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Climate change impacts on production and dynamics of fish populations
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Byström Karlsson)
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Ongoing climate change is predicted to increase water temperatures and export of terrestrial dissolved matter (TDOM) to aquatic ecosystems influencing ecosystem productivity, food web dynamics and production of top consumers. Ecosystem productivity is mainly determined by the rates of primary production (GPP) in turn controlled by nutrients, light availability and temperature, while temperature alone affect vital rates like consumption and metabolic rates and maintenance requirements of consumers. Increased level of TDOM causes brownification of water which may cause light limitation in algae and decrease GPP and especially so in the benthic habitat. Temperature increase has a been suggested to increase metabolic rates of consumers to larger extent than the corresponding effect on GPP, which suggest reduced top consumer biomass and production with warming.

The aim of this thesis was to experimentally study the effects of increased temperature and TDOM on habitat specific and whole ecosystem GPP and fish densities and production. In a replicated large-scale pond experiment encompassing natural food webs of lotic ecosystems I studied population level responses to warming and brownification in the three- spined stickleback (Gasterosteus aculeatus).

Results showed overall that warming had no effect on whole ecosystem GPP, likely due to nutrient limitation, while TDOM input decreased benthic GPP but stimulated pelagic GPP. In fish, results first of all suggested that recruitment in sticklebacks over summer was negatively affected by warming as maintenance requirements in relation to GPP increased and thereby increased starvation mortality of young-of-the-year (YOY) sticklebacks. Secondly, brownification increased mortality over winter in YOY as the negative effect on light conditions likely decreased search efficiency and caused lower consumption rates and starvation over winter in sticklebacks. Third, seasonal production of YOY, older, and total stickleback production was negatively affected by warming, while increased TDOM caused decreased YOY and total fish production. The combined effect of the two was intermediate but still negative. Temperature effects on fish production were likely a result of increased energy requirements of fish in relation to resource production and intake rates whereas the negative effect of TDOM likely was a result of decreased benthic resource production. Finally, effects of warming over a three-year period caused total fish density and biomass and abundance of both mature and old fish to decrease, while proportion of young fish increased. The main cause behind the strong negative effects of warming on fish population biomass and changes in population demographic parameters were likely the temperature driven increased energy requirements relative to resource production and cohort competition.

The results from this thesis suggest that predicted climate change impacts on lentic aquatic ecosystems will decrease future densities and biomass of fish and negatively affect fish production and especially so in systems dominated by benthic resource production.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet , 2016. , 30 p.
Keyword [en]
Temperature, terrestrial dissolved organic carbon, light extinction, GPP, recruitment, winter mortality, metabolism, cohort competition, fish production, fish biomass
National Category
Ecology
Identifiers
URN: urn:nbn:se:umu:diva-128007ISBN: 978-971-7601-604-6OAI: oai:DiVA.org:umu-128007DiVA: diva2:1048637
Public defence
2016-12-16, Lilla hörsalen, Linnaeus väg, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2016-11-25 Created: 2016-11-21 Last updated: 2016-11-23Bibliographically approved
List of papers
1. Warming but not increased terrestrial doc has negative effects on fish recruitment
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Water temperature and export of terrestrial dissolved organic carbon (DOC) to recipient aquatic ecosystems have strong impacts on ecosystem productivity. Increased DOC concentration causing brownification of water is argued to reduce fish production by decreasing light availability for autotrophic production. On the other hand, higher temperatures have been shown to correlate positively with fish recruitment. This increase has been related to increased growth rates and survival of young-of-the-year (YOY) fish with warming. However, whether or not increased temperature results in higher growth depends on resource availability, suggesting a relationship between individual gain and recruitment mediated via the interplay between resource production and temperature. In a replicated, large scale experimental pond ecosystem, we tested the effects of increased temperature (+3oC) and terrestrial DOC concentrations (+4 mg/l) on recruitment (size, density and biomass) of three-spined sticklebacks over one growth season. Gross primary production (GPP) was similar between treatments, whereas zooplankton and benthic invertebrate biomass were negatively affected by increased temperature and if any higher at increased DOC levels. Increased temperature had no effect on individual size but negative effects on body condition and recruitment of YOY sticklebacks, while increased DOC concentration had no effect on recruitment. No positive effect of temperature increase on GPP and decreased resource levels in combination with higher metabolic costs, are suggested to increase starvation mortality and to be the main mechanism behind observed negative effects of warming on recruitment. Based on our results, we suggest that climate change may, counter intuitively, have negative effects on fish recruitment due to decreased carrying capacity of nursery habitats as a consequence of increased energy requirements in juvenile fish in relation to the net effects on resource production and ecosystem productivity. 

