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Baltic Sea phytoplankton in a changing environment
Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. (Centre for Ecology and Evolution in Microbial Model Systems (EEMiS))
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Future climate scenarios in the Baltic Sea project increasing sea surface temperature, as well as increasing precipitation and river runoff resulting in decreased salinity. These changes can severely impact the dynamics and function of brackish water communities, specifically phytoplankton. Phytoplankton are a significant source of organic matter to other trophic levels, and some species can be toxic. Their response to future climate conditions is of great relevance for the health of humans and aquatic ecosystems. The aim of this thesis was to assess the potential for climate-induced changes, such as decreasing salinity, to affect phytoplankton dynamics, physiology and chemical profiles in the Baltic Sea.

     Phytoplankton successional patterns in the Baltic Proper consist of a spring bloom where diatoms and dinoflagellates co-occur and a summer bloom dominated by filamentous/colonial cyanobacteria. The consensus is that future warmer conditions will promote filamentous/colonial cyanobacteria blooms. This thesis shows that phytoplankton biomass in the spring bloom was lower in years with milder winters compared with cold winters. This suggests that in terms of annual carbon export to higher trophic levels, loss of biomass from the spring bloom is unlikely to be compensated by summer cyanobacteria. High frequency sampling of phytoplankton performed in this thesis revealed a strong relationship between the dynamics of pico- and filamentous cyanobacteria. Large genetic diversity was found in cyanobacterial populations with high niche differentiation among the same species. At community level, high temperature and low salinity were the main factors shaping the summer cyanobacterial composition. These conditions may promote the predominance of opportunistic filamentous cyanobacteria, e.g. Nodularia spumigena. This species produces various bioactive compounds, including non-ribosomal peptides such as the hepatotoxin nodularin. In this work, N. spumigena subpopulations evolved different physiological strategies, including chemical profiles, to cope with salinity stress. This high phenotypic plasticity ensures survival in future climate conditions. Under salinity stress, some subpopulations displayed shorter filaments as a trade-off. This indicates that the future freshening of the Baltic Sea may promote grazing on filamentous cyanobacteria and modify carbon flows in the ecosystem. In this thesis, Baltic N. spumigena chemotypes and genotypes grouped into two main clusters without influence of geographical origin. Thus, chemical profiling can be used to explore conspecific diversity in closely genetically related N. spumigena subpopulations.

     Overall, this thesis has significantly expanded the knowledge on phytoplankton community and population responses to short- and long-term environmental changes, relevant to project the impacts of future climate conditions in the Baltic Sea.

Place, publisher, year, edition, pages
Växjö: Linnaeus University Press, 2016. , 160 p.
Series
Linnaeus University Dissertations, 267/2016
Keyword [en]
phytoplankton ecology, cyanobacteria, dynamics, environmental factors, successional patterns, interactions, life strategies, non-ribosomal peptides, diversity, nodularin, N. spumigena
National Category
Ecology
Research subject
Ecology, Aquatic Ecology
Identifiers
URN: urn:nbn:se:lnu:diva-57860ISBN: 978-91-88357-43-4OAI: oai:DiVA.org:lnu-57860DiVA: diva2:1045521
Public defence
2016-11-25, Fullriggaren, Sjöfartshögskolan, Landgången 4, Kalmar, 09:30 (English)
Opponent
Supervisors
Funder
Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGESwedish Institute
Available from: 2016-11-10 Created: 2016-11-08 Last updated: 2016-11-30Bibliographically approved
List of papers
1. Interannual variability of phyto-bacterioplankton biomass and production in coastal and offshore waters of the Baltic Sea
Open this publication in new window or tab >>Interannual variability of phyto-bacterioplankton biomass and production in coastal and offshore waters of the Baltic Sea
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2015 (English)In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 44, no supplement 3, S427-S438 p.Article in journal (Refereed) Published
Abstract [en]

The microbial part of the pelagic food web is seldom characterized in models despite its major contribution to biogeochemical cycles. In the Baltic Sea, spatial and temporal high frequency sampling over three years revealed changes in heterotrophic bacteria and phytoplankton coupling (biomass and production) related to hydrographic properties of the ecosystem. Phyto- and bacterioplankton were bottom-up driven in both coastal and offshore areas. Cold winter temperature was essential for phytoplankton to conform to the successional sequence in temperate waters. In terms of annual carbon production, the loss of the spring bloom (diatoms and dinoflagellates) after mild winters tended not to be compensated for by other taxa, not even summer cyanobacteria. These results improve our ability to project Baltic Sea ecosystem response to short- and long-term environmental changes.

