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Food Quality Effects on Zooplankton Growth and Energy Transfer in Pelagic Freshwater Food Webs
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Effekter av födokvalitet på djurplanktons tillväxt och på energiöverföringen i födovävar i sjöar (Swedish)
Abstract [en]

Poor food quality can have large negative effects on zooplankton growth and this can also affect food web interactions. The main aims of this thesis were to study the importance of different food quality aspects in Daphnia, to identify potentially important differences among zooplankton taxa, and to put food quality research into a natural context by identifying the importance of food quality and quantity in lakes of different nutrient content.

In the first experiment, the RNA:DNA ratio was positively related to the somatic growth rate of Daphnia, supporting a connection between P content, RNA content, and growth rate. The second experiment showed that EPA was important for Daphnia somatic growth, and 0.9 µg EPA mg C-1 was identified as the threshold below which negative effects on Daphnia growth occurred.

A field survey identified patterns in the PUFA content of zooplankton that could be explained by taxonomy and trophic position. Cladocera enriched EPA and ARA relative to seston, and Copepoda primarily enriched DHA. In a whole-lake experiment, gentle fertilization of an oligotrophicated reservoir increased the seston P content and the biomass of high quality phytoplankton (Cryptophyceae, high EPA content). This was followed by increases in zooplankton and fish biomasses.

An empirical model based on data from a literature survey predicted that food quantity is most important for zooplankton growth in oligotrophic lakes, and that food quality factors are more important in eutrophic lakes. Thus, zooplankton growth, and energy transfer efficiency in the food web, is predicted to be highest in mesotrophic lakes. The results predict that the strength and nature of food quantity and quality limitation of Daphnia growth varies with lake trophic state, and that some combination of food quantity and/or quality limitation should be expected in nearly all lakes.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2007. , p. 43
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 292
Keywords [en]
Ecology, elemental stoichiometry, phosphorus, polyunsaturated fatty acids, EPA, oligotrophic lakes, empirical modelling, Daphnia, Cladocera, Copepoda
Keywords [sv]
Ekologi
National Category
Ecology
Identifiers
URN: urn:nbn:se:uu:diva-7811ISBN: 978-91-554-6859-0 (print)OAI: oai:DiVA.org:uu-7811DiVA, id: diva2:170062
Public defence
2007-05-04, Zootissalen, Gamla Zoologen, Norbyvägen 18, Uppsala, 10:00
Opponent
Supervisors
Available from: 2007-04-11 Created: 2007-04-11 Last updated: 2016-04-28Bibliographically approved
List of papers
1. The influence of food quality (P:C ratios) on RNA:DNA ratios and somatic growth rate of Daphnia
Open this publication in new window or tab >>The influence of food quality (P:C ratios) on RNA:DNA ratios and somatic growth rate of Daphnia
2002 In: Limnology and Oceanography, Vol. 47, p. 487-494Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-95732 (URN)
Available from: 2007-04-11 Created: 2007-04-11Bibliographically approved
2. Dietary threshold concentrations of three polyunsaturated fatty acids for Daphnia somatic growth and reproduction
Open this publication in new window or tab >>Dietary threshold concentrations of three polyunsaturated fatty acids for Daphnia somatic growth and reproduction
Manuscript (Other academic)
Identifiers
urn:nbn:se:uu:diva-95733 (URN)
Available from: 2007-04-11 Created: 2007-04-11 Last updated: 2010-01-13Bibliographically approved
3. Polyunsaturated fatty acids in zooplankton: variation due to taxonomy and trophic position
Open this publication in new window or tab >>Polyunsaturated fatty acids in zooplankton: variation due to taxonomy and trophic position
2006 In: Freshwater Biology, Vol. 51, p. 887-900Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-95734 (URN)
Available from: 2007-04-11 Created: 2007-04-11Bibliographically approved
4. Responses in zooplankton populations to food quality and quantity changes after whole lake nutrient enrichment of an oligotrophic sub-alpine reservoir
Open this publication in new window or tab >>Responses in zooplankton populations to food quality and quantity changes after whole lake nutrient enrichment of an oligotrophic sub-alpine reservoir
2008 (English)In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 70, no 2, p. 142-155Article in journal (Refereed) Published
Abstract [en]

