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Nitrogen fixation by cyanobacteria stimulates production in Baltic food webs
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
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Number of Authors: 13
2015 (English)In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 44, 413-426 p.Article in journal (Refereed) Published
Abstract [en]

Filamentous, nitrogen-fixing cyanobacteria form extensive summer blooms in the Baltic Sea. Their ability to fix dissolved N-2 allows cyanobacteria to circumvent the general summer nitrogen limitation, while also generating a supply of novel bioavailable nitrogen for the food web. However, the fate of the nitrogen fixed by cyanobacteria remains unresolved, as does its importance for secondary production in the Baltic Sea. Here, we synthesize recent experimental and field studies providing strong empirical evidence that cyanobacterial nitrogen is efficiently assimilated and transferred in Baltic food webs via two major pathways: directly by grazing on fresh or decaying cyanobacteria and indirectly through the uptake by other phytoplankton and microbes of bioavailable nitrogen exuded from cyanobacterial cells. This information is an essential step toward guiding nutrient management to minimize noxious blooms without overly reducing secondary production, and ultimately most probably fish production in the Baltic Sea.

Place, publisher, year, edition, pages
2015. Vol. 44, 413-426 p.
Keyword [en]
Diazotrophic cyanobacteria, Food webs, Zooplankton grazing, Secondary production, Fish
National Category
Environmental Engineering Earth and Related Environmental Sciences
Research subject
Marine Ecology
Identifiers
URN: urn:nbn:se:su:diva-122130DOI: 10.1007/s13280-015-0660-xISI: 000362290800009OAI: oai:DiVA.org:su-122130DiVA: diva2:864333
Available from: 2015-10-26 Created: 2015-10-26 Last updated: 2017-12-01Bibliographically approved
In thesis
1. Trophic complexity of zooplankton–cyanobacteria interactions in the Baltic Sea: Insights from molecular diet analysis
Open this publication in new window or tab >>Trophic complexity of zooplankton–cyanobacteria interactions in the Baltic Sea: Insights from molecular diet analysis
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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).

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2015. 42 p.
Keyword
bloom-forming filamentous cyanobacteria, diazotrophs, picocyanobacteria, zooplankton, grazing, molecular diet analysis, stable isotopes, biochemical indices
National Category
Biological Sciences Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-116219 (URN)978-91-7649-118-8 (ISBN)
Public defence
2015-05-22, Stora föreläsningssalen, Institutionen för ekologi, miljö och botanik, Lilla Frescativägen 5, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Baltic Ecosystem Adaptive Management (BEAM)Swedish Research Council Formas
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Accepted.

Available from: 2015-04-28 Created: 2015-04-14 Last updated: 2015-10-26Bibliographically approved

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Karlson, Agnes M. L.Duberg, JonMotwani, Nisha H.Klawonn, IsabellBarthel Svedén, JennieSundelin, BritaHajdu, SusannaLarsson, UlfElmgren, RagnarGorokhova, Elena
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