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See detailTrophic tracers reveal considerable diversity among diets of dominant amphipods from Posidonia oceanica seagrass meadows
Michel, Loïc ULg; Dauby, Patrick ULg; Gobert, Sylvie ULg et al

Poster (2012, August 20)

Mediterranean Posidonia oceanica meadows shelter a high biomass and an important biodiversity of amphipod crustaceans. In other temperate meadows, the amphipods play an important part in the functioning ... [more ▼]

Mediterranean Posidonia oceanica meadows shelter a high biomass and an important biodiversity of amphipod crustaceans. In other temperate meadows, the amphipods play an important part in the functioning of the ecosystem, notably in organic matter transfers from producers to higher level consumers. However, the situation in Posidonia oceanica meadows remains unclear, and little is known about the trophic ecology of amphipods, which are generally regarded as generalist herbivores/detritivores despite the lack of precise studies. Here, we combined gut content examination and trophic markers (fatty acids, stables isotopes of C and N) to delineate the diet of the dominant species of amphipods from Posidonia oceanica seagrass meadows and to highlight trophic diversity among this community. Our results indicate that contribution of microepiphytic diatoms and of benthic and suspended particulate organic matter to the diet of amphipods were anecdotal. On the other hand, all dominant species heavily relied on macroalgal epiphytes, suggesting a certain extent of overlapping in the diets of the dominant species. Considerable interspecific differences nonetheless existed, notably concerning grazing preferences towards epiphytes from leaves or litter fragments vs. epiphytes from rhizomes. In addition, the use of the SIAR isotopic mixing model showed that most species had a mixed diet, and relied on several food items. None of the examined species seemed to graze on their seagrass host, but Gammarus aequicauda partly relied on seagrass leaf detritus. Overall, our findings demonstrate that amphipods have the potential to be key-items in trophic and functional interactions occurring among Mediterranean Posidonia oceanica meadows. [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 detailCombination of trophic biomarkers to distinguish among Antarctic amphipods trophic guilds
Nyssen, Fabienne ULg; Dauby, Patrick ULg; Graeve, Martin

Conference (2004, July)

Peracarid crustaceans and amphipods in particular are an important group in the Southern Ocean and one of the most diverse in the macrozoobenthos. As a part of a multidisciplinary study of the amphipods ... [more ▼]

Peracarid crustaceans and amphipods in particular are an important group in the Southern Ocean and one of the most diverse in the macrozoobenthos. As a part of a multidisciplinary study of the amphipods ecological roles in Antarctic benthic systems, about 150 specimens belonging to 25 species of 10 of the most common amphipod families occurring in the Southern Ocean have been involved in this study of amphipod trophic patterns. Beside “classical” stomach content analysis or field observations, the use of naturally occurring stable isotopes of carbon (δ13C) and nitrogen (δ15N) has recently provided new insights into food web ecology. This method is based on the direct relationship established between the isotopic signature of an organism and that of its preys. Nitrogen-15 typically shows a step-wise increase with trophic level within a food chain. Closer to the value of the diet, carbon-13 is preferentially used to assess the relative proportion of potential primary sources in a trophic web (ex.: pelagic vs benthic contribution to food intake). Furthermore, for several species, the lipid signature – which has already been used successfully to help understand marine trophodynamics – and more particularly the fatty acid composition has been investigated as trophic biomarkers to reveal more precisely to which trophic guild they belong to. [less ▲]

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See detailStable isotopes and fatty acids used as biomarkers to distinguish among Antarctic amphipods trophic guilds
Nyssen, Fabienne ULg; Graeve, Martin

Conference (2003)

Peracarid crustaceans and amphipods in particular are an important group in the Southern Ocean and one of the most diverse in the macrozoobenthos (Jazdzewski et al., 1991). As a part of a ... [more ▼]

Peracarid crustaceans and amphipods in particular are an important group in the Southern Ocean and one of the most diverse in the macrozoobenthos (Jazdzewski et al., 1991). As a part of a multidisciplinary study of the amphipods ecological roles in Antarctic benthic systems (De Broyer et al., 2001, Nyssen et al., 2002), about 150 specimens belonging to 25 species of 10 of the most common amphipod families occurring in the Southern Ocean have been involved in this study of amphipod trophic patterns. Beside “classical” stomach content analysis or field observations, the use of naturally occurring stable isotopes of carbon (δ13C) and nitrogen (δ15N) has recently provided new insights into food web ecology (Hobson & Welch, 1992, Lepoint et al., 2000). This method is based on the direct relationship established between the isotopic signature of an organism and that of its preys (DeNiro & Epstein, 1978, 1981, Peterson & Fry, 1987). Nitrogen-15 typically shows a step-wise increase with trophic level within a food chain (Cabana & Rasmussen, 1994). Closer to the value of the diet, carbon-13 is preferentially used to assess the relative proportion of potential primary sources in a trophic web (ex.: pelagic vs benthic contribution to food intake) (Dauby et al., 1998, Hobson et al., 1995). Furthermore, for several species, the lipid signature – which has already been used successfully to help understand marine trophodynamics (Graeve et al., 2001, Nelson et al., 2001, Phleger et al. 1998) – and more particularly the fatty acid composition has been investigated as trophic biomarkers to reveal more precisely to which trophic guild they belong to. [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)

Detailed reference viewed: 8 (0 ULg)