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We present the results of a study on the number of indicator bacterial groups of the nitrogen cycle in plankton and epilithon of the littoral zone of Lake Baikal in the spring and autumn of 2017–2019. The number of ammonifying bacteria (AB) varied from 25 to 6.0 × 105 cells/mL in lake waters and from 3.5 × 103 to 9.5 × 106 cells/cm2 in epilithic biofilms. Stations exposed to anthropogenic impact showed a high number of AB as evidence of the active mineralization of nitrogen-containing organic compounds. The maximum number of AB in the water column and the biofilms from stony substrates was detected in June 2017 in the water area of the town of Severobaikalsk. The average number of AB in the water column over the 3-year period was 5.0 ± 2.8 × 102 cells/mL in June and 6.0 ± 1.3 × 102 cells/mL in September. In epilithic biofilms, it was an order of magnitude lower in June than in September: 3.4 ± 1.2 × 104 cells/cm2 and 2.6 ± 1.4 × 105 cells/cm2, respectively. The number of denitrifying bacteria (DB) in water and epilithic biofilms varied from 0 to 60 cells/mL and 6 to 2.5 × 103 cells/cm2, respectively. Throughout the research period, the highest number of DB in the epilithon was detected in June at the station near Cape Elokhin. The average number of DB over the 3-year period was 13 ± 4 cells/mL in June and 7 ± 6 cells/mL in September in the water column, 7.9 ± 2.4 × 102 cells/cm2 in June and 4.8 ± 0.5 × 102cells/cm2 in September in epilithic biofilms. The number of planktonic AB positively correlates with the concentration of ammonium ions; the number of DB directly depends on the nitrate concentration and inversely depends on nitrites at some stations.

Mass development of the cyanobacteria Dolichospermum (D. lemmermannii as the dominant species) was reported in the coastal zone of Bol shye Koty Bay (western coast of the southern basin), towards the end of July to the beginning of August in 2019. Blooms were observed as 1 1.5-m wide bands adjoining the shoreline and stretched uninterrupted over 2 km. Abundance of cyanobacteria in blooms varied within 7.2 71.9 thousand cell mL-1, with 0.73 7.20 g m-3 biomass attained. Maximal concentration was observed opposite the biological station of Irkutsk State University, a frequently visited place that was hosting participants of several conferences at that time. Hydrochemical analysis of samples collected four days after continuous heavy rains showed much higher concentrations of nutrients in contrast with the data obtained a week before (24 July), which is normal for that season. Nutrient concentrations were elevated relative to long term averages by 3 to 30 fold: with phosphate concentrations up to 0.200 mg L-1, ammonium ions 0.29 mg L-1, and nitrates 0.31 mg L-1. Possible reasons for the harmful freshwater cyanobacterial bloom that is unusual for this part of the lake are discussed. Excessive proliferation of common cyanobacteria D. lemmermannii in the open lake areas was affected by several factors: long-lasting heavy rains, zero wind, high air (from 13 15 at night to 29 in daytime) and water temperatures (from 15 to 19.2 ); and absence of isolated septic tanks in the nearshore zone.

This study investigates in detail species diversity of cyanobacteria which proliferated on the surface of diseased sponges and bedrock in Lake Baikal (Siberia, Russia) during the ecological crisis that has been progressing in the littoral zone since 2011 and caused numerous negative changes in biota. In 2014–2015, we examined samples from diseased and healthy sponges as well as rock substrates using Sanger sequencing and high-throughput 16S rRNA gene analysis. Based on morphology, we identified 15 cyanobacterial species in biofoulings. Tychonema sp., Symplocastrum sp., Pseudanabaena galeata and Tolypothrix distorta dominated on diseased sponges. In communities of healthy sponges, we detected mainly picocyanobacteria Synechococcus. Fascicles of Symplocastrum sp. and T. distorta dominated on bedrock substrates. Phylogenetically, most 16S rDNAs clustered among Tychonema, Pseudanabaena, Geitlerinema, Kamptonema, Leptolyngbya, and Tolypothrix spp. Cyanobacterial proliferation in the littoral zone of Lake Baikal should be considered as one of the most important negative ecological processes in recent times which requires an urgent study in order to understand the causes of its emergence and development. Mat-forming cyanobacteria Tychonema characterized by the highest tropism to sponges plays a special role in the disease and death of sponges.

