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We investigated the diversity of benthic algal communities as well as phytoplankton in Lake Baikal. The structure of benthic algal communities changed in comparison to the period before 2000 due to intense development of filamentous algae, particularly Spirogyra. Percent cover of filamentous algae in different areas of the coastal zone varied from 0 to 100%. The lowest Spirogyra biomass was recorded in the surf and wave-breaking zones, whereas the highest biomass was observed in the area of the bottom less affected by waves. Fragments of Spirogyra thallomes were also recorded in the phytoplankton community of Lake Baikal's southern basin which is a new phenomena not previously recorded in the lake. Hydraulic characteristics of Spirogyra were similar to those of planktonic diatoms. Currents and wave effects on the bottom favored transfer and distribution of Spirogyra from locations with intense development to the coastal area of Lake Baikal. Spirogyra is now found throughout Lake Baikal.

Molecular phylogeny inferred from rbcL nucleotide sequences obtained from the single sterile filaments of green algae collected around the perimeter of Lake Baikal indicates the polyphyletic origin of the representatives of genus Spirogyra Link., 1820 inhabiting the lake. The common ancestor of all Baikal Spirogyra dates back at least to 20 MYA. This roughly coincides with the age of continuously existing freshwater body in the confines of current Baikal. The descendants of this node include both Baikal and non-Baikal species and thus suggesting a complex history of multiple emigrations and immigrations. There is at least one major lineage of the Baikal Spirogyra in the phylogeny descending uninterruptedly from the common ancestor of all Spirogyra species found so far in the lake. The likely explanation is its permanent presence in the ecosystem. All this allows us to hypothesize that the current bloom is a spectacular but natural response of the Baikal ecosystem to the increased pollution.

The diversity of algal communities of phytoplankton and meio-and macrophytes was investigated in Lake Baikal. Fragments ofSpirogyrathallomes were recorded in the phytoplankton community of Southern Baikal, which had never been recorded before in its composition. It was also established that the structure of benthic algal communities changed in comparison with that in 2000 due to intense development of filamentous algae, particularlySpirogyra. Its lowest biomass was recorded in the surf zone and wave breaking, whereas the highest biomass was registered in the area of weakened effect of waves on the bottom. The cover percent of the bottom with filamentous algae in different areas of the coastal zone varied from 0 to 100%. Hydraulic characteristics ofSpirogyrawere the same as those of planktonic diatoms. The circulation currents and wave effect on the bottom favoured transfer and distribution ofSpirogyrafrom the location of its intense development into the coastal area of Lake Baikal.

A local eutrophication process is noted for the first time in Listvennichnyi Bay in Lake Baikal. Using morphological and molecular-genetic methods, species of filamentous green algae that form mats at site of the lake subjected to anthropogenic impact are identified. The presence of species of the genus Spirogyra Link., atypical for this part of the lake, as well as their distribution, together with species Ulothrix zonata (Web. et Mohr) Kurz. in an atypically large depth, indicates the serious disturbance of the structure of plant community of the studied site of Baikal.

For the first time, species of the genus Spirogyra , non-typical of the open nearshore waters of Lake Baikal, formed algal mats with Ulothrix zonata , Ulothrix tenerrima , and Ulothrix tenuissima near the village of Listvyanka, Russia. Normally widely distributed in the 0- to 1.5-m depth range, the growth of U. zonata was now evident and dominant (63% of the biomass) in the 2- to 5-m depth range. The overgrowth of the lake bottom by filamentous green algae, changes in distributional boundaries, the emergence and mass development of species of the genus Spirogyra , the presence of the eutrophic diatom indicator Fragilaria capucina var. vaucheriae , elevated abundances of coliform bacteria, and elevated levels of nutrients suggest an early stage of cultural eutrophication in the nearshore of Lake Baikal near Listvyanka, a popular tourist destination. The unusual abundance of Fragilaria associated with the filamentous green algae consisted of long-ribbon colonies of F. capucina var. vaucheriae , a eutrophic species, wound around the filamentous green algae, enhancing the dense algae mats. Historically dominant species, such as Didymosphenia geminata , Tetraspora cylindrica var. bullosa , and Draparnaldioides baicalensis typically observed at deeper depths of Lake Baikal, are now subdominants or minor species in the nearshore along the shoreline near Listvyanka.

Background. A local eutrophication process is noted for the first time in Listvennichnyi bay in Lake Baikal. High level of biogenic elements in the water of the bay led to nuisance growth of filamentous algae. Rapid identification of these algae's taxa was necessary to assess ecosystem damage in the polluted area of the lake. Materials and methods. We determined a boundary of bottom fouling by locating transects ranging from 0 to 10 meters in different areas of the bay. Algae samples were examined using microscopic techniques as well as SSU 18S rDNA sequencing. Phylogenetic trees were estimated using Bayesian inference (BI) based on SSU alignment. Results. Our results showed intensive filamentous algae fouling in depth from 3 to 10 meters along the coastline of the eastern part of the bay. Morphological and molecular analysis demonstrated prevalence in samples of Ulothrix zonata (Web. et Mohr) Kütz. Using SSU 18S rDNA sequencing data we also showed presence of three species of Spirogyra Link. genus. Conclusion. Detection of Spirogyra species which are normally not typical for such areas of the lake along with Ulothrix zonata extended more deeply than usually observed reveals severe phytocenosis disturbance of the polluted part of Lake Baikal.

In shallow water areas of open Lake Baikal, filamentous green alga of the genus Spirogyra grows abundantly. Together with alga of the genus Ulothrix, it forms algal mats. According to our observations from 2010 to 2013, the spawning habitat conditions for the yellowfin sculpin Cottocomephorus grewingkii (Dybowski, 1874) (Cottidae) proved to be significantly disturbed in the littoral zone of Listvennichnyi Bay (southern Baikal), which, in turn, reduced the number of egg layings. With a 100% projective cover of the floor and a high density of green filamentous algae, the shallow-water stony substrate becomes completely inaccessible for spawning of the August population.