| 1. |
- Degerman, Rickard, et al.
(författare)
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Effect of resource availability on bacterial community responses to increased temperature
- 2013
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Ingår i: Aquatic Microbial Ecology. - : Inter-Research Science Center. - 0948-3055 .- 1616-1564. ; 68:2, s. 131-142
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Tidskriftsartikel (refereegranskat)abstract
- Climate change is predicted to cause higher temperatures and increased precipitation, resulting in increased inflow of nutrients to coastal waters in northern Europe. This has been assumed to increase the overall heterotrophy, including enhanced bacterial growth. However, the relative importance of temperature, resource availability and bacterial community composition for the bacterial growth response is poorly understood. In the present study, we investigated effects of increased temperature on bacterial growth in waters supplemented with different nutrient concentrations and inoculated with microbial communities from distinct seasonal periods. Seven experiments were performed in the northern Baltic Sea spanning an entire annual cycle. In each experiment, bacterioplankton were exposed to 2 temperature regimes (in situ and in situ + 4 degrees C) and 5 nutrient concentrations. Generally, elevated temperature and higher nutrient levels caused an increase in the bacterial growth rate and a shortening of the response time (lag phase). However, at the lowest nutrient concentration, bacterial growth was low at all tested temperatures, implying a stronger dependence on resource availability than on temperature for bacterial growth. Furthermore, data indicated that different bacterial assemblages had varying temperature responses and that community composition was strongly affected by the combination of high nutrient addition and high temperature. These results support the concern that climate change will promote heterotrophy in aquatic systems, where nutrient levels will increase considerably. In such environments, the bacterial community composition will change, their growth rates will increase, and their response time will be shortened compared to the present situation.
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| 2. |
- Dinasquet, Julie, et al.
(författare)
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Cascading effects of the ctenophore Mnemiopsis leidyi on the planktonic food web in a nutrient-limited estuarine system
- 2012
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Ingår i: Marine Ecology Progress Serie. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 460, s. 49-61
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Tidskriftsartikel (refereegranskat)abstract
- Increasing biomasses of gelatinous zooplankton presumably have major implications for the structure and function of marine food webs at large; however, current data on lower trophic levels are scarce, as most studies have focused on the immediate effects on zooplankton and fish larvae only. We examined the short-term impact of larvae and adults of the invasive ctenophore Mnemiopsis leidyi on a summer planktonic food web in the estuarine southern Baltic Sea, with special emphasis on the microbial loop. Grazing by M. leidyi reduced the mesozooplankton biomass, followed by increased dinoflagellate biomass in treatments with M. leidyi. While chlorophyll a increased most in the treatments with M. leidyi, small phytoplankton and ciliates decreased in all treatments. M. leidyi had a slight effect on bacterial abundance, but not on bacterial production, ectoenzymatic activities, or community composition. Undetectable levels of phosphate and a gradual accumulation of dissolved organic carbon during the experiment suggested a malfunctioning microbial loop scenario. The experiment shows that direct and indirect short-term effects of M. leidyi on the estuarine food web are limited to higher trophic levels and indicates that top-down and bottom-up consequences of M. leidyi expansions on the microbial loop will likely depend on local nutrient conditions.
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| 3. |
- Dinasquet, Julie, et al.
(författare)
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Functional and compositional succession of bacterioplankton in response to a gradient in bioavailable dissolved organic carbon
- 2013
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Ingår i: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 15:9, s. 2616-2628
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Tidskriftsartikel (refereegranskat)abstract
- Studies indicate that bacterial taxa utilize different fractions of the dissolved organic carbon (DOC) pool, while others suggest functional redundancy among constituents of bacterioplankton, implying only a weak coupling between community structure and function. We examined bacterial compositional and functional [ectoenzymatic activities and growth efficiency; bacterial growth efficiency (BGE)] responses to a gradient in bioavailable DOC (bDOC). This was achieved over 10 days in DOC utilization assays containing Baltic Sea water with variable amounts of natural bDOC. Measurements of bacterial growth, O-2 and DOC consumption in the assays using non-invasive sampling showed that BGE changed over time and that the bDOC utilized accounted for 4-13% of the DOC pool. Pyrosequencing of 16S rRNA genes demonstrated minor differences at the phylum level between samples, whereas larger successional differences were discernible at lower phylogenetic levels. Our study suggests that changes in concentrations of bDOC affect bacterioplankton BGE and community structure by selecting for some taxa while the relative abundance of most taxa remained unaffected. Ectoenzymes activities suggested preferential degradation of protein-rich compounds by bacteria, switching to carbohydrate-rich DOC when proteins were depleted. Hence, there was a fairly weak linkage between bacterial community composition and DOC utilization suggesting that overall bacterioplankton community structure only to some extent has predictive power for processing of the DOC pool.
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| 4. |
- Dinasquet, Julie, et al.