Age-related changes in telomere length (TL) in somatic tissues are not limited only to shortening. It is known that many organisms show different TL dynamics. Such species specificity indicates the complexity of the mechanisms involved in the regulation of TL. Owing to their morphological, physiological, and ecological features, Baikal planarians are an interesting model for studying the TL dynamics and the factors influencing it in comparison with species living outside Baikal. In this work, we investigated telomerase activity and age-related changes in TL in three endemic species of planarians from the Dendrocoelidae family. Two species are giant deep-water species (7-12 cm long, Sorocelis hepatizon and Rimacephalus arecepta), and one is a coastal shallow species (1 cm long, Baikalobia guttata). In addition, we investigated the telomere biology in another small Siberian species from the Planariidae family (2 cm in length, Phagocata sibirica), which is not found in Baikal. TL and telomerase activity were determined using real-time PCR and the TRAP method. Three types of age-related TL dynamics were detected with active telomerase: (1) TL shortening at the juvenile stage of development and subsequent maintenance (R. arecepta, Ph. sibirica), (2) gradual TL shortening during ontogeny (S. hepatizon) and (3) cyclic dynamics of TL (B. guttata). Thus, the changes of TL in the studied planarians does not have an obvious connection with body size, habitat depth, phylogenetic relationship and is probably a consequence of species features in the regulation of telomerase activity.

A sanitary–bacteriological and hydrochemical survey of rivers flowing into Lake Baikal near Listvyanka Settl. was carried out in period from 2014 to 2015. Water quality at the mouths of the rivers of Bol’shaya Cheremshanka, Malaya Cheremshanka, and Kamenushka was found not to meet the standards of the normative and technical documentation introduced in Russia and abroad (in the United States and Europe) in terms of thermotolerant coliform bacteria, thermotolerant E. coli, and enterococci. In terms of hydrochemical characteristics, such as phosphates, water quality at the mouths of the Bol’shaya Cheremshanka, Malaya Cheremshanka, and Kamenushka rivers also failed to meet Russian standards. The coastal water of Lake Baikal at the mouth of the Bol’shaya Cheremshanka in July (at the peak of tourist season) 2015 showed the abundance of the group of thermotolerant coliform bacteria (TCB) more than 10 times in excess of the standard. Therefore, the study suggests the conclusion that the quality of water sampled at river mouths is much poorer than that in river reaches upstream of the settlement. Moreover, in July, when the recreational load increases appreciably, the abundance of the analyzed bacteria in water in river reaches within the settlement and in water samples taken upstream of it (background points) is found to differ radically. Hydrochemical and sanitary–bacteriological analysis of the coastal water of Lake Baikal was carried out at the mouths of the rivers flowing into it and revealed an effect of river water on the quality of coastal Baikal water.

Our investigation was conducted during a period of ecological crisis in the coastal zone of Lake Baikal. Mass disease and mortality of the endemic sponges inhabiting the nearshore zone of the lake is one of the characteristics of this crisis. We identified and quantified infaunal organisms associated with Lubomirskia baikalensis (Pallas, 1776), which is experiencing mass morbidity and mortality. L. baikalensis specimens were subdivided into three groups depending on the degree of body damage they presented: “healthy”, diseased, or dead. We found that infauna was almost absent from “healthy” sponges. Infaunal abundance in diseased sponges was 1820 times greater than that in “healthy” sponges, and varied in relation to the type of damage suffered by the sponges. Unaffected fragments of diseased sponges were inhabited by communities that exhibited an average abundance of 13 ind/dm2, with Oligochaeta, Nematoda, Harpacticoida, and Chironomidae predominating. In the bleached fragments of morbid sponges, the average abundance of infauna was 1303 ind/dm2, with Harpacticoida, Tardigrada, Cyclopoida, and Oligochaeta dominating. The highest concentration of infaunal animals (18,293 ind/dm2) was observed in spots that were covered by filamentous cyanobacteria. Diverse and densely populated infaunal communities (4767 ind/dm2) occurred in the dead sponges, with Nematoda, Tardigrada, Turbellaria, and Oligochaeta particularly abundant.

Using the metagenomics approach and high throughput sequencing of the 16S rRNA gene amplicons, we studied the taxonomic diversity of nitrifying bacteria in microbial communities from epilithic biofilms and plankton of the littoral zone of Lake Baikal. The family Nitrosomonadaceae represents the diversity of ammonia-oxidizing bacteria; the genera (Nitrospirae) and Candidatus Nitrotoga (Gammaproteobacteria) nitrite-oxidizing bacteria; and the phyla Nitrospinae unidentified bacteria. Microbial communities from epilithic biofilms and the near-bottom water layer showed the highest diversity and those from the surface water layer the lowest one. Among ammonia oxidizers, bacteria of the uncultured genus Ellin6067 (27 phylotypes) dominated and were ubiquitous, and among nitrite oxidizers bacteria of the genus Nitrospira (7 phylotypes).

An illustrated description of Boreusyrtis maksimovae gen. et sp. n., a representative of a new genus of Otoplanidae turbellarians (Proseriata) from Lake Baikal, is given. This flatworm shows a peculiar pattern of the ciliated epithelium of the rostral body end, a special morphology of the pharynx and copulative apparatus, and a distinguished topography of the sexual organs. A comparative morphological analysis of the Baikal otoplanid and related forms has allowed us to carry out their partial taxonomic revision, resulting in the isolation of a new genus Boreusyrtis Lukhnev et Timoshkin gen. n., to which, in addition to the endemic species, the morphologically similar species Pseudosyrtis neiswestnovae Riemann 1965 from the Elbe River was attributed. A molecular genetic analysis was carried out for the 18S rRNA gene, based on which a phylogenetic tree was constructed.