To sustain production of higher trophic levels in oligotrophic systems it is important that the trophic transfer of energy and nutrients is efficient. The phytoplankton-zooplankton interface is of specific interest since nutritional constraints can decouple energy flow in this step. Increased nutrient loading to oligotrophic systems with initially low abundance of high quality phytoplankton could induce changes in seston composition that reduces the nutritional value for zooplankton. We carried out a whole lake enrichment experiment for five years in two ultraoligotrophic subalpine hydroelectric power reservoirs in Sweden. The first year was an untreated reference year. Phosphorus and nitrogen were added to Lake Stora Mjolkvattnet during the following four years, and upstream Lake Burvattnet was used as an untreated reference lake. The phosphorus content of seston in the experimental lake increased in the years of fertilization and seston phosphorus to carbon ratios (atomic) were non-limiting for zooplankton growth. Decreasing concentrations of phosphorus in the reference lake lead to low phosphorus to carbon ratios that probably affected zooplankton growth negatively. The seston fatty acid concentrations and phytoplankton composition indicated good food quality in both lakes. The phytoplankton increased in the experimental lake despite an increase in zooplankton biomass. Some changes in the relative contributions of plankton species occurred but the same species were present. The crustacean zooplankton community composition shifted towards smaller species during the latter years in the experimental lake, indicating increased predation pressure from fish. A major result of this whole-lake ecosystem fertilization experiment is that gentle fertilization can significantly boost phytoplankton production while food quality remains high, and plankton community composition is not substantially altered.

Keywords
elemental stoichiometry, essential fatty acids, Cladocera, Holopedium, Bosmina, trophic transfer efficiency
National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-95735 (URN)10.1007/s00027-007-7013-1 (DOI)000256426400005 ()
Available from: 2007-04-11 Created: 2007-04-11 Last updated: 2017-12-14Bibliographically approved
5. Food quantity and quality regulation of trophic transfer between primary producers and a keystone grazer (Daphnia) in pelagic freshwater food webs
Open this publication in new window or tab >>Food quantity and quality regulation of trophic transfer between primary producers and a keystone grazer (Daphnia) in pelagic freshwater food webs
2007 (English)In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 116, no 7, p. 1152-1163Article in journal (Refereed) Published
Abstract [en]

The transfer of energy and nutrients from plants to animals is a key process in all ecosystems. In lakes, inefficient transfer of primary producer derived energy can result in low animal growth rates, accumulation of nuisance phytoplankton blooms and dissipation of energy from the ecosystem. Most research on carbon transfer efficiency in pelagic food webs has focused on either food quantity or food quality, with the latter considered separately as either elemental stoichiometry or biochemical composition. The natural occurrence and magnitude of these types of growth limitations and their combined effects on Daphnia, a keystone grazer in pelagic freshwater ecosystems, are largely unknown. Our empirical models predict that the strength and nature of food quantity and quality limitation varies greatly with lake trophic state (total phosphorus, TP) and that Daphnia growth rates and thus energy and nutrient transfer efficiency are highest in lakes with intermediate trophic status (TP 10-25 μg l−1). We predict that food availability place the greatest constraint on Daphnia growth in nutrient poor lakes (TP≤4 μg l−1). Phosphorus limitation of Daphnia growth increased with decreasing TP, but the overall effect was never predicted to be the dominant constraining factor. Eicosapentaenoic acid (EPA, 20:5ω3) limitation was predicted to occur in both nutrient poor and nutrient rich lakes and placed the primary constraint on food quality in the most productive lakes. Two contrasting EPA-models gave different results on the magnitude of EPA-limitation, implying that additional food quality factors decrease Daphnia growth at high TP. In conclusion, the model predicts that Daphnia growth should peak in mesotrophic lakes, food quantity will place the greatest constraint on growth in oligotrophic lakes and EPA will primarily limit growth in eutrophic lakes.

National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-95736 (URN)10.1111/j.0030-1299.2007.15639.x (DOI)000247438000007 ()
Available from: 2007-04-11 Created: 2007-04-11 Last updated: 2017-12-14Bibliographically approved

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