(författare)
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Mixing of water masses caused by a drifting iceberg affects bacterial activity, community composition and substrate utilization capability in the Southern Ocean
- 2017
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Ingår i: Environmental Microbiology. - : Wiley-Blackwell. - 1462-2912 .- 1462-2920. ; 19:6, s. 2453-2467
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Tidskriftsartikel (refereegranskat)abstract
- The number of icebergs produced from ice-shelf disintegration has increased over the past decade in Antarctica. These drifting icebergs mix the water column, influence stratification and nutrient condition, and can affect local productivity and food web composition. Data on whether icebergs affect bacterioplankton function and composition are scarce, however. We assessed the influence of iceberg drift on bacterial community composition and on their ability to exploit carbon substrates during summer in the coastal Southern Ocean. An elevated bacterial production and a different community composition were observed in iceberg-influenced waters relative to the undisturbed water column nearby. These major differences were confirmed in short-term incubations with bromodeoxyuridine followed by CARD-FISH. Furthermore, one-week bottle incubations amended with inorganic nutrients and carbon substrates (a mix of substrates, glutamine, Nacetylglucosamine, or pyruvate) revealed contrasting capacity of bacterioplankton to utilize specific carbon substrates in the iceberg-influenced waters compared with the undisturbed site. Our study demonstrates that the hydrographical perturbations introduced by a drifting iceberg can affect activity, composition, and substrate utilization capability of marine bacterioplankton. Consequently, in a context of global warming, increased frequency of drifting icebergs in polar regions holds the potential to affect carbon and nutrient biogeochemistry at local and possibly regional scales.
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| 5. |
- Dinasquet, Julie, et al.
(författare)
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Stimulated bacterioplankton growth and selection for certain bacterial taxa in the vicinity of the ctenophore Mnemiopsis leidyi
- 2012
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Ingår i: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- Episodic blooms of voracious gelatinous zooplankton, such as the ctenophore Mnemiopsis leidyi, affect pools of inorganic nutrients and dissolved organic carbon by intensive grazing activities and mucus release. This will potentially influence bacterioplankton activity and community composition, at least at local scales; however, available studies on this are scarce. In the present study we examined effects of M. leidyi on bacterioplankton growth and composition in incubation experiments. Moreover, we examined community composition of bacteria associated with the surface and gut of M. leidyi. High release of ammonium and high bacterial growth was observed in the treatments with M. leidyi relative to controls. Deep 454 pyrosequencing of 16 S rRNA genes showed specific bacterial communities in treatments with M. leidyi as well as specific communities associated with M. leidyi tissue and gut. In particular, members of Flavobacteriaceae were associated with M. leidyi. Our study shows that M. leidyi influences bacterioplankton activity and community composition in the vicinity of the jellyfish. In particular during temporary aggregations of jellyfish, these local zones of high bacterial growth may contribute significantly to the spatial heterogeneity of bacterioplankton activity and community composition in the sea.
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| 6. |
- Dinasquet, Julie
(författare)
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Substrate control of community composition and functional adaptation in marine bacterioplankton
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A drop of sea-water is teeming with a million of bacteria, on which pelagic food-webs and biogeochemical cycles depend. These bacteria thrive on a wide range of dissolved organic carbon (DOC) compounds produced through biotic and abiotic processes. Molecular analyses have over the past decades shown that specific bacterial taxa differ in their capacity to exploit DOC, suggesting a tight link between bacterial community composition (BCC) and ocean biogeo-chemistry. Therefore, an understanding of how resource availability and mortality agents drive BCC and bacterial functional adaptation is a prerequisit for predictions of how marine ecosystems will respond to future global change.In this thesis, I have studied BCC and bacterial functionality in response to various controlling factors relevant in an environmental changes perspective. For instance, the extensive regional warming in Antarctica induces the proliferation of icebergs. By investigating the bacterioplankton in the surrounding of a drifting iceberg, hydrographical perturbations driven by the iceberg were found to affect BCC, functionality and the capacity of indigenous taxa to utilize specific DOC compounds. Furthermore, a study of community succession during DOC utilization assays demonstrated that bacterial assemblages adapt to the gradual exhaustion of available DOC through community compositional succession. In addition, the variation in substrate availability and temperature may also affect BCC in eutrophic systems.While substrate availability can have an important impact on BCC and bacterial functionality, it is also important to study the cascading effects of higher trophic levels on bacteria. During a mesocosm experiment, the presence of an invasive gelatinous top-predator was shown to have only limited effects on the structure and function of the bacterial community in the Baltic Sea due to nutrient limiting conditions and to the overall complexity of the food-web. However, this top-predator may have direct bottom-up impact on bacteria in its close surrounding.The results presented in this thesis show that the bacterioplankton is sensitive to the availability of substrates and that bacterial community composition responds to contemporary environmental conditions. These results contribute to our understanding of how ecosystem disturbances affect marine bacterioplankton; insights of relevance to biogeochemistry and food-webs in the oceans.
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| 7. |
- Hosia, Aino, et al.