ICP-MS method was used to study the element composition of green algae Ulothrix zonata (F. Weber et Mohr) Kutzing, sampled in the coastal zone of the Southern Baikal. Dominating in Ulothrix composition are S, Ca, P, Mg and microelements Fe, Al, Ti, Mn, Sr, Ba, Cu, Zn, La, Ce, As, Br, and Pb. The concentrations of all analyzed elements in alga thallomes is greater than the respective concentrations in coastal zone water. The dry mass of U. zonata accumulates more P, As, S, I, Br, Ni, Cd, Ca, and Mg than the stone substrate does. The effect of U. zonata on the formation of element composition of water medium in the coastal zone is demonstrated.

Lake Baikal, the oldest lake in the world, is home to spectacular biodiversity and extraordinary levels of endemism. While many of the animal species flocks from Lake Baikal are famous examples of evolutionary radiations, the lake also includes a wide diversity of endemic algae that are not well investigated with regards to molecular-biological taxonomy and phylogeny. The endemic taxa of the green algal order Cladophorales show a range of divergent morphologies that led to their classification in four genera in two families. We sequenced partial large- and small-subunit rDNA as well as the internal transcribed spacer region of 14 of the 16 described endemic taxa to clarify their phylogenetic relationships. One endemic morphospecies, Cladophora kusnetzowii, was shown to be conspecific with the widespread Aegagropila linnaei. All other endemic morphospecies formed a monophyletic group nested within the genus Rhizoclonium (Cladophoraceae), a very surprising result, in stark contrast to their morphological affinities. The Baikal clade represents a species flock of closely related taxa with very low genetic differentiation. Some of the morphospecies were congruent with lineages recovered in the phylogenies, but due to the low phylogenetic signal in the rDNA sequences the relationships within the Baikal clade were not all well resolved. The Baikal clade appears to represent a recent radiation, based on the low molecular divergence within the group, and it is hypothesized that the large morphological variation results from diversification in sympatry from a common ancestor in Lake Baikal.

Lake Baikal, one of the world’s largest and most biologically diverse lakes, has recently begun to experience uncharacteristic nuisance blooms of filamentous benthic algae. To contribute to...

Lake Baikal, an ancient lake in Siberia, contains more endemic species than any other lake in the world with most of them residing in the benthic littoral zone. Explosive growth of benthic Spirogyra, a filamentous green alga, began approximately in 2011 in localized coastal areas, with the most severe examples occurring near coastal towns that lack a wastewater treatment facility or have a malfunctioning system. At other sites (small settlements, harbors), however, the cause of its excess growth is less obvious. Multiple hypotheses have been offered including lake level fluctuations, climate warming, a relaxation of grazing pressure, and coastal eutrophication. We assessed these hypotheses using data on historical lake levels, water temperature, the spatial-temporal distribution of Spirogyra along inhabited and non-inhabited shorelines, and measurements of fecal coliform bacteria and nutrients in ground water, interstitial water, and lake water. These data suggest that groundwater contamination is the primary cause of coastal eutrophication. Most houses and buildings in small settlements around Lake Baikal lack septic tanks but use unlined cesspools to collect human waste. This untreated human waste enters groundwater via passive filtration through permeable soils and flows to the coastal zone where it drives excess growth of Spirogyra. Remediation — including installation of septic systems, modernization of existing sewage treatment plants in coastal towns, and the adoption of non-phosphate containing detergents — as well as a reconsideration of the federal monitoring system regarding the coastal zone is urgently needed to protect this extraordinary lake.

The first data on feeding spectrum of Baikal enchytraeids are given. Previously we found that Mesenchytraeus bungei Michaelsen, 1901 dominates in abundance in splash zone Oligochaeta community of Bolshie Koty Bay, Lake Baikal. Feeding spectrum of M. bungei was investigated in summer (partially also in spring and autumn) of 2010–2012 and 2015. Our study is based on pellet content analyses of more than 200 M. bungei specimens. Diverse components in different ratio were found during the investigation period, namely green algae, diatoms, higher plants debris, various animal remains, some minor components and sediment particles. All the pellet content was subdivided into phytogenous and animal material, unidentified matter and sediment particles. Phytogenous material appeared to be a dominant component of pellets (up to 87%) in almost all cases. Our analysis showed that M. bungei is a saprophage with a preference to phytogenous detritus.

