Amazing Discoveries of Benthic Fauna from the Abyssal Zone of Lake Baikal

SIMPLE SUMMARY: Lake Baikal is the deepest and oldest freshwater ecosystem in the world. Since more than half of the currently known species of aquatic organisms inhabiting Lake Baikal are endemic, it is called a natural laboratory for the study of species diversity and evolution. However, despite many years of research, the true biodiversity of the lake is clearly insufficiently studied. As before, the deep-water zones of the lake remain white spots: there is little information about small benthic organisms, especially sessile forms. Therefore, when, for the first time, during deep-sea trawls, fragments of packaging plastic were raised from the bottom of Lake Baikal, the main goal was to determine the diversity of aquatic organisms inhabiting it. Analysis of the standard fragment of the mitochondrial genome allowed the obtaining of the first nucleotide data for the endemic Baikal bryozoans Hislopia placoides, two new species of leeches (Rhynchobdellida, Piscicolidae) and an unknown representative of stramenopiles that is genetically equidistant from the fungi-like organisms, Oomycetes and Chromulinales (Chrysophyta). Nucleotide data of H. placoides indirectly confirmed the hypothesis of the partial origin of Baikal fauna from Tethys derivatives. Thus, the abyssal zone of Baikal is an inexhaustible source of information about biodiversity and the evolution of life on the planet. ABSTRACT: Lake Baikal is a natural laboratory for the study of species diversity and evolution, as a unique freshwater ecosystem meeting the all of the main criteria of the World Heritage Convention. However, despite many years of research, the true biodiversity of the lake is clearly insufficiently studied, especially that of deep-water benthic sessile organisms. For the first time, plastic waste was raised from depths of 110 to 190 m of Lake Baikal. The aim of this study was to examine the biological community inhabiting the plastic substrate using morphological and molecular genetic analysis. Fragments of plastic packaging materials were densely populated: bryozoans, leeches and their cocoons, capsules of gastropod eggs, and turbellaria cocoons were found. All the data obtained as a result of an analysis of the nucleotide sequences of the standard bar-coding fragment of the mitochondrial genome turned out to be unique. Our results demonstrate the prospects for conducting comprehensive studies of artificial substrates to determine the true biodiversity of benthos in the abyssal zone of Lake Baikal.