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Effects of Meiofauna and Cable Bacteria on Oxygen, Ph and Sulphide Dynamics in Baltic Sea Hypoxic Sediment

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Effects of Meiofauna and Cable Bacteria on Oxygen, Ph and Sulphide Dynamics in Baltic Sea Hypoxic Sediment Effects of meiofauna and cable bacteria on oxygen, pH and sulphide dynamics in Baltic Sea hypoxic sediment A sediment core experiment with focus on different abundances of meiofauna and meiofaunal bioturbation in hypoxic Baltic Sea sediments. Meiofaunal effect on redox biogeochemistry of the sediment was studied in co-existence with cable bacteria. Johanna Hedberg Department of Ecology, Environment and Plant sciences M.Sc. Thesis 60 ECTS credits Marine biology Master´s Programme in Marine Biology (120 ECTS credits) Spring term 2019 Supervisor: Stefano Bonaglia Effects of meiofauna and cable bacteria on oxygen, pH and sulphide dynamics in Baltic Sea hypoxic sediment A sediment core experiment with focus on different abundances of meiofauna and meiofaunal bioturbation in hypoxic Baltic Sea sediments. Meiofaunal effect on redox biogeochemistry of the sediment was studied in co-existence with cable bacteria. Johanna Hedberg Abstract Oxygen depleted areas in the Baltic Sea are wide spread and affecting sediment biogeochemistry leading to faunal migration by formation of toxic sulphide. In sediments where reoxygenation events occur, re- colonization of meiofauna and cable bacteria are believed to enhance ideal conditions and facilitate recolonization of other fauna. In sediments world-wide most abundant are bioturbating meiofauna representing various phyla grouped by body size (>0.04 and <1 mm) and known to enhance bacterial activity. Meiofaunal abundance and meiofaunal bioturbation in sulfidic sediments and effects on bacterial community structure is currently poorly understood. As second thesis to find filament building sulphide oxidising cable bacteria in the Baltic Proper, their co-existence with meiofauna and effect on sediment were also studied. Alive meiofauna was added to otherwise intact cores creating gradients of abundance (CTR = unmanipulated cores, DEBRIS = debris addition, LM = low meiofauna abundance and HM = high meiofauna abundance, n = 3) and microsensor profiles of oxygen, pH and sulphide were measured weekly for three weeks to obtain effects. Cores were then sliced to confirm meiofaunal gradient and to obtain samples for cable bacteria presence and bacterial community structure. High meiofauna abundance and meiofaunal bioturbation increased oxygen penetration depths (OPDs) at week two (ANOVA: F2,6 = 6.395, p = 0.033; Tukey test: � = 0.613) and deepened sulphide apparent appearance boundaries (SAABs) at week one, though this difference was not statistically significant. Fluorescence in situ hybridisation (FISH) confirmed cable bacteria in all cores and insignificant different densities. Cable bacteria eventually deepened SAABs in CTR, DEBRIS and LM to same depth. Metabarcoding and sequencing revealed significant different microbial community structures between treatments, suggesting effects from meiofaunal abundances and meiofaunal bioturbation. The work in this thesis suggests that (1) cable bacteria and meiofauna coexist in sediments recently exposed to reoxygenation events, (2) high meiofauna abundance and meiofaunal bioturbation increase OPDs and (3) high meiofauna abundance and meiofaunal bioturbation changes bacterial community structure. Keywords Meiofauna, Bioturbation, Cable bacteria, Sediment, Oxygen, pH, Sulphide 2 Sammanfattning Syrefattiga områden i Östersjön är vitt spridda och påverkar sedimentets biogeokemi och resulterar i migration av fauna pga. toxisk sulfid. I sulfidiska sediment där återkommande syresättning förekommer, tror man att kolonisering av meiofauna och kabelbakterier förbättrar sedimentet och därmed underlättar för vidare fauna att återkolonisera. Mest förekommande i sediment jorden runt, är bioturberande meiofauna som är representerade från olika fyla, grupperade efter kroppsstorlek (>0.04 and <1 mm) och kända för att förstärka bakterieaktivitet. Förekomsten av meiofauna och dess bioturbation i sulfidiska sediment och påverkan på bakteriesamhällsstrukturen är mindre studerad. Som den andra som upptäckt filamentbildande sulfidoxiderande kabelbakterier i Egentliga Östersjön så studerades även deras samverkan med meiofauna. Levande meiofauna adderades till annars intakta sedimentproppar i ett försök att få en gradient av förekomst (CTR = ej manipulerade sedimentproppar, DEBRIS = addition av debris, LM = låg förekomst av meiofauna och HM = hög förekomst av meiofauna, n = 3) och microsensorprofiler av syre, pH och sulfid undersöktes varje vecka i tre veckor för att studera sedimentets påverkan. Sedimentpropparna skivades sedan för att konfirmera meiofauna gradienten och samla prover för förekomst av kabelbakterier och den bakteriella