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Stoichiometric changes in planktonic food web upon environmental fluctuations in northern oligotrophic coastal ecosystem
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF). Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.ORCID iD: 0000-0002-3246-7508
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Climate-driven changes, e.g. increasing precipitation, will increase terrestrial runoff and freshwater inputs to coastal ecosystems in the future. Consequently, we expect that altered availability of inorganic and organic forms of carbon (C), nitrogen (N) and phosphorus (P) will lead to spatial and temporal variation in the elemental composition of coastal organisms. To identify the major spatiotemporal patterns in seston and zooplankton elemental (C, N and P) composition, we sampled four bays of northern Baltic Sea from May to September 2018. This sampling design covers spatial and temporal variation in freshwater input, as it includes the spring flood driven by snowmelt in May, and bays receiving varying catchment areas. We analyzed CNP composition for different size fractions of seston, and dominant zooplankton taxa. Our results showed that the stoichiometric composition of individual seston size fractions varied more through time than in space. The concentrations of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in water were the major explanatory variables for seston stoichiometry. We also found that zooplankton stoichiometry was relatively similar between taxa within specific months, although the dominant zooplankton taxa differed over time and among sites. This could partly be explained by the similar stoichiometric requirements and homeostasis among zooplankton taxa. Our findings imply that the spatiotemporal variation in physicochemical characteristics of coastal ecosystems will alter the quality of seston and zooplankton. Yet, further investigations on the role of zooplankton in stoichiometry related nutrient cycling in the Baltic Sea coastal ecosystems are needed.

National Category
Earth and Related Environmental Sciences
Research subject
environmental science
Identifiers
URN: urn:nbn:se:umu:diva-167426OAI: oai:DiVA.org:umu-167426DiVA, id: diva2:1387027
Available from: 2020-01-20 Created: 2020-01-20 Last updated: 2020-02-04
In thesis
1. Consequences of consumer-resource stoichiometric imbalance in planktonic food webs
Open this publication in new window or tab >>Consequences of consumer-resource stoichiometric imbalance in planktonic food webs
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Resource imbalance between consumers and their resources can come from inadequate resource quantity or quality. The ecological stoichiometry theory focuses on understanding the consequences of imbalance in elemental composition.  In this thesis, I have used both resource quality (e.g., inorganic vs organic forms of nutrients) and resource quantity (e.g., terrestrial and freshwater nutrient loading to natural coastal systems) to address the consequences of consumer-resource imbalance in planktonic food webs. First, I provided a framework that summarizes how the stoichiometric imbalance is transferred from one biological level to another. The framework highlights the importance of the distribution of elements among different chemical forms and the distribution of elements among connected ecosystems. The framework then served as a guideline for the empirical work of my thesis.  Second, I studied the response of bacterial community mineralization to the relative availability of different forms of nitrogen (inorganic vs. organic form) in a batch culture experiment. The study shows that different forms of nitrogen can significantly influence the growth of bacteria. More importantly, my results show that it is crucial to measure the actual bacterial carbon to nitrogen consumption ratio, rather than use classical theoretical models, to be able to make an accurate prediction of bacterial ammonium regeneration. Third, I tested the effect of different forms of nitrogen on microplankton food web dynamics in a microcosm experiment. I found that differences between nitrogen forms have a strong impact on food web dynamics that is channeled by the bacteria-phytoplankton interaction at the base of the food web. The whole microplankton food web benefits from organic forms of nitrogen as a result of increased mutualistic interactions between bacteria and phytoplankton. Hence, the form of nitrogen is an important factor to be considered in microplanktonic food web dynamics, at least on the short-term. In the final part of this thesis, I explored resource quality and quantity effects on the stoichiometric response of a natural coastal ecosystem in a field study. I expected that the relative availability of inorganic or organic forms of carbon, nitrogen and phosphorus in our sampling bays may affect organismal elemental composition both temporally and spatially. The results indicate that the stoichiometry among seston size fractions and zooplankton varied more through time than in space. However, zooplankton stoichiometry was relatively stable among species within specific months. Overall, the concentration of dissolved organic carbon and dissolved organic nitrogen in the water column were the major explanatory variables for the seston stoichiometry. In summary, this thesis uses multiple systems to elucidate how the form and input of nutrients shape the plankton food web dynamics and its stoichiometric responses.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2020. p. 36
National Category
Earth and Related Environmental Sciences
Research subject
environmental science
Identifiers
urn:nbn:se:umu:diva-167427 (URN)978-91-7855-182-8 (ISBN)978-91-7855-183-5 (ISBN)
Public defence
2020-02-28, Lilla Hörsalen, KBC, Umeå, 14:12 (English)
Opponent
Supervisors
Available from: 2020-02-07 Created: 2020-02-03 Last updated: 2020-02-05Bibliographically approved

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Guo, JunwenBrugel, SoniaAndersson, AgnetaLau, Danny C. P.

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