Sinking Stars and Fatal Fungi: Asterionella formosa, Chytrids, and the Spring Bloom in Lake Maarsseveen

Diplôme Master Sinking Stars and Fatal Fungi: Asterionella formosa, Chytrids, and the Spring Bloom in Lake Maarsseveen eng 2024-09-03 author Kotnik Grace Elizabeth 0009-0009-8283-6250 986901 director Alvarez Nadir 948712 Département de génétique et évolution (Genev) (BIANI) director Ibelings Bastiaan Willem 781963 Forel Communs (FOREL) director van de Waal Dedmer NIOO Phytoplankton Ecology Group 203 Phytoplankton play a vital role in aquatic ecosystems and the global carbon cycle. Fungal parasites of phytoplankton can impact how phytoplankton grow and how they cycle nutrients. Asterionella formosa Hassall, 1850 is a large stellate colonial bloom-forming freshwater diatom widely found in temperate lake ecosystems. Due to its large size, density, and peculiar shape, A. formosa may have a high potential for sedimentation. A. formosa is also parasitized upon by chytrid fungal parasites, which can lyse the host cell and fragment colonies, leading to a potential redistribution of nutrients. While the nature of host-parasite interactions has been studied in the past 50+ years, the implications of parasitism on carbon fluxes to lake sediment have yet to be addressed. In this thesis, I show that, in a year of low bloom density, infections lead to smaller A. formosa colony sizes (i.e. fewer cells per colony). This impact of infections is especially pronounced in the sediment trap where the colony size is half of that observed in the surface layer. My research shows that colony shape influences sedimentation, contrary to Stoke’s law which suggests that larger colonies will sink faster or more often into the sediment trap. Despite reduced sedimentation and carbon accumulation potential, I observed higher carbon-to-nitrogen (C: N) ratios in the sediment trap compared to the productive layer. My thesis shows how the A. formosa and chytrid host-parasite dynamics function throughout a spring bloom and the implications on carbon fluxes in Lake Maarsseveen. As lake ecosystems are one of the most efficient carbon sinks, understanding how the processes of parasitism and sedimentation of dominant phytoplankton species like A. formosa can provide insights into carbon fluxes, which are imperative within the context of the global carbon budget. Asterionella formosa Chytrids Host-parasite dynamics Sedimentation Carbon fluxes Stoke's law Dewey 550 Dewey 570 BIOLOGY (BIODIVERSITY AND SYSTEMATICS) 41 Département F.-A. Forel des sciences de l'environnement et de l'eau 153 30 Section de biologie 16 false 757 Microbial Ecology de0d2b41-c495-4d46-ac98-8b24c8c31458 Master thesis Restricted GKotnik_Final_MScBiology_Thesis_30..pdf 7899859 application/pdf 53c5a5cf582e291dc9745b8a8c6e9e7f81d4d89c01cc8182af8def111f8e2171 Vignette Public researchQscheme.png 71709 image/png restrictedAccess Faculté des sciences / Section des sciences de la Terre et de l'Environnement / Département F.-A. Forel des sciences de l'environnement et de l'eau Faculté des sciences / Section de biologie

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Sinking Stars and Fatal Fungi: Asterionella formosa, Chytrids, and the Spring Bloom in Lake Maarsseveen				2024	98	7

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Kotnik, Grace Elizabeth

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