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Impacts of elevated terrestrial nutrient loads and temperature on pelagic food web efficiency and fish production
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). (EcoChange ; UMFpub)
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). (EcoChange)
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Arcum ; EcoChange)
Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
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2013 (English)In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 19, no 5, 1358-1372 p.Article in journal (Other academic) Published
Abstract [en]

Both temperature and terrestrial organic matter have strong impacts on aquatic food-web dynamics and production. Temperature affects vital rates of all organisms, and terrestrial organic matter can act both as an energy source for lower trophic levels, while simultaneously reducing light availability for autotrophic production. As climate change predictions for the Baltic Sea and elsewhere suggest increases in both terrestrial matter runoff and increases in temperature, we studied the effects on pelagic food-web dynamics and food-web efficiency in a plausible future scenario with respect to these abiotic variables in a large-scale mesocosm experiment. Total basal (phytoplankton plus bacterial) production was slightly reduced when only increasing temperatures, but was otherwise similar across all other treatments. Separate increases in nutrient loads and temperature decreased the ratio of autotrophic:heterotrophic production, but the combined treatment of elevated temperature and terrestrial nutrient loads increased both fish production and food-web efficiency. CDOM: Chl a ratios strongly indicated that terrestrial and not autotrophic carbon was the main energy source in these food webs and our results also showed that zooplankton biomass was positively correlated with increased bacterial production. Concomitantly, biomass of the dominant calanoid copepod Acartia sp. increased as an effect of increased temperature. As the combined effects of increased temperature and terrestrial organic nutrient loads were required to increase zooplankton abundance and fish production, conclusions about effects of climate change on food-web dynamics and fish production must be based on realistic combinations of several abiotic factors. Moreover, our results question established notions on the net inefficiency of heterotrophic carbon transfer to the top of the food web.

Place, publisher, year, edition, pages
John Wiley & Sons, 2013. Vol. 19, no 5, 1358-1372 p.
Keyword [en]
bacterial production, Baltic Sea, climate change, terrestrial dissolved organic matter, three-spined stickleback
National Category
Ecology
Identifiers
URN: urn:nbn:se:umu:diva-54026DOI: 10.1111/gcb.12134OAI: oai:DiVA.org:umu-54026DiVA: diva2:515086
Available from: 2012-04-11 Created: 2012-04-11 Last updated: 2017-10-24Bibliographically approved
In thesis
1. Effects of temperature and terrestrial carbon on fish growth and pelagic food web efficiency
Open this publication in new window or tab >>Effects of temperature and terrestrial carbon on fish growth and pelagic food web efficiency
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Both temperature and terrestrial dissolved organic carbon (TDOC) have strong impacts on aquatic food web dynamics and production. Temperature affects vital rates of all organisms and terrestrial carbon has been shown to alter the dynamics of phytoplankton and bacterial production and affect the trophic structure of planktonic food webs. As climate change predictions for the Baltic Sea suggests future increases in both terrestrial carbon run-off and increases in temperature, the aim of thesis was to adopt a system-ecological approach and study effects of these abiotic variables, not only on interactions within planktonic food webs, but also on the growth and consumption rates of one of the most common zooplanktivorous fish in the Baltic Sea, the three-spined stickleback Gasterosteus aculeatus. Results showed that three-spined sticklebacks display a high degree of resilience against increasing temperatures, as both growth rates as well as consumption rates on zooplankton were high at temperatures well over 20 °C. Furthermore, it was shown that the minimal resource densities required to sustain individual and population growth, actually decreased with increasing temperatures, implying that sticklebacks around their optimum temperature for growth at 21 °C will actually have an increased scope for growth. As stickleback population densities have increased over the last decade in the Baltic Sea and are now suggested to out-compete other coastal fish species for shared zooplankton resources, the results presented in this thesis suggest that increased water temperatures would only serve to increase sticklebacks competitive advantage. As the structuring role of this small zooplanktivore on pelagic communities might be considerable, further studies investigating competitive interactions as well as patterns of population abundances are definitely warranted. TDOC was overall shown to stimulate bacterial production and the microbial food web. Because of the longer trophic pathways required to transport carbon from bacterial production to higher trophic levels, the addition of TDOC always reduced food web transfer efficiency. However, it became apparent that the full effect of TDOC additions on pelagic food webs was complex and depended heavily not only on the existing trophic structure to which the carbon was introduced, but also on ambient temperature levels. When three-spined sticklebacks were part of food webs with significant TDOC inputs, the presence of fish, indirectly, through predator release of lower trophic levels, amplified the magnitude of the effects of carbon addition on bacterial production, turning the base of the system significantly more heterotrophic, which ultimately, impacted negatively on their own production. However, when a pelagic food web containing sticklebacks was simultaneously subjected to realistic increases in temperature and TDOC concentrations, food web efficiency and fish production increased compared to present day conditions. These results were explained by a temperature dependent increased production potential of zooplankton, sustained by an increased production of heterotropic microzooplankton via TDOC additions, which lead to higher fish production. Although the increased number of trophic linkages in heterotrophic food webs should have reduced energy transfer efficiency, these negative effects seem here to have been overridden by the positive increases in zooplankton production as a result of increased temperature. These results show that heterotrophic carbon transfer can be a viable pathway to top-consumers, but also indicates that in order to understand the full effects of climate change on trophic dynamics and fish production, abiotic variables cannot be studied in isolation. 

