N. G. Kosolapova

Dynamics of planktic microorganisms and viruses in the littoral zone of the Rybinsk Reservoir: Influence of water-bird colonies

The influence of gull and heron colonies on the dynamics of heterotrophic bacteria, flagellates, and viruses in the coastal waters of the Rybinsk Reservoir is studied. The littoral zone of the reservoir is found to contain abundant microorganisms and virioplankton. The specifics of the seasonal dynamics of these components of the microbial community in the areas colonized by water birds are revealed. An increase in the abundance and biomass of bacteria has been found in open coastal waters near a heron colony, but not in the background biotope. Maximum values of these parameters are recorded in the protected part of the littoral near the nesting area of gulls. During the period of strong ornithogenic pressure, the abundance of microorganisms and viruses is higher in areas located near water-bird colonies. It is shown that gulls have the greatest influence on the microbial planktic community in the protected littoral zone separated from the open part of the reservoir and characterized by high concentrations of soluble organic compounds and nitrogen.

Activity and growth efficiency of heterotrophic bacteria in Rybinsk Reservoir

The active fraction, production, and respiration of heterotrophic bacteria are determined to assess their growth efficiency and their role in the carbon cycle in the pelagic zone of Rybinsk Reservoir in summer. The greater part of organic substances assimilated by bacteria is mineralized to CO2. It has been established that the essential part of the constructive and energy metabolism of bacteria is supported by the input of allochthonous substances. Bacterioplankton, producing the biomass at their expense, performs functions similar to the functions of phytoplankton, and substantially supports the structural and functional organization of the planktonic food web in the reservoir.

Heterotrophic nanoflagellates in water column and bottom sediments of the Rybinsk Reservoir: Species composition, abundance, biomass and their grazing impact on bacteria

Abundance, biomass, and taxonomic composition of heterotrophic nanoflagellates (HNFs) have been determined in the water column and bottom sediments of the large lowland meso-eutrophic reservoir (Rybinsk Reservoir, Upper Volga) in summer. The role of HNFs in the consumption of the bacterial production is estimated. In the reservoir, 55 species from 15 large taxa, including 35 species from the plankton, are identified and 45 species are from benthos samples. The orders Kinetoplastida, Choanomonada, and Chrysomonadida are distinguished by the highest species diversity. Abundance and biomass of HNFs in the water column average 991 ± 326 cells/mL and 41.4 ± 14.1 mg/m3, while in the bottom sediments they are (236 ± 61) × 103 cells/mL and 10.7 ± 4.0 μg/mL, respectively. The biomass of HNFs average 11.2% of the bacterial biomass in the water column and only 0.8% of that in the sediments. Flagellates are found to be a major factor which control the development of bacterioplankton grazing, on average, 32.3% of its daily production, whereas their impact on bacteriobenthos is insignificant, as they consume, on average, only 2.0% of its production.

Trophic relationships between planktonic bacteria, heterotrophic nanoflagellates and viruses in a mesoeutrophic reservoir

The abundance, biomass, and production (РВ) of bacrerioplankton; the taxonomic composition, abundance, biomass of heterotrophic nanoflagellates (HNF) and the rate of consumption of bacteria by HNFs; and the abundance of virioplankton, frequency of visibly infected bacterial cells, virus-induced mortality of bacterioplankton, and viral production were estimated in the mesoeutrophic Rybinsk Reservoir. The rate of bacterial mortality due to viral lysis (7.8–34.1%, on average 17.2 ± 2.0% of daily РВ) was lower than the consumption of bacteria by the HNF community (15.4–61.3%, on average 32.0 ± 4.2% of daily РВ). While consuming bacteria, HNFs simultaneously absorbed a significant number of viruses residing on the surface and inside the bacterial cells.

Bacterioplankton in the area of gull colonies (Laridae) in the Rybinsk Reservoir

The effect of a colony of hydrophilic birds of the family Laridae on the dynamics of bacterioplankton, heterotrophic nanoflagellates, and extracellular virus particles is studied in the protected overgrown littoral of the Rybinsk Reservoir. Coastal waters of the reservoir are characterized by high quantitative characteristics of microorganisms and viruses. Compared to background parts, more pronounced variations in bacterioplankton biomass and an increase in the other quantitative characteristics of the planktonic microbial community during an intensive ornithogenic load are found in the areas occupied by bird colonies.

