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Lake warming and microbial food web dynamics in spring: a focus on ciliates

English title Lake warming and microbial food web dynamics in spring: a focus on ciliates
Applicant Posch Thomas
Number 182489
Funding scheme Project funding
Research institution Limnologische Station Universität Zürich
Institution of higher education University of Zurich - ZH
Main discipline Ecology
Start/End 01.01.2019 - 31.12.2022
Approved amount 499'261.00
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Keywords (7)

Microbial food webs; Algal spring blooms; Lake warming; Climate change; Ciliates; Lake Zurich; Limnology

Lay Summary (German)

Lead
Die Klimaerwärmung bewirkt eine massive Veränderung des Wärmebudgets unserer Seen im Alpenraum. Die Änderungen der physikalischen Strukturen (temperaturbedingte Wasserschichtungen) führen zu sinkenden Nährstoffverfügbarkeiten und damit Störungen in der Nahrungskette. Besonders auffällig sind die starken Reduktionen der Organismen im Frühjahr. Werden Nahrungsnetze immer schwächer, beeinflusst dies negativ die Funktionalität von Seen.
Lay summary

Inhalt und Ziele des Forschungsprojekts
Ziel des Projektes ist es, die Auswirkungen der klimabedingten Nährstoffverarmung auf das Nahrungsnetz im Zürichsee zu verstehen, zu quantifizieren und experimentelle Lösungsansätze zu testen. Besonders auffällig ist die starke Reduktion des alljährlichen Algenwachstums im Frühjahr. Die ersten und wichtigsten Konsumenten dieser natürlichen ‚Algenblüten‘ stellen Wimpertiere (Ciliaten) dar. Diese sind wiederum Nahrungsquelle (die trophische Verbindung) für Kleinkrebse und Fischlarven. Wir untersuchen, wie sich eine Reduktion der Ciliaten im Frühjahr auf das gesamte Nahrungsnetz auswirkt. Zudem werden die Langzeitdaten zum Nahrungsnetz ausgewertet um das aktuelle Geschehen historisch einzuordnen. In Experimenten wird überprüft, welche Folgen die zunehmend schwächere Frühjahrs-Vollzirkulation des Wasserkörpers für das Nahrungsnetz hat.

Wissenschaftlicher und gesellschaftlicher Kontext des Forschungsprojektes
Die beobachtete Verarmung der Nahrungsnetze spiegelt sich in einigen Seen bereits in stark rückläufigen Fischerträgen wider. Dies führte zu öffentlichen Diskussionen, ob Seensanierungen (v.a. Reduktion des Phosphors) zu restriktiv waren. Dieses Projekt soll aufzeigen, welchen Anteil der Klimawandel am beobachteten Nährstoffrückgang hat, und ob Seen immer noch das Potential zu höheren Produktionen hätten, vorausgesetzt dass die Durchmischungsdynamik funktioniert.

Direct link to Lay Summary Last update: 23.10.2018

Responsible applicant and co-applicants

Employees

Publications

Publication
Aquatic food webs in deep temperate lakes: Key species establish through their autecological versatility
Qu Zhishuai, Forster Dominik, Bruni Estelle P., Frantal Daniela, Kammerlander Barbara, Nachbaur Laura, Pitsch Gianna, Posch Thomas, Pröschold Thomas, Teubner Katrin, Sonntag Bettina, Stoeck Thorsten (2021), Aquatic food webs in deep temperate lakes: Key species establish through their autecological versatility, in Molecular Ecology, 30(4), 1053-1071.
Microbial food webs in hypertrophic fishponds: Omnivorous ciliate taxa are major protistan bacterivores
Šimek Karel, Grujčić Vesna, Nedoma Jiří, Jezberová Jitka, Šorf Michal, Matoušů Anna, Pechar Libor, Posch Thomas, Bruni Estelle P., Vrba Jaroslav (2019), Microbial food webs in hypertrophic fishponds: Omnivorous ciliate taxa are major protistan bacterivores, in Limnology and Oceanography, 64(5), 2295-2309.
Seasonality of Planktonic Freshwater Ciliates: Are Analyses Based on V9 Regions of the 18S rRNA Gene Correlated With Morphospecies Counts?
Pitsch Gianna, Bruni Estelle Patricia, Forster Dominik, Qu Zhishuai, Sonntag Bettina, Stoeck Thorsten, Posch Thomas (2019), Seasonality of Planktonic Freshwater Ciliates: Are Analyses Based on V9 Regions of the 18S rRNA Gene Correlated With Morphospecies Counts?, in Frontiers in Microbiology, 10, 248.

