Abstract
Here we report new data describing the biodiversity of phytobenthic communities based on DNA-metabarcoding using the 18S rDNA marker and the Illumina MiSeq system. The study was initiated due to the blooming of f ilamentous algae (mainly of the genus Spirogyra) and cyanobacteria in the coastal zone of Lake Baikal under climate change and anthropogenic impact. The composition and taxonomic diversity of algae and other organisms associated with them on different sites of Lake Baikal (near Bolshoi Ushkaniy Island, in Listvennichny Bay) and in the Kaya (within the city of Irkutsk, located in the same drainage basin as Lake Baikal) were determined using DNAmetabarcoding. About 15 thousand reads of the 18S rRNA marker were obtained by applying NGS (next-generation sequencing). The species of algae dominating in the number of reads, as well as the diff icult-to-identify taxa (Stramenopiles, Alveolata, Euglenozoa, Chromista, Rhizaria, Amoebozoa, etc.), which play an important role in the functioning and formation of the structure of algal communities, were revealed. The Shannon index of the communities studied ranges from 1.56 to 2.72. The advantages and weaknesses of using DNA-metabarcoding based on the 18S rRNA gene fragment for studying the structure of algal communities are shown. The advantage of this method is the possibility to more fully determine the diversity of eukaryotes taxa, which are diff icult to identify by morphology, without involving a large number of specialists, while the disadvantage of the method is the distortion that may occur during the PCR. Here, ways of solving this problem are proposed. The results of the study show that the analysis of the minor component of the eukaryotic community in samples (organisms with low biomass) consisting of a mixture of multicellular and unicellular organisms requires a read-depths of at least 100,000 sequences per sample. In general, the DNA-metabarcoding method is recommended for studying the structure of algal communities and eukaryotes associated with them.
Highlights
A number of catastrophic and rapidly developing ecological phenomena, including the expansion of fila mentous Chlorophyta and Cyanobacteria, took place in some areas of the coastal zone of Lake Baikal (Timoshkin et al, 2016)
OTUs grouped at genetic distances of 1 % (0.01) had dif ferent numbers of sequences: 88 OTUs contained more than one sequence (2 – 4000), and 378 OTUs were presented by a single sequence
According to the practice of metabarcoding research (Kozich et al, 2013), only those OTUs that included 4 or more sequences were used for analysis (Table 2)
Summary
A number of catastrophic and rapidly developing ecological phenomena, including the expansion of fila mentous Chlorophyta and Cyanobacteria, took place in some areas of the coastal zone of Lake Baikal (Timoshkin et al, 2016). Since 2011, researchers have begun to note the overgrowth of the bottom with filamentous algae in Listvennichny Bay (Kravtsova et al, 2012, 2014). The overgrowth of the bottom with filamentous algae is recorded in other areas of the lake near the settlements Kultuk, Baikalsk, Severobaikalsk (Ti moshkin et al, 2018; Kravtsova et al, 2020). Among the filamentous algae blooms in the littoral zone near the List vyanka, representatives of the genus Spirogyra dominate. For the first time (in almost 100 years of research), benthic filamentous algae Spirogyra were found in the plankton communities of the coastal zone (Bondarenko, Logacheva, 2016). The spe cies S. f luviatilis was discovered This species dominated in the littoral zone of Listvennichny Bay in accumulations of filamentous algae in 2012 (Timoshkin et al, 2014). The question about the number of species occurred in accumulations of filamentous algae remains open
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