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Public defence

Public defence in ecology: Laura Seidel

Title: The Baltic Sea from the present to future - microbial carbon and nutrient cycling in a changing climate
Subject: Ecology
Faculty: Faculty of Health and Life Sciences 
Date: Friday June 3 2022 at 09.00 am  
Place: Room Fullriggaren, Building Magna, Kalmar and via Zoom
External reviewer: Professor Stefan Hulth, Göteborgs University
Examining committee: Docent Jenni Hultman, University of Helsinki, Finland
Associate Professor Laura Villanueva, Utrecht University, Netherlands
Professor Jens Harder, Max Planck Institute for Marine Microbiology, Germany
Chairperson: Professor Marcelo Ketzer, Department of Biology and Environmental Science, Linnaeus University
Main supervisor: Professor Mark Dopson, Department of Biology and Environmental Science, Linnaeus University
Examiner: Professor Anders Forsman, Department of Biology and Environmental Science, Linnaeus University
Spikning: Friday May 13 2022 at 09.00 am, University Library, Kalmar

In order to receive the Zoom link for the thesis defense, please contact Faculty Administrator Linnéa Larsson: linnea.larsson@lnu.se



Climate Change is caused by the accelerated increase of anthropogenic greenhouse gas emissions to the atmosphere and affects all ecosystems on our planet. A result of higher CO2 uptake by the oceans as well as an increase of heat trapped in the atmosphere leads to, for example acidification, stratification, sea-level rise, oxygen loss, and temperature increase of the earth’s waterbodies. The Intergovernmental Panel on Climate Change (IPCC) predicts the earth’s surface temperature to rise between 1.0-5.7°C by the year 2100 and ocean temperatures are predicted to rise by up to 2.0°C.

This thesis focuses on the effects of environmental changes on microbes and their functions in coastal Baltic Sea sediments and overlying bottom-waters. The studies examine potential effects of ongoing climate change in combination with coastal eutrophication, as well as long-term warming due to e.g. climate change within a natural fluctuating system and a laboratory based incubation experiment.

Investigation of coastal sediment and overlying bottom-waters showed that potential future changes on bacterial communities due to eutrophication in combination with climate change relies on the water depth and oxygen supply. In addition, the study of a natural seasonal fluctuating and long-term artificially heated coastal bay (compared to an unaffected control bay) gave insights into how the ecosystem might react to future climate change. On one hand, bottom waters in the heated bay showed decreased bacterial diversity, suspended seasonal patterns plus elevated and prolonged cyanobacterial blooming. On the other hand, surface sediment communities in the heated bay had an altered microbial community with decreased seasonal variation and higher diversity likely due to a shallowing of geochemical layers. Furthermore, increased energy production occurred although higher stress RNA transcripts suggested that the microbial community’s temperature optima were below that of the water. Nevertheless, incubation experiments showed that exposure to short-term elevated temperatures shifted the control bay microbial community closer to that of the heated bay with a similar response on RNA level at higher temperatures (28 °C).

In summary, this thesis provides new insights into ongoing and likely future climate change effects on coastal microbial communities, which are key players for nutrient- and energy cycling of the marine ecosystem.

Keywords: Climate change, coastal sediments, Baltic Sea, eutrophication, bacterial communities, 16S rRNA, metatranscriptomics, geochemical layers, diversity, nutrient- & energy cycling.