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3. Doktoritööd

Selle kollektsiooni püsiv URIhttp://hdl.handle.net/10492/2490

Sirvi

Sirvi 3. Doktoritööd Autor "Agasild, Helen (advisor)" järgi

Nüüd näidatakse 1 - 2 2
  • Pisipilt
    Kirje
    From microscopy to genes – tracing toxic cyanobacteria in a shallow eutrophic lake
    (Estonian University of Life Sciences, 2022) Panksep, Kristel; Kisand, Veljo (advisor); Agasild, Helen (advisor); Sivonen, Kaarina (advisor); Institute of Agricultural and Environmental Sciences; Vasas, Gabor (opponent)
    Global warming paired with eutrophication processes is shifting phytoplankton communities towards the dominance of bloom-forming and potentially toxic cyanobacteria. Cyanobacterial blooms are considered an increasing threat in freshwater. Traditional monitoring predominantly relies on cyanobacterial biomass as an indicator of potential toxin presence, disregarding that toxin concentrations can rapidly increase even when cyanobacterial biomass is low. The concentration of toxins in the water is related to the abundance of toxin-producing species and the amount of toxin per cell – toxin quota. My research provides valuable information about the cyanobacterial community composition, the abundance of toxic genotypes, microcystin concentrations, microcystin quota and the environmental factors that promote toxic cyanobacterial blooms in the large and shallow freshwater lake Peipsi. This is the first study to utilise molecular methods as complementary to routine monitoring to determine cyanobacterial toxicity potential in lake Peipsi. In situ studies on zooplankton taxon-specific ingestion of potentially toxic cyanobacteria are still limited. My study focused on the importance of cyanobacteria as a food source for the dominant crustacean grazers. Among the first studies using qPCR targeting cyanobacterial genus-specific mcyE synthase genes in zooplankton gut content analysis, we show that potentially toxic strains of Microcystis can be ingested directly or indirectly by different zooplankton grazers. Information gathered from this study expanded our knowledge on the ecology of toxic cyanobacteria, provided an indication of how molecular methods can improve traditional risk assessment concerning the abundance of cyanobacteria and their cyanotoxins and broadened our knowledge of how target specific molecular tools could be further used in aquatic food-web studies. In the current thesis, I present a synthesis of spatial and temporal variability of potentially toxic cyanobacteria and the importance of cyanobacteria as a food source for crustacean zooplankton in large and shallow lake. The thesis is based on three published papers each dedicated to a different aspect of the whole. This thesis improves our knowledge of potentially toxic cyanobacteria and cyanotoxins in large and shallow eutrophic lakes and also provides the first insight into the in-situ consumption of toxic Microcystis by cladoceran and copepod grazers dominating in the lake. The knowledge gained from this study will guide us to further important questions that should be addressed in future research regarding the functioning of the food web of lake Peipsi. Phytoplankton community through high throughput sequencing would allow analysing the relation of cyanobacterial community composition along with concentration and diversity of cyanotoxins. This would include small-sized cyanobacteria in analysis, which are now excluded from the research. To elucidate the processes underlying cyanotoxin dynamics in more detail, further exploration focusing on the expression of toxin genes along with toxin concentration would be beneficial. Toxin gene expression could better indicate potential risks, especially in water bodies comprising mixed assemblages of toxic and non-toxic cyanobacteria.
  • Pisipilt
    Kirje
    Occurrence and trophic interactions of the potentially toxic bloom-forming cyanobacterial genus Microcystis in shallow temperate lakes
    (Estonian University of Life Sciences, 2026) Gonzales Ferraz, Margarita Esmeralda; Agasild, Helen (advisor); Panksep, Kristel (advisor); Nõges, Tiina (advisor); Institute of Agriculture and Environmental Sciences; Dimante-Deimantovica, Inta (opponent)
    ABSTRACT. The increasing frequency and intensity of toxic cyanobacterial blooms pose a serious threat to aquatic ecosystems and the services they provide. Among the dominant bloom-forming genera, Microcystis is commonly observed in highly eutrophic waterbodies and represents a major concern due to its toxin production and potential contamination of food webs. As toxic and non-toxic strains of Microcystis often coexist within the same assemblage, qPCR targeting the genus-specific microcystin synthetase gene mcyE is a valuable tool for determining toxigenic strains in the environment and in the consumer diet. The research focused on bloom-forming and potentially toxic cyanobacteria, Microcystis, by characterizing the dynamics of its toxic strains and environmental drivers, as well as its trophic interactions in the aquatic food webs of lakes Võrtsjärv and Peipsi. The research demonstrated that in temperate, ice-covered lakes, Microcystis's ability to produce toxigenic strains may persist year-round. Application of genus-specific qPCR detection in zooplankton gut contents revealed that in natural waterbodies, various cladoceran and copepod species can consume toxigenic Microcystis strains, potentially posing a risk to higher trophic levels. It also showed that even in lakes with very low levels of toxigenic Microcystis, toxic cell trophic pathways can still occur, as evidenced in Lake Võrtsjärv. The research further emphasizes that, to assess the toxicity risk of Microcystis to the food web, the knowledge of grazer assemblages and their dynamics is essential. Further research on Estonia’s large lakes, Võrtsjärv and Peipsi, should focus on directly measuring cyanotoxin concentrations to better assess the potential risks of microcystin contamination in these ecosystems.