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.     

Ecological development and genetic diversity of <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> from artificial reservoir in Russia

Microcystis aeruginosa is a well-known Cyanobacterium responsible for the formation of toxic water blooms around the world. Shallow, warm, and eutrophic reservoirs provide the most favourable conditions for M. aeruginosa development. Numerous studies have been devoted to this species, but there still is a necessity to develop additional approaches for the monitoring of cyanobacteria in reservoirs. In this study, M. aeruginosa in the water column of a hypereutrophic Siberian reservoir was investigated by fluorescence, light, and electron microscopy as well as genetic analysis using a mcyE marker. Here, we demonstrate the genetic diversity and features of the fluorescence spectra for different ecotypes of this species. We suggest that a fluorescence approach can be used to identify M. aeruginosa in a natural environment in order to increase the effectiveness of ecological monitoring and water quality evaluation.     

Vertical structure and photosynthetic activity of Lake Shira phytoplankton

This study was conducted to analyse vertical dynamics of phytoplankton distribution in Shira Lake during the summer stratification regime. From late June to September phytoplankton in Shira Lake were stratified with the maximum in the lower part of the thermocline, at a depth of 8–12 m, with a chlorophyll concentration up to 23 g and biomass up to 5 mg l^–1. Maxima of chlorophyll and biomass of cyanobacteria and green algae were in different layers. From June to September a major part of chlorophyll a was in green algae, while under ice – in cyanobacteria. The variable fluorescence proves high photosynthetic activity of algae in the depth assemblage. Epifluorescent analysis disclosed that additional light-harvesting pigments were better developed in cells from the depth maximum. The maximum of gross primary production calculated from fluorescence corresponded to the depth maximum of phytoplankton. Primary production over a season was 2.7 gO₂ m^–2. Formation mechanisms of the depth maximum of phytoplankton are discussed in this paper.     

Gut content analysis of Gammarus lacustris from a Siberian lake using biochemical and biophysical methods

We studied the gut contents of Gammarus lacustris from the littoral of Shira lake, a Siberian salt lake, by microscopic analysis in conjunction with measuring of fluorescence of chlorophyll and composition of fatty acids. Gammarus ingested primarily fresh seston, probably settled on the bottom. Additionally, the amphipods obtained essential polyunsaturated fatty acids of 3 family by selectively consuming bottom sediment particles. A considerable part of the ingested seston comprised cells of Botryococcus sp., which passed the intestinal tract in living form and their photosynthetic activity increased. This viable gut passage was likely one of the causes of bloom of Botryococcusin the littoral. Unlike a number of literature data, there was no selective digestion of any fatty acid species, including polyunsaturated acids, in the intestinal tract.     

Contribution of different groups of autotrophs to the primary production of the mountain Lake Oiskoe

Productivity characteristics of phytoplankton, phytoperiphyton, and five species of macrophytes in the mountain oligotrophic Lake Oiskoe (Ergaky Mountain Range, West Sayan) have been studied. High primary productivity has been noted for phytoperiphyton and macrophyte communities. Photosynthetic parameters of the macrophyte leaves have been compared using a PAM fluorimeter.