Zhorova A. Spatial and temporal dynamics of epiphytic algae in lotic and lentic ecosystems

The thesis considers the patterns of spatial and temporal dynamics of epiphytic algae in lotic and lentic ecosystems depending upon the major ecological factors (case study of the Ros River with affluents and Kaniv Reservoir). In the Ros River and its affluents, a total of 230 species (234 infraspecies taxa including the nomenclature species type) from 107 genera, 59 families, 35 orders, 13 classes and 7 phyla have been identified; the cell count varied from 23 to 5847 thousand cells  10 cm-2, and biomass – from 0.008 to 7.364 mg  10 cm-2. In the upper section of the Kaniv Reservoir, a total of 224 species (230 infraspecies taxa) from 100 genera, 50 families, 31 orders, 12 classes and 6 phyla have been identified; the cell count varied within 4 and 1049 thousand cells  10 cm-2, the biomass – within 0.005 and 0.628 mg  10 cm-2. The number of algal species common to both ecosystems made up 149, and the Sørensen similarity index was equal to 0.64. The comparative analysis of epiphytic algal communities in lotic, lentic and transitional sections has shown that the algal abundance tends to decline with the flow decreasing. This trend was observed both in the Ros River with the affluents and in the Kaniv Reservoir and was manifested in such parameters as the total cell count, biomass of epiphytic algae, the biomass of low-profile and high-profile algae and some dominan species (Brebissonia lanceolata, Cocconeis placentula, Oedogonium sp.). This is because the water flow if favorable for nutrients and oxygen supply to epiphytic algae, and benefits species exchange among the communities. Besides, the such low-profile species as Brebissonia lanceolata, Cocconeis placentula are firmly attached to the substratum and have a competitive advantage over other species under conditions of flow. At the same time the biomass of unattached motile and planktonic forms does not depend on the flow degree. The lotic, transitional and lentic areas of the ecosystems under study with different character of temporal dynamics: the unregulated section of the Ros River – the highest biomass in the middle of summer; the near-channel area of the Kaniv Reservori – the lowest biomass in the middle of summer (the period of algal blooms), the marchy pond with oxygen deficiency – the gradual decrease of the biomass from early summer to autumn. The effect of the spatial factors upon the epiphytic algae species similarity depends on hydrological connectivity between the sites.It has been found that the higher abundance of Chlorophyta in the epiphytic algal communities of the Ros River and its affluents, as compared with the Kaniv Reservoir, is driven by the significantly higher inorganic nitrogen content in the river and is supported by positive correlations between Ninorg. and the share of Chlorophyta (for the number of species r = 0.55 p = 0.02, for the cell count r = 0.60 p = 0.009). The complex effect of various ecological factors upon the qualitiative and quantitative characteristics of epiphytic algae has been estimated using the regression analysis technique. The interspecies relations in the epiphytic algal communities have been analysed. For this purpose we calculated the correlation coefficients between the biomass values of the dominant species in space and time. The effect of the abundance and the structure of invertebrates upon epiphytic algae has been studies (case-study of the Kaniv Reservoir). A relationship has been found between the prevalence of different groups of herbivorous and detritivorous invertebrates and epiphytic algae biomass. At sites with good water exchange dominated by gammarids the biomass of epiphytic algae was higher than at stagnant sites dominated by pulmonate gastropods. The most prominent difference in biomass values has been recorded for the adnate diatom Cocconeis placentula, which is evidently unavailable for gammarids, but can be efficiently grazed by mollusks. This is supported by the inverse relation between the biomass of C. placentula та herbivorous and detritivorous invertebrates at sites dominated by pulmonate gastropods. The water quality assessment according to epiphytic algae has shown that both ecosystems correspond to -mesosaprobic zone, however in the Ros River and its affluents the share of --saprobes is lower, and  and -saprobes higher, than in the Kaniv Reservoir, which is indicative of the higher organic matter content in the reservoir. The use of the Trophic Diatom Index (TDI) has made it possible to find differences between the lotic sections and the reservoirs of the Ros River and its affluents: in the reservoirs the TDI index was significantly higher. We have identified a number of special features pertaining to epiphytic algal communities in the Ros River compared to the Kaniv Reservoir.