Elena A. Ivanova

Comparative Analysis of Ecophysiological Characteristics of Stephanodiscus hantzschii Grun. in the Periods of Its Bloom in Recreational Water Bodies

In the periods of summer and autumn bloom of the Stephanodiscus hantzschii Crun. in recreational water bodies, studies on the vertical distribution of chlorophyll a, its contents per unit biomass, efficiency in using photosynthetically active radiation (EPhAR), and assimilative activity of microalgae were performed. The results confirmed the existence of two ecophysiological forms of St. hantzschii and provided evidence that both forms are typically autotrophic and can efficiently use low-intensity PhAR for photosynthesis.

Seasonal dynamics of amino acids in two small Siberian reservoirs dominated by prokaryotic and eukaryotic phytoplankton

The comparison of the dynamics of phytoplankton biomass and total amino acid composition was made for two water bodies: in one the phytoplankton were dominated by prokaryotes (i.e., there was a bloom of cyanobacteria) and by eukaryotic microalgae in the other. The dynamics of phytoplankton biomass and of total amino acid composition of water were investigated during the vegetation season. It was found that the only factor that significantly changed the percentages of amino acids in water was the bloom of cyanobacteria in the “blooming” water body. During the bloom of cyanobacteria, the absolute and relative content of the Leu-Glu group increased, while the contents of other acids generally dropped. Before and after the bloom, no significant variations in the total amino acid composition were recorded. In the reservoir where eukaryotic microalgae dominated, no significant variations in amino acid composition were recorded during the season.

Seasonal dynamics of akinetes of Anabaena flos-aquae in bottom sediments and water column of small Siberian reservoir

Seasonal dynamics of Anabaena flos-aquae (Lyngb.) Breb., including vegetative cells, akinetes and akinete envelopes, in bottom sediments and water column at both littoral and deeper central stations of a small Siberian reservoir was studied. Two types of akinetes were observed: in the first half of summer Anabaena formed akinetes, which served for vegetative reproduction and germinated in water column soon after differentiation, while in the second half of summer the akinetes produced served as a resting stages, which were deposited to bottom sediments. Canonical correlation analyses revealed that decrease of water temperature was the main environmental factor that stimulated the akinete formation. In contrast to the general opinion, concentration of inorganic phosphorus slightly, but positively influenced the akinete formation. Thus, akinetes formed in response to the temperature decrease, needs a certain level of this nutrient. At littoral and open-water stations abundance and seasonal dynamics of akinetes in water column and their sinking pattern were very similar. However, seasonal dynamics of abundance of akinetes in sediments in these two reservoir locations differed: whereas the abundance of akinetes in open water increased permanently during the summer, that in the littoral decreased soon after their sedimentation. The cause for decrease in abundance of akinetes in bottom sediments in winter is unknown.

Selective grazing on Cryptomonas by Ceriodaphnia quadrangula fed a natural phytoplankton assemblage

Grazing of C. quadrangula from a Siberian forest pond on natural phytoplankton assemblages was studied in a modified flow-through system. Ceriodaphniastrongly selected subdominant Cryptomonas erosarather than the dominant diatoms of comparable size. Using Cryptomonas as the sole microalgae food, Ceriodaphnia demonstrated significant somatic and population growth. Seasonal biomass maximum of Ceriodaphnia and Cryptomonas coincidedin the pond. Although bacterial component cannot be excluded, it was concluded that Cryptomonaswas the principal algal food source for Ceriodaphnia.

On one Model of Generalized Continuum and its Thermodynamical Interpretation

We consider the mechanical model of a two-component medium whose first component is a classical continuum and the other one is a continuum having only rotational degrees of freedom. We show that the proposed model can be used for the description of thermal and dissipative phenomena. It is the presence of additional rotational degrees of freedom and, accordingly, additional inertia and elastic characteristics which can be interpreted as thermodynamical material parameters that distinguish the proposed model among other continuum models. In special cases the mathematical description of the proposed model is proved to reduce to the well-known equations such as the heat conduction, the self-diffusion and the coupled thermoelastic equations. The mathematical description of the proposed mechanical model includes not only the classical formulation of the coupled problem of thermoelasticity but also the formulation of the coupled problem of thermoelasticity with the hyperbolic type heat conduction equation. In the context of the introduced theory we consider the original model of internal damping.