Keyword
Temperature, metabolism, search efficiency, dissolved organic carbon (DOC), Gross primary production (GPP), somatic growth, macroinvertebrates
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-127938 (URN)
Funder
The Kempe FoundationsSwedish Research Council for Environment, Agricultural Sciences and Spatial Planning, 621-2011-3908Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGE
Available from: 2016-11-21 Created: 2016-11-21 Last updated: 2016-11-23
2. Brownification increases winter mortality in fish
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(English)Manuscript (preprint) (Other academic)
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-127940 (URN)
Funder
The Kempe FoundationsSwedish Research Council for Environment, Agricultural Sciences and Spatial Planning, 621-2011-3908Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGE
Available from: 2016-11-21 Created: 2016-11-21 Last updated: 2016-11-23
3. Population and size dependent responses in fish production to climate change
Open this publication in new window or tab >>Population and size dependent responses in fish production to climate change
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Climate change is predicted to increase water temperatures and export of terrestrial dissolved matter (TDOM) to aquatic ecosystems with concomitant effects on ecosystem productivity and production of consumers at the top of the food web. Here we study how increased level of TDOM and temperature alone or in combination affect benthic and pelagic primary production and biomass production of fish in replicated large scale outdoor pond experiment. We increased temperature (+3 ̊C) and TDOM concentrations (×2.5) using natural high TDOM water from a small creek and used naturally reproducing three-spine sticklebacks (Gasterosteus aculeatus) populations as model fish species. Gross primary production (GPP) was similar to ambient control conditions in all treatments although increased TDOM concentrations deceased benthic but stimulated pelagic GPP, presumably as a result of decreased light availability and increased nutrient availability, respectively. The production of young-of-the-year (YOY), older, and total fish population were negatively affected by warming, whereas increased TDOM caused decreased YOY and total fish production. Effect of temperature on fish production were likely a result of increased metabolic cost in relation to resource production and intake rates whereas the negative effect of TDOM on fish production was likely a result of decreasing benthic resource production. However, the combined effect on fish production of warming and TDOM was only intermediate compared to individual treatments. Our study suggest climate change will lead to decreased fish production and that the effect may be most pronounced in clear systems dominated by benthic GPP . 

National Category
Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:umu:diva-127935 (URN)
Funder
The Kempe FoundationsSwedish Research Council for Environment, Agricultural Sciences and Spatial Planning, 621-2011-3908Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGE
Available from: 2016-11-21 Created: 2016-11-21 Last updated: 2016-11-23
4. Warming decrease fish population densities and biomass
Open this publication in new window or tab >>Warming decrease fish population densities and biomass
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Temperature impact all biota and ecosystems through its direct effect on the vital rates of primary producers and consumers. Still, how these changes in rates translates through ecosystem feed backs to the population level of top consumers are poorly understood. Here, we studied effects of temperature increase (+ 3 ̊C during ice free season) on fish population dynamics in a replicated large scale pond ecosystem experiment over 3 years. Increased temperature had no significant effect on whole ecosystem gross primary production while top down effects of warming on intermediate consumers changed from negative to positive due to negative effects of warming on fish population abundance. Total fish density and biomass and abundance of both mature and old fish decreased with warming, while proportion of young fish increased, with warming. The effects of warming on fish population demographics were likely due to that temperature increased cohort competition and fish energy requirements relative to resource production. Our results suggest that global warming may increase competition, favor young individuals and overall decrease fish population densities and biomass. 

National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-127936 (URN)
Available from: 2016-11-21 Created: 2016-11-21 Last updated: 2016-11-23

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