Some species of cyanobacteria synthesize toxins whose concentration during water bloom can reach values dangerous for human and animal health. Planktonic cyanobacteria are the most common and well-studied microcystins producers, hepatotoxic cyclic heptapeptides, whereas microcystin-producing benthic cyanobacteria are less known. In recent years, the mass development of benthic cyanobacteria forming extensive fouling on different substrates has been detected in the littoral zone of Lake Baikal. We found microcystins produced by benthic cyanobacteria in the biofouling on different natural and artificial substrates, including diseased and dead endemic sponges Lubomirskia baicalensis and Baikalospongia spp. collected from the littoral area of Lake Baikal. Microscopic analysis of the biofouling revealed prevalence of representatives of Nostocales and Oscillatoriales with predominance of Tolypothrix distorta that is likely the main microcystin producer in Lake Baikal. According to enzyme-linked immunosorbent assay (ELISA), microcystin concentrations in biofouling were 29.8–3050 μg/kg dry weight. We identified eight microcystin variants using MALDI-TOF/TOF; [Dha7]MC-YR was detected in most samples. The presence of microcystins in biofilms formed on the surface of the artificial substrate by Phormidium autumnale was also recorded. The data obtained demonstrated the necessity to monitor potentially toxic species and concentrations of cyanotoxins in plankton and benthos in the littoral zone of Lake Baikal, especially in the regions with intense tourist and recreational activities.

Mass-spectrometry with inductively coupled plasma was used to determine the element composition of 19 amphipod species, most of which are widespread in the stony littoral of Lake Baikal. Amphipod composition was found to be dominated by Ca > P ≥ S > K ≥ Na > Cl > Mg > Sr ≥ Br ≥ Si. The concentrations of all elements determined in amphipods is greater than the respective concentrations in water. The amphipods were found to concentrate P > Br > Cu > Zn > Cd to the greatest extent relative to the element composition of water and Br > P ≥ I > Ca > S > Cl ≥ As > Sr relative to that of the stone substrate. The concentrations of Cr, Mn, Fe, Co, Cu, Zn, As, Mo, Cd, Pb, and Hg in 2003–2006 in the amphipods of the stony littoral of Baikal was not greater than their concentrations in the amphipods from conventionally non-polluted or weakly polluted aquatic ecosystems. The obtained results can be used as background values in environmental monitoring.

The species diversity of free-living nematodes has been studied in the fresh waterbodies and watercourses of the Lena River basin, northern Irkutsk oblast: in the Chuya, Mama, Yuhtinka, and Vitim rivers; in Lake Teterinskoe and Lake Krasnoyarskoe; and in an unnamed lake near the settlement of Mama. Twenty-eight species belonging to 16 families and 9 orders are registered, and 6 species of these 28 are identified at the genus level only. Twenty-two species have been identified with certainty; 11 of them are eurybiont, 2 species are characterized by Holarctic distribution, 5 species are found in Eurasia, 1 species is found in Eastern Siberia, and 3 species are found at one site each. The species composition of the studied waterbodies and watercourses is usual and is presented mostly by the widespread nematode species. The most interesting findings include Tripyla dybowskii Tsalolikhin, 1976, which was previously considered a subendemic species of Lake Baikal. Three species are common to the fauna of Lake Baikal (two of them inhabit the splash zone). An illustrated description of the female of the rare species Aporcelaimellus samarcandicus (Tulaganov, 1949) is given.

This paper gives an illustrated description of a new genus and species of endemic Baikal planarians, Microarchicotylus ochroleucus gen. et sp. n. The morphological similarity in the structure of the pharynx, male copulative organs, and external features allowed the authors to include two more species, M. stringulatus (Korotneff 1912) and M. elegans (Porfiriev et Timoshkin 2009), formerly belonging to a poorly investigated genus Archicotylus, into the new genus. Microarchicotylus gen. et sp. n. planarians are attributed to dwarf forms, since their maximal body length does not exceed 5–6 mm. One more distinctive external feature of these Microarchicotylus species is a bright and uneven coloration of the dorsal part of the body, sometimes being dark brown, light brown, or ochreous with distinct white transverse strokes or without them. The anterior part of the body is bright orange or blackish, its color always being different from the remaining body, separated by a white transverse collar behind the pair of eyes. The pharynx is either short cylindrical barrelshaped (length-to-width ratio of ~1) or elongated cylindrical (ratio, 3: 1). The copulative organ is compact and resides behind the pharynx, with its apical part directed downwards. The seminal receptacle, its canal, and the male and common atriums are asymmetrically located relative to the medial longitudinal body axis and centrally located gonopore.

Cyanobacteria were screened from the surface of diseased sponges, stone and bedrock in Lake Baikal for the presence of saxitoxin using enzyme-linked immunosorbent assay. In sequel, eight paralytic shellfish toxin (PST) variants were identified using a MALDI mass spectrometry. Microscopic examination found that Tolypothrix distorta dominated in the biofouling samples. PCR and sequencing detected sxtA gene involved in saxitoxin biosynthesis, thereby providing evidence of the PST producing potential of Baikal cyanobacterial communities inhabiting different substrates.

