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Effects of temperature and terrestrial carbon on fish growth and pelagic food web efficiency
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (EcoChange)
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 [en]
Attack rates, Bacterial production, Climate change, Critical resource density, Growth rates, Microbial food web, Three-spined stickleback
National Category
Ecology
Identifiers
URN: urn:nbn:se:umu:diva-54028ISBN: 978-91-7459-412-6 (print)OAI: oai:DiVA.org:umu-54028DiVA: diva2:515098
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
List of papers
1. A temperature-dependent growth model for the three-spined stickleback Gasterosteus aculeatus
Open this publication in new window or tab >>A temperature-dependent growth model for the three-spined stickleback Gasterosteus aculeatus
2011 (English)In: Journal of Fish Biology, ISSN 0022-1112, E-ISSN 1095-8649, Vol. 79, no 7, 1815-1827 p.Article in journal (Refereed) Published
Abstract [en]

Specific growth rates of individually reared juvenile three-spined sticklebacks Gasterosteus aculeatus were investigated under laboratory conditions to parameterize a complete temperature-dependent growth model for this species. To test the applicability of experimentally derived optima in growth response rates to natural conditions, the effects of commercial pellets and natural prey on growth rates were investigated. In addition, to test for seasonal effects on growth, laboratory trials were performed in both spring and winter. Growth took place from 5 to 29° C with a temperature for optimum growth reaching a sharp peak at 21° C. Modelled optimal temperature for maximum growth was estimated to be 21.7° C and lower and upper temperatures for growth were estimated to be 3.6 and 30.7° C, respectively. There were no significant differences in growth rates between fish reared on invertebrates or commercial pellets. Seasonal effects on growth were pronounced, with reduced growth rates in the winter despite similar laboratory conditions. On average, 60% higher growth rates were achieved at the optimum temperature in summer compared to the winter. The strong seasonality in the growth patterns of G. aculeatus indicated here reduces the applicability of the model derived in this study to spring and summer conditions.

National Category
Biological Sciences
Identifiers
urn:nbn:se:umu:diva-52223 (URN)10.1111/j.1095-8649.2011.03121.x (DOI)000298014800009 ()22141889 (PubMedID)
Available from: 2012-02-14 Created: 2012-02-14 Last updated: 2017-10-24Bibliographically approved
2. Temperature and size dependent attack rates of the three-spined stickleback (Gasterosteus aculeatus); are sticklebacks in the Baltic sea resource-limited?
Open this publication in new window or tab >>Temperature and size dependent attack rates of the three-spined stickleback (Gasterosteus aculeatus); are sticklebacks in the Baltic sea resource-limited?
(English)Manuscript (preprint) (Other academic)
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-54025 (URN)
Available from: 2012-04-11 Created: 2012-04-11 Last updated: 2012-04-12
3. Bottom-up and top-down control of pelagic food web efficiencies
Open this publication in new window or tab >>Bottom-up and top-down control of pelagic food web efficiencies
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-54027 (URN)
Available from: 2012-04-11 Created: 2012-04-11 Last updated: 2017-08-31
4. 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

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