Vol 9, No 3 (2016)

The blackfly fauna and biodiversity of some physiographic regions in eastern Trans-Baikal have been described. The structural characteristics of blackfly communities in the highlands and lowlands in the southern and northern territories of the region have been reported. A regional list of forty seven species in five genera of the Simuliidae family has been produced for the first time. The species distribution in three major river basins, Upper Amur, Lena, and Yenisei, are examined. A comparative cluster analysis of the similarities in species composition between the blackflies in the observed area and the adjacent regions is carried out. The blackfly species composition of the Upper Amur basin is more similar to the population of the Selenga River basin and significantly differs from the fauna in the middle and lower reaches of the Amur River; only three blackfly species typical for the Far East fauna have been indicated.

The morphology of the genera of diatoms Ochigma and Khursevichia based on new data from LM and SEM is discussed. The genera have been described from Lake Baikal. The morphology of raphe and pore occlusions resembles those in cymbelloid diatoms. We suggest including these genera in the order Cymbellales and the family Cymbellaceae. The role of different morphological features that are important for the taxonomy is discussed. Symmetry plays a minor role in diatom taxonomy. The morphology of raphe and pore occlusions is the most important factor. Pore occlusions within the genus Khursevichia belong to the tectulum type. Pore occlusions within the genus Ochigma are more complicated: they are represented by a tectulum inside and a foricula outside. The broadened description of the species Ochigma dubiosa is given.

Illustrated descriptions of two new species of free-living nematodes found in sediments of small water bodies of Vietnam are presented. Laimydorus propinquus sp. n. is morphologically similar to L. papillatus Ahmad, Ahmad, 2002, but it is distinguished from it by a relatively longer and thicker body, a longer tail in females, a more anterior position of vulva, a longer prerectum in females, longer spicules, and large number of precloacal supplements in males. Ischiodorylaimus paracognatus sp. n. differs from the similar species I. cognatus Andrássy, 1983 by a longer body, relatively short pharynx, thicker cuticle, wider lip area, and shorter spicules.

The total number and morphological and size composition of viriobenthos, number of bacteria infected by viruses, and burst size, as well as virus-induced mortality, abundance, and production of bacteriobenthos, have been estimated in bottom sediments of the Rybinsk Reservoir. The total number of viriobenthos in the reservoir varies within (1.1–10.9) × 10⁹ (on average, (5.9 ± 0.6) × 10⁹) particles/cm³; the total number of virus-to-bacteria ratio ranges within 0.2–2.1 (on average 0.9 ± 0.3). A weak positive correlation is found between the abundance of benthic viruses and the abundance and production of benthic bacteria. In most surveyed parts of the reservoir, infected benthic bacteria were not found or the portion of visibly infected bacterial cells (FVIC) did not exceed 0.5% of the total abundance of bacteriobenthos (N_B). A comparatively high infection of bacteria by viruses was recorded in bottom sediments only at one deep-water station, where FVIC was 2.5 of N_B.

The relation of the photosynthetic activity of phytoplankton biomass in the Volga River reservoirs to environmental factors has been analyzed. It is revealed that values of A/B and P/B coefficients depend to the largest extent on the content of total nitrogen, as well as on the temperature and illumination, the factors integrating the effect of geographical zonality. Among the proper phytoplankton parameters, its production capabilities are determined by the taxonomic composition, cenotic diversity and cell sizes, biomass, and physiological state of populations. Maximal values of A/B and P/B coefficients are characteristic of the algal communities with prevailing small-celled green, dinophytic, and cryptophytic algae.

