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  • 1.
    Dahlgren, Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Food web structures and carbon transfer efficiencies in a brackish water ecosystem2010Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Two differently structured food webs can be distinguished in the pelagic habitat of aquatic systems; the classical one (autotrophic) with phytoplankton as a base and the microbial food web (heterotrophic) with bacteria as a base. Energy (produced at the basal trophic level) reaches higher trophic levels, i.e. zooplankton, directly in the classical food web in contrast to the microbial food web where it passes through additional trophic levels before reaching zooplankton. Energy is lost between each trophic level and therefore less energy should reach higher trophic levels in the microbial food web than in the classical food web. However, factors such as edibility of prey, temperature and properties of the predator, might also influence the food web structures and functions.

    In this thesis I studied which factors are important for an efficient carbon transfer and how a potential climate change might alter the food web efficiency in pelagic and pelagic-benthic food webs in the Baltic Sea. Furthermore, one of the most dominant zooplankton in the northern Baltic Sea, Limnocalanus macrurus, was studied in order to establish the seasonal pattern of lipid reserves in relation to food consumption.

    My studies showed that the carbon transfer efficiency during summer was not directly connected to the basal production, but factors such as the ratio between heterotrophs and autotrophs, the relationship between cladocerans and calanoid copepods and the size and community structure of both phytoplankton and zooplankton were important for the carbon transfer efficiency. In a climate change perspective, the temperature as well as the relative importance of the microbial food web is likely to increase. A temperature increase may have a positive effect on the pelagic food web efficiency, whereas increasing heterotrophy will have a negative effect on the pelagic and pelagic-benthic food web efficiency, reduce the fatty acid content of zooplankton and reduce the individual weight of both zooplankton and the benthic amphipod Monoporeia affinis. During the seasonal study on the calanoid copepod L. macrurus, I found that this species is mainly a carnivore, feeding on mesozooplankton during most of the year but switches to feeding on phytoplankton when these are abundant. Furthermore, when food is scarce, it utilizes lipids that are built up during the course of the year.

    From these studies I can draw some major conclusions; there are many factors that influence how efficient carbon is transferred in the food web and different factors are probably of various importance in different areas. In order to determine the carbon transfer efficiency, the various strategies exerted by different organism groups have to be considered, as for example that some zooplankton utilize lipid reserves instead of feeding all year around. Also, in a climate change perspective, the pelagic-benthic food web efficiency will decrease, as will the quality of zooplankton and M. affinis, possibly having implications for higher trophic levels such as fish.

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  • 2.
    Dahlgren, Kristin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Andersson, Agneta
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Larsson, Ulf
    Department of Systems Ecology, Stockholm University, 10691 Stockholm, Sweden.
    Hajdu, Susanna
    Department of Systems Ecology, Stockholm University, 10691 Stockholm, Sweden.
    Båmstedt, Ulf
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Planktonic production and carbon transfer efficiency along a north-south gradient in the Baltic sea2010Inngår i: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 409, s. 77-94Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A 1 yr study was conducted along a brackish-water production gradient to enhance the understanding of factors governing pelagic food web function. This was achieved by measuring carbon transfer efficiency (TE) from the basal resource to an intermediate trophic level. TE was defined as mesozooplankton carbon consumption rate divided by production at the basal trophic level, which is composed of phytoplankton and bacteria. A north–south transect in the Baltic Sea was used as a model system, with 2 stations each in the Bothnian Bay, Bothnian Sea and Baltic Proper being sampled 5 to 8× during 2006. In addition, data from monitoring programmes were used, which comprised 10 to 22 samplings stn–1. TE was expected to be governed by the size distribution of phytoplankton and due to the nutrient gradient, we expected to find an optimal cell size, and thus also a high TE, in the intermediate-productive Bothnian Sea. The basal production during summer/autumn increased 5-fold from north to south, while the mesozooplankton carbon consumption rate exhibited a peak inthe Bothnian Sea, being ~3× higher than in both Bothnian Bay and Baltic Proper. TE was found to be intermediate in the Bothnian Bay (average: 0.8), highest in the Bothnian Sea (1.6), and lowest in the Baltic Proper (0.2). We suggest that the variation in carbon transfer efficiency can be explained by the composition of the phytoplankton community, the abundance balance between copepods and cladocerans, as well as the species composition of mesozooplankton in relation to the size structure of phytoplankton.