Ecological degradation of the benthic littoral zone is an emerging, urgent problem at Lake Baikal (East Siberia), the most species-rich lake on Earth. Within the last 5 years, multiple changes have occurred in the nearshore benthos where most of the lake's endemic species reside. These changes include proliferation of benthic algae, death of snails and endemic sponges, large coastal wash-ups of dead benthic algae and macrophytes, blooms of toxin-producing benthic cyanobacteria, and inputs of industrial contaminants into parts of the lake. Some changes, such as massive coastal accumulations of benthic algae, are currently shared with the Laurentian Great Lakes (LGLs); however, the drivers of these changes differ between Lake Baikal and the LGLs. Coastal eutrophication from inputs of untreated sewage is causing problems at multiple sites in Lake Baikal, whereas in the LGLs, invasive dreissenid mussels redirect pelagic nutrients to the littoral substrate. At other locations in Lake Baikal, ecological degradation may have different causes including water level fluctuations and the input of toxic industrial contaminants. Importantly, the recent deterioration of the benthic littoral zone in both Lake Baikal and the LGLs has occurred while little change has occurred offshore. This highlights the necessity of monitoring both the littoral and pelagic zones of large lakes for assessing ecosystem health, change and conservation.

Actinobacteria is a ubiquitous major group in freshwater bacterioplankton and sponge microbial communities. We were first to analyse the diversity of Actinobacteria inhabiting Lake Baikal water and endemic sponges Lubomirskia baikalensis (healthy and diseased) using highthroughput 16S rRNA sequencing. In total, we have assigned of three classes, fourteen orders and twenty-six families of Actinobacteria. The diversity and composition of actinobacteria were common in bacterioplankton and healthy sponges. The environmental crisis in the coastal zone of Lake Baikal led to a colonization of the L. baikalensis by benthic and soil-derived representatives of Actinobacteria. Some amplicon sequences of opportunistic genera were detected in the coastal water. The example of Actinobacteria has dramatically demonstrated the response of bacterial populations caused by negative environmental impact.

Telomeres are the end regions of eukaryotic chromosomes. In addition to maintaining the integrity of the genome, they are involved in aging, regeneration, stress, and disease. We study the telomere biology in Baikal and Siberian planarians, mollusks, and fish. Using these hydrobionts as an example, we study how changes in body size, life expectancy, reproductive strategy, and habitat have reflected in telomeres during evolution, how telomere length changes during ontogeny, and whether stress factors affect its dynamics. We observe both the common features in the telomere biology of such different hydrobionts and their species-specific features. The obtained data indicatea possible influence of physiological and environmental features on the functioning of telomeres.

A histological analysis of the tissue structure in different species of Baikal sponges was performed. The material was collected at a depth of 3–4 m at the Berezovyi test site (southern Lake Baikal) in various seasons of 2001–2003. During the entire year, representatives of the family Lubomirskiidae had a well-developed irrigation system with numerous choanocyte chambers. In Trochospongilla sp. (Spongillidae) from open Baikal, such a tissue pattern was observed only during the summer time. Annually, these sponges undergo tissue regression, i.e., a reduction of the irrigation system accompanied by changes in the cell composition in autumn with subsequent recovery in spring. The onset and termination of tissue regression are adapted to the environment of Lake Baikal.

This paper is the third in a series of publications devoted to the fauna of Otomesostomidae in Lake Baikal. Illustrated descriptions and diagnoses of three species and two genera endemic to Lake Baikal were given in the previous articles. The close morphological resemblance of endemic Baikal otomesostomids to Otomesostoma auditivum Forel et Du Plessis 1874 widely spread in Europe and North America is evident. Therefore, this species was considered as closely related to a hypothetical ancestor of endemics (Timoshkin et al., 2010; Lukhnev et al., 2011). Recently, O. auditivum was found in the open littoral of Baikal. An illustrated description of this rare species is given. A record of Holarctic O. auditivum coexisting with endemic species in the littoral of the open lake is of particular interest not only from a zoogeographical viewpoint (the first record to the south of the Urals) and the origin of the fauna of endemic Otomesostomidae but also with respect to the so-called immiscibility of Baikalian and Palearctic faunas.

The green filamentous alga Ulothrix zonata inhabits Lake Baikal and overgrows the underside of hummocky ice during winter and spring. To clarify physiological adaptations of U. zonata to low temperature and the potential contribution of membrane water permeabilities, the expression level of aquaporins from a winter population growing under the lake ice and in interstitial water was compared with that of benthic summer and autumn populations of algae by immuno-detection using an anti-maize PIP1 (plasma membrane intrinsic protein) antiserum. Algal, and in particular Ulvophycean, transcriptome sequences are only partially available and this higher plant-specific PIP1 epitope has not been detected so far in available genomic datasets. PIP1 expression levels were highest in the ice population and the rise in water temperature during summer was correlated with a drop in PIP1 amounts, which slightly increased again in autumn. ITS2 rDNA (internally transcribed spacer region 2) sequences revealed conspecificity of...

