Small Organisms in a Large River: What Provides the High Diversity of Scaled Chrysophytes in the Ob River?

Abstract

Currents are one of the main factors favoring the dispersal of microscopic planktic organisms over inland lakes and rivers. Large rivers of the northern hemisphere, flowing from south to north, can increase the diversity of northern latitudes with boreal species, while high water levels and floods expand the range of ecotopes and the biodiversity of rivers. We studied the distribution of the taxonomic structure and species richness of scaled chrysophytes downstream of the Ob river—a large river in West Siberia—at the end of the high-water period (June). Methods of scanning and transmission microscopy allowed the determination of a high taxonomic richness of these organisms, 67 species in total. The species were unevenly distributed by stations, with the maximum number of species (54) occurring in a shallow still bay without current and with minimum turbidity and a small number of diatoms. The species diversity in the main current was represented mainly by ubiquitous and cosmopolitan species.Water level fall usually coincides with the end of the vegetation of many scaled chrysophytes and the formation of stomatocysts. The stomatocysts of different species may drift downstream and then germinate when they find suitable conditions at theappropriatetime. Large rivers that are subject to significant changes in water level during their hydrologicalperiodsare able to host ahigh diversity of microscopic planktic organisms. Studying this capacity may reinforce the hypothesis of an omnipresence, i.e., that “everything is everywhere”.