrodynamics, influenced by both river and marine factors. Due to the considerable challenges of conducting field hydrological studies in remote areas, numerical hydrodynamic modelling has emerged as a valuable method for obtaining information on the flow and water level regime in tidal estuaries. This paper presents an application of one-dimensional HEC-RAS and two-dimensional STREAM_2D CUDA numerical models to investigate the parameters of reverse currents in the hypertidal Syomzha estuary flowing into the Mezen Bay of the White Sea. The limitations and accuracy of the models are discussed, along with the potential for their improvement considering recent advancements in understanding the hydraulics of reverse currents.

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Data are presented on changes in the activity of the membrane-bound osmoregulatory enzyme Na+/K+-ATPase and lipid composition in the gills of pink salmon Oncorhynchus gorbuscha during spawning migration from the White Sea to the river environment through the estuary. The compensatory reaction of pink salmon in a hypoosmotic environment is accompanied by a decrease in Na+/K+-ATPase activity and a change in the content of phosphatidylserine and polyunsaturated fatty acids (linoleic, eicosapentaenoic and docosahexaenoic). The results obtained indicate that effective osmoregulation in pink salmon during spawning migration from the sea to the river allows the implementation of a reproductive strategy. [ABSTRACT FROM AUTHOR]

The temperature of the water surface layer in the Arctic may increase significantly in the coming decades. To what extent will shallow-water fauna be affected by warming? We investigated this issue using an example of one species of colonial hydroid, Dynamena pumila. We judged its reaction to warming via its pulsation activity and the growth of stolons. Pulsations of the coenosarc in colonial hydroids are a sensitive indicator of the body’s reaction to the influence of environmental factors. We tested the ability of D. pumila colonies to survive and adapt to existing at 25 °C for five days. After raising the temperature from 14 °C to 25 °C, colony growth and the pulsation of stolon growth tips on the first day increased and then decreased during the day. In the following days, the growth pulsations almost ceased, the colonies stopped growing, and their coenosarcs began to exfoliate from their perisarcs. However, by the fourth day, this process slowed down, and the colonies existed in an economy mode of experiencing unfavourable conditions. The thermal shock continued in the experiment for five days. Then, after the temperature dropped from 25 °C to 15–16 °C, all the colonies recovered within five days and continued to grow.

Reconstructing interglacial marine environments helps us understand the climate change mechanisms of the past. To contribute to this body of knowledge, we studied a high-resolution 455 cm-thick sediment sequence of the Boreal (Eemian) marine beds directly overlying Moscovian (Saalian) moraine in the Bychye-2 section on the Pyoza River. We analyzed lithological and microfossil (foraminifers, ostracods, pollen, aquatic palynomorphs) variations at the studied site. Stratigraphical zonation is based on the local and well-established regional pollen zones, correlated with the western European pollen zones. The studied marine beds accumulated from the end of the Moscovian glacial (>131 ka) until ca. 119.5 ka. We distinguished three successive phases: a seasonally sea-ice-covered, relatively deep, freshened basin in the initial rapid flooding stage (>131–130.5 ka); a deep basin in the maximum flooding phase with less extensive sea ice cover (130.5–130.25 ka); and a shallow basin with reduced sea ice cover (130.25–119.5 ka). According to a pollen zone comparison with other sites, the regional glacioisostatic rebound started ca. 130 ka. The diverse warm-water assemblages of benthic foraminifers and ostracods containing typical Baltic Sea species occurred during the regression, mainly 128–124 ka, thus giving evidence for a relatively long-lasting connection between the White and Baltic Seas. [ABSTRACT FROM AUTHOR]

The article presents the results of a study of modern geodynamic movements in bottom structures of the White Sea (Baltic Shield). Based on expeditionary work in the White Sea, data were obtained on the formation of the seabed relief and thickness of unconsolidated sediments under the influence of modern seismotectonic events and geodynamic movements, as well as long-term neotectonic processes. It is shown that the Kandalaksha Bay depression is a modern graben developing along faults activated in the Quaternary. Graben development continues to the northwest, where a new Quaternary structure is being formed. Signs of modern geodynamic movements have been identified. The authors demonstrate the role of disjunctive tectonics in the formation of slopes and tectonic structures transverse to the strike of the bay, morphologically represented by relief ridges cutting the Sredny Ludy rise in Kandalaksha Bay. The influence of modern geodynamic processes on the distribution of thicknesses of Quaternary sediments of various genesis and the mosaic distribution of modern bottom sediments has been established. The influence of gravitational processes involved in the formation of underwater landslides, leading to the appearance of abnormally thick layers of the unconsolidated sedimentary cover, has been studied. [ABSTRACT FROM AUTHOR]