Spatial distribution of resting stages (akinetes) of the cyanobacteria Anabaena flos-aquae in sediments and its influence on pelagic populations

Recruitment of pelagic populations of cyanobacteria from littoral bottom sediments is assumed to be one of the key factors for the development of harmful blooms. Therefore, it is necessary to obtain more information on the possible factors influencing the spatial distribution of the resting stages in littoral bottom sediments. To test the hypothesis that akinete abundances in littoral bottom sediments are associated with silt and the presence of higher water plants, we sampled spatial and vertical distribution and seasonal dynamics of akinetes of cyanobacterium Anabaena flos-aquae in a small Siberian reservoir. We found that akinetes accumulate in silt at stations located in macrophyte beds. Two experiments were carried out to test if there is relationship between size of inoculum and size of the pelagic population of A. flos-aquae. The proportion of A. flos-aquae in total phytoplankton biomass depended on the initial abundance of akinetes in bottom sediments. The model based on laboratory experiments gave good qualitative description of the field data. These findings can be useful to predict the location of the main akinete accumulation zones in a water body and plan the removal of sediment to prevent the cyanobacterial blooms.

Seasonal variations of metal concentrations in periphyton and taxonomic composition of the algal community at a Yenisei River littoral site

The concentrations of metals K, Na, Ca, Mg, Fe, Mn, Zn, Cu, Ni, Pb, Co and Cr, in the water and periphyton (epilithic algal communities) were studied at a site in the middle stream of the Yenisei River (Siberia, Russia) during three years using monthly sampling frequencies. Despite considerable seasonal variations in aquatic concentrations of some metals, there was no correlation between metal contents in the water and in periphyton. Seasonal concentration variations of some metals in periphyton were related to the species (taxonomic) composition of periphytic microalgae and cyanobacteria. Enhanced levels of Ni and Co in periphyton in late autumn, winter, and early spring were likely caused by the predominance of cyanobacteria in the periphytic community, and annual maximum levels of K in periphyton in late spring and early summer were attributed to the domination of Chlorophyta, primarily Ulothrix zonata.

Species-specific stimulation of cyanobacteria by silver carp Hypophthalmichthys molitrix (Val.).

ISSN 0012-4966, Doklady Biological Sciences, 2006, Vol. 408, pp. 223–225.

Seasonal dynamic of phototrophic epibionts on crustacean zooplankton in a eutrophic reservoir with cyanobacterial bloom

Seasonality of burden and prevalence of phototrophic (microalgal) epibionts Characidiopsis ellipsoidea, Colacium vesiculosum and Colacium sp. on dominating crustacean zooplankton (Daphnia longispina, Cyclops vicinus and Mesocyclops leuckarti) were studied in a small reservoir Bugach with cyanobacterial bloom. The correlations between the seasonal dynamics of prevalence and the dynamics of others biotic and abiotic factors were calculated. The conclusions were as follows. The substrate species, that determined the development of the epibionts on the three studied crustacean zooplankton, was Daphnia longispina (Cladocera). Despite intensive epibiotic infestation of crustacean zooplankton, epibionts did not appear to have caused non-consumptive mortality of the crustacean zooplankton. But they could have contributed to the Daphnia summer decline by increasing mortality due to its consumption by planktivorous fishes. The phototropic epibionts may successfully coexist with cyanobacterial bloom. The possible role of the epibionts in changing nutrient fluxes in pelagic food web is discussed.

5-HT1A receptor antagonist p-MPPI attenuates acute ethanol effects in mice and rats

Abstract The effect of a selective 5-HT 1A antagonist, 4-(2′-methoxy-)phenyl-1-[2′-( N -2′′-pyridinyl)- p -iodobenzamino-]ethyl-piperazine (p-MPPI), on acute ethanol-induced hypothermia, sleep and suppression of acoustic startle reflex in C3H/He mice and Wistar rats was studied. Administration of p-MPPI at the doses of 0.4, 0.7 and 1.0 mg/kg reduced in a dose-dependent manner the ethanol-induced hypothermia and the sleep time and attenuated the ethanol-induced decrease of acoustic startle reflex magnitude in mice. Similar p-MPPI (0.4 mg/kg) effects on ethanol-induced sleep and hypothermia were obtained in rats. It was concluded that 5-HT 1A receptors were involved in the mechanisms of the ethanol-induced hypothermia and sleep, and that 5-HT 1A antagonist increased acute ethanol tolerance.