| 1. |
- Pontiller, Benjamin, MSc, 1985-
(författare)
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Molecular mechanisms involved in prokaryotic cycling of labile dissolved organic matter in the sea
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Roughly half of the global primary production originates from microscopic phytoplankton in marine ecosystems, converting carbon dioxide into organic matter. This organic matter pool consists of a myriad of compounds that fuel heterotrophic bacterioplankton. However, knowledge of the molecular mechanisms – particularly the metabolic pathways involved in the degradation and utilization of dissolved organic matter (DOM) – and transcriptional dynamics over spatiotemporal gradients are still scarce. Therefore, we studied the molecular mechanisms of bacterioplankton communities, including archaea, involved in the cycling of DOM, over different spatiotemporal scales in experiments and through field observations.In seawater experiments, we found a divergence of bacterioplankton transcriptional responses to different organic matter compound classes (carbohydrates, nucleic acids, and proteins) and condensation states (monomers or polymers). These responses were associated with distinct bacterial taxa, suggesting pronounced functional partitioning of these compounds in the Sea. Baltic Proper mesocosms amended with two different river loadings (forest versus agriculture river water) revealed a divergence in gene expression patterns between treatments during bloom decay. This was particularly true for genes in phosphorus and nitrogen metabolism, highlighting the importance and sensitivity of interaction effects between river- and phytoplankton-derived DOM in regulating bacterial activity responses to changes in precipitation-induced riverine runoff.In shipboard mesocosms in an Atlantic coastal upwelling system, we found significant changes in bacterioplankton transcription of hydrolyzing enzymes and membrane transporters from phytoplankton bloom development to senescence, primarily driven by phytoplankton-derived DOM and dissolved organic carbon dynamics. These responses differed substantially between bacterial orders, suggesting that functional resource partitioning is dynamically structured by temporal changes in DOM quantity and quality. Further analysis of these gene systems in a stratified fjord revealed pronounced divergence in transcription with depth and between bacterial taxa; moreover, transcription was more variable in the surface waters. This highlights the interplay between functional and physical partitioning of biogeochemical cycles. Collectively, the findings in this thesis contribute novel insights into the interdependency between prokaryotes and DOM by shedding light on the mechanisms involved in DOM cycling over ecologically relevant spatiotemporal scales.
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| 2. |
- Motwani, Nisha H., 1982-
(författare)
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Trophic complexity of zooplankton–cyanobacteria interactions in the Baltic Sea : Insights from molecular diet analysis
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Blooms of nitrogen fixing cyanobacteria (NFC) occur in many freshwater and marine systems, including the Baltic Sea. By fixing dissolved nitrogen, they circumvent general summer nitrogen limitation, while also generating a supply of novel bioavailable nitrogen for non-diazotrophic primary producers and ultimately supporting secondary production. Elucidating trophic links between primary consumers and NFC is essential for understanding role of these blooms for secondary production. However, until recently, there was no reliable method to quantify individual prey species for zooplankter feeding in situ. The development of PCR-based methods to detect prey-specific DNA in the diet of consumers, including microscopic animals, allows identification and quantification of trophic linkages in the field.Using molecular diet analysis in combination with egg production measurements, biochemical markers of growth and condition; and stable isotope approach, we explored a possibility to determine (1) whether cyanobacteria are grazed and assimilated by mesozooplankters (Papers I and II), (2) which species/groups are particularly efficient consumers of cyanobacteria (Papers II and III), and (3) how feeding on cyanobacteria affects zooplankton growth and development (Paper I and III). Taken together, these laboratory and field observations, provided evidence that NFC contribute to feeding and reproduction of zooplankton during summer and create a favorable growth environment for the copepod nauplii (Paper I). The favorable growth conditions for juvenile copepods observed during NFC blooms were hypothesized to be mediated by picoplankton that take up bioavailable nitrogen exuded from cyanobacterial cells. This hypothesis found support in Paper II that provided quantitative estimates for the direct picocyanobacteria → mesozooplankton pathway, with highest weight-specific consumption observed in nauplii. Further, using field observations on zooplankton and phytoplankton development during a growth season in the northern Baltic proper, we found that NFC nitrogen is assimilated and transferred to zooplankton via both direct grazing and indirectly through grazing on small-sized phyto- and bacterioplankton (Paper III). Finally, these and other findings emphasizing the importance of NFC for Baltic Sea secondary production during growth season were synthesized to show that diazotrophic nitrogen enters food webs already at bloom initiation (Paper III) and is transferred via multiple pathways to pelagic and benthic food webs and, ultimately, to fish (Paper IV).
