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Response of marine food webs to climate-induced changes in temperature and inflow of allochthonous organic matter
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)
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 [en]
Climate change, bacterial production, mesocosm, food web efficiency, Baltic Sea
National Category
Ecology
Identifiers
URN: urn:nbn:se:umu:diva-102791ISBN: 978-91-7601-266-6 (print)OAI: oai:DiVA.org:umu-102791DiVA: diva2:809648
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
List of papers
1. Effect of resource availability on bacterial community responses to increased temperature
Open this publication in new window or tab >>Effect of resource availability on bacterial community responses to increased temperature
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2013 (English)In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 68, no 2, 131-142 p.Article in journal (Refereed) Published
Abstract [en]

Climate change is predicted to cause higher temperatures and increased precipitation, resulting in increased inflow of nutrients to coastal waters in northern Europe. This has been assumed to increase the overall heterotrophy, including enhanced bacterial growth. However, the relative importance of temperature, resource availability and bacterial community composition for the bacterial growth response is poorly understood. In the present study, we investigated effects of increased temperature on bacterial growth in waters supplemented with different nutrient concentrations and inoculated with microbial communities from distinct seasonal periods. Seven experiments were performed in the northern Baltic Sea spanning an entire annual cycle. In each experiment, bacterioplankton were exposed to 2 temperature regimes (in situ and in situ + 4 degrees C) and 5 nutrient concentrations. Generally, elevated temperature and higher nutrient levels caused an increase in the bacterial growth rate and a shortening of the response time (lag phase). However, at the lowest nutrient concentration, bacterial growth was low at all tested temperatures, implying a stronger dependence on resource availability than on temperature for bacterial growth. Furthermore, data indicated that different bacterial assemblages had varying temperature responses and that community composition was strongly affected by the combination of high nutrient addition and high temperature. These results support the concern that climate change will promote heterotrophy in aquatic systems, where nutrient levels will increase considerably. In such environments, the bacterial community composition will change, their growth rates will increase, and their response time will be shortened compared to the present situation.

Place, publisher, year, edition, pages
Inter-Research, 2013
Keyword
Temperature increase, Resource availability, Bacterial growth response, Climate change, Community dynamics
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-67607 (URN)10.3354/ame01609 (DOI)000315598900004 ()
Available from: 2013-05-22 Created: 2013-03-25 Last updated: 2017-08-31Bibliographically approved
2. Food web interactions determine energy transfer efficiency and top consumer responses to inputs of dissolved organic carbon
Open this publication in new window or tab >>Food web interactions determine energy transfer efficiency and top consumer responses to inputs of dissolved organic carbon
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2018 (English)In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 805, no 1, 131-146 p.Article in journal (Refereed) Published
Abstract [en]

Climate change projections indicate increased precipitation in northern Europe, leading to increased inflow of allochthonous organic matter to aquatic systems. The food web responses are poorly known, and may differ depending on the trophic structure. We performed an experimental mesocosm study where effects of labile dissolved organic carbon (DOC) on two different pelagic food webs were investigated, one having zooplankton as highest trophic level and the other with planktivorous fish as top consumer. In both food webs, DOC caused higher bacterial production and lower food web efficiency, i.e., energy transfer efficiency from the base to the top of the food web. However, the top-level response to DOC addition differed in the zooplankton and the fish systems. The zooplankton production increased due to efficient channeling of energy via both the bacteria land the phytoplankton pathway, while the fish production decreased due to channeling of energy mainly via the longer and less efficient bacterial pathway. We conclude that the added DOC either acted as a subsidy by increasing the production of the top trophic level (mesozooplankton), or as a sink causing decreased top consumer production (planktivorous fish).

Keyword
Food web efficiency, Carbon transfer, Allochthonous dissolved organic carbon, Mesocosm, Planktivorous fish
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-102789 (URN)10.1007/s10750-017-3298-9 (DOI)
Funder
Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGE
Note

Originally published in manuscript form with title Food web interactions determine transfer efficiency and top consumer responses to increased allochthonous carbon input

Available from: 2015-05-05 Created: 2015-05-05 Last updated: 2017-11-27Bibliographically approved
3. Impacts of elevated terrestrial nutrient loads and temperature on pelagic food web efficiency and fish production
Open this publication in new window or tab >>Impacts of elevated terrestrial nutrient loads and temperature on pelagic food web efficiency and fish production
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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
Keyword
bacterial production, Baltic Sea, climate change, terrestrial dissolved organic matter, three-spined stickleback
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-54026 (URN)10.1111/gcb.12134 (DOI)
Available from: 2012-04-11 Created: 2012-04-11 Last updated: 2017-10-24Bibliographically approved
4. Modelling effects of river inflow of allochthonous dissolved organic carbon on coastal production
Open this publication in new window or tab >>Modelling effects of river inflow of allochthonous dissolved organic carbon on coastal production
(English)Manuscript (preprint) (Other academic)
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-102790 (URN)
Available from: 2015-05-05 Created: 2015-05-05 Last updated: 2015-05-06Bibliographically approved

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