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- Calliari, D., et al.
(författare)
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Density dependent grazing rates in a natural microzooplankton community
- 2019
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Ingår i: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 622, s. 83-92
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Tidskriftsartikel (refereegranskat)abstract
- Density dependence is a common phenomenon that affects individual performance in a wide range of organisms. Negative density dependence involves diminished individual rates, e.g. feeding and growth, under high organismal concentration. Microzooplankton (µZ) are key consumers in marine ecosystems and their grazing is frequently estimated by the dilution technique, which involves experimental manipulation of population concentrations of both grazer and prey. However, the potential interference of density dependent processes on grazing estimates has not been evaluated in the general context of µZ ecology, nor in the specific context of the dilution technique. Density dependent effects on µZ grazing rates were evaluated for a natural community of grazers in the Gullmar Fjord (Skagerrak, Sweden) across a wide but realistic range of µZ densities and under controlled algal prey concentrations. Net algal growth rates (k), grazing rate of the µZ community (G), and per capita grazing rates (SG) by the components of the µZ community were estimated based on algal cell counts and chlorophyll a (as metrics for prey concentration) and µZ counts (as a measure of predator concentration). The 3 responses (k, G and SG) showed clear evidence of negative density dependence under moderate and high levels of µZ concentrations. Results imply that negative density dependent effects on µZ grazing rates may actually occur in marine ecosystems. © Inter-Research 2019.
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| 6. |
- Rodriguez-Grana, Laura, 1969, et al.
(författare)
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Food web of a SW Atlantic shallow coastal lagoon: spatial environmental variability does not impose substantial changes in the trophic structure
- 2008
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Ingår i: Marine Ecology-Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 362, s. 69-83
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Tidskriftsartikel (refereegranskat)abstract
- We performed a detailed analysis of the food web structure of Laguna de Rocha, a temporally open coastal lagoon in the Southwest Atlantic, characterised by spatial gradients in salinity, nutrient levels and trophic status. Carbon and nitrogen stable isotopes of main producers, invertebrate and vertebrate consumers, and stomach contents of ichthyofauna were analysed seasonally at freshwater (north) and marine-influenced (south) sites to determine whether environmental differences induced changes in food web structure. Contribution of primary and secondary food sources and trophic linkages were assessed with the multisource-partitioning model IsoSource and an index that quantifies the contribution of each organism as food for the ecosystem. Isotopic analyses were performed for 10 primary organic matter sources (OM), 13 invertebrates and 9 fish species. Suspended and sediment OM constituted the most important primary sources, while direct consumption of macrophytes and macroalgae was marginal. The small invertebrates Neomysis americana, Nephtys fluviatilis, Pseudodiaptomus richardii and an amphipod were the most important intermediate consumers at both sites (except F richardii, which was present only in the north). Top predators were the fish species Micropogonias furnieri, Paralichthys orbygnianus and Hoplias malabaricus, and the maximum estimated trophic level (between 3.4 and 4.8) varied seasonally, but not between sites. Fish stomach content analyses largely confirmed results from the IsoSource mixing model. Overall results indicated that, despite environmental differences between sites, the structure of the biological assemblages and general trophic patterns were similar at both sites.
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- Åström, E., et al.
(författare)
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Precision measurements of linear scattering density using muon tomography
- 2016
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Ingår i: Journal of Instrumentation. - : Institute of Physics Publishing. - 1748-0221. ; 11:7
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that muon tomography can be used to precisely measure the properties of various materials. The materials which have been considered have been extracted from an experimental blast furnace, including carbon (coke) and iron oxides, for which measurements of the linear scattering density relative to the mass density have been performed with an absolute precision of 10%. We report the procedures that are used in order to obtain such precision, and a discussion is presented to address the expected performance of the technique when applied to heavier materials. The results we obtain do not depend on the specific type of material considered and therefore they can be extended to any application.
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