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2012. 28 p.
Keyword
Attack rates, Bacterial production, Climate change, Critical resource density, Growth rates, Microbial food web, Three-spined stickleback
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-54028 (URN)978-91-7459-412-6 (ISBN)
Public defence
2012-05-04, Naturvetarhuset, N 360, Umeå Universitet, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2012-04-13 Created: 2012-04-11 Last updated: 2017-09-01Bibliographically approved
2. Response of marine food webs to climate-induced changes in temperature and inflow of allochthonous organic matter
Open this publication in new window or tab >>Response of marine food webs to climate-induced changes in temperature and inflow of allochthonous organic matter
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Global records of temperature show a warming trend both in the atmosphere and in the oceans. Current climate change scenarios indicate that global temperature will continue to increase in the future. The effects will however be very different in different geographic regions. In northern Europe precipitation is projected to increase along with temperature. Increased precipitation will lead to higher river discharge to the Baltic Sea, which will be accompanied by higher inflow of allochthonous organic matter (ADOM) from the terrestrial system. Both changes in temperature and ADOM may affect community composition, altering the ratio between heterotrophic and autotrophic organisms. Climate changes may thus have severe and complex effects in the Baltic Sea, which has low species diversity and is highly vulnerable to environmental change. The aim of my thesis was to acquire a conceptual understanding of aquatic food web responses to increased temperature and inputs of ADOM. These factors were chosen to reflect plausible climate change scenarios. I performed microcosm and mesocosm experiments as well as a theoretical modeling study. My studies had a holistic approach as they covered entire food webs, from bacteria and phytoplankton to planktivorous fish. The results indicate a strong positive effect of increased temperature and ADOM input on the bacterial community and the microbial food web. However, at the prevailing naturally low nutrient concentrations in the Baltic Sea, the effect of increased temperature may be hampered by nutrient deficiency. In general my results show that inputs of ADOM will cause an increase of the bacterial production. This in turn can negatively affect the production at higher trophic levels, due to establishment of an intermediate trophic level, consisting of protozoa. However, the described effects can be counteracted by a number of factors, as for example the relatively high temperature optimum of fish, which will lead to a more efficient exploitation of the system. Furthermore, the length of the food web was observed to be a strong regulating factor for food web responses and ecosystem functioning. Hence, the effect of environmental changes may differ quite drastically depending on the number of trophic levels and community composition of the system. The results of my thesis are of importance as they predict possible ecological consequences of climate change, and as they also demonstrate that variables cannot be examined separately.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2015. 28 p.
Keyword
Climate change, bacterial production, mesocosm, food web efficiency, Baltic Sea
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-102791 (URN)978-91-7601-266-6 (ISBN)
Public defence
2015-05-28, KBC-huset, Lilla Hörsalen, KB3A9, Umeå universitet, Umeå, 10:00
Opponent
Supervisors
Funder
Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGESwedish Research Council Formas, AA and SL (217-2006-674)
Note

This thesis was supported by grants from the Swedish Research Council FORMAS to AA and SL (217-2006-674), the Centre for Environmental Research in Umeå (CMF) to UB, AA and SL, and by the Swedish strategic research program ECOCHANGE to Umeå University.

Available from: 2015-05-07 Created: 2015-05-05 Last updated: 2017-09-01Bibliographically approved

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Lefebure, RobertDegerman, RickardAndersson, AgnetaLarsson, StefanBåmstedt, UlfByström, Pär
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