  • 3.
    Dahlgren, Kristin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Eriksson Wiklund, Ann-Kristin
    Department of Applied Environmental Science, ITM, Stockholm University, 106 91 Stockholm, Sweden.
    Andersson, Agneta
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Influence of plankton structure and temperature on pelagic food web efficiency in a brackish water system2011Inngår i: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 45, s. 307-323Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    As part of one climate change scenario, water temperature as well as the ratio between heterotrophic and autotrophic production is expected to increase; the latter at least in higher latitudes. In order to test how this scenario would affect organisms, such as metazooplankton, at higher trophic levels and carbon transfer up the food chain, a mesocosm experiment was performed at two different temperatures; 5 and 10°C, with two food webs; one phytoplankton-based (NP; autotrophic) and one bacteria-based (CNP; heterotrophic).  The groups of pelagic organisms included in the mesocosms were bacteria, flagellates, ciliates, phytoplankton and metazooplankton. Metazooplankton production was observed to increase with temperature, but was not significantly affected by food web structure. A change in food web structure, i.e. increased heterotrophy, did however lead to decreased fatty acid content and lower individual weight of the metazooplankton. Food web efficiency (FWE), defined as metazooplankton production divided by basal production, increased with autotrophy and temperature: 5CNP (0.2%) < 10CNP (0.4%) < 5NP (1.2%) < 10NP (7.3%). Our results indicate that in the climate change scenario under consideration, the temperature will have a positive effect on FWE whereas the increase in heterotrophy will have a negative effect on FWE. Furthermore, the quality, in terms of fatty acid content and individual weight of the metazooplankton, will be reduced with possible negative effects on higher trophic levels.

  • 4.
    Dahlgren, Kristin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Olsen, Bernt Rydland
    Troedsson, Christofer
    Båmstedt, Ulf
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Seasonal variation in wax ester concentration and gut content in a Baltic Sea copepod [Limnocalanus macrurus (Sars 1863)]2012Inngår i: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 34, nr 4, s. 286-297Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Limnocalanus macrurus from Bothnian Bay in the northern part of the Baltic Sea was studied during the ice-free period (AprilDecember) in order to understand its life history and feeding biology. Our data on the population dynamics indicated that reproduction occurred during the ice-covered period, during which lipid storage was reduced to a minimum. From spring to late summer, the lipid reserve increased by a factor of 3, while the gonads of adult females were immature during this period, continuing to December as indicated by the small size of the eggs. Average stomach fullness was always ca. 50 indicating continuous feeding activity. A newly developed denaturing high-performance liquid chromatography method was used to analyse the gut contents over the study period. More than 30 taxa (at different taxonomic levels) could be identified. However, phytoplankton was only represented by one taxon (Diatomophycea), and was restricted to July. Thus, adult L. macrurus seems to have a strongly carnivorous feeding preference in the northern Baltic Sea.

