O. P. Dubovskaya

Efficiency of transfer of essential polyunsaturated fatty acids versus organic carbon from producers to consumers in a eutrophic reservoir

One of the central paradigms of ecology is that only about 10% of organic carbon production of one trophic level is incorporated into new biomass of organisms of the next trophic level. Many of energy-yielding compounds of carbon are designated as ‘essential’, because they cannot be synthesized de novo by consumers and must be obtained with food, while they play important structural and regulatory functions. The question arises: are the essential compounds transferred through trophic chains with the same efficiency as bulk carbon? To answer this question, we measured gross primary production of phytoplankton and secondary production of zooplankton and content of organic carbon and essential polyunsaturated fatty acids of ω-3 family with 18–22 carbon atoms (PUFA) in the biomass of phytoplankton and zooplankton in a small eutrophic reservoir during two summers. Transfer efficiency between the two trophic levels, phytoplankton (producers) and zooplankton (consumers), was calculated as ratio of the primary production versus the secondary (zooplankton) production for both carbon and PUFA. We found that the essential PUFA were transferred from the producers to the primary consumers with about twice higher efficiency than bulk carbon. In contrast, polyunsaturated fatty acids with 16 carbon atoms, which are synthesized exclusively by phytoplankton, but are not essential for animals, had significantly lower transfer efficiency than both bulk carbon, and essential PUFA. Thus, the trophic pyramid concept, which implicitly implies that all the energy-yielding compounds of carbon are transferred from one trophic level to the next with the same efficiency of about on average 10%, should be specified for different carbon compounds.

Study of non-consumptive mortality of Crustacean zooplankton in a Siberian reservoir using staining for live/dead sorting and sediment traps

We studied non-consumptive (non-predatory) mortality of Daphnia and Cyclops vicinus during four sampling seasons. Mortality estimations were based on live/dead sorting using special staining and measurements of sedimentation rates for dead individuals, depended on wind speed. Original equations were used for calculations. The estimated specific non-consumptive mortality never had biologically senseless negative values, which were often obtained on the basis of the other ways of mortality estimations, and was in a good agreement with other components of population dynamics. As found, the non-consumptive mortality was the important, often the determinant component of the zooplankton population dynamics.

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.

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.

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.

Evaluation of the Effect of Light Intensity on the Measurement of the Photosynthetic Rate in Plankton Microalgae by the Chlorophyll Fluorescence Method

The use of relative variable fluorescence (RVF) of chlorophyll, as measured in the presence of Diuron, an inhibitor of electron transfer, for the estimation of the photosynthetic activity of plankton microalgae was analyzed under a wide range of light intensities in the PAR region. Oxygen evolution rates (estimated by the method of light and dark bottles and the amperometric method), RVF, and chlorophyll a concentration were measured in parallel in natural algal cenoses and microecosystems. When the previously used regression equation, in the form A = b(ΔF/Fd)CchlI, where A is O2 evolution rate (g/(m3 h), ΔF/Fd is RVF (relative units), Cchl is chlorophyll a concentration (mg/m3), and I is light intensity (W/m2), was verified in the PAR region, we observed a nonlinear dependence of the correction coefficient b on I, which can be described by the formula b = 6.227 × 103√I. This result agrees with the hypothesis that chlorophyll a fluorescence quenching comprises photochemical (qQ) and energy (qE) components. On the basis of the energy model, we determined the upper limit bmax = 0.003 for light intensity range I< 4.4 W/m2 and the lower limit bmin = 0.0003 for I = 400 W/m2.

Evaluation of the potential fish productivity of lake oiskoe (Ergaky Mountain Range, West Sayan) basing on food supply

As a result of integrated studies carried out at the end of August–September 2008–2010, the icthyofauna and food reserve for fish in Oiskoe lake (Ergaky range) were investigated. The trophic status of the lake was estimated based on the biomass of phyto- and zooplankton and zoobenthos. The potential icthyomass, fish production and possible fishing amount were estimated based on calculations of the average biomass and production per season for zooplankton and zoobenthos.

Content of polyunsaturated fatty acids essential for fish nutrition in zoobenthos species

Content of eicosapentaenoic acid (EPA, 20∶5n-3) and docosahexaenoic acid (DHA, 22∶6n-3) and the n-3/n-6 ratio are important indicators of nutritive value of aquatic invertebrates as food for fish. We studied fatty acid (FA) content and composition of 68 zoobenthic species. Benthic invertebrates differed significantly in their contents of EPA and DHA and n-3/n-6 ratios. The most valuable food for fish were Insecta, especially Ephemeroptera and Trichoptera, Gammaridae, and Turbellaria (Dendrocaelopsis sp.). The invertebrates of low food quality for fish were Hirudinea, Mollusca, Oligochaeta, Bryozoa (Plumatella emarginata), and Coleoptera (Dytiscus lapponicus). Our data suggest that the recent and ongoing global replacement of native species, mainly Insecta, by invaders, mostly represented by Mollusca, Crustacea, Polychaeta, Oligochaeta, Bryozoa, and Hirudinea, probably will reduce the nutritive value of food sources for benthivorous fish. In addition, some of the taxa studied have peculiar FAs, which may be useful as their markers in trophic webs. Thus, 20∶1n-13, 20∶2n-6, 22∶5n-3, and 22∶6n-3 are likely to be considered markers of Mollusca, Hirudinea, Turbellaria, and Gammaridae, respectively, for tracing food webs in freshwater ecosystems.

Production of polyunsaturated fatty acids by zoobenthos in rivers with contrasting temperatures.

308 In the last decade, one of the most urgent tasks of aquatic ecology is the study of the influence of climate change on the functioning of aquatic ecosystems [1]. Global warming causes changes in the species compo sition of aquatic communities, which may be accom panied by changes not only in the quantity but also in the quality of production of aquatic ecosystems. For example, it was found that the zooplankton biomass in the cold lakes contains much more long chain poly unsaturated fatty acids (PUFA) of the omega 3 family (eicosapentaenoic acid (20:5n 3, EPA) and particu larly docosahexaenoic acid (22:6n 3, DHA)) as com pared to the warm lakes [2]. It is known that DHA is an essential component of cell membranes of the nerve tissue and retina of vertebrates and its deficiency in food suppresses the growth and development of fish [3, 4]. The influence of climate warming on the production of EPA and DHA by the zoobenthos, which is the main food of fish in fast flowing rivers remains virtually unstudied.

Comparison of fatty acid composition of cladocerans and copepods from lakes of different climatic zones

We have studied the fatty acid (FA) contents and composition of cladocerans and copepods from warm and cold lakes. We have found no significant differences in FA percent levels and per carbon contents of cladocerans from warm and cold lakes or of copepods from warm and cold lakes. A discriminant analysis showed that all cladocerans differed from all copepods mainly due to the content of docosahexaenoic acid. Compared to cladocerans, copepods had significantly higher levels of all C22 polyunsaturated FA. Thus, we conclude that cladocerans and copepods in all environments had comparatively invariant taxon-specific compositions and contents of long-chain highly unsaturated fatty acids (HUFAs). According to HUFA content, all studied copepods can be regarded as a valuable food for fish.