The diatom assemblages of the surface sediments have been studied in 53 urban ponds and lakes of St. Petersburg for the first time. In total, 350 species and infraspecific taxa have been registered; the species of Achnanthidium, Cocconeis, Cyclostephanos, Cyclotella, Gomphonema, Lemnicola, Navicula, Nitzschia, and Stephanodiscus genera were the most common. The wide distribution of small centric planktonic taxa, Cyclostephanos dubius, C. invisitatus, Cyclotella pseudostelligera, Stephanodiscus hantzschii, and S. minutulus, is preconditioned by the depletion of dissolved silica, which is a result of the high phosphorus load. The high abundance of macrophytes in the shallowest sites favors the dominance of epiphytic Fragilaria, Staurosira, and Staurosirella taxa. Bottom-living diatoms in the shallow eutrophic and hypereutrophic urban ponds are light-limited; this is a result of either macrophytes or phytoplankton development. Alkaliphilous and alkalibiontic species prevail among the pH-indicative species, while eutraphentic and hypereutraphentic diatoms, as well as those thriving in a wide range of trophic conditions, dominate over other trophic groups. The β- and α-mesosaprobic species are the most common saprobity-indicative taxa.

An increased anthropogenic impact on the hydrophilic ecosystems of technogenic ponds of the Volga–Caspian basin has enhanced the migration of Typha latifolia L. and closely related species. Due to backcrossings and anomalies among bractless sections of the genus Typha, new morphological traits have been formed in T. latifolia via the stage of a nonspecific form development. Morphological anomalies revealed in an association of Typhetum latifoliae Soó 1927 of a small anthropogenic pond in the Yaroslavl region have been studied.

An analysis of the reproductive potential of roach in the Volga reach of the Rybinsk Reservoir is made on the basis of published data and our own data obtained from 1953 to 2012. Values of fecundity obtained in the 2000s are the most similar to the results of 1976. Parameters of the intensity of the generative exchange of females (absolute and relative fecundity and size and mass of eggs) were high in 2007 and 2012, which indicates a sufficient food supply, especially of medium and large roach.

We have investigated a sequence of visits to arms in a cross maze in juvenile (1-year-old) roach Rutilus rutilus (L.). Fish embryos of one group are raised under a natural geomagnetic field. The embryos of another group are exposed to the main phase of a simulated geomagnetic storm (changes in geomagnetic field up to 100 nT for each component). It turns out that the sequence of visits does not differ from random in both groups. Thus, the exploratory behavior in juvenile roach differs from other animal taxa investigated earlier. In the latter taxa a spontaneous alternation was observed: a tendency to visit the arm which was visited least recently.

The reproductive structure of the hemipopulation of the Cosmocerca ornata (Dujardin, 1845) in different age groups of the marsh frog has been studied. It is established that the main role in the formation of the reproductive structure of the hemipopulation and maintenance of C. ornata abundance belongs to 2- and 3-year-old amphibians. The dynamics of the age structure of C. ornata hemipopulation during the period of amphibian activity (from May to October) varies in different age groups of marsh frogs. The addition of new generations of C. ornata by amphibians of all ages occurs during the warm period of a year. During the winter period, the reproductive structure of C. ornata hemipopulation in the amphibians of all age groups is characterized by the existence of only mature parasites. The addition of young nematodes to the population of marsh frogs during this period does not occur.

The content of mercury has been determined in the muscle tissue of 18 fish species in rivers, lakes, and reservoirs of Central and South Vietnam. The region is characterized by lower metal concentrations than those in water bodies in temperate and northern latitudes. In 76% of samples (n = 986), the content of Hg was ≤0.5 μg Hg/g of dry (≤0.1 μg/g of wet) tissue weight. In water bodies and watercourses of tropical latitudes, interspecific variations in fish can be one of the factors responsible for a wide range of Hg variation within the same species.

The efficiency of neuston sampling from freshwater Lake Baikal with Garrett’s metal screen and polycarbonate membrane filters has been estimated. It is revealed that both sampling methods demonstrate similar results. Method selection is determined by climatic and hydrological factors. The results of the present work demonstrate that sampling using a metal screen can be recommended for the complex characterization of neuston biofilm and estimation not only microbiological, but also molecular and chemical parameters, because it allows collecting the water volume required for all analyses.