Chitin is one of the most widespread biopolymers on Earth and occurs in high quantities in the exoskeletons of marine invertebrates. Chitinolytic bacteria are therefore typical components of marine ecosystems and play an important part in biodegradation. The Kandalaksha Bay area near the White Sea Biological Station, Moscow State University, which is inhabited by numerous invertebrates, is a promising site for the isolation of such bacteria. The composition of environmental prokaryotic communities and enrichment cultures grown on chitin was determined, and pure cultures of active chitinolytics were isolated and identified as Pseudoalteromonas undina and Vibrio alginolyticus. The chitinolytic potential of the genera predominant in enrichment cultures was assessed; these may include previously unknown chitinolytic microorganisms. [ABSTRACT FROM AUTHOR]

The article presents the results of studying of materials from the burials of the Eneolithic – Bronze Age in the White Sea basin and adjacent regions. An analysis of received data made it possible to identify for the first time changes in the composition of the burial goods and the spatial structure of the burial grounds of ancient hunters and fishermen who lived in the White Sea region in the IV – II millennium BC. The results of the study make it possible to judge the local and chronological features of the burial rite of the ancient population in the region, the directions and nature of its relationship and can serve as the basis for reconstructing the worldview of prehistoric people. The chronology of the burial grounds has been established mainly by identifying analogies in the burial goods and settlement complexes, dated on the basis of radiocarbon data and analysis of the altitudinal location of archaeological sites above sea level (Western White Sea region and Kola Peninsula). The author also publishes materials from five burial complexes, studied in the southwestern part of the White Sea basin.

Mikulinian (Eemian) marine deposits are widespread in the northern Arkhangelsk Region, Russia. Shoreface deposits have been found in exposures along the Pyoza and Vaskha rivers; however, deposits of undoubtedly tidal origin have not hitherto been recognized there. By contrast, here we show that shells of Macoma balthica (Linnaeus, 1758) (Tellinidae, Bivalvia) unearthed from the shoreface deposits show growth patterns indicating that the bivalves lived in an environment affected by tidal periodicity. The periodicity was a mixed tide with significantly diurnal inequality in the height of the low waters. In the Arkhangelsk Region, the Mikulinian hydrodynamical conditions of the tidally influenced regime are still poorly known. Because the spatial and temporal distribution of M. balthica is broad in the fossil record, its shells have a large potential for tidal interpretations, as contribution to hydrological reconstructions. [ABSTRACT FROM AUTHOR]

Investigation of prokaryotic communities from different horizons of the bottom sediments in the Kandalaksha Gulf, White Sea revealed two characteristic groups of sampling points. The first group demonstrated stratification of prokaryotic communities depending on the horizon depth, while the second one, with uniform prokaryotic communities, was typical of the sections with active organic matter decomposition. Microorganisms involved in decomposition of labile organic compounds (Woeseia and Sandaracinaceae), as well as sulfate reducers (SEEP-SRB1 and Sva0081) predominated in the upper horizons of the stratified sediments (the first group of samples). In the lower layers (30 and 50 cm), the share of microorganisms potentially involved in the degradation of complex compounds (e.g., Desulfatiglans, Hyphomicrobiaceae, and Mycobacterium) increased. The share of prokaryotes with unknown metabolism, such as JS1, SG8-4, WCHB1-81, Aerophobales, and S085, increased as well. Thus, the structure of prokaryotic communities was affected by the presence and abundance of organic matter, which decreased with depth. [ABSTRACT FROM AUTHOR]

Microbial communities of the sediments of the Kandalaksha Bay (White Sea) remain insufficiently studied. While the data on the rates of some microbial processes are available, very little is known about microorganisms inhabiting these sediments. In the this study, high-throughput sequencing of variable regions of 16S rRNA genes was used to characterize the microbial communities of 47 Kandalaksha Bay sediment samples collected at 10 cm below the bottom surface. Pseudomonadota and Desulfobacterota were the most abundant phyla, comprising together about a half of all prokaryotes. Determination of the dominant genus-level taxon proved impossible. The most represented chemoorganotrophic microorganisms were uncultured Sandaracinaceae (up to 10.8%) and Woeseia (up to 7.5%). Sulfate-reducing bacteria were important community components in the studied upper sediment layers, with uncultured groups SEEP-SRB1 (up to 7.0%) and Sva0081 (up to 5.9%) being the most abundant. In some samples, the genera Sulfurovum (up to 15.5%) and Thiohalophilus (up to 7.0%) involved in the oxidation of sulfur compounds were found to be important components of the community. Among the archaeal ASVs, the genus Nitrosopumilus oxidizing ammonium to nitrite exhibited the highest relative abundance (up to 6.9% of the total number of prokaryotes). Numerous sequences identified as the 16S rRNA gene fragments of chloroplasts were found in the samples, indicating that the rate of organic matter delivery to the upper sediment layers exceeded the rate of its degradation. [ABSTRACT FROM AUTHOR]

