Litmanen, J. (2025). Biomolecule-Based Estimation Methods in Determining Seston Composition and Herbivorous Zooplankton Diets. Doctoral Dissertation, Faculty of Mathematics and Science, University of Jyväskylä, Jyväskylä, Finland. 171 pp. [In English; abstract in Finnish].

508630

Litmanen, J.

2025

171 pp. [In English; abstract in Finnish]

Publication

https://urn.fi/URN:ISBN:978-952-86-0597-3

Available for editors  

Microscopic phytoplankton form the foundation of pelagic aquatic food webs as primary producers, with herbivorous cladocerans and copepods consuming both phytoplankton and microscopic heterotrophs in the seston. Phytoplankton are the main producers of essential biomolecules, such as fatty acids (FA)particularly polyunsaturated FAs (PUFA)—and herbivorous zooplankton transfer these compounds to higher trophic levels. FAs and carotenoids can serve as biotracers, enabling computational estimation of consumer diets and seston composition. However, limited comparison of computational methods and biotracer types, and lack of dietary FA source library for copepods, prevents comprehensive estimation of plankton food web dynamics. This thesis evaluated modern computational methods (CHEMTAX, FASTAR, MixSIAR, and QFASA) for estimating seston and herbivorous zooplankton diet composition. Using simulated and field-derived datasets, QFASA emerged as the most accurate method, with carotenoids producing more accurate seston composition estimates. A dietary FA source library was developed for copepod Eudiaptomus. A seven-year dataset from Lake Vesijärvi, Finland, was analysed to estimate seston and zooplankton diets. QFASA provided robust phylum-level seston composition estimates. Cladocerans exhibited generalist feeding, periodically exploiting high-quality patches, while Eudiaptomus preferred golden algae and appeared decoupled from phytoplankton dynamics, potentially synthesising essential PUFAs. It was shown that phytoplankton samples represent only what remains after consumer feeding. Frequent sampling revealed that high-quality phytoplankton enhanced cladoceran biomass, while low-quality taxa reduced it. These findings highlight the importance of long-term, high-resolution sampling and provide insights for lake restoration and biomolecule-based monitoring.

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