  • 5.
    Eriksson Wiklund, Ann-Kristin
    et al.
    Department of Applied Environmental Science, ITM, Stockholm University, 106 91 Stockholm, Sweden.
    Dahlgren, Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Sundelin, Britta
    Department of Applied Environmental Science, ITM, Stockholm University, 106 91 Stockholm, Sweden.
    Andersson, Agneta
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå marina forskningscentrum (UMF).
    Effects of warming and shifts of pelagic food web structure on benthic productivity in a coastal marine system2009Inngår i: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 396, s. 13-25Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It has been predicted that climate change will lead to increased temperature and precipitation in northern latitudes, which in turn may lead to brownification of coastal sea areas. This will increase the importance of the heterotrophic microbial food web in areas like the northern Baltic Sea. Such a structural change in the pelagic food web would hamper benthic productivity, since microheterotrophs have lower settling rates than phytoplankton. We tested how variation in temperature and alteration of the pelagic food web structure affected the productivity of a key benthic species, the amphipod Monoporeia affinis, and the pelagic-benthic food web efficiency (FWE). Using water from the northern Baltic Sea, a mesocosm experiment was performed in which the temperature was altered by 5°C. The structure of the pelagic food web changed from one based on algae to one based on bacteria. Amphipod productivity was 3 times higher and FWE was 25 times higher in the algae than in the bacteria-based food web, showing that an altered pelagic food web will have severe effects on benthic productivity. Temperature variation, on the other hand, did not cause any changes in either growth of M. affinis or FWE. Our data indicate that indirect effects of climate change, leading to structural changes in the pelagic food web, will have much more severe effects on benthic productivity than the direct effect of increased temperature.

  • 6. Holmborn, Towe
    et al.
    Dahlgren, Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Holeton, Claire
    Hogfors, Hedvig
    Gorokhova, Elena
    Biochemical proxies for growth and metabolism in Acartia bifilosa (Copepoda, Calanoida)2009Inngår i: Limnology and Oceanography: Methods, ISSN 1541-5856, E-ISSN 1541-5856, Vol. 7, nr 11, s. 785-794Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    Biochemical proxies are becoming increasingly common for growth assessment in zooplankton. Their suitability is often unknown, however, and proper calibration is lacking. We investigated correlations between physiological variables (ingestion, egg production, and respiration rates) and biochemical indices related to protein synthesis (RNA content, RNA: DNA ratio, RNA: protein ratio, and protein specific aminoacyl-tRNA synthetases [spAARS] activity) in copepods Acartia bifilosa exposed to different algal concentrations (0-1200 mu g C L-1). All variables assayed increased with increasing food concentration either linearly (spAARS) or nonlinearly (all other variables). Egg production and ingestion rates were significantly and positively correlated with RNA content and RNA: protein ratio, whereas correlations with spAARS and RNA: DNA ratio were weaker or nonsignificant. However, when RNA: DNA ratio and spAARS activity were used as predictors of ingestion, together they had higher explanatory value than did either variable separately. As there were substantial differences in saturating food concentrations among the assayed variables, applicability of biomarkers as proxies of physiological rates will be more reliable if restricted to the nonsaturated phase of the functional response of either variable, unless both variables saturate simultaneously. These findings contribute to methodology of zooplankton growth assessment and to our understanding of biochemical processes underlying growth and metabolism in copepods.

  • 7. Olsen, Bernt Rydland
    et al.
    Dahlgren, Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Schander, Christoffer
    Båmstedt, Ulf
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Rapp, Hans Tore
    Troedsson, Christofer
    PCR-DHPLC assay for the identification of predator-prey interactions2012Inngår i: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 34, nr 4, s. 277-285Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Denaturing high-performance liquid chromatography (DHPLC) is a relatively new method for separating amplicons in a mixture, and was recently developed for parasite detection in the blue crab Callinectes sapidus. That assay used a peptide nucleic acid (PNA) PCR hybridization blocking probe (PNAPCRDHPLC) to decrease the generic PCR bias of dominant templates (the host) in the mixture prior to separation on the DHPLC column, thus enhancing the less abundant parasite DNA. The same assay and rational can be used to investigate predatorprey interactions. However, in ecosystem studies with many predatorprey relationships, development of specific PNA-blocking probes for each predator would be too laborious. Here, we have developed a PCRDHPLC assay excluding the dominant predator amplicons in a first DHPLC run, followed by re-amplification of the non-predator retention volumes and further separation and characterization in a second DHPLC run. This assay generated data on the specific trophic interactions between the calanoid copepod Limnocalanus macrurus and its prey from a seasonal sampling programme. The assay provides an efficient way for an unbiased screening of predatorprey relationships, and although developed for L. macrurus in this study, the approach has wide applicability for any predatorprey interaction.

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