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| 3. |
- Novotny, Andreas, 1991-
(författare)
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Functional diversity of zooplankton in marine food webs : Integrating DNA metabarcoding and network modeling
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The oceans are important regulators of the Earth’s climate system by sequestering carbon from the atmosphere taken up by primary producers. Zooplankton, including protozoans and metazoans of different phyla and size classes, occupies several trophic niches and regulates energy flow between primary producers and fish. The structural configuration of the food web determines the rates at which primary production is either enriched to sustain organisms at higher trophic levels or exported to the ocean floor. However, limited knowledge about plankton interactions causes uncertainty of how the oceans will respond to climate changes. This thesis presents a framework for studying and modeling pelagic food webs using novel implementations of DNA metabarcoding. Study I shows that DNA metabarcoding of zooplankton sampled in their natural environment reveals a broader and more complex diet than zooplankton in classic grazing observations. We also show that differential feeding strategies facilitate species coexistence and that the zooplankton diet is largely dependent on prey availability. The approach was extended in Study II, where we include the smaller fraction of zooplankton that is often overseen in food web studies to broaden the perspective of functional diversity in pelagic food webs. We show that different populations have unique functions in channeling the primary production of different sources and especially highlight the role of filter-feeders in making detrital nutrients available for other organisms in the food web. In Study III, we shifted focus to trophic links between zooplankton and fish by comparing niche overlap between the three main planktivorous fish in the Baltic Sea - stickleback, sprat, and herring. The results from the three first studies were finally used to calculate selectivity indices between each predator and prey. This information was implemented in Study IV in a network model quantifying fluxes of energy through the food web. The model revealed cyanobacteria as the primary contributor to secondary production in the Baltic Sea food web and that the spring bloom of diatoms and dinoflagellates remains largely unutilized by the zooplankton. This is the first time DNA metabarcoding is used to compare niche differences of several zooplankton species in a pelagic guild and to quantify fluxes in a food web model. The thesis refines our knowledge of pelagic community and food web structure, and the framework presented here is a suitable entry point for food web modeling in other ecosystems.
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| 4. |
- Persson, Karl-Johan, 1982-
(författare)
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Influence of cyanobacterial blooms on coastal fish recruitment
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cyanobacteria are the oldest oxygen-producing organisms on Earth and can be found in almost every terrestrial and aquatic habitat. Their long evolutionary history has enabled them to develop diverse adaptations in order to increase their survival in environments subjected to natural and anthropogenic changes. The frequency and intensity of cyanobacterial blooms in the Baltic Sea have increased during the last century. Summer blooms consisting of the filamentous cyanobacterial genera Nodularia, Aphanizomenon and Anabaena may cover up to 50 % of the Baltic Sea surface, which are the largest cyanobacterial blooms in the world. Simultaneously, recruitment of spring spawning fish such as perch (Perca fluviatilis) and pike (Esox Lucius) have decreased along the Baltic Sea coast. Temporal variations in adult fish abundance have been linked to recruitment success, which is dependent on growth of juvenile fish. Generally, low growth rates affect survival of juvenile fish by causing an increase in the time spent in stages prone to predation and by increasing winter mortality which is negatively size selective. Since growth is a crucial factor determining fish recruitment, all parameters that have the potential to influence fish growth could affect fish recruitment dynamics. Cyanobacteria negatively influence fish growth directly (toxicity, turbidity and changes in water quality) and indirectly (toxin transfer, changes in zooplankton community structure). Cyanobacterial toxins i.e. nodularin accumulate in common coastal fish species (flounders, perch and roach) resulting in an energetic cost associated with detoxification. Cyanobacteria, toxic or non-toxic, also affect the behavior of fish (prey capture) further increasing energetic costs. In nature, spatial variations of both cyanobacteria and salinity are a deadly combination for juvenile fish leading to increased detrimental effects of cyanobacteria on juvenile fish in brackish waters compared to freshwater. However, different fish populations react differently to cyanobacteria i.e. a marine population had higher tolerance to cyanobacteria compared to an oligotrophic population. At the coastal ecosystem level, cyanobacteria cannot explain the decline of juvenile fish. Nevertheless, at the local scale cyanobacteria certainly influence the recruitment of juvenile fish.
