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See detailDifferential isotopic turnover (C and N) detected in Antarctic scavenger amphipods
Nyssen, Fabienne ULg; Michel, Loïc ULg; Dauby, Patrick ULg et al

Poster (2008, August)

Metabolic activity is positively related to temperature, inversely to body mass and is a function of taxon specific life style features, in particular activity such as level of active movement. Therefore ... [more ▼]

Metabolic activity is positively related to temperature, inversely to body mass and is a function of taxon specific life style features, in particular activity such as level of active movement. Therefore, the isotope signal transfer velocity is expected to be lower in cold environments and in larger as well as less active organisms. Our study explores whether this may be a problem in trophic studies of a comparatively “slow” because cold system such as the high Antarctic shelf ecosystem and in comparatively large organisms such as benthic amphipod species within this system. We compare experimentally the velocity of stable isotope signal transfer from prey to consumer in three lysianassoid amphipods, Waldeckia obesa, Abyssorchomene plebs and Pseudorchomene coatsi. They have similar alimentation, but different size and lifestyle. Indeed, W. obesa is a very sedentary species spending most of the time immobilized on diverse substrates whereas P. coatsi is very motile, swimming rapidly around the aquarium. The third species, A. plebs has an intermediate behaviour, sharing time between short swim and resting on bottom. Those species also differ significantly in size: and are good representative of scavenger trophic guild on Antarctic shelf. After being starved, amphipods were kept by species and fed ad libitum with lyophilized fish during fifty days. Individuals were sacrificed weekly for isotopic analysis. At the end of the 7-week incubation with standardized food, rank correlation of δ13C and δ15N against time did not show any consistent trend for A. plebs (δ13C: p = 0.51 and δ15N p = 0.04) neither for the species W. obesa (δ13C: p = 0.77 and δ15N p = 0.26). By contrast, for P. coatsi, rank correlations were highly significant (p < 0.0001). The linear regression illustrated a clear increase of isotopic ratios all along the experiment. This metabolic discrepancy between species is probably a size-mass effect. Furthermore, for this species, ANCOVA of the individually measured isotopic ratios first transformed to an offset value (rate vs carbon ↔ nitrogen, covariate time) provided evidence for significant effects of the parameter “isotope” on isotopic temporal evolution. Indeed, the δ13C values evolve much faster than the δ15N ones. According to data, it would take double time for P. coatsi to balance its nitrogen isotopic signature than its carbon isotopic ratio when changing food. Those results are critically discussed. [less ▲]

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See detailTrophic position of Antarctic amphipods: enhanced analysis by a 2-dimensional biomarker assay
Nyssen, Fabienne ULg; Brey, Thomas; Dauby, Patrick et al

in Marine Ecology. Progress Series (2005), 300

The discrepancy between the ecological significance of amphipods in the Antarctic and our poor knowledge of their ecofunctional role calls for a more detailed investigation of their trophic status in this ... [more ▼]

The discrepancy between the ecological significance of amphipods in the Antarctic and our poor knowledge of their ecofunctional role calls for a more detailed investigation of their trophic status in this ecosystem. A total of 12 amphipod species from suspension feeder to scavenger have been considered in this study. Our objective was to investigate whether the combination of fatty-acid and stable-isotope signatures into a 2-dimensional trophic biomarker assay would increase accuracy in the identification of Antarctic benthic amphipod trophic position. Amphipod isotopic averages ranged from -29.3 parts per thousand (delta(13)C) and 4.1 parts per thousand (delta(15)N) for the suspension feeder Ampelisca richardsoni to -21.7 parts per thousand (delta(13)C) and 11.9 parts per thousand (delta(15)N) for the high predator Iphimediella sp. Cluster analysis of the fatty-acid composition separated the amphipod species into 4 trophic groups: suspension feeders, macroherbivores, omnivores and scavengers. The suspension feeder was isolated due to an important proportion of 18:4(n-3), a fatty-acid biomarker of phytoplankton. Macro-herbivores were found to rely heavily on macroalgal carbon, containing a high percentage of arachidonic acid (20:4(n-6)). Scavenger amphipods revealed a unique fatty-acid composition dominated by 1 single fatty acid, 18:1(n-9), probably the result of a very intensive de novo biosynthesis to cope with starvation periods. Our data emphasise the need to combine different types of information to be able to draw the right conclusions regarding trophic ecology. Indeed, in some cases, the exclusive use of 1 type of tracing method, fatty acids or stable isotopes, would have resulted in misleading/false conclusions in the trophic classification of amphipods. Therefore, a 2-dimensional biomarker assay is a useful tool to elucidate the trophic positions of benthic amphipods. [less ▲]

