Publications
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Poste, Amanda E; Hoel, Cathrine Skaar; Andersen, Tom; Arts, Michael T; Færøvig, Per-Johan & Borgå, Katrine
(2019).
Terrestrial organic matter increases zooplankton methylmercury accumulation in a brown-water boreal lake.
Science of the Total Environment.
ISSN 0048-9697.
674,
p. 9–18.
doi:
10.1016/j.scitotenv.2019.03.446.
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Increases in terrestrial organic matter (tOM) transport from catchments to boreal lakes can affect methylmercury (MeHg) accumulation in aquatic biota both directly by increasing concentrations of aqueous MeHg, and indirectly through effects on MeHg bioavailability and on energy pathways in the lower food web. We carried out a detailed seasonal study of water chemistry, zooplankton diet, and MeHg accumulation in zooplankton in two lakes with contrasting tOM concentrations. Between-lake differences explained 51% of the variability in our water chemistry data, with no observed effect of season or sampling depth, contrary to our expectations. Higher tOM was correlated with higher aqueous Hg concentrations, lower areal pelagic primary productivity, and an increased contribution of terrestrial particles to pelagic particulate organic matter. Based on dietary marker analysis (δ13C, δ15N, and fatty acid [FA] composition), zooplankton diet was strongly linked to feeding mechanism, with dietary reliance on phytoplankton highest in the selective-feeding calanoid copepods, and lowest in filter feeding cladocerans. Zooplankton dietary reliance on phytoplankton and their concentrations of high-quality lipids, including polyunsaturated fatty acids, were higher in the clear-water lake than in the brown-water lake, where bacterial and terrestrial food sources were more prevalent. MeHg was highest in zooplankton from the brown-water lake, with highest concentrations in the 200–500 μm zooplankton size fraction for both lakes. Contrary to our expectations, there was no effect of season on zooplankton dietary markers or MeHg. Our results suggest that, overall, higher tOM results in higher MeHg concentrations in water and zooplankton, and reduces zooplankton dietary reliance on phytoplankton. Increased tOM thus leads to a decrease in the nutritional quality of zooplankton (i.e. higher MeHg concentrations, and lower concentrations of essential fatty acids), which may cascade up the food web with negative implications for higher trophic levels.
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Lindholm, Markus; Hessen, Dag Olav; Færøvig, Per-Johan; Rognerud, Bjørg; Andersen, Tom & Stordal, Frode
(2015).
Is distribution of cold stenotherms constrained by temperature? The case of the Arctic fairy shrimp (Branchinecta paludosa O.F. Müller 1788).
Journal of Thermal Biology.
ISSN 0306-4565.
53,
p. 46–52.
doi:
10.1016/j.jtherbio.2015.08.005.
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Hessen, Dag Olav; Frigstad, Helene; Færøvig, Per-Johan; Wojewodzic, Marcin & Leu, Eva
(2012).
UV radiation and its effects on P-uptake in arctic diatoms.
Journal of Experimental Marine Biology and Ecology.
ISSN 0022-0981.
411,
p. 45–51.
doi:
10.1016/j.jembe.2011.10.028.
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Hessen, Dag Olav; Leu, Eva; Færøvig, Per-Johan & Falk-Petersen, Stig
(2008).
Light and spectral properties as determinants of C:N:P-ratios in phytoplankton.
Deep-Sea Research Part II: Topical Studies in Oceanography.
ISSN 0967-0645.
55,
p. 2169–2175.
doi:
10.1016/j.dsr2.2008.05.013.
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Light is a major determinant not only for carbon (C)-fixation in autotrophs, but also for the cellular proportions of major elements like C, nitrogen (N) and phosphorus (P). High intensities of photosynthetically active radiation (PAR) increase C:P-ratios in experiments with arctic marine and freshwater phytoplankton species. While high levels of PAR promote high autotrophic productivity, the increased C:P may invoke a “paradox of enrichment” effect since this means lower stoichiometric food quality for herbivores. In contrast, exposure to ultraviolet radiation (UVR) gave reduced cellular C:P-ratios (and N:P) in phytoplankton. This was partly owing to a strong reduction in C-fixation under UVR, but also due to enhanced uptake of P, presumably in response to increased demands for nucleotide repair under UVR stress. The net outcome of these opposing effects will depend on optical properties and mixing depth in the water column. These stoichiometric responses could cause deviations from Redfield ratio in phytoplankton as well as affecting biogeochemical cycling and trophic transfer efficiency in aquatic food-webs.
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Andersen, Tom; Færøvig, Per-Johan & Hessen, Dag Olav
(2007).
Growth rate versus biomass accumulation: Different roles of food quality and quantity for consumers.
Limnology and Oceanography.
ISSN 0024-3590.
52,
p. 2128–2134.
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Leu, Eva; Færøvig, Per-Johan & Hessen, Dag Olav
(2006).
UV effects on stoichiometry and PUFAs of Selenastrum capricornutum and their consequences for the grazer Daphnia magna.
Freshwater Biology.
ISSN 0046-5070.
51,
p. 2296–2308.
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Darchambeau, Francois; Færøvig, Per-Johan & Hessen, Dag Olav
(2003).