Place, publisher, year, edition, pages
Springer, 2015
Keyword
Phytoplankton, Bacteria, Baltic Sea, Production, Climate change, Microbial foodwebs
National Category
Oceanography, Hydrology, Water Resources
Research subject
Natural Science, Aquatic Ecology
Identifiers
urn:nbn:se:lnu:diva-45554 (URN)10.1007/s13280-015-0662-8 (DOI)000362290800010 ()26022325 (PubMedID)
Projects
ECOCHANGE
Funder
Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGESwedish Research Council Formas
Available from: 2015-07-25 Created: 2015-07-25 Last updated: 2016-11-10Bibliographically approved
2. Unscrambling Cyanobacteria Community Dynamics Related to Environmental Factors
Open this publication in new window or tab >>Unscrambling Cyanobacteria Community Dynamics Related to Environmental Factors
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2016 (English)In: Frontiers in Microbiology, ISSN 1664-302X, E-ISSN 1664-302X, Vol. 7, 625Article in journal (Refereed) Published
Abstract [en]

Future climate scenarios in the Baltic Sea project an increase of cyanobacterial bloom frequency and duration, attributed to eutrophication and climate change. Some cyanobacteria can be toxic and their impact on ecosystem services is relevant for a sustainable sea. Yet, there is limited understanding of the mechanisms regulating cyanobacterial diversity and biogeography. Here we unravel successional patterns and changes in cyanobacterial community structure using a 2-year monthly time series during the productive season in a 100 km coastal-offshore transect using microscopy and high-throughput sequencing of 16S rRNA gene fragments. A total of 565 cyanobacterial OTUs were found, of which 231 where filamentous/colonial and 334 picocyanobacterial. Spatial differences in community structure between coastal and offshore waters were minor. An "epidemic population structure" (dominance of a single cluster) was found for Aphanizomenon/Dolichospermum within the filamentous/colonial cyanobacterial community. In summer, this cluster simultaneously occurred with opportunistic clusters/OTUs, e.g., Nodulana spumigena and Pseudanabaena. Picocyanobacteria, Synechococcus/Cyanobium, formed a consistent but highly diverse group. Overall, the potential drivers structuring summer cyanobacterial communities were temperature and salinity. However, the different responses to environmental factors among and within genera suggest high niche specificity for individual OTUs. The recruitment and occurrence of potentially toxic filamentous/colonial clusters was likely related to disturbance such as mixing events and short-term shifts in salinity, and not solely dependent on increasing temperature and nitrogen-limiting conditions. Nutrients did not explain further the changes in cyanobacterial community composition. Novel occurrence patterns were identified as a strong seasonal succession revealing a tight coupling between the emergence of opportunistic picocyanobacteria and the bloom of filamentous/colonial clusters. These findings highlight that if environmental conditions can partially explain the presence of opportunistic picocyanobacteria, microbial and trophic interactions with filamentous/colonial cyanobacteria should also be considered as potential shaping factors for single-celled communities. Regional climate change scenarios in the Baltic Sea predict environmental shifts leading to higher temperature and lower salinity; conditions identified here as favorable for opportunistic filamentous/colonial cyanobacteria. Altogether, the diversity and complexity of cyanobacterial communities reported here is far greater than previously known, emphasizing the importance of microbial interactions between filamentous and picocyanobacteria in the context of environmental disturbances.

Keyword
cyanobacteria, community, environmental factors, climate change, temperature, salinity
National Category
Microbiology Ecology
Research subject
Ecology, Aquatic Ecology
Identifiers
urn:nbn:se:lnu:diva-53266 (URN)10.3389/fmicb.2016.00625 (DOI)000375401300001 ()
Available from: 2016-06-10 Created: 2016-06-10 Last updated: 2016-11-10Bibliographically approved

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