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| 5. |
- Sörenson, Eva, 1979-
(författare)
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Functional and structural characterizations of phytoplankton-bacteria interactions in response to environmental challenges
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Microorganisms, such as phytoplankton and bacteria, make up ≈70% of aquatic biomass and contribute 50-85% of the oxygen in Earth’s atmosphere. The microbial loop concept and the discovery of the large diversity in microbial communities acknowledge that biotic interactions between microorganisms in addition to resource competition enable the recycling of energy and nutrients in aquatic food webs. In this thesis, I have studied interactions between phytoplankton and bacteria in three brackish systems of increasing complexity. Interactions were characterized in terms of structure and function, species-specificity aspects, influence on community resilience, and the link between interactions and cycling of energy and nutrients, using a combined approach of molecular techniques, morphology and biochemical analyses, and network analysis. Species-specific core microbiomes were identified in cultures of dinoflagellate isolates with varying genotypes or phenotypes, or from locations with varying levels of anthropogenic impact. We argue that the structure of phytoplankton-bacterial communities is influenced by predictable species-specific interactions, in addition to local abiotic conditions (such as salinity). When microalgal productivity exposed to seasonal variations in light and temperature was examined in photobioreactor polycultures, the stability of microalgal biomass linked to a high bacterial response diversity, primarily seen as shifts in taxonomy. When the structural and functional response of microalgae and bacteria to temperature shifts was coupled to resilience theories (adaptive cycles, panarchy and cross-scale resilience), results suggest that resilience was enabled through internal shifts in function and diversity within and across microalgal and bacterial levels, leading to maintenance of overall community function and diversity. Further, the results suggest that phytoplankton and bacteria in a coastal eutrophied location avoid competition for both energy and nutrients by resource partitioning, indicating that phytoplankton and bacteria might coexist more frequently in dynamic shallow coastal ecosystems than previously thought.The results from this thesis emphasize the importance of considering community interactions between phytoplankton and bacteria when studying aquatic microbial communities, both in cultures and in complex field environments.
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| 6. |
- Aguilera, Anabella, et al.
(författare)
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Ecophysiological analysis reveals distinct environmental preferences in closely related Baltic Sea picocyanobacteria
- 2023
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Ingår i: Environmental Microbiology. - Chichester : John Wiley & Sons. - 1462-2912 .- 1462-2920. ; 25:9, s. 1674-1695
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Tidskriftsartikel (refereegranskat)abstract
- Cluster 5 picocyanobacteria significantly contribute to primary productivity in aquatic ecosystems. Estuarine populations are highly diverse and consist of many co-occurring strains, but their physiology remains largely understudied. In this study, we characterized 17 novel estuarine picocyanobacterial strains. Phylogenetic analysis of the 16S rRNA and pigment genes (cpcBandcpeBA) uncovered multiple estuarine and freshwater-related clusters and pigment types. Assays with five representative strains (three phycocyanin rich and two phycoerythrin rich) under temperature (10–30°C), light(10–190 μmol photons m-2s-1), and salinity (2–14 PSU) gradients revealed distinct growth optima and tolerance, indicating that genetic variability was accompanied by physiological diversity. Adaptability to environmental conditions was associated with differential pigment content and photosynthetic performance. Amplicon sequence variants at a coastal and an offshore station linked population dynamics with phylogenetic clusters, supporting that strains isolated in this study represent key ecotypes within the Baltic Sea picocyanobacterial community. The functional diversity found within strains with the same pigment type suggests that understanding estuarine picocyanobacterial ecology requires analysis beyond the phycocyanin and phycoerythrin divide. This new knowledge of the environmental preferences in estuarine picocyanobacteria is important for understanding and evaluating productivity in current and future ecosystems.