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%, respectively. The cultures of green and purple sulfur bacteria were isolated from lake water, and their physiological and genetic characteristics were determined. Two strains of green sulfur bacteria (brown-colored BrKhr17 and green-colored GrKhr17) contained gas vacuoles in their cells. Phylogenetically they were most closely related to the green-colored strain Chlorobium phaeovibrioides DSM 265 and were identified as new strains of the species Chlorobium phaeovibrioides. [ABSTRACT FROM AUTHOR]

Contemporary climate change in the Arctic is causing the reduction of the ice habitat. This process induces rearrangements in the community composition of ice-dwelling microbial eukaryotes, with heterotrophic picoeukaryotes being one of the least studied groups. Here, we report the results of a DNA metabarcoding investigation of heterotrophic picoeukaryote diversity in the ice of the Kandalaksha Gulf of the White Sea by Illumina high-throughput sequencing of the 18S rRNA V4 gene region. In total, 121 operational taxonomic units (OTUs) belonging to heterotrophic protists were revealed. The communities of heterotrophic picoeukaryotes in first-year ice were represented by seven eukaryotic domains (Stramenopiles, Alveolata, Rhizaria, Cryptista, Haptista, Apusozoa, Opisthokonta) and within 15 phyla. Rhizaria was the most dominant domain accounting for 48% of the total relative read abundance and included only Cercozoa. The taxonomic composition of heterotrophic picoeukaryotes was analyzed in detail with attention to rare and important microbial eukaryotes and unusual finds in sea ice habitats, such as the parasitic Perkinsea. Unknown Cercozoa clade was revealed. We have demonstrated that the White Sea heterotrophic picoeukaryote communities are diverse but insufficiently studied. Only 39% of OTUs were classified down to the order, family, or genus level, and only 11% of OTUs were classified to the genus level. This demonstrates that many unsequenced unicellular eukaryotes are found in sea ice and highlights some limitations of the V4 18S rRNA gene metabarcoding approach—the incompleteness of databases (lack of reference sequences) and shortness of the V4 region (inability to classify OTUs to species level). [ABSTRACT FROM AUTHOR]

This paper presents the results of our investigation of the zooplankton communities from Sukhoe More Bay, located in the southeastern part of Dvina Bay of the White Sea, in July–August, 2018. The species composition, quantitative characteristics and spatial distribution of zooplankton were studied. The zooplankton communities are composed of 34 species of hydrobionts. Copepods were the dominant group in the entire study area. The zooplankton communities were characterized by high quantitative indicators. Juvenile stages of copepods were a significant contribution to the formation of the total number of zoocenoses. During high water level, the abundance of zooplankton was 37 000 ind./m3, biomass, 0.6 g/m3 (wet weight). During low water level, these parameters were 210 000 ind./m3 and 1.7 g/m3 (wet weight), respectively. The structure, abundance and spatial distribution of zooplankton in the bay are determined by the morphometric features of the reservoir (shallow water), the influence of a complex of environmental factors (temperature and salinity), as well as tidal phenomena. [ABSTRACT FROM AUTHOR]

The temperature of the water surface layer in the Arctic may increase significantly in the coming decades. To what extent will shallow-water fauna be affected by warming? We investigated this issue using an example of one species of colonial hydroid, Dynamena pumila. We judged its reaction to warming via its pulsation activity and the growth of stolons. Pulsations of the coenosarc in colonial hydroids are a sensitive indicator of the body's reaction to the influence of environmental factors. We tested the ability of D. pumila colonies to survive and adapt to existing at 25 °C for five days. After raising the temperature from 14 °C to 25 °C, colony growth and the pulsation of stolon growth tips on the first day increased and then decreased during the day. In the following days, the growth pulsations almost ceased, the colonies stopped growing, and their coenosarcs began to exfoliate from their perisarcs. However, by the fourth day, this process slowed down, and the colonies existed in an economy mode of experiencing unfavourable conditions. The thermal shock continued in the experiment for five days. Then, after the temperature dropped from 25 °C to 15–16 °C, all the colonies recovered within five days and continued to grow. [ABSTRACT FROM AUTHOR]

We have studied the differential influence of light and temperature on the regulation of daily cercarial emission of ten species of littoral trematodes of the White Sea (Cryptocotyle lingua, C. concava, Himasthla elongata, H. continua, Cercaria parvicaudata, Levinseniella brachysoma, Maritrema subdolum, Microphallus claviformis, M. similis, and Paramonostomum alveatum) and two freshwater species from Lake Chudskoe (Diplostomum pseudospathaceum and Moliniella anceps). The experiments tested short-term (2 h) exposure to illumination (darkness and light 800 lux) and temperature (10, 20, 25°C) on the intensity of cercariae emission from infected molluscan host. The experimental setup and experimental design made it possible to separate the effects of the studied factors of all gradations. It was found that light plays a significant role in stimulating the emission of cercariae with pigmented eyes and echinostomatoid larvae Moliniella anceps and Himasthla spp., which are expected to have nonpigmented photoreceptors. However, even in these larvae in the dark, the emission was controlled by temperature. For almost all studied species, the high significance of the interaction between temperature and light factors in the regulation of cercariae emission was revealed. With the same values illumination can act as an emission trigger, and at other temperatures it can act as an inhibitor. It has been suggested that the temperature dependence of the rhythm and intensity of daily cercarial emission is especially favorable in polar latitudes, where most of the seasonal window of trematode transmission occurs during the polar day with minor changes illumination during the day. [ABSTRACT FROM AUTHOR]