(författare)
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Autumnal bottom-up and top-down impacts of Cyanea capillata: a mesocosm study
- 2015
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 37:5, s. 1042-1055
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Tidskriftsartikel (refereegranskat)abstract
- Jellyfish are effective predators on mesozooplankton and release large amounts of dissolved organic matter. Nevertheless, jellyfish initiated trophic cascades and bottom-up influences impacting lower trophic levels have received limited attention. We conducted a mesocosm experiment to quantify simultaneous top-down and bottom-up effects of a common jellyfish, Cyanea capillata, in a natural plankton community during autumn. Treatments were 0, 2 or 5 jellyfish per 2.5 m3 mesocosm, four replicates each, with initial additions of inorganic nutrients. Primary and bacterial production, species abundance and composition of several trophic levels and nutrient and carbon dynamics were followed during the 8-day experiment. Multivariate statistics and generalized additive mixed modelling were applied to test whether jellyfish carbon concentration (0–1.26 mg jellyC L−1) in the mesocosms affected the variables monitored. Unexpected negligible predatory impact of jellyfish on mesozooplankton was observed, potentially related to jellyfish senescence. Community compositions of bacteria, phytoplankton and mesozooplankton changed with time, but did not differ between treatments. However, nutrient regeneration by jellyfish was evident, and jellyfish had a positive impact on total and specific bacterial production, total primary production and the >10 µm chlorophyll a fraction. Bottom-up influences from abundant jellyfish could thus stimulate productivity in nutrient depleted autumnal surface waters.
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| 8. |
- Olofsson, Malin, et al.
(författare)
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Limited response of a spring bloom community inoculated with filamentous cyanobacteria to elevated temperature and pCO2
- 2019
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Ingår i: Botanica Marina. - : Walter de Gruyter GmbH. - 0006-8055 .- 1437-4323. ; 62:1
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Tidskriftsartikel (refereegranskat)abstract
- Temperature and CO2 levels are projected to increase in the future, with consequences for carbon and nutrient cycling in brackish environments, such as the Baltic Sea. Moreover, filamentous cyanobacteria are predicted to be favored over other phytoplankton groups under these conditions. Under a 12-day outdoor experiment, we examined the effect on a natural phytoplankton spring bloom community of elevated temperature (from 1°C to 4°C) and elevated pCO2 (from 390 to 970 μatm). No effects of elevated pCO2 or temperature were observed on phytoplankton biovolumes, but a significantly higher photosystem II activity was observed at elevated temperature after 9 days. In addition, three species of diazotrophic filamentous cyanobacteria were inoculated to test their competitive capacity under spring bloom conditions. The toxic cyanobacterium Nodularia spumigena exhibited an average specific growth rate of 0.10 d−1 by the end of the experiment, indicating potential prevalence even during wintertime in the Baltic Sea. Generally, none of the inoculated cyanobacteria species were able to outcompete the natural phytoplankton species at temperatures ≤4°C. No direct effects were found on heterotrophic bacteria. This study demonstrates the highly efficient resistance towards short-term (12 days) changes in abiotic factors by the natural Baltic Sea spring bloom community.
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| 9. |
- Richert, Inga, et al.
(författare)
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Spatial patterns of marine bacterioplankton along gradients of primary production in the Amundsen Sea Polynya, Southern Ocean
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- During austral summers, the Southern Ocean's biota experience a sharp increase in primary production and a steepening of biotic and abiotic gradients, resulting from increased solar radiation and retreating ice. In one of the largest ice-free patches - the Amundsen Sea Polynya - we aimed to identify connections between spatial diversity patterns of heterotrophic bacterioplankton and gradients of phytoplankton biomass. We gathered samples from throughout the depth profile at 15 sites during the austral summer of 2010/2011, collecting bacterioplankton and measuring several biotic and abiotic factors in the surrounding seawater. We assessed bacterial community structure by targeting the 16S rRNA gene for pyrosequencing. Our overall goal was to identify patterns of spatial diversity in heterotrophic bacterioplankton and to generate and test mechanistic hypotheses for bacterioplankton community structure related to phytoplankton biomass, biotic and abiotic nutrients, and hydrological relationships due to depth and water mass.We found that processes acting within the photic surface related to the level of phytoplankton biomass induce a strong filtering effect by decreasing bacterioplankton community richness while increasing bacterioplankton abundance as phytoplankton biomass increases. We also found that the bacterioplankton community in the photic surface represents a subset of that found in the underlying dark water masses, likely reformed annually as the polynya appears; bacterial communities in surface waters reflect the communities found beneath, though as phytoplankton biomass increases, the similarity of these communities between different sites within the polynya increases, likely due to the filtering effect. The high phytoplankton biomass in the photic surface represents an important pool of organic matter and inorganic nutrients, fueling the underlying dark water with nutrients in a cascading effect; we found that in contrast to the community response in shallower water, the bacterioplankton community at the bottom of the phytoplankton biomass increased in diversity as phytoplankton biomass in overlying waters increased, while deeper waters remained largely unaffected. We propose that this lack of, response in deeper water masses gives rise to the observed high group dispersal in bacterial community composition in all water masses and the relatively homogenous community in the bottom water mass.
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| 10. |
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