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| 7. |
- Alegria Zufia, Javier, Ph.D. 1992-, et al.
(författare)
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Growth and mortality rates of picophytoplankton in the Baltic Sea Proper
- 2024
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Ingår i: Marine Ecology Progress Series. - Oldendorf : Inter-Research. - 0171-8630 .- 1616-1599. ; 735, s. 63-76
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Tidskriftsartikel (refereegranskat)abstract
- Picophytoplankton (<2 µm diameter), a diverse group of picocyanobacteria and photosynthetic picoeukaryotes, are significant contributors to primary production. Predatory mortality controls picophytoplankton biomass and thereby energy transfer in the marine food web. The 2 major pathways of picophytoplankton mortality are grazing and viral lysis. Grazing passes carbon directly to higher trophic levels, while lysis products are passed into the viral loop. Picophytoplankton are abundant in the Baltic Sea but little is known about their predatory mortality. Using a modification of the dilution approach, we calculated growth and mortality rates of picophytoplankton and studied the effect of predation on community structure during late August and September. The experiments were conducted coinciding with the peak in picophytoplankton abundance (similar to 10(5) cells ml(-1)) at the Linnaeus Microbial Observatory in the Baltic Sea Proper. The results showed that grazing is an important controller of picocyanobacteria and photosynthetic picoeukaryote populations, while no significant viral lysis effect was detected. Grazing on picocyanobacteria was proportional to growth rates, while grazing on photosynthetic picoeukaryotes exceeded growth. Selective grazing of phylogenetically distinct picocyanobacterial clades had a significant effect on community structure, suggesting that grazing has an impact on the seasonal dynamics of co-occurring clades. Picocyanobacteria had a higher carbon transfer contribution to higher trophic levels than photosynthetic picoeukaryotes at the time of the experiments. The study shows that picophytoplankton are important contributors to carbon cycling in the Baltic Sea microbial food web and should be considered for future ecological models.
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| 8. |
- Alegria Zufía, Javier, Ph.D. 1992-
(författare)
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Picophytoplankton seasonal dynamics in the Baltic Sea
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Picophytoplankton (<2 μm diameter) is a diverse group of picocyanobacterial and photosynthetic picoeukaryotes (PPE).Picophytoplankton contribute significantly to total phytoplankton biomassand can dominate primary production in oceans, lakes and estuaries. In the estuarine Baltic Sea, the composition of picophytoplankton is linked to the north to south salinity gradient but knowledge of the seasonal dynamics interms of abundance, biomass and diversity is largely unknown. This thesis investigated the in situ dynamics, bottom up and top down controls of picocyanobacteria (SYN; consisting of primarily Synechococcus and Cyanobium among other genuses) and PPE at two sampling stations, one coastal and one offshore. Monitoring data over three years (2018-2020) showed high biomass contribution across all seasons. Picocyanobacterial peak abundances occurred from spring to summer at the coastal station and in late-summer to autumn at the offshore station (up to 4.7 × 105 cells mL-1).Differentiation of pigment populations showed that phycoerythrin rich(PE)-SYN was the main contributor to SYN abundances except at the coastalstation during summer, when PE-SYN and phycocyanin rich (PC)-SYN had equal contributions. PPE peak abundances occurred during late summer to autumn (up to 1.1 × 105 cells mL-1 cells ml-1). Temperature was linked topicophytoplankton growth and abundance, with PE-SYN, PCSYN and PPEadapted to different temperature ranges. Temperature also affected SYNnitrogen preference: SYN was nitrogen limited during early summer and at>15°C there was a preference for ammonium over nitrate. Clade A/B dominated the SYN community, except during summer at the coastal station when low nitrate and warm temperatures promoted S5.2 dominance. Grazing was observed to control SYN and PPE abundances and had an effect on the SYN community structure. Identification and laboratory experiments of key Synechococcus strains using a range of salinity, temperature and light conditions provided important insights into the physiological diversity of co-occurring ecotypes and links to the SYN dynamics that were observed in the field. In summary, this thesis provided novel information of picophytoplankton dynamics and community structure in the Baltic Sea. The results show that picophytoplankton play a relevant role in Baltic Sea and shows the importance of monitoring programs to understand picophytoplankton dynamics.