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
39th Meeting of the German Society for Protozoology Talk given at a conference Sequencing versus morphotype-based monitoring of phytoplankton in Lake Zurich - facts and future challenges 04.03.2020 Kaiserslautern, Germany Posch Thomas; Pitsch Gianna;
39th Meeting of the German Soviety for Protozoology Poster FISHing for ciliates - fluorescence in situ hybridization for the detection of planktonic freshwater ciliates 04.03.2020 Kaiserslautern, Germany Posch Thomas; Bassin Barbara; Bühler Dominique; Dirren Gianna;
39th Meeting of the German Society for Protozoology Poster Artificially induced versus natural protistan spring bloom dynamics in Lake Zurich 04.03.2020 Kaiserslautern, Germany Schuler Martina; Posch Thomas;


Awards

Title Year
Wahl zum Vizepräsidenten der Deutschen Gesellschaft für Protozoologie (DGP) 2020

Associated projects

Number Title Start Funding scheme
160603 Co-occurrence networks in aquatic food webs: ciliates as models 01.11.2015 Project funding

Abstract

The multi-decadal rise in air temperatures has a deep impact on thermal budgets of temperate lakes. Warmer water directly affects the phenology of aquatic organisms, however, ‘indirect climate effects’ (changes in physical and chemical parameters) may have even a stronger influence on the biota within food webs. During the last years, we could describe striking effects of changing climate on Lake Zurich. As a key issue, warming of surface (epilimnetic) waters increasingly disrupted complete water turnover (holomixis) in spring, causing an insufficient transport of deep water orthophosphate into the epilimnion. Since the year 2013, there was a continuous series of partial water turnovers. Thus, the phototrophic spring bloom community, formerly consisting of centric diatoms and cryptophytes, was cut off from essential nutrients. This reduction in primary production will definitely affect the entire food web as algae are the major source of substrates for bacteria and of food for consumers. As the succession of various ciliate species is tightly coupled to dynamics of their algal and bacterial food items, any lake warming induced shifts will strongly affect the ciliate assemblage and depending higher trophic levels. In several large temperate lakes, the strong decrease in spring primary production was documented and seemed to have propagated up to the level of top predators. This caused public debates that restoration measures were over-done, and that anthropogenic re-fertilizations or artificial turnovers are needed to ensure lakes’ productivity. Nevertheless, before executing potentially harmful measures hastily, it is crucial to understand cascading effects of changes in phytoplankton spring blooms, and focus especially on the pivotal role of ciliates as key consumers of primary producers and as major food source for higher levels in the food web.The following scientific key questions should be answered in the context of the proposed project: -Are years with partial water turnover indeed characterized by a loss of typical trophic cascades?-Is there a shift from strictly photoautotrophic to mixotrophic algal taxa which may guarantee survival during the surplus oligotrophication caused by lake warming?-Does this also implicate a shift to less edible algal morphotypes for herbivorous ciliates?-How does the ciliate assemblage react on changes of phytoplankton spring blooms in regard to biomass and taxonomic composition? Is there less ciliate biomass for higher trophic levels?-Is there a shift from strictly algivorous to bacterivorous and omnivorous ciliate species?-Do we find an increasing importance of mixotrophic ciliates?-Is there an exploitative competition between mixotrophic primary producers and HNF as well as bacterivorous/omnivorous/mixotrophic ciliates?-What will happen in Lake Zurich after years of partial mixis, when holomixis is reached again?-Which effects on microbial food web dynamics would result from artificial turnovers as technical restoration measures?
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