Size-morphological structure and ecological strategies of prokaryotoplankton in a large mountain lake Sevan (Armenia)

Abstract

The dynamics of the size-morphological groups of heterotrophic prokaryotoplankton of the largest freshwater reservoir in the Caucasus, Lake Sevan (Armenia) has been studied, which makes it possible to explain its spatio-temporal organization and succession. The lake is characterized by an alternation of stable and unstable periods of existence of hydrobionts due to abrupt changes in environmental conditions, mainly caused by anthropogenic impacts. In the community of planktonic prokaryotes of the lake, the following size-morphological groups were distinguished: small cocci and coccobacilli, small rods and vibrios, medium-sized cocci and coccobacilli, large rods and vibrios, filaments, as well as cells associated with detrital particles. The main contribution (on average 55.5%) to the formation of the prokaryotoplankton biomass of the lake was made by small rods and vibrios. The biomass of each of the groups fluctuated in time and space within relatively narrow limits, and the development of the groups occurred in close relationship with each other. Apparently, different size-morphological groups of prokaryotes are adapted to exist within similar ecological and phylogenetic niches, and jointly and consistently perform common functions in the mineralization of organic matter and trophic interactions in the lake. At the same time, these groups implement various ecological strategies that can be successful at different periods of the ecosystem’s existence.