This research presents a classification and analysis of the spatial distribution of Holocene aeolian landforms on the White Sea Coast. The authors have identified five types of secondary dunes based on interpretation of detailed satellite images and topographic charts, as well as analysis of literature sources: foredune plains and beach ridge plains, cliff-top dunes, blowouts and parabolic dunes, transgressive dunefields, and sand sheets. The dunes formed mainly since the Middle–Late Holocene. They are confined to sandy coasts, where postglacial uplift rates did not exceed ~3 mm/year during the Middle–Late Holocene. The coastal dunes were formed in connection with sediments that entered the coastal zone with solid river runoff and from selective erosion of glacial sediments. The rhythmic patterns of the activation of aeolian processes in different parts of the White Sea Coast were asynchronous. [ABSTRACT FROM AUTHOR]

The article presents the results of study in the White Sea region of stone inventory and mineral conditioners into the molding mass of ceramic vessels of the end of II millennium BC – second half of I millennium BC. As a result of the spatial and chronological study of artificial mineral inclusions used in the hand-modeling of pottery at the end of the Bronze Age – the Early Iron Age, it was possible to receive new data on cultural and historical processes taking place in the region at that time. The results of statistical and typological analysis of set of stone items, studied by excavations in the White Sea region and dated by altitude location above sea level or associated with a certain type of ceramics are presented. The chronological stages in the development of the stone industry revealed in the course of the study are compared with the data on metalworking in the White Sea basin. The article for the first time publishes the results of radiocarbon analysis of some objects excavated on the territory of Karelia: complexes with Luukonsaari and Lebyazhye types ceramics, iron-smelting furnace in the form of a stone box.

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. [ABSTRACT FROM AUTHOR]

The results of the comprehensive study (diatom and pollen and spore analysis, and 14С-dating) of Holocene bottom sediments from a lake on the shore of Kandalaksha Bay, White Sea, at the Keret' River mouth, are reported. Three stages in the evolution of the lake basin: marine, transitional, and lacustrine, were recognized. Diatom complexes, typical of each facies, were described. Pollen, spores and non-pollen palynomorphs were shown to indicate marine, transitional, and freshwater sedimentation conditions. Sea level was found to decrease 7200 cal. y.a. A marine sedimentation environment was succeeded by a lacustrine environment ca.6700 cal. y.a. The position of the sea shoreline in the study area at that time was determined. Data obtained by pollen and spore analysis were used for relative dating of postglacial strata. Vegetation, evolving from the end of the Early Holocene to the present, was reconstructed. [ABSTRACT FROM AUTHOR]

The research area includes the White Sea and adjacent land located in the junction zone of the eastern part of the Fennoscandian Shield and the Russian Plate. The purpose of the study is to construct a model of the lithospheric structure of the region using decomposition of anomalous gravitational and magnetic fields and inverse problem solving for components of gravity and magnetic fields, respectively. The decompositions of the fields were provided by the singular spectral method in the software package "R 4.3.1". The inverse problems were solved using the programs of the "Integro" complex. The components of the fields help to identify and analyze buried geological structures. The rift system of the White Sea is most clearly represented by the fourth component of the gravitational and magnetic fields. The positions of density and magnetic inhomogeneities of the Earth’s crust corresponding the components of the fields have been determined. The component model is compared with the seismic density and magnetic models of the lithosphere along the 3-AР geotraverse (Kem – White Sea Throat).

(1) Background: An estuary is a zone in which sea and river waters mix. It is a specific area with a very non-stable environment and salinity gradient. However, little is known about the diversity of ciliate communities in estuarine benthic ecosystems in the Arctic. The aim of this paper is to describe the diversity of intertidal ciliates in the Chernaya river estuary (Kandalaksha Gulf, White Sea), which is characterized by a pronounced salinity gradient (0–22‰), on the basis of a recently published dataset. (2) Methods: We conducted our own investigations during the summer periods of 1998–2000. Material was collected at five permanent stations along the salinity gradient (0–22%) of the estuary. For each observation, the coordinates of the sampling sites, the number of individuals observed and the sampling date were recorded. The total effort comprised 35 sampling days, with five sampling sites at each date. (3) Results: The dataset contains 4270 unique occurrences of 119 ciliates taxa (109 species, 8 unidentified species of the genus level and 2 unidentified species on the family level). The total number of specimens represented is 64,475. (4) Conclusions: The largest classes in terms of species diversity are Hypotrichea (27 species), Gymnostomatea (26 species), Oligohymenophorea (17 species) and Karyorelictea (16 species). Dataset:  https://doi.org/10.15468/ccku5d. Dataset License: Creative Commons Attribution (CC-BY) 4.0 License. [ABSTRACT FROM AUTHOR]