The first finding of freshwater nemerteans from the genus Prostoma (Duges 1828) from the relic Ohrid Lake is described in the article. Genetic analysis of the gene fragment CO1 was performed, according to which Prostoma of Ohrid Lake should be considered as conspecific with the widespread species P. graecense (Bohmig 1892). It has been assumed that P. graecense and P. eilhardi (Montgomery 1894) belong to the same species, which should be called Prostoma clepsinoides Duges 1828 (the type species of the genus Prostoma). Data from the molecular and phylogenetic analysis prove that the family Prostomatidae is independent.

The majority of naturally occurring biofilms contain numerous microorganisms that have not yet been cultured. Additionally, there is little information available regarding the genetic structure and species diversity of these communities. Therefore, we characterised the species diversity, structure and metagenome of biofilms grown on stones and steel plates in the littoral zone of Lake Baikal (East Siberia, Russia) by applying three different approaches. First, light microscopy enabled identification of the species diversity of biofilm-forming cyanobacteria on different substrates with the dominance of Rivularia rufescens, Tolypothrix limbata, Chamaesiphon fuscus, Ch. subglobosus, and Heteroleibleinia pusilla. Additionally, scanning electron microscopy was used to show the spatial structure of biofilms. Finally, sequence analysis of 30,660 16S rRNA clones indicated a high diversity within the biofilm communities, with the majority of the microbes being closely related to Cyanobacteria (8-46% sequences), Proteobacteria (14-43%), and Bacteroidetes (10-41%). Rivularia sp., Pseudanabaena sp., and Chamaesiphon spp. were the dominant cyanobacterial phylotypes.

This article presents an analysis of the microbial community growing on a stainless steel plate. A sample from this plate has been tested for the rpoC gene. Dominant biofilm species (clones) were identified with the help of molecular cloning and nucleotide sequencing of a 16S rRNA gene fragment. The activities of planktonic microorganisms and biofilm microorganisms attached to the plate were compared. Seven of nineteen sequences (37%) were found to belong to the Sphingobacteria group. Analysis of 16S rRNA gene sequences cloned from natural biofilms sampled from Lake Baikal showed a great variety of microorganisms in the biofilm. The following taxonomic groups were revealed among them: sphingobacteria, α-proteobacteria, cyanobacteria, verrucomicrobia, bacilli, γ-proteobacteria, flavobacteria, and β-proteobacteria. This kind of analysis was done in Lake Baikal for the first time.

Dynamics of the telomeric DNA (tDNA) length and the phylogeny of Baikal and Siberian planar� ians have been studied based on analysis of 18S rDNA and β�actin gene fragments. It was shown that there is a relationship between tDNA length and planarian size. Giant planarians, with a minor exception, have longer tDNA than do smaller planarians. Phylogenetic affinity between species that have stretched tracks of tDNA, large sizes, and similar habitats denotes the possible role of tDNA in the development of the high regenerative capacity of planarians.

ICPMS analyses of encrusting sponges indicate that their predominant chemical elements are, along with Si, by P, Al, Fe, Ca, S, Mg, K, Na, Cu, Mn, Zn, Ti, Ba, and Br. The sponges are most signifi� cantly enriched in Al > Cu > Ti > REE > Mn > P relative to their aqueous habitat and in Cu > I > Cd > P > Br > As ≥ S relative to the relatively rudaceous bottom sediments. One of the sources of elements occurring the aqueous habitat and being of vital importance for the activity of the sponges was proved to be the rock substrates.

Based on materials collected in 2003–2007, data on aquatic lichens of the genus Verrucaria from the rocky littoral zone of Lake Baikal are discussed. The maximum density of their occurrence was observed at a depth of 1.5 m; 95–100% of rock fragments recovered from depths of 1.5–2.2 m are encrusted by 24–43% with the thalli of Verrucaria spp. It was found that the lichens contribute actively to the physical and physicochemical weathering of their rock substrate and prefer to reside on the rocks of granitic composition. The chemical composition of aquatic verrucaria is dominated by the same elements that are most abundant in the rocks (Ca > K > Fe > Al > Mg > P > S > Na > Mn > Sr > Ba), and, in most cases, the characteristic element ratios of the rock compositions are preserved in the composition of the thalli of Verrucaria spp. Compared with the elemental composition of the near-bottom water layer, the lichens most extensively concentrate the elements that slowly migrate in water: Gd > Sm > Pr > Nd > Al > La > Dy > Tb > Y > Lu > Ce > Yb > Be > Tm > Co > Nb > Mn > Zn. Compared with the composition of rocks, the mineral composition of the thalli of Verrucaria spp. is enriched by a factor of 100–10 in Hg > As > P > Zn > Li > S > U > Mo > Se > Cd > Ca > Tl > Sr > Pb > Be.