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| 9. |
- Alegria Zufia, Javier, Ph.D. 1992-, et al.
(författare)
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Seasonal dynamics in picocyanobacterial abundance and clade composition at coastal and offshore stations in the Baltic Sea
- 2022
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Ingår i: Scientific Reports. - London : Nature Publishing Group. - 2045-2322. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Picocyanobacteria (< 2 um in diameter) are significant contributors to total phytoplankton biomass. Due to the high diversity within this group, their seasonal dynamics and relationship with environmental parameters, especially in brackish waters, are largely unknown. In this study, the abundance and community composition of phycoerythrin rich picocyanobacteria (PE-SYN) and phycocyanin rich picocyanobacteria (PC-SYN) were monitored at a coastal (K-station) and at an offshore station (LMO; similar to 10 km from land) in the Baltic Sea over three years (2018-2020). Cell abundances of picocyanobacteria correlated positively to temperature and negatively to nitrate (NO3) concentration. While PE-SYN abundance correlated to the presence of nitrogen fixers, PC-SYN abundance was linked to stratification/shallow waters. The picocyanobacterial targeted amplicon sequencing revealed an unprecedented diversity of 2169 picocyanobacterial amplicons sequence variants (ASVs). A unique assemblage of distinct picocyanobacterial clades across seasons was identified. Clade A/B dominated the picocyanobacterial community, except during summer when low NO3, high phosphate (PO4) concentrations and warm temperatures promoted S5.2 dominance. This study, providing multiyear data, links picocyanobacterial populations to environmental parameters. The difference in the response of the two functional groups and clades underscore the need for further high-resolution studies to understand their role in the ecosystem.
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| 10. |
- Alegria Zufia, Javier, et al.
(författare)
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Seasonality of Coastal Picophytoplankton Growth, Nutrient Limitation, and Biomass Contribution
- 2021
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Ingår i: Frontiers in Microbiology. - Lausanne : Frontiers Media S.A.. - 1664-302X. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Picophytoplankton in the Baltic Sea includes the simplest unicellular cyanoprokaryotes (Synechococcus/Cyanobium) and photosynthetic picoeukaryotes (PPE). Picophytoplankton are thought to be a key component of the phytoplankton community, but their seasonal dynamics and relationships with nutrients and temperature are largely unknown. We monitored pico- and larger phytoplankton at a coastal site in Kalmar Sound (K-Station) weekly during 2018. Among the cyanoprokaryotes, phycoerythrin-rich picocyanobacteria (PE-rich) dominated in spring and summer while phycocyanin-rich picocyanobacteria (PC-rich) dominated during autumn. PE-rich and PC-rich abundances peaked during summer (1.1 x 10(5) and 2.0 x 10(5) cells mL(-1)) while PPE reached highest abundances in spring (1.1 x 10(5) cells mL(-1)). PPE was the main contributor to the total phytoplankton biomass (up to 73%). To assess nutrient limitation, bioassays with combinations of nitrogen (NO3 or NH4) and phosphorus additions were performed. PE-rich and PC-rich growth was mainly limited by nitrogen, with a preference for NH4 at >15 degrees C. The three groups had distinct seasonal dynamics and different temperature ranges: 10 degrees C and 17-19 degrees C for PE-rich, 13-16 degrees C for PC-rich and 11-15 degrees C for PPE. We conclude that picophytoplankton contribute significantly to the carbon cycle in the coastal Baltic Sea and underscore the importance of investigating populations to assess the consequences of the combination of high temperature and NH4 in a future climate.
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