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    Food web interactions, habitat complexity, and human pressure as key determinants of fish community dynamics in temperate lakes
    (Estonian University of Life Sciences, 2026) Puncule, Linda; Zingel, Priit (advisor); Zagars, Matiss (advisor); Institute of Agriculture and Environmental Sciences; Lauridsen, Torben Linding (opponent)
    ABSTRACT. Food web interactions, habitat complexity, and human pressure as key determinants of fish community dynamics in temperate lakes. This doctoral thesis investigates the ecological drivers of fish community dynamics and food web stability in northern temperate lakes across Latvia and Estonia. By synthesizing three research articles, the study examines how the interplay between habitat complexity, food availability, and anthropogenic pressures shapes the growth and recruitment of fish populations. A primary focus is placed on young-of-the-year (YOY) fish, whose physiological vulnerability and reliance on specific nursery habitats make them sensitive early-warning indicators of ecosystem health and shifts in trophic regulation. The research demonstrates that the biomass and composition of zooplankton in littoral zones are fundamental determinants of YOY diet, growth, and condition, establishing a clear bottom-up link between productivity and fish recruitment. Furthermore, the study identifies the structural role of diverse macrophyte assemblages, particularly floating-leaved vegetation, in providing essential refugia and modulating planktonic food web interactions. These vegetated habitats enhance ecological resilience by facilitating resource partitioning and buffering against environmental disturbances, thereby maintaining the structural integrity of the aquatic community. Conversely, the thesis highlights the destabilizing effects of human activities, such as overfishing and poaching, which disproportionately target large piscivores. The loss of these keystone predators triggers a trophic cascade, leading to an overabundance of planktivorous fish and a subsequent decline in water quality through increased nutrient resuspension. The findings conclude that ensuring long-term lake sustainability requires an integrated management approach that prioritizes the conservation of complex littoral habitats alongside rigorous fisheries enforcement to safeguard top-down regulatory mechanisms.