samhällsstrukturen. Hög förekomst av meiofauna och dess bioturbation ökade syrepenetrationen i vecka två (ANOVA: F2,6 = 6.395, p = 0.033; Tukey test: � = 0.613) och fördjupade sulfiduppkomstbarriärerna redan i vecka ett, men ej statistiskt signifikant. Fluorescerande in situ hybridisering (FISH) konfirmerade kabelbakterier i all sedimentproppar och ej signifikant skillnad mellan deras densitet. I slutet av experimentet fördjupande kabelbakterierna sulfiduppkomstbarriärerna i CTR, DEBRIS och LM till samma djup som i HM. Metabarkodning och sekvensering visade signifikant skillnad i den bakteriella samhällsstrukturen, vilket påvisar en möjlig effekt av meiofauna och dess bioturbation. Den här uppsatsen drar slutsatserna att (1) kabelbakterier och meiofauna samexisterar, (2) hög meiofauna förekomst och dess bioturbation ökar syrepenetrationen och (3) hög meiofauna förekomst och dess bioturbation påverkar den bakteriella samhällsstrukturen. Nyckelord Meiofauna, Bioturbation, Kabelbakterier, Sediment, Syre, pH, Sulfid 3 Contents INTRODUCTION ................................................................................................................................................ 1 AIM/RESEARCH QUESTIONS............................................................................................................................. 6 METHODS ........................................................................................................................................................ 7 RESULTS ......................................................................................................................................................... 13 DISCUSSION ................................................................................................................................................... 20 ACKNOWLEDGEMENTS .................................................................................................................................. 27 REFERENCES ................................................................................................................................................... 28 SUPPLEMENTARY INFORMATION................................................................................................................... 33 4 Introduction Oxygen depleted areas in aquatic environments develops when the oxygen demand is higher than oxygen supply (Snoeijs-Leijonmalm and Andrén 2017) and caused by factors, such as eutrophication and climate change (Vahtera et al. 2007; Markus Meier, Eilola, and Almroth 2011). Eutrophication enhances primary production that causes higher oxygen consumption by the degradation of increased settled organic material (Vahtera et al. 2007). Ongoing climate change with warmer waters are projected by models to lower the solubility of oxygen in water and increase the oxygen consumption by enhancing aerobic respiration, leading to further oxygen depletion in aquatic systems (Markus Meier, Eilola, and Almroth 2011). Figure 1. The positive feedback-loop. External load of nutrients increases the uptake by and the production of phytoplankton. Higher loads of organic material from the phytoplankton settle on the sediment and require more oxygen when aerobic bacteria degrade the settled organic material. As the aerobic degradation consumes oxygen, the oxygen concentration in the bottom water and sediment decreases and eventually affects the chemical and biological redox reactions causing benthic release of phosphorous. The bioavailable phosphorous eventually reaches the surface waters and increases the already high concentration of phosphorous that further enhances the primary production. The loop continues into a second round, and for every loop each step is enhanced (Vahtera et al. 2007). Illustration inspired by Vahtera et al. (2007) and created with the Courtesy of the Integration and Application Network, University of Maryland Center for Environmental Science (ian.umces.edu/symbols/). In the debate about eutrophication and oxygen depleted areas the Baltic Sea is often mentioned due to the fact that the sea holds one of the largest areas of oxygen depletion. Oxygen depleted areas in the Baltic Sea are increasing (Carstensen et al. 2014), and this trend is caused by nutrient loading from anthropogenic actions (Hansson, Andersson, and Axe 2011) during the last two centuries (Noffke et al. 2016). Nutrients can reach the water mass in aquatic environments by two paths: (1) External loading where nutrients are coming from land, e.g. via run-off, precipitation or sewage outlets (Snoeijs- Leijonmalm and Andrén 2017), or (2) internal loading by benthic release due to changed sediment chemistry. Internal load of the macronutrient phosphorous (P) from oxygen depleted sediments is eight times higher than the external load (Noffke et al. 2016) and one important part in the positive feedback loop that slows down the
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