Illustrated descriptions of the representatives of the new genus Baikalotomesostoma and two new species of Turbellaria Proseriata from Lake Baikal are given. The pattern of their morphological organization allows considering them as representatives of the Otomesostomidae family. The most important generic character of the new genus is the presence of another (the third one) sexual opening (continuing into the blint, sack-shaped organ — bursa?) located between the male and female sexual openings. According to the morphological structure, the second new species is a true representative of the Otomesostoma genus, but it is a real giant among freshwater Proseriata. This discovery of the new species and the new genus, having such a peculiar morphological structure, should be considered as evidence of the existence of another endemic species flock of free-living flatworms — Turbellaria Proseriata. Evidently, the new taxa of Lake Baikal are closely related to the Holarctic Otomesostoma auditivum Du Plessis 1874.

Baikalian cyclopoids represent one of the richest endemic faunas of freshwater cyclopoid copepods. The genus Diacyclops Kiefer, 1927 is the most numerous by species number in the lake. In this work, molecular-phylogenetic analysis of 14 species and 1 sub-species from Lake Baikal and its water catchment basin is performed. The regions of mitochondrial cytochrom-oxydase I (COI) and of nuclear small-subunit 18S rRNA were used as evolution markers. In the obtained set of COI gene sequences, an effect of synonymous substitution saturation is revealed. Baikalian representatives of the genus Diacyclops form at phylogenetic schemes by two markers a monophyletic group, it suggest their origin from a common ancestral form. Preliminary estimate of this group age is 20–25 My.

The bottom and biota of Lake Baikal (near Gorevoi Utes cape) in the places of natural oil uploading were investigated in summer 2008. This study was carried out at a depth of 900 m by means of the Mir submers� ible (1). Bottom irregularities (bituminous construc� tions), places of gas ("torches") and oil ("droppers") uploading, and structures with the presence of gas hydrates were examined. These objects are densely inhabited by deepwater invertebrates. Microorgan� isms oxidizing hydrocarbons are obviously the basis of the food chains of these ecosystems. A brief survey of the literature on the appearance of oil in Baikal (2, 3) and data from investigation of oil gathered from water surface near Gorevoi Utes cape and bottom sediments lifted to the surface were pub� lished earlier (1, 3). The district was investigated by means of echolocation and with a lateral locator. In examining the data cited below, it is necessary to keep in mind that it was difficult to determine the location of the Mir apparatus. When it touched bottom, Mir stirred up the water with suspension, which compli� cated visibility around it. In an investigation of the bottom in 2007 near Gor� evoi Utes cape, a relief depression from 870 to 920 m deep was revealed. There was an isolated hill with a height of 10 m and diameter of 50 m in the center of the depression. The hill had "torches" on its margins

Water crustose lichens of g. Verrucaria (V. scabra Vězda, V. rheitrophyla Zsch., V. maura Wahlenb. in Ach., and V. hydrela Ach.) and water foliose lichen Collema ramenskii Elenk. were studied in the stony littoral of the western coast of Lake Baikal in 2002–2006. Their densities were highest at depths of 1.5 to 2 m; 95–100% of rock fragments collected from the depths of 1.5–2.2 m were covered by plentiful crustose thalli of Verrucaria spp. Lichens make a large contribute to the destruction of the stony ground in the shallow-water zone. Unlike water, foliose and crustose lichens concentrate Ti, La, Ce, Y, Mn, and Th. Thalli of Collema ramenskii differ from Verrucaria species in their ability to accumulate Zn, Co, and Ni. Compared to the bottom sediments, all the studied water lichen species concentrate Zn, while Collema ramenskiiconcentrate Zn and Mo.

S. Osipova, L. Dudareva, N. Bondarenko, A. Nasarova, N. Sokolova, L. Obolkina, O. Glyzina and Oleg Timoshkin. 2009. Temporal variation in fatty acid composition of Ulothrix zonata (Chlorophyta) from ice and benthic communities of Lake Baikal. Phycologia 48: 130–135. DOI: 10.2216/08-49 Fatty acid (FA) composition of total lipids was compared between populations of the freshwater alga Ulothrix zonata growing in the interstitial water of the ultrapure ice cover of Lake Baikal in early spring (ice population) and on the shallow stony bottom of the lake during the ice-free season (benthic population). FA content was analysed by chromatographic mass spectrometry. Our observations over two years indicated that the FA profiles of both Baikalian ice and benthic populations of U. zonata, as are typical for other green algae, showed a high level of polyunsaturated FAs (50–70% depending on season) related to the adaptation of the alga to low temperature. Rising temperature in the algal habitat entailed a pro...