The strain WBS, an anaerobic, psychro- and halotolerant bacterium belonging to the genus Fusibacter, was isolated from the littoral bottom sediments of the White Sea, Arctic, Russia. Fusibacter bizertensis WBS grew at temperatures between 8 and 32 °C (optimum growth at 18–20 °C), pH between 5.2 and 8.3 (optimum growth at pH 7.2), and at NaCl concentrations between 0 and 70 g L−1 (optimum growth at 32 g L−1). It reduced sulfate, thiosulfate, and elemental sulfur into sulfide, and, probably, the strain is able to disproportionate thiosulfate. The strain also utilized a wide range of substrates as it is a chemoorganotrophic bacterium. Analysis of the sequenced genome revealed genes for all enzymes involved in the Embden–Meyerhof glycolytic pathway as well as genes for the non-oxidative stage of the pentose phosphate pathway. The presence of genes encoding aldehyde dehydrogenases and alcohol dehydrogenases also suggests that, in addition to acetate, alcohols can also be the fermentation products. The strain possessed superoxide dismutase and peroxidase activities and the ability to consume O2, which is in full accordance with the presence of corresponding genes of antioxidant defense in the genome. The phylogenetic analysis suggested that the strain WBS is the closest relative of Fusibacter bizertensis LTF Kr01T (16S rRNA gene sequence similarity 98.78%). Based on biochemical and genomic characteristics, the strain WBS is proposed to represent a novel aero-, halo- and psychrotolerant strain from the genus Fusibacter, isolated for the first time among its members from cold oxygenated marine bottom sediments. [ABSTRACT FROM AUTHOR]

The article presents an integrated approach to considering the tourism vector of Karelian Arctic development. Six municipalities of the Republic of Karelia, included into the Arctic zone of the Russian Federation, have become a model site for the study. Severe natural and climatic North conditions, along with challenges of socio-economic development, actualize the perspective of tourism and recreation, including for the local population. For the first time in the study, the territory of the Karelian Arctic was comprehensively examined from the standpoint of tourist and recreational development. The study analyzes tourist and recreational potential, tourist infrastructure, including infrastructure of accommodation, catering, leisure and recreation, tourist flow and types of tourism; projects of tourist orientation, strategic directions of tourism development in the municipal context. The opinion of the residents of the Karelian Arctic about the tourist and recreational development of the territory is also taken into account, and limitations and current challenges are highlighted. The study reveals the diversity of municipal districts in the Karelian Arctic in terms of tourism and recreational potential, the degree of tourist development of the territory, tourism development opportunities, the constraints. Despite the existing limitations, on the basis of the identified opportunities, the significance of the tourism development vector of the Karelian Arctic is shown as a promising direction of domestic tourism in the Russian North, as well as a tool to restore physical and emotional strength of the local population.

It was revealed that the parameter Ntot./Ptot. in the tidal mouths of the rivers of the western sector of the Russian Arctic tends to increase in the zone of the biological stage of the marginal filter as it approaches the waters of the open waters of the sea. Here, the concentrations of total nitrogen in dissolved form clearly exceed the concentrations of total phosphorus, approaching their ratio determined for their mineral salts. Minimum parameter Ntot./Ptot. is observed in the zone of the coagulation-sorption stage of the marginal filter, but in the mouths of some small rivers it can also be observed in the zone of the gravitational stage. Here, the concentrations of total phosphorus can reach the level of total nitrogen or even exceed it. This situation is apparently related to the peculiarities of the spatial distribution of boundary surfaces (water-coast, water-bottom, water-macrophytes) in estuarine objects with the presence of tidal drylands.

Microorganisms associated with algae and able to utilize complex substrates (e.g., plant heteropolysaccharides) may be important producers of hydrolytic enzymes. The microbial communities of the red algae Corallina sp. and Phyllophora sp. sampled in the Kandalaksha Gulf basin of the White Sea were analyzed using high-throughput sequencing of the V4-variable region of the 16S rRNA gene. The dominant phyla in microbiomes of both samples were Pseudomonadota and Bacteroidota (GTDB classification, https://gtdb.ecogenomic.org/). For the Corallina sp. sample, dominance of the Vibrio, Agarivorans, and Photobacterium genera was shown, while Granulosicoccus and Aliivibrio dominated in the Phyllophora sp. sample. The analyzed red macroalgae with associated microbiota were used as an inocula to obtain microbial enrichment cultures growing on β-1,4-xylan or β-1,3-glucan (curdlan). It was shown that, similar to environmental samples Pseudomonadota and Bacteroidota phyla representatives were prevalent in all enrichment cultures. However, unlike the environmental samples, in the enrichment cultures the dominant genera were Marinomonas, Reinekea, Polaribacter, and Pseudoalteromonas. The latter, as well as the representatives of Vibrio sp., were isolated in pure cultures for which the xylanolytic activity was shown. [ABSTRACT FROM AUTHOR]

