MSc Jaakko Litmanen will present his doctoral research.
TITLE: Biomolecule based estimation methods in determining seston composition and zooplankton diets
ABSTRACT: Climate change, nutrient pollution, and land use alterations influence the primary and secondary production of lakes. Biomolecules, such as fatty acids (FA), can serve as dietary biomarkers, while FAs and carotenoid pigments can act as phytoplankton group biomarkers. In this thesis, the performance of current biomolecule-based seston community composition and herbivorous zooplankton diet estimation methods were assessed. Quantitative Fatty Acid Signature Analysis (QFASA), utilizing chi-squared distance measure, aligned most closely with phytoplankton community composition estimation when compared to light microscopy counting. When using FAs and carotenoids simultaneously, QFASA also provided accurate estimates of the proportions of terrestrial organic matter and aquatic bacteria in seston. Furthermore, the same method produced the least absolute error when compared to simulated Cladoceran diet profiles and accurately estimated the proportions of terrestrial and bacterial food sources. However, the dietary FA profile library required for estimation was lacking for another important herbivorous zooplankton group, Calanoid copepods. To address this, a library was created using compound-specific stable isotope analysis. While Cladocerans eat what they find, loosely selecting against nutritionally poor-quality cyanobacteria, Calanoid copepods actively seek out and strongly prefer nutritionally high-quality golden algae over other food sources. This results in different grazing pressures throughout the year. Overall, this thesis demonstrates that biomolecule-based composition estimation offers a cost-effective way of assessing phytoplankton and other constituents fuelling the aquatic food web, both before and after being consumed. Furthermore, the method provides a valuable tool for the rapid assessment of changes in lake food webs and the effectiveness of lake restoration efforts.
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