Data on semiaquatic epilithic and aquatic lichens predominant in the surf and littoral zones of the test site Cape Berezovyi (Southern Baikal) obtained in 2002–2005 are presented. This is the first report on the distribution of rare and unfamiliar aquatic lichen species, Collema ramenskii Elenk. and Verrucaria spp. on the stony littoral of the western Baikal shore. The lichens form dense aggregations at depths from 1–1.5 to 3–3.5 m, where Verrucaria spp. thalli densely cover 60–70% of the rock debris. Only occasional lichens are observed below 7 m. Features of the penetration of aquatic Verrucaria spp. thalli into the rock debris were examined by electron microscopy. The chemical composition of aquatic lichens was analyzed for the first time. It was shown that aquatic lichens are capable of accumulating Ti, Ga, Y, and rare earths poorly soluble in the water of the stony littoral. The original data point to the active role of aquatic lichens in biogeochemical destruction of rocks of the Baikal stony littoral.

Development of benthic communities on rocks from the interdisciplinary test site near Cape Berezovyi (southern Baikal) is analyzed. Rock plates were placed on the bottom in the shallow-water zone of Baikal for six months, and a community consisting of microorganisms, microphytobenthos, and meiobenthos developed on them. The development and activity of hydrobionts depended on the chemical composition and structure of the rock. Marble and granite plates were populated by them more selectively than amphibolite plates. It is supposed that the biota plays an important role in destruction of rocks in the shallow-water zone of Baikal.

The trace element composition of dominant gastropod species from the littoral of southern Baikal was investigated. Both different mollusk species and their parts (shells and soft tissues) show specific trace element characteristics. The highest Sr and Ba contents were observed in Maackia herderiana. The highest Zn, Cu, and Cd and lowest Pb contents were detected in Megalovalvata baicalensis. Choanomphalus sp. shows high Mn and Ti and very low Sr, Cu, and Cd contents. Most of Cu, Zn, and Cd and a considerable fraction of Rb, Pb, Mo, Sc, Ce, W, Ga, Y, and Th are incorporated in the gastropod bodies. The maximum concentration of U is also characteristic of the body tissues. The foot tissues of Maackia herderiana and Megalovalvata baicalensis are depleted in the majority of elements compared with their bodies. Sr and Ba are prevalent in the mollusk shells, where high Mn contents were also detected. A close relationship was observed between the chemical compositions of the gastropods, stony substrate, and bottom water. Group concentration of trace elements is common in the species investigated. Relative to the bottom water layer, the gastropod species concentrate Ti, Mn, La, Co, Y, and V and show similarly low extraction of U, W, Mo, and Cs. Compared with the bottom sediments, the mollusks accumulate Sr. In addition, Maackia herderiana and Megalovalvata baicalensis accumulate Cd and Zn. Megalovalvata baicalensis is distinguished by the ability to concentrate Cu. The following sequence is formed by the gastropods with respect to their capacity to accumulate Cd, Zn, and Cu: Megalovalvata baicalensis > Maackia herderiana > Choanomphalus sp.

Planktonic sculpins (Comephorus baicalensis and Comephorus dybowskii) are endemic to Lake Baikal, and their migration behavior is characterized by their strange movements, which occur only vertically. We investigated their detailed food sources at each growth stage by stable isotope analyses in combination with stomach content analysis. At all growth stages, both fishes and amphipods were the main diet for C. baicalensis, whereas amphipods alone were the main diet for C. dybowskii. Our results indicate that the relationship between the two species shifts from a competitive interaction to a predator–prey interaction with the growth stages of C. baicalensis.

Boreal Lake Baikal, temperate Lake Biwa, and tropical Lakes Malawi and Tanganyika each possess high biodiversities of benthic organisms in their littoral areas. Two general mechanisms influencing the evolutionary development of these high biodiversities can be hypothesized; i.e., a bottom-up constraint depending on the availability of food resources, and a top-down effect exerted by predators especially within the fish assemblage. The bottom-up constraint may be prominent where the abundance of benthic organisms in the grazing-food-chain is restricted by a seasonally lowest production, referring chiefly to attached algae, and large fluctuations in the abundance of primary producers provide a resource that is eventually utilized by benthic organisms of the detritus-food-chain. The top-down effect may be realized where the most of benthic organisms are supported by a constantly large primary production. These hypotheses help to explain, for the lakes we cite, the facts that diverse grazing-food-chain organisms live on the littoral bottom of tropical lakes where there is relatively constant large algal production due to suitable conditions of water temperature and light penetration through the year; while on the other hand, detritus-food-chain organisms are predominant on the littoral bottom of a boreal lake with seasonally fluctuating algal production and its pronounced lowest production in a year. In fish communities, segregations in habitat and food resource are important mechanisms allowing development of high species packing, while cohabitation within predatory fishes increases their feeding success due to the decrease of defensive efficiency by the threat of a variety of attacking methods. A further top-down effect may be exerted by scale-eating fishes, especially in Lake Tanganyika. The presence of such predatory and harmful members may promote more dense packing of prey members to increase their mutual defense efficiency.