The species composition and taxonomic diversity of the Solovetsky Archipelago freshwater ichthyofauna have been revealed. A description of the current state of the fish is provided. The attribution of fish to different freshwater faunistic complexes and ecological groups (feeding patterns and mode of natural reproduction) has been considered. Currently, 14 fish species are recorded in the inland waters of the Solovetsky Islands, including local and alien species with varying degrees of acclimatization effect. The possible annual catch of freshwater fish which could be considered optimal has been evaluated. If it is necessary to organize freshwater aquaculture, lacustrine ranching of the whitefish complex in the lakes of the Solovetsky Archipelago seems to be promising. This type of aquaculture is based on the collection and fertilization of eggs at temporary fish breeding stations, its subsequent incubation at fish farms, and the release of reared juveniles into feeding lakes. [ABSTRACT FROM AUTHOR]

Lipid and fatty acid modifications induced by the effects of various salinity patterns on the juvenile pink salmon Oncorhynchus gorbuscha (the Olkhovka River and the White Sea) within the experiment have been revealed. Concentrations of steroids, saturated fatty acids, and signaling molecules such as phospholipids (phosphatidylserine and phosphatidylinositol) and arachidonic acid under the hyperosmotic stress-related effects (keeping the fish for 1 h in the seawater after the time of transfer from the freswater) tend to increase. Decreases in phosphatidylcholine and n-6 saturated, monounsaturated, and polyunsaturated fatty acids are recorded in the juvenile pink salmon fish kept for 24 h in the seawater after the time of transfer them from the freswater, while the levels of phosphatidylethanolamine and n-3 polyunsaturated fatty acids (especially eicosapentaenoic and docosahexaenoic acids), on the contrary, tend to rise significantly. Lipid composition modifications in the juvenile pink salmon fish kept under the hypoosmotic stress conditions (24 h in freshwater after 24 h in seawater) induce stabilization of functioning the cell membrane structure, since the levels of bioeffectors including phosphatidylserine, phosphatidylinositol, and arachidonic, eicosapentaenoic, and docosahexaenoic acids tend to decrease. A reduced amount of lipids (triacylglycerols) stored as an energy reserve is shown for all the experimental fish groups. The outcomes indicate the high levels of adaptive potential of the juvenile pink salmon fish kept under the effects of abrupt salinity change in the water environments and their readiness for downstream migration not long before leaving the nests. [ABSTRACT FROM AUTHOR]

Reconstructing interglacial marine environments helps us understand the climate change mechanisms of the past. To contribute to this body of knowledge, we studied a high-resolution 455 cm-thick sediment sequence of the Boreal (Eemian) marine beds directly overlying Moscovian (Saalian) moraine in the Bychye-2 section on the Pyoza River. We analyzed lithological and microfossil (foraminifers, ostracods, pollen, aquatic palynomorphs) variations at the studied site. Stratigraphical zonation is based on the local and well-established regional pollen zones, correlated with the western European pollen zones. The studied marine beds accumulated from the end of the Moscovian glacial (>131 ka) until ca. 119.5 ka. We distinguished three successive phases: a seasonally sea-ice-covered, relatively deep, freshened basin in the initial rapid flooding stage (>131–130.5 ka); a deep basin in the maximum flooding phase with less extensive sea ice cover (130.5–130.25 ka); and a shallow basin with reduced sea ice cover (130.25–119.5 ka). According to a pollen zone comparison with other sites, the regional glacioisostatic rebound started ca. 130 ka. The diverse warm-water assemblages of benthic foraminifers and ostracods containing typical Baltic Sea species occurred during the regression, mainly 128–124 ka, thus giving evidence for a relatively long-lasting connection between the White and Baltic Seas.

The biodiversity of Cephalaspidea (Gastropoda: Heterobranchia) is poorly studied, and novel findings often lead to revisions at different taxonomic levels. The family Philinidae has a distinct set of defining characters in the shell, copulatory apparatus, and gizzard morphology, but several species, considered part of the family, deviate from it significantly. Philine denticulata (J. Adams, 1800) was considered to be a Philinidae despite the species morphology not fitting well with the family diagnosis. This species has an oval cylindrical external shell, jaws, and a gizzard lined with a chitinous layer with three thickened ridges. We studied Philine denticulata morphology on samples from the White and Barents Seas using the light and scanning electron microscopy methods in addition to computer microtomography. We also reconstructed its phylogenetic position using COI, 16S, 28S, and H3 genetic markers. Our integrative analysis revealed close relationships of this species to the family Aglajidae. Thus, we describe a new genus Philinissima gen. nov., including a single species Philinissima denticulata (J. Adams, 1800) comb. nov. which is the first aglajid registered from the Arctic waters. Our findings highlight possible problems in the Aglajidae taxonomical composition and an overall need for a dedicated integrative revision of the Cephalaspidea. [ABSTRACT FROM AUTHOR]

