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Mechanisms structuring the pelagic microbial food web: Importance of resource and predation
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Temporal and spatial variations of pelagic microorganisms in the northern Baltic Sea were studied, as well as factors influencing their abundance and growth rates. Three main questions were asked 1) How does increased productivity influence the structure of the microbial food web? 2) Does predation limitation vary between trophic levels? 3) What is the relative importance of resource and predation limitation at different trophic levels?

A field study in the northern Baltic Sea showed that dominating protozoa, flagellates and ciliates, increased with increasing primary productivity from north to south. Furthermore, relatively small protozoan cells dominated in the low productive north, while larger cells became more dominant in the south. The relationship between plankton size structure and productivity was further studied in an experimental system. In agreement with present theories regarding nutrient status of pelagic food webs, increased productivity caused a lengthening of the food chain as well as a change in plankton size structure. While microplankton dominated in nutrient rich treatments pico- and nanoplankton dominated during nutrient poor treament. The flagellate community was dominated by a potentially mixotroph, Chrysochromulina sp., at low nutrient concentrations. To our knowledge this is the first experimental study showing that Chrysochromulina sp. in resemblance with other mixotrophs is favoured by nutrient poor conditions compared to strict autotrophs and heterotrophs.

During a stratified summer period autotrophic microorganisms in the northern Baltic Sea did not respond to removal of potential predators, indicating that they were primarily limited by inorganic nutrients. An exception was small eucaryotic picoplankton that showed a large response to predator removal. Among the heterotrophic microorganisms direct effect of predation seemed to increase from ciliates, heterotrophic bacteria, small heterotrophic flagellates, medium flagellates to large flagellates. No quick indirect effect was observed, but after four days trophic cascades were detected.

The relative importance of resource and predation limitation was studied among heterotrophic bacteria, flagellates and ciliates in the northern Baltic Sea. For all these groups, resource limitation seemed to prevail during the summer period. The results also indicated that the relative importance of predation increased with the productivity of the system. To our knowledge there are no earlier measurements on the relative importance of resource and predation limitation for micoorganisms in the pelagic environment.

Place, publisher, year, edition, pages
2003. , 36 p.
Keyword [en]
Ecology, pelagic microbial food web, bacteria, flagellates, ciliates, phytoplankton, mixotrophy, nutrient status, predation limitation, resource limitation, Baltic Sea
Keyword [sv]
Ekologi
National Category
Ecology
Identifiers
URN: urn:nbn:se:umu:diva-188ISBN: 91-7305-464-X (print)OAI: oai:DiVA.org:umu-188DiVA: diva2:142292
Public defence
2003-06-12, Umeå, 09:00
Opponent
Supervisors
Available from: 2004-01-30 Created: 2004-01-30Bibliographically approved
List of papers
1. Structural changes in an aquatic microbial food web caused by inorganic nutrient addition
Open this publication in new window or tab >>Structural changes in an aquatic microbial food web caused by inorganic nutrient addition
2002 In: Aquatic Microbial Ecology, ISSN 0948-3055, Vol. 29, no 1, 29-38 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-3537 (URN)
Available from: 2004-01-30 Created: 2004-01-30Bibliographically approved
2. Fate of increased production due to nutrient enrichment in late-summer plankton communities of the Baltic Proper
Open this publication in new window or tab >>Fate of increased production due to nutrient enrichment in late-summer plankton communities of the Baltic Proper
Show others...
2003 (English)In: Aquatic Microbial Ecology, ISSN 0948-3055, Vol. 32, no 1, 47-60 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-3538 (URN)
Available from: 2004-01-30 Created: 2004-01-30 Last updated: 2017-10-24Bibliographically approved
3. Factors structuring the protozoan community along a brackish water productivity gradient
Open this publication in new window or tab >>Factors structuring the protozoan community along a brackish water productivity gradient
Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-3539 (URN)
Available from: 2004-01-30 Created: 2004-01-30 Last updated: 2010-01-13Bibliographically approved
4. Predation limitation of the pelagic microbial food web in an oligotrophic aquatic system
Open this publication in new window or tab >>Predation limitation of the pelagic microbial food web in an oligotrophic aquatic system
2003 In: Aquatic Microbial Ecology, ISSN 0948-3055, Vol. 30, no 3, 239-250 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-3540 (URN)
Available from: 2004-01-30 Created: 2004-01-30Bibliographically approved
5. Simultaneous resource and predation limitation in the marine microbial food web
Open this publication in new window or tab >>Simultaneous resource and predation limitation in the marine microbial food web
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Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-3541 (URN)
Available from: 2004-01-30 Created: 2004-01-30 Last updated: 2010-01-13Bibliographically approved

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Citation style
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