Mass disease and mortality of Baikal sponges

Abstract

Lake Baikal is sometimes called The Galapagos Islands of Russia because of its exceptional biodiversity and importance for the evolutionary science. The age, isolation and deep oxygen-saturated waters of Lake Baikal formed one of the world's richest freshwater ecosystems. Lake Baikal located in the centre of Eurasia has many features inherent to the ocean: abyssal depths and a huge mass of water, internal waves and seiches, strong storms and high waves, upwelling, expansion of the basin due to the separation of the coast similar to the separation of the continents of Africa and South America, large magnitudes of magnetic anomalies, etc. (Kondratyev, 1992). Lake Baikal is the only deep-water lake, where the water saturated with oxygen stretches to the very bottom, like in the ocean. The ecosystem of Lake Baikal is also close to oceanic ecosystems by structure and other characteristics, e.g. the presence of a pelagic community of the organisms and zones with high productivity of macroplankton in the area of the slope similar to the highly productive zones of upwelling in the ocean. The benthic community is characterized by extraordinary species diversity and high production, and it mainly consists of oligochaetes, molluscs, amphipods, chironomids and sponges. The biomass of sponges exceeds tenfold the biomass of all littoral macroorganisms (Kozhov, 1972; Masuda, 2009). The biological diversity of plants and animals inhabiting Baikal is greater than in other lakes of the world. For example, the number of known species and subspecies is more than twice higher than in Lake Tanganyika, which is comparable to Baikal in dimensions and origin. At present, there are approximately 2500 species of animals and more than 1000 species of plants in Lake Baikal. The Baikal fauna is formed autochthonous, i.e. the diversity of endemics has developed in Lake Baikal itself. Baikal is one of the most transparent lakes in the world. The amazing transparency (approximately 40 meters) has resulted from the low content of mineral salts in the lake and a great filtering ability of sponge communities and other filtration organisms. Recently, Lake Baikal is facing increasing threats to environment. Global climate change can threaten its

Metagenomic analysis of viral communities in diseased Baikal sponge Lubomirskia baikalensis

“…The understanding of the origin and causative agents of sponge disease is still insufficient. Some works indicated potential bacterial pathogens in sponges, however, most studies showed only shift in the microbial community of diseased sponges (dysbiosis) in comparison with healthy individuals (Webster, 2007;Belikov et al, 2018). To our knowledge, no viral putative pathogens have been found in diseased sponges.…”