Photogranules Formed by Filamentous Cyanobacteria and Algae of the Genus Spirogyra Link in the Coastal Zone of Lake Baikal

Abstract

Biological aggregations, in particular photogranules, can be found in different environments as one of the forms of existence of microorganisms, algae and small invertebrates. As far as they are systems, in which multiple ecological functions are performed by different elements simultaneously, they are considered a promising means for use in wastewater treatment. This paper provides description and composition of photogranules for the first time discovered in mass, 2,5 m away from the water edge in Listvennichnyi Bay of Lake Baikal in October 2015. The photogranules were maroon, free-floating, with a diameter of 0,5 to 1,5 cm, and were not hollow. Their main component was radially divergent filaments of oscillatorian cyanobacteria dominated by the members of the genus Symplocastrum. Photogranules with a diameter of less than 1 cm contained a large number of filaments of Spirogyra sp. ster., which in recent years have become widespread in the littoral of Lake Baikal and in the Angara River. In addition, there were fragments of numerous filamentous green algae, as well as diatom cells with Didymosphenia spp. dominance. The identified taxa are typical for the stony littoral zone of the lake at the depths from 0 to 3 m. Photogranulation in Baikal may be the result of overproduction of bottom communities of algae and cyanobacteria under conditions of increased anthropogenic load in the shallow water zone. Probably, photogranules can act as one of the mechanisms that perform the functions of natural self-purification in Baikal.