The article considers the species composition as well as characteristics of the spatial and trophic structure of the macrobenthos in Nikolskaya Bay (Guba) of the White Sea. The bay belongs to the heavily silted-up lagoon ecosystems with a dominance of the trophic group of detritophages that are the surface deposit feeders ("collecting" detritophages). The accumulation of a large amount of the organic matter in the sediments of the lagoon and its freshening in the spring period contribute to the development of the predominantly small species of the detritophages more resistant to siltation and water freshening as well as to oxygen deficiency. These processes are especially evident in the apex region of the bay. Twenty-six species of invertebrates and nine species of seagrasses and algae were detected in the lagoon. Analysis of the obtained data on the species composition, diversity, and structure of the macrobenthos communities suggests the predominantly estuarine nature of the fauna of the Nikol'skaya Bay lagoon ecosystem compared to other lagoons of the White Sea since it is well protected from sea waves and currents by islands, luodos (rocky islets or shoals), and korgas (screes, continuing into a water body). [ABSTRACT FROM AUTHOR]

This is a first report on diversity of the micromycetes associated with living thalli of the edible red algae Palmariapalmata (dulse). Samples were collected in the Kandalaksha Gulf of the White Sea at upper (10 thalli in the littoral zone) and lower (10 thalli in the sublittoral zone) boundaries of this species distribution. The study was conducted using the culture techniques; fungi were isolated from the surface of thalli. The maximum number of morphotypes was 24; from 0 to 55 colonies were isolated from one thallus. The total diversity amounted to 52 morphotypes, of which 48 were mycelia and four were yeast. All identified yeasts belong to Basidiomycota; of filamentous fungi, two species belong to Zygomycota, and others belong to Ascomycota, the absolute majority of which were represented by the anamorphic stages. The most diverse genera included Acremonium (ten morphotypes), Penicillium (nine), and Cladosporium (six); Acremonium (158 colonies) and Cladosporium (103 colonies) were the most numerous. Acremoniumfuci was the most commonly occurring species on the studied thalli (122 colonies on 15 thalli). The habitat is a critical factor for the formation of the surface mycobiota of dulse: littoral and sublittoral algal populations differed significantly in the fungal communities' population size and structure. The thalli of the littoral population are appreciably richer in the fungi. Dark-colored species, as well as Acremonium fuci and Sarocladium strictum, were dominant in mycobiota of littoral samples, whereas mycobiota of sublittoral samples largely contained light-colored species, while the majority of yeasts were likewise isolated from the sublittoral samples. [ABSTRACT FROM AUTHOR]

We studied the reproductive behaviour associated with mate choice by size in three species of White Sea molluscs of the genus Littorina—L. saxatilis, L. obtusata and L. fabalis. Three behavioural patterns were revealed after a comparative analysis of the behaviour of the male snails. The males of L. obtusata, regardless of their size, could mate with all females but preferred to mate with larger ones. The males of L. fabalis chose females of their own size or larger. The males of L. saxatilis mated with females of approximately their own size. In the first case (L. obtusata), there is a free exchange of genes between all the size groups in the population. In the second case (L. fabalis), the gene transfer from small males to females of any size is free but the gene transfer from large males to small females is limited. In the third case (L. saxatilis), the gene flow is limited between groups of individuals of dramatically different size. Thus, in the case of L. saxatilis and L. fabalis, to varying degrees restriction of random mating associated with size assortativity in choosing a mating partner was expressed, which under certain circumstances (divergence of individuals in different econiches, the presence of ecotypes differing in size, lack of stronger natural selection in the other direction) can favour sympatric speciation. The males of all the three periwinkles' species preferred larger females but sexual selection in favour of larger females was found only in L. obtusata. In the other two species, there were no statistically significant size differences between copulating and non-copulating females. This appears to be due to the occurrence of size-assortative mating in these species, which limits the ability of males to choose larger female partners. [ABSTRACT FROM AUTHOR]

