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Spatial patterns of marine bacterioplankton along gradients of primary production in the Amundsen Sea Polynya, Southern Ocean
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
(Marine Biological Section, University of Copenhagen, Helsingør, Denmark)
(Institute of Marine Sciences, CSIC, Barcelona, Spain)
(Marine Biological Section, University of Copenhagen, Helsingør, Denmark)
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

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.

Keyword [en]
marine bacterioplankton, community dynamics, Southern Ocean
National Category
Biological Sciences
Research subject
Biology with specialization in Microbiology
URN: urn:nbn:se:uu:diva-229137OAI: oai:DiVA.org:uu-229137DiVA: diva2:735855
Swedish Research Council
Available from: 2014-08-01 Created: 2014-08-01 Last updated: 2015-05-07
In thesis
1. Environmental filtering of bacteria in low productivity habitats
Open this publication in new window or tab >>Environmental filtering of bacteria in low productivity habitats
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Microbes fulfill important ecosystem functions by contributing as drivers of global nutrient cycles. Their distribution patterns are mainly controlled by environmental heterogeneities. So far, little is known about the mode of action of particular environmental drivers on the microbiota, particularly in low productivity habitats.

The aim of this thesis was to investigate the relationships between local environmental drivers and the microbial responses at the level of communities, individuals and realized function, using three structurally different model habitats sharing the feature of overall low productivity. Using a hypothesis-based approach and extensive 16S rRNA amplicon mapping of bacterioplankton colonizing the polar Southern Ocean, I identified how the seasonal formation of open-water polynyas and coupled phytoplankton production affected the diversity of surface bacterial communities and resulted in a cascading effect influencing the underlying dark polar water masses. Additional laboratory experiments, with cultures exposed to light, resulted in reduction in alpha diversity and promoted opportunistic populations with most bacterial populations thriving in the cultures typically reflected the dominants in situ.

Furthermore it was experimentally tested how induced cyclic water table fluctuations shaping environmental heterogeneity in a constructed wetland on temporal scale, by directly affecting redox conditions. Twelve months of water table fluctuations resulted in enhanced microbial biomass, however a shift in community composition did not lead to a significant increase in pollutant removal efficiency when compared to a static control wetland. I detected phyla that have previously been proposed as key players in anaerobic benzene break-down using a protocol that was developed for single cell activity screening using isotope-substrate uptake and microautoradiography combined with taxonomic identification based on fluorescent in situ hybridization targeting the 16S rRNA. Eventually, I provide an example of how anthropogenic pollution with polyaromatic hydrocarbons induced a strong environmental filtering on intrinsic microbial communities in lake sediments.

In conclusion, my studies reveal that microorganisms residing in low productivity habitats are greatly influenced by environmental heterogeneity across both spatial and temporal scales. However, such variation in community composition or overall abundance does not always translate to altered community function.


Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 44 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1157
bacteria, environmental filtering, diversity, ecosystem service, hydrocarbon utilization, Southern Ocean, sediment
National Category
Natural Sciences Biological Sciences
Research subject
Biology with specialization in Microbiology
urn:nbn:se:uu:diva-229144 (URN)978-91-554-8986-1 (ISBN)
Public defence
2014-09-16, Fries salen, Evolutionsbiologiskt centrum, EBC, Norbyvägen 18, 752 36 Uppsala, Uppsala, 10:00 (English)
Available from: 2014-08-26 Created: 2014-08-01 Last updated: 2014-09-08

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