How Daphnia copes with excess carbon in its food.
Oecologia.
ISSN 0029-8549.
136,
p. 336–346.
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Færøvig, Per-Johan & Hessen, Dag Olav
(2003).
Allocation strategies in crustacean stoichiometry: the potential role of phosphorus in the limitation of reproduction.
Freshwater Biology.
ISSN 0046-5070.
48,
p. 1782–1792.
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Hessen, Dag Olav; Færøvig, Per-Johan & Andersen, Tom
(2002).
Light, nutrients, and P:C ratios in algae; grazer performance related to food quality and food quantity.
Ecology.
ISSN 0012-9658.
83,
p. 1886–1898.
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Continuous cultures of the green algae Selenastrum capricornutum were
grown at different concentrations of total phosphorus (1-50 µM P) and
different light levels (10-200 µmol quanta m-2 s-1). Growth yields in
terms of C, N, and P were positively correlated to total P level. Total
biomasses in terms of C and N, but not P, were also positively
correlated to light level. The cell quotas of C were positively
correlated with light, whereas cell quotas of P were negatively
correlated with light. The resulting elemental ratios gave a quite
consistent pattern, where high light caused significant reductions in
both N:C and P:C ratios, as well as strong reductions in chlorophyll to
carbon ratios. The increase in P:C ratio with increasing total P and
decreasing light can be interpreted as an adaptive response to
self-shading. In that case, our results indicate that light adaptation
not only involves a cost in terms of increased chlorophyll synthesis,
but also in terms of increased P demands. This provides new insight not
only into the physiological regulation of C and P uptake in algae, but
it could also explain deviations from the Redfield ratio.
The growth of juvenile Daphnia magna fed S. capricornutum from the
different light and phosphorus treatments was studied in a series of
short term assays (7 days) covering a gradient of food concentrations.
The response of Daphnia growth rate along this quantity (0.5 - 5.0 mg
C/L) and quality (0.5 - 12 µg-at P [mg-at C] -1) gradient gave a close
fit to a double hyperbola model. Changes in elemental ratios of the
algae were reflected in the growth rate of Daphnia, such that up to 40%
reduction in its growth rate could be attributed to increased
C:P-ratios.
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Færøvig, Per-Johan; Andersen, Tom & Hessen, Dag Olav
(2002).
Image analysis of Daphnia populations: non-destructive determination of demography and biomass in cultures.
Freshwater Biology.
ISSN 0046-5070.
47,
p. 1956–1962.
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Abstract
An image analyzing technique was developed for automatic enumeration and size and biomass determination of Daphnia magna in a two step chemostat system. This allowed for continuous recording of population growth, size distribution and biomass accumulation of live animals, and the problems with harvesting a sub-fraction of the population was avoided. The image analyzing system was tested and gave very reliable counts of numbers, even in cultures with high densities and large fractions of juveniles. Individual biomass calculation using an elliptic model was based on maximum animal width, and gave improved estimates of biomass compared with manual counting and length:dry-weight regressions, since animal width co-vary with nutritional status, while total length does not. Populations development and demography was followed in Daphna feeding on the green algae Selestrum capricornutuum in a two-step chemostat system . By growing the algae in low P (2.5 and 5 µM P l-1) at high and low light (70 and 10 µmol quanta) at a fixed dilution rate (0.4 d-1) a stable output in terms of biomass and P:C ratio was provided for the Daphnia that were raised in separate growth chambers over a 40 d period. This combination of image analysis on live animals in continuous cultures provide a very useful tool for assessing how food quantity and quality are regulating population growth and demographic strategies in zooplankton.
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Hessen, Dag Olav & Færøvig, Per-Johan
(2001).
The photo-protective role of humus-DOC for Selenastrum and Daphnia.
Plant Ecology.
ISSN 1385-0237.
154,
p. 225–235.
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Cell numbers and fluorescence of the green algae Selenastrum capricornutum and survival of Daphnia magna exposed to simulated sun-light was assessed along a gradient of DOC (0, 1, 5 10 and 50 mg C l-1). When exposed to UV-doses and spectral distribution (295-750 nm) closely resembling surface solar radiation during mid summer, Selenastrum showed major losses of cell fluorescence. In the absence of DOC, fluorescence was severely depressed, with successively decreasing effects with increased DOC. Surviving cells also required an extensive recovery period (10-12 d) for regrowth after exposure, while an almost immediate recovery was observed at concentrations above 1 mg DOC l-1. For Daphnia, survival was reduced to less than 10% after 4 h exposure, and almost zero after 8 h exposure in the absence of humus DOC, while no effects were observed in treatments with 10 and 50 mg C l-1. Selenastrum and Daphnia that were not directly irradiated, but exposed to UV-irradiated with the same concentrations of DOC did not reveal negative effects. This indicate negligible indirect effects mediated by long-lived free radicals or other toxic compounds. Irradiation of Daphnia under increased oxygen concentration (200% saturation) did not indicate acute effects, suggesting that effects of ambient radicals and oxidants would be of minor importance relative to intracellular photoproducts.
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Published
Nov. 3, 2010 3:26 PM
- Last modified
Jan. 25, 2011 9:47 AM
