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Bloom-Forming Cyanobacteria Support Copepod Reproduction and Development in the Baltic Sea
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
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2014 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 11, e112692Article in journal (Refereed) Published
Abstract [en]

It is commonly accepted that summer cyanobacterial blooms cannot be efficiently utilized by grazers due to low nutritional quality and production of toxins; however the evidence for such effects in situ is often contradictory. Using field and experimental observations on Baltic copepods and bloom-forming diazotrophic filamentous cyanobacteria, we show that cyanobacteria may in fact support zooplankton production during summer. To highlight this side of zooplankton-cyanobacteria interactions, we conducted: (1) a field survey investigating linkages between cyanobacteria, reproduction and growth indices in the copepod Acartia tonsa; (2) an experiment testing relationships between ingestion of the cyanobacterium Nodularia spumigena (measured by molecular diet analysis) and organismal responses (oxidative balance, reproduction and development) in the copepod A. bifilosa; and (3) an analysis of long term (1999-2009) data testing relationships between cyanobacteria and growth indices in nauplii of the copepods, Acartia spp. and Eurytemora affinis, in a coastal area of the northern Baltic proper. In the field survey, N. spumigena had positive effects on copepod egg production and egg viability, effectively increasing their viable egg production. By contrast, Aphanizomenon sp. showed a negative relationship with egg viability yet no significant effect on the viable egg production. In the experiment, ingestion of N. spumigena mixed with green algae Brachiomonas submarina had significant positive effects on copepod oxidative balance, egg viability and development of early nauplial stages, whereas egg production was negatively affected. Finally, the long term data analysis identified cyanobacteria as a significant positive predictor for the nauplial growth in Acartia spp. and E. affinis. Taken together, these results suggest that bloom forming diazotrophic cyanobacteria contribute to feeding and reproduction of zooplankton during summer and create a favorable growth environment for the copepod nauplii.

Place, publisher, year, edition, pages
2014. Vol. 9, no 11, e112692
National Category
Biological Sciences Earth and Related Environmental Sciences
Research subject
Marine Ecology
Identifiers
URN: urn:nbn:se:su:diva-111918DOI: 10.1371/journal.pone.0112692ISI: 000345533200032OAI: oai:DiVA.org:su-111918DiVA: diva2:778338
Note

AuthorCount:9;

Available from: 2015-01-09 Created: 2015-01-08 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Summer cyanobacterial blooms in the Baltic Sea - implications for copepod recruitment
Open this publication in new window or tab >>Summer cyanobacterial blooms in the Baltic Sea - implications for copepod recruitment
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

During summer, the Baltic Sea is subjected to the world’s largest cyanobacterial blooms. These blooms are linked to eutrophication and raise many questions concerning their effects on the ecosystem. To understand their impacts on the food web dynamics, it is essential to assess growth responses of grazers to these cyanobacteria. In the northern Baltic proper, copepods are the most important herbivores providing an essential link between the primary producers and higher trophic levels. In this Thesis, Papers I & II evaluate methods to estimate copepod growth in response to feeding conditions in situ. The most conspicuous diazotrophic filamentous cyanobacterium in the Baltic Sea is Nodularia spumigena, a producer of nodularin which is highly toxic to vertebrates, yet its ecological role is largely unknown. In Paper III, reciprocal interactions between cyanobacteria, sympatric algae and copepods are studied. The results suggest that nodularin is likely involved in allelopathic interactions, but it is not an inducible defense against grazers. Furthermore, the results of Papers IV & V, indicate that natural assemblages of N. spumigena and Anabaena spp. may support copepod reproduction and that total diazotrophic filamentous cyanobacteria appear to provide a beneficial feeding environment for the feeding stages of copepod nauplii, most probably by stimulating the microbial communities that nauplii feed upon. Since cyanobacterial blooms are projected to increase due to global climate change, the combined effects of toxic cyanobacteria, ocean acidification and global warming predicted for year 2100 are further investigated on copepods in Paper IV. Taken together, these studies indicate that filamentous diazotrophic cyanobacteria contribute to sustaining secondary productivity and have potential implications of management practices with respect to combating eutrophication, global climate change and sustaining fish feeding conditions.

Place, publisher, year, edition, pages
Stockholm: Department of Systems Ecology, Stockholm University, 2012. 56 p.
Keyword
Cyanobacteria, Calanoid copepods, Food web interactions, Harmful algae blooms, Zooplankton, Nodularin, Allelopathy, Baltic Sea, Biochemical markers, RNA-based indices, Acidification, Global Climate Change
National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-81680 (URN)978-91-7447-566-1 (ISBN)
Public defence
2012-12-03, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Manuscript.

Available from: 2012-11-12 Created: 2012-10-30 Last updated: 2015-04-13Bibliographically approved
2. 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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