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See detailThe role of benthic amphipods in Antarctic trophodynamics: a multidisciplinary study
Nyssen, Fabienne ULg; Graeve, Martin; Brey, Thomas

Conference (2002, July)

Long-term controlled feeding experiments have been performed with four Antarctic amphipod species. For several weeks three scavenger and one herbivore species (Abyssorchomene plebs, Pseudorchomene coatsi ... [more ▼]

Long-term controlled feeding experiments have been performed with four Antarctic amphipod species. For several weeks three scavenger and one herbivore species (Abyssorchomene plebs, Pseudorchomene coatsi, Waldeckia obesa and Djerboa furcipes, respectively) have been fed ad libitum with an isotopically known food. The aim of those experiments was primarily to determine the isotopic fractionation factor between animals and diet. Secondly, turnover rates of tissues have been estimated by following their isotopic ratios evolution due to the shift of the food. Comparison has been made between herbivore and scavenger species. Such experimental data are necessary to improve isotope-based trophic models. [less ▲]

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See detailThe role of benthic amphipods in the eastern Weddell Sea trophic web as determined from stable isotope and fatty acid analyses
Nyssen, Fabienne ULg; Brey, Thomas; Graeve, Martin et al

Conference (2001, August)

Within the Southern Ocean, amphipods have achieved a conspicuous adaptative radiation which gave rise to the development of numerous feeding strategies (Jazdzewski et al. 1996; Dauby et al. in press; De ... [more ▼]

Within the Southern Ocean, amphipods have achieved a conspicuous adaptative radiation which gave rise to the development of numerous feeding strategies (Jazdzewski et al. 1996; Dauby et al. in press; De Broyer et al. in press). The discrepancy between the ecological significance of amphipods in the Antarctic and our poor knowledge of their ecofunctional role calls for a more detailed investigation of their importance in this ecosystem trophodynamics. This study focused on the eight amphipods species which were collected and from which isotopic and lipidic (when available) (Graeve et al. in press) compositions were compared to their respective gut contents previously described (Dauby et al. in press). The interest of both first techniques rely upon the direct relationship between the isotopic signatures and the lipid composition of organisms and those of their diet (De Niro and Epstein 1978, 1981; Peterson and Fry 1987; Graeve et al. 1994; Cripps et al 1999). Amphipod stable isotope ratios and fatty acids composition correspond rather accurately to the trophic classification based on gut contents and attest to their high spectrum of feeding types. Since the fundamental difference between the approaches to diet studies is the time scale each method addresses, this coincidence indicates that there would be no significant changes in feeding strategies over time. Three levels of the food web are covered by the eight species and, instead of belonging strictly to one trophic category, amphipods display a continuum of values from the suspension-feeder to scavengers. [less ▲]

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See detailUse of stable isotopes to delineate amphipod trophic status in the High Antarctic
Nyssen, Fabienne ULg; Graeve, Martin; Brey, Thomas et al

Poster (2001, July)

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See detailA stable isotope approach to the eastern Weddell Sea trophic web: focus on benthic amphipods
Nyssen, Fabienne ULg; Brey, Thomas; Lepoint, Gilles ULg et al

in Polar Biology (2001), 25(4),

isotope (C-13/C-12 and N-15/N-14) analyses were performed on 90 species belonging to different benthic communities sampled in the eastern Weddell Sea. The study focused on eight amphipod species whose ... [more ▼]

isotope (C-13/C-12 and N-15/N-14) analyses were performed on 90 species belonging to different benthic communities sampled in the eastern Weddell Sea. The study focused on eight amphipod species whose isotopic composition was compared to their previously described respective gut contents. Amphipod stable isotope ratios correspond fairly accurately to the trophic classification based on gut contents and attest to their wide spectrum of feeding types. Since the fundamental difference between the isotope and the gut content approaches to diet studies is the time scale each method addresses. this coincidence indicates that there would be no significant changes in feeding strategies over time. Three levels of the food web are covered by the eight species and, instead of belonging strictly to one trophic category, amphipods display a continuum of values from the suspension-feeder to scavengers. [less ▲]

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See detailUse of stable isotopes to delineate amphipod trophic status in Antarctic food webs
Nyssen, Fabienne ULg; Brey, Thomas; Lepoint, Gilles ULg et al

Poster (2000, May)

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