This study presents the results of lithological, diatom, geochemical analyses and radiocarbon chronology of the bottom lake sediments and peat bogs in the central part of the Onega Peninsula (the southern coast of the White Sea): Lake Maloye Murakanskoye (11.0 m a.s.l.), Lake Zhirovskoye (9.5 m a.s.l.), Lake Murakanskoye (7 m a.s.l.), and the Gorbovatiy Mokh bog (6.5 m a.s.l.). The bottom topography and sediments of Lake Murakanskoye were examined using sonar and ground penetration radar (GPR) survey, whereas in the other locations only the water depth was measured. Then, the digital models of the lake bottom topography were created. As an additional indicator of the relative sea-level (RSL) position, we used data on the altitude of the coastal terraces. Evidences of two transgressions in the White Sea (late glacial and Middle Holocene) are revealed. The transgressions were interrupted by two regressions (Early and Late Holocene). Our studies do not allow us to make a clear conclusion about the time and maximum level of the late glacial transgression. However, we may suggest that its level was above 11 m a.s.l. The regression of the Early Holocene started before 10.6–10.2 ka cal BP when the water level in the study area dropped below the altitude of 11m. At 9.4–9.1 ka cal BP the RSL was at an altitude of ca 7m. The Middle Holocene transgression (Tapes) started after 8.4 ka cal BP. The maximum level was reached before 7.4 ka cal BP and did not exceed an altitude of 9.5 m. The RSL stabilized at an altitude about 8.5–8 m during 7.4–6.0 ka cal BP. During 6.0–3.9 ka cal BP RSL very slowly decreased or fluctuated by the level of 8–7 m. RSL began to fall from the 7 m altitude about 4.0–3.9 ka cal BP and by 2.7–2.3 ka cal BP the sea-level reached 4.5 m. After that RSL dropped to its modern position. During the last 4.0 ka cal BP the rate of RSL fall was approximately 0.17–0.18 cm/year. [ABSTRACT FROM AUTHOR]

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, C org /N org 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. [ABSTRACT FROM AUTHOR]

This paper discusses the results of siliceous microfossils studies performed in a "staircase" of four isolation basins (33.7 m–2.9 m a.s.l.) on Big Solovetskiy Island (Solovki Archipelago, the White Sea). Diatoms were used as a primary group for paleoinferences, while chrysophyte cysts and sponge spicules also demonstrated high indicative potential. In all study lakes, the siliceous microfossils stratigraphy revealed three main stages of their evolution, i.e. large-basin, transitional and small-lake stages, each characterized by certain composition of the diatom assemblages and floristic diversity, relative abundances of chrysophyte cysts and sponge spicules, and siliceous microfossils concentrations. In the uppermost lake, glaciolacustrine environments unfavorable for aquatic biota existed during the large-basin stage. The proglacial lake stage terminated prior to ca. 10.4 cal ka BP, followed by a (semi)terrestrial episode before the transition to small-lake environments. In the other three lakes, marine environments were inferred at the earlier stage, characterized by the predominance of marine and brackish-marine diatoms, increased proportions of sponge spicules and low "cysts to diatoms" ratio. At the transitional marine-freshwater stage, mass growth of small fragilarioid diatoms and decreased abundances of spicules indicated unstable environments, while increased proportions of cysts pointed to progressive freshening of the basins. The duration of the marine-freshwater transition expectedly prolonged from ca. 200 yr in the upper basin (16.6 m a.s.l) to ca. 500 yr in the lowermost lake (2.9 m a.s.l.). The isolation from the sea took place between ca. 6.3 and 1.4 cal ka BP. At the small-lake stage, siliceous microfossils stratigraphies reflected local specifics of the basins and their catchments. We argue that besides traditionally used diatom data, relative and absolute abundances of siliceous microfossils also possess high indicative value for isolation basin studies. Our study demonstrated that marine waters on Big Solovetskiy Island never reached ca. 34 m a.s.l. during the Holocene, unlike the western coast of the Onega Bay where the Preboreal marine intrusion was recorded even at higher elevated localities. Different rates and amplitudes of shoreline displacement are thus suggested for the inner and outer parts of the Onega Bay. During the mid-Holocene Tapes transgression, before ca. 6.3 cal ka BP, the relative sea level on Big Solovetskiy Island exceeded 17 m a.s.l. The average estimated rates of the shoreline retreat during the second half of the Holocene gradually decreased from 0.28 cm year−1 to 0.2 cm year−1, indicating slowed isostatic uplift. [ABSTRACT FROM AUTHOR]

The Zoogonidae is the only digenean family where known cercariae lack the tail but actively search for the second intermediate host. However, the data on the zoogonid life cycles are scarce. In the present study, we elucidated and verified life cycles of the Zoogonidae from the White Sea. Using rDNA data, we showed that Pseudozoogonoides subaequiporus utilizes gastropods from the family Buccinidae as the first intermediate host and protobranch bivalves as the second one. This life cycle can be facultatively truncated: some cercariae of P. subaequiporus encyst within the daughter sporocysts. Molecular data also confirmed previous hypotheses on Zoogonoides viviapus life cycle with buccinid gastropods acting as the first intermediate hosts, and annelids and bivalves as the second intermediate hosts. We demonstrated the presence of short tail primordium in the developing cercariae of both species. Based on the reviewed and our own data, we hypothesize that the emergence of tailless cercariae in the evolution of the Zoogonidae is linked to the switch to non-arthropod second intermediate hosts, and that it possibly happened only in the subfamily Zoogoninae. Basally branching zoogonids have retained the ancestral second intermediate host and might have also retained the tail. [ABSTRACT FROM AUTHOR]