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Summer cyanobacterial blooms in the Baltic Sea - implications for copepod recruitment
Stockholm University, Faculty of Science, Department of Systems Ecology.
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 [en]
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: urn:nbn:se:su:diva-81680ISBN: 978-91-7447-566-1 (print)OAI: oai:DiVA.org:su-81680DiVA: diva2:563819
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
List of papers
1. Biochemical proxies for growth and metabolism in Acartia bifilosa (Copepoda, Calanoida)
Open this publication in new window or tab >>Biochemical proxies for growth and metabolism in Acartia bifilosa (Copepoda, Calanoida)
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2009 (English)In: Limnology and Oceanography: Methods, ISSN 1541-5856, E-ISSN 1541-5856, Vol. 7, 785-794 p.Article in journal (Refereed) Published
Abstract [en]

Biochemical proxies are becoming increasingly common for growth assessment in zooplankton. Their suitability is often unknown, however, and proper calibration is lacking. We investigated correlations between physiological variables (ingestion, egg production, and respiration rates) and biochemical indices related to protein synthesis (RNA content, RNA:DNA ratio, RNA:protein ratio, and protein specific aminoacyl-tRNA synthetases [spAARS] activity) in copepods Acartia bifilosa exposed to different algal concentrations (0–1200 µg C L–1). All variables assayed increased with increasing food concentration either linearly (spAARS) or nonlinearly (all other variables). Egg production and ingestion rates were significantly and positively correlated with RNA content and RNA:protein ratio, whereas correlations with spAARS and RNA:DNA ratio were weaker or nonsignificant. However, when RNA:DNA ratio and spAARS activity were used as predictors of ingestion, together they had higher explanatory value than did either variable separately. As there were substantial differences in saturating food concentrations among the assayed variables, applicability of biomarkers as proxies of physiological rates will be more reliable if restricted to the nonsaturated phase of the functional response of either variable, unless both variables saturate simultaneously. These findings contribute to methodology of zooplankton growth assessment and to our understanding of biochemical processes underlying growth and metabolism in copepods.

National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-32862 (URN)000273294600007 ()
Available from: 2009-12-17 Created: 2009-12-17 Last updated: 2012-10-31Bibliographically approved
2. Does female RNA content reflect viable egg production in copepods?: A test with the Baltic copepod Acartia tonsa
Open this publication in new window or tab >>Does female RNA content reflect viable egg production in copepods?: A test with the Baltic copepod Acartia tonsa
2011 (English)In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 33, no 9, 1460-1463 p.Article in journal (Refereed) Published
Abstract [en]

Biomarkers are very useful for in situ assessments of zooplankton growth. In particular, RNA-based methods have been developed to estimate egg production in copepods. However, RNA-growth relationships can potentially depend on a variety of factors, such as egg quality. This study shows that in Acartia tonsa, female RNA-content reflects egg production irrespective of egg viability, implying that this growth proxy is not applicable for recruitment studies if the proportion of viable eggs fluctuates widely.

Keyword
RNA, egg viability, biomarker, copepods, nucleic acids, egg production, Acartia, tonsa
National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-68026 (URN)10.1093/plankt/fbr043 (DOI)000293634400012 ()
Note

authorCount :4

Available from: 2012-01-03 Created: 2012-01-02 Last updated: 2017-12-08Bibliographically approved
3. Toxin-producing cyanobacterium Nodularia spumigena, potential competitors and grazers: testing mechanisms of reciprocal interactions
Open this publication in new window or tab >>Toxin-producing cyanobacterium Nodularia spumigena, potential competitors and grazers: testing mechanisms of reciprocal interactions
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2011 (English)In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 62, no 1, 39-48 p.Article in journal (Refereed) Published
Abstract [en]

Interactions among toxic cyanobacteria, sympatric algae and planktivorous grazers are key processes governing plankton dynamics and cyanobacterial blooms. We studied interactions between the cyanobacterium Nodularia spumigena and microalgae (Rhodomonas salina and Tetraselmis suecica) as well as effects of zooplankton (copepod Eurytemora affinis) grazing on these interactions. N. spumigena was incubated without algae or with algae at different concentrations and with or without copepods. Following similar to 24 h incubation, we assayed changes in N. spumigena and algae abundance, concentration of intracellular (IC) and dissolved nodularin (toxin produced by N. spumigena) and quantity of Nodularia DNA in copepod guts (as a proxy for grazing pressure on the cyanobacterium). In the presence of algae, IC nodularin levels increased in a concentration-dependent manner; however, when copepods were present in the mixtures of algae and cyanobacterium, this increase was significantly less. The presence of T. suecica negatively affected the growth rate of N. spumigena, whereas the presence of the cyanobacterium strongly impeded growth of R. salina, but not of T. suecica. The IC nodularin quota correlated negatively with growth of R. salina, implicating the toxin's involvement in the observed growth suppression of the eukaryotic alga. Copepods actively ingested N. spumigena, even when the alternative food was plentiful, and neither N. spumigena quantity nor its toxin concentrations influenced copepod feeding rates and survival. These findings suggest complex allelopathic interactions between the autotrophs, whereas mesozooplankton grazers have an indirect negative effect on the nodularin concentrations by suppressing the competitors. These findings underscore the need to study ecologically important interactions among toxic cyanobacteria, sympatric algae and grazers, if we are to understand mechanisms regulating cyanobacterial blooms.

Keyword
Algae, Allelopathy, Grazers, Molecular diet analysis, Nodularin, Toxic cyanobacteria, Trophic interactions
National Category
Ecology Oceanography, Hydrology, Water Resources
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-68394 (URN)10.3354/ame01456 (DOI)000285935100004 ()
Note

authorCount :6

Available from: 2012-01-04 Created: 2012-01-03 Last updated: 2017-12-08Bibliographically approved
4. Projected marine climate changes: effects on copepod oxidative status and reproduction
Open this publication in new window or tab >>Projected marine climate changes: effects on copepod oxidative status and reproduction
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Because of their important role between primary producers and fish, it is crucial to address zooplankton responses when predicting effects of climate change on pelagic ecosystems. For realistic community-level predictions, several biotic and abiotic climate-related variables should be examined in combination. We studied the combined effects of ocean acidification and global warming predicted for year 2100 with toxic cyanobacteria on a calanoid copepod, Acartia bifilosa. Together, acidification and temperature increase reduced copepod antioxidant capacity. Egg viability, nauplii development and oxidative status also decreased at above-ambient temperature. Exposure to cyanobacteria and its toxin had a negative effect on egg production but, surprisingly, a positive effect on oxidative status and egg viability. This resulted in no net effects on viable egg production. Additionally, nauplii development was enhanced by presence of cyanobacteria, which partially alleviated the otherwise negative effects of forecasted climate change on the copepod population.

National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-81677 (URN)
Available from: 2012-10-30 Created: 2012-10-30 Last updated: 2012-10-31Bibliographically approved
5. Bloom-Forming Cyanobacteria Support Copepod Reproduction and Development in the Baltic Sea
Open this publication in new window or tab >>Bloom-Forming Cyanobacteria Support Copepod Reproduction and Development in the Baltic Sea
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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.

National Category
Biological Sciences Earth and Related Environmental Sciences
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-111918 (URN)10.1371/journal.pone.0112692 (DOI)000345533200032 ()
Note

AuthorCount:9;

Available from: 2015-01-09 Created: 2015-01-08 Last updated: 2017-12-05Bibliographically approved

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