Distribution patterns of heterotrophic flagellates and bacteria in acidic and neutral Karelian lakes

The abundance and taxonomic and trophic structures of the community of planktonic heterotrophic nanoflagellates, as well as the quantitative distribution of bacteria as their main object of food, have been studied in six lakes of Karelia with differing pH values, concentrations and compositions of organic substances, and degrees of anthropogenic load. Thirty-eight species and forms of colorless flagellates from seven orders and groups of uncertain taxonomic statuses have been recorded. Most of them belong to the trophic group of bacteriodetritophages. The minimal abundance and the lowest diversity of flagellates have been documented in clear- and brown-water lakes with low pH values, and maximal values have been observed in the polluted Kondopoga Bay in Lake Onega.

The diversity and distribution of heterotrophic nannoflagellates in the eutrophic Lake Nero

The fauna and abundance of heterotrophic nannoflagellates (HNF) and the quantitative distribution of their main food items (bacteria) have been studied in the highly eutrophic Lake Nero (Yaroslavskaya oblast). A total of 70 HNF species and forms were found, with representatives of the order Choanoflagellida dominant. Abundances of HNF and bacteria were high, reaching levels typical for productive waters. The pattern of HNF seasonal dynamics was characterized by two peaks in June and September and one low in August. The minimal levels of HNF coincided with the peak of bacterioplankton abundance.

Structure and functioning of the microbial loop in a boreal reservoir

The abundance and biomass of the main components of the microbial plankton food web (“microbial loop”)—heterotrophic bacteria, phototrophic picoplankton and nanoplankton, heterotrophic nanoflagellates, ciliates and viruses, production of phytoplankton and bacterioplankton, bacterivory of nanoflagellates, bacterial lysis by viruses, and the species composition of protists—have been determined in summer time in the Sheksna Reservoir (the Upper Volga basin). A total of 34 species of heterotrophic nanoflagellates from 15 taxa and 15 species of ciliates from 4 classes are identified. In different parts of the reservoir, the biomass of the microbial community varies from 26.2 to 64.3% (on average 45.5%) of the total plankton biomass. Heterotrophic bacteria are the main component of the microbial community, averaging 63.9% of the total microbial biomass. They are the second (after the phytoplankton) component of the plankton and contribute on average 28.6% to the plankton biomass. The high ratio of the production of heterotrophic bacteria to the production of phytoplankton indicates the important role of bacteria, which transfer carbon of allochthonous dissolved organic substances to a food web of the reservoir.

Relations between bacterioplankton, heterotrophic nanoflagellates, and virioplankton in the littoral zone of a large plain reservoir: Impact of bird colonies

Interactions of the main components of microbial planktonic food web (bacteria, heterotrophic nanoflagellates, and viruses) were studied in a protected overgrown littoral zone of the Rybinsk Reservoir (Upper Volga). The effect of colonial bird settlements (the Laridae family) on these processes was determined. The following systems exhibited significant negative correlations: “heterotrophic nanoflagellates–large rod-shaped bacteria” (“predator–prey”), “viruses-bacteriophages–bacterial products” (“parasite–host”) and “heterotrophic nanoflagellates–viruses-bacteriophages”. Relations between biotic factors controlling bacterial development were more pronounced outside the zone affected by colonial bird settlements. Near the bird colony the role of viruses in mortality of planktonic bacteria increased. Reproduction of bacterial cells accelerated in response to the increase in feeding activity of heterotrophic nanoflagellates. Virusesbacteriophages and heterotrophic nanoflagellates probably eliminate different targets until medium-sized cells become predominant in the bacterial community. Then heterotrophic nanoflagellates consume bacterial cells infected with viruses.

First records of centrohelid heliozoans (Centrohelida) in Mongolia

Species composition, distribution, and morphological characters of centrohelid heliozoans (Centrohelida) in fresh lentic and lotic waterbodies of Mongolia have been studied using scanning electron microscopy methods. Six species of the families Raphidiophryidae Mikrjukov, 1996 and Acanthocystidae Claus, 1874 have been recorded in this region for the first time. The morphology of the heliozoans mostly matches the available published descriptions. The recorded species are described and figured.