| 1. |
- Gutseit, Kelly, et al.
(författare)
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Essential fatty acids and phosphorus in seston from lakes with contrasting terrestrial dissolved organic carbon content
- 2007
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 52:1, s. 28-38
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- 1. It is often assumed that lakes highly influenced by terrestrial organic matter (TOM) have low zooplankton food quality because of elemental and/or biochemical deficiencies of the major particulate organic carbon pools. We used the biochemical [polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA) - 20:5 omega 3] and elemental (C : P ratio) composition of particulate matter (PM) as qualitative measures of potential zooplankton food in two categories of lakes of similar primary productivity, but with contrasting TOM influence (clear water versus humic lakes). 2. C : P ratios (atomic ratio) in PM were similar between lake categories and were above 400. The concentration (mu g L-1) and relative content (mu g mg C-1) of EPA, as well as the particulate organic carbon concentration, were higher in the humic lakes than in the clear-water lakes. 3. Our results show high fatty acid quality of PM in the humic lakes. The differences in the biochemical quality of the potential zooplankton food between lake categories can be attributed to the differences in their phytoplankton communities. 4. High biochemical quality of the food can result in high efficiency of energy transfer in the food chain and stimulate production at higher trophic levels, assuming that zooplankton are able to ingest and digest the resource available.
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| 2. |
- Gutseit, Kelly, et al.
(författare)
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Food quality for Daphnia in humic and clear water lakes
- 2007
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 52:2, s. 344-356
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Tidskriftsartikel (refereegranskat)abstract
- 1. Growth and reproduction of Daphnia fed lake seston were measured in two categories of meso- to eutrophic lakes differing with respect to terrestrial organic matter influence (humic and clear water lakes). The content of highly unsaturated fatty acids (HUFA), P and N, as well as the taxonomical composition of seston were analysed.2. Seston HUFA and C : P ratios were similar between lake categories, whereas C : N ratios were lower in the clear water lakes in both spring and summer. Despite the similarity in HUFA and P content of seston, Daphnia growth rate, clutch size and the proportion of gravid females were, respectively, about 1.5, 3 and 6 times higher in the clear water lakes.3. Differences in growth and reproduction were related to a combination of higher N content and good fatty acid quality of the seston in the clear water lakes. Relatively high biomass of edible algae, such as Rhodomonas sp. and Cryptomonas sp., in the clear water lakes, and differences in water pH likely contributed to the observed differences in Daphnia growth and reproduction between lake categories. Additionally, it is possible that Daphnia was energy limited in the humic lakes despite high particulate organic carbon (POC) concentrations, as the contribution of non-algal and detrital C to the POC pool was high.4. Our results suggest that dietary HUFA content has the potential to improve herbivore growth and reproduction if N and P are not limiting. N merits more attention in studies of zooplankton nutrition.
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| 3. |
- Gutseit, Kelly
(författare)
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Food Quality for Zooplankton in Humic Lakes
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Food quality affects growth, reproduction and community structure of zooplankton, and has implications for nutrient cycling and the transfer of energy and matter in aquatic food chains. While the issue of food quality in clear water lakes has received great recent attention, studies on food quality for zooplankton in humic lakes are scarce. Humic lakes are largely influenced by carbon of terrestrial origin, and the effect of this large terrestrial carbon influence on the total quality of the resource available for zooplankton is poorly known. On the one hand, there is usually a large contribution of low-quality detritus and bacteria to the particulate carbon pool of humic lakes. On the other hand, cryptophytes and chrysophytes, algal groups generally considered of high quality for zooplankton, are rather common in humic lakes. In this thesis, I assess the quality of the food available for zooplankton in humic lakes, and compare it to lakes that are less influenced by terrestrial organic matter (clear water lakes). In a long-term laboratory experiment, in which zooplankton were kept in humic and in clear lake water in the presence or in absence of recent phytoplankton production, differences in zooplankton community composition between lake types as well as comparatively high zooplankton biomass were observed in the humic lake by the end of the study. It was unclear from that study whether the differences in zooplankton community composition and biomass could be due to differences in food quality between lake types. In a series of subsequent studies, I measured the content of fatty acids and elements in seston (suspended particulate matter) to assess the quality of the food available for zooplankton in humic and clear water lakes. I hypothesized that food quality is higher in humic than in clear water lakes of comparable trophy. In a field survey, I found higher food quality (in terms of fatty acids) in humic than in clear water lakes closer to an oligotrophic (low total phosphorus concentration) state. However, in meso- to eutrophic lakes, food quality (in terms of both elements and fatty acids) was lower in humic lakes than in clear water lakes, which resulted in comparatively low growth and reproduction of zooplankton in the humic lakes. My results show that there are differences in food quality between humic and clear water lakes that affect zooplankton growth and reproduction, and, consequently, energy transfer in the food chain. The large influence of terrestrial organic matter in humic lakes can have bearings on food quality for zooplankton, since it can affect, for instance, the relative contribution of algal (high food quality), non-algal and detrital (low food quality) carbon to the total organic carbon pool, as well as microplankton community structure and composition.
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| 4. |
- Hylander, Samuel, et al.
(författare)
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Complementary UV protective compounds in zooplankton
- 2009
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 54:6, s. 1883-1893
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Tidskriftsartikel (refereegranskat)abstract
- Zooplankton accumulate several groups of photoprotective compounds to shield against damaging ultraviolet radiation (UV). One of these groups, the carotenoids, makes the animals more conspicuous to visually hunting predators, whereas others, such as the mycosporine-like amino acids (MAAs) may not. The blend of photoprotective compounds is therefore important for the UV defense but also for the ability to escape predation through crypsis. Here we assess laboratory and field data from different latitudes to examine how UV, predation threat, and pigment availability ( in food) affects the mixture of UV-protective compounds in copepods. Overall, the blend of MAAs and carotenoids was partly explained by the availability of MAAs in the food, the UV-threat, and the presence of predators. Copepods upregulated their MAA content when UV threat was increasing (i.e., if MAAs were abundant in food), and in field data this accumulation only occurred at high levels of predation threat. If MAAs were scarce, copepods instead compensated with higher carotenoid accumulation. However, when there was a high predation threat this carotenoid compensatory effect was disadvantageous, and low concentrations of both MAAs and carotenoids at high UV-threat resulted in lower reproduction. In all, these results showed that carotenoids and MAAs are complementary substances, i.e., one is high when the other is low, and copepods are, hence, able to adjust their blend of different UV-protective compounds to optimize their defenses to the threats of UV and predation. These defense systems may buffer against direct food-web interactions and help the zooplankton to survive in environments with high UV threat.
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