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See detailOrganisms as ecosystems engineers: the case of amphipod grazers from Posidonia oceanica meadows
Michel, Loïc ULg; Schnitzler, Joseph ULg; Dupont, Alessandra et al

Poster (2011, February 25)

Posidonia oceanica is a seagrass endemic to the Mediterranean Sea, and is able to form large monospecific areas, called meadows. These meadows shelter high biomasses and biodiversities of amphipod ... [more ▼]

Posidonia oceanica is a seagrass endemic to the Mediterranean Sea, and is able to form large monospecific areas, called meadows. These meadows shelter high biomasses and biodiversities of amphipod crustaceans. Moreover, It is now established that several species of these amphipods feed on the macro-epiphytes present on the leaves of the seagrass. Here, we performed in situ experiments to assess whether this grazing activity could impact the dynamics of the leaves’ epiphytic cover, and thus influence the functioning of the meadow as an ecosystem. We used microcosms containing monospecific populations of 3 amphipods taxa (Apherusa chiereghinii, Dexamine spiniventris and Gammarus spp.), and placed them directly in the meadow, at a depth of 10m. Biomasses of erected macroalgae and erected animals (hydrozoans, bryozoans) were lower in all grazed treatments. However, none of the studied taxa seemed to consume encrusting epiphytes, either vegetal or animal. This selective grazing pressure by amphipods may release encrusting epiphytes from competition for space, light and/or nutriments with the fast-growing erected algae, and could thus play an important role in the structuring of the epiphytic cover from P. oceanica leaves. Moreover, this top-down control might keep erected algae biomass to a normal, sustainable level, therefore also benefiting the seagrass itself. Our results also indicate that amphipod trophic activity caused nitrogen enrichment in both grazed (erected algae) and non-grazed (encrusting algae & seagrass leaves) vegetal tissues. A plausible interpretation could be that sloppy feeding and excretion by the grazers enhanced availability of this nutrient, which is typically limiting for photosynthesis in shallow P. oceanica meadows. This emphasizes the fact that grazing is not a simple negative interaction, but that it can also benefit the primary producers. Our results thus indicate that amphipods from P. oceanica meadows seem to be bound to the epiphytic cover of the leaves by complex and multilateral trophic interactions, and have an indirect influence on the seagrass itself. Amphipods may therefore play an important part in the functioning of the epiphyte/seagrass/grazer system of these meadows, and thus act as ecosystems engineers. This abstract is dedicated to the freshly born Adèle and Côme. [less ▲]

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See detailUse of C & N stable isotopes to evaluate interspecific trophic diversity among amphipods from Posidonia oceanica meadows
Michel, Loïc ULg; Lepoint, Gilles ULg; Nyssen, Fabienne ULg et al

Poster (2009, January 27)

Amphipods are one of the most diverse and abundant taxa of vagile invertebrates associated to Mediterranean Posidonia oceanica meadows. Therefore, they likely play an essential part in those ecosystems’ ... [more ▼]

Amphipods are one of the most diverse and abundant taxa of vagile invertebrates associated to Mediterranean Posidonia oceanica meadows. Therefore, they likely play an essential part in those ecosystems’ functioning, notably in organic matter transfers from producers to higher level consumers. Nevertheless, their trophic ecology remains poorly known, and they are generally regarded as epiflora grazers or generalist detritivores. Here, we focused on interspecific trophic diversity, and on the importance of other food sources (epifauna, Posidonia leaves & litter, suspended organic matter, …) in those amphipod’s diet. To achieve these goals, we used C and N stable isotopes ratios as trophic tracers. We noticed considerable trophic diversity among amphipods from different species, with δ13C values ranging from -16 to -26 ‰. Moreover, while some species (such as Apherusa chiereghinii and Aora spinicornis) seem to feed mainly on epiphytes, others, like Dexamine spiniventris, exploit other food sources. This study enhances the comprehension of the feeding ecology of these amphipods, and therefore of the way they interact with the Posidonia meadow ecosystem. [less ▲]

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See detailBiodiversity of three representative groups of the Antarctic zoobenthos - Coping with change (BIANZO II)
Raes, Maarten; Vanreusel, Ann; Pasotti, Francesca et al

Report (2009)

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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 detailBIANZO: biodiversity of three representative groups of the Antarctic Zoobenthos: comparative structure, distribution and fucntion
De Broyer, Claude; Vanreusel, Ann; Vanhove, Sandra et al

Report (2007)

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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 detailThe crustacean scavenger guild in Antarctic shelf, bathyal and abyssal communities
De Broyer, Claude; Nyssen, Fabienne ULg; Dauby, Patrick ULg

in Deep-Sea Research Part II, Topical Studies in Oceanography (2004), 51(14-16), 1733-1752

Peracarid crustaceans form a significant part of the macrobenthic community that is responsible for scavenging on large food falls onto the sea floor. Although several studies are available about ... [more ▼]

Peracarid crustaceans form a significant part of the macrobenthic community that is responsible for scavenging on large food falls onto the sea floor. Although several studies are available about scavengers from tropical and temperate seas, very little information has been published about such species living in Antarctic waters, particularly at greater depths. The present paper is based on a collection of 31 baited trap sets deployed in the Weddell Sea, Scotia Sea, and off the South Shetland Islands, and presents results on the geographical and bathymetric distribution of the different taxa and on the eco-functional role of scavengers. <br /> <br />Some 68,000 peracarid crustaceans from 62 species were collected. About 98% of individuals belonged to the amphipod superfamily Lysianassoidea, and 2% to the isopod family Cirolanidae. Of these species, 31, including 26 lysianassoids (1400 individuals), were collected deeper than 1000 m. <br /> <br />High species richness was discerned for the eastern Weddell Sea shelf compared with other Antarctic areas. The Antarctic slope also seems to be richer in species than other areas investigated in the world, while in the abyss, scavenger species richness appears to be lower in Antarctica. A richness gradient was thus observed from the shelf to the deep. For amphipods, a number of species extend their distribution from the shelf to the slope and only one to the abyssal zone. <br /> <br />Amphipod species showed degrees of adaptation to necrophagy. The functional adaptations of the mandible and the storage function of the gut are discussed. Feeding experiments conducted on lysianassoid species collected at great depths and maintained in aquaria showed a mean feeding rate of about 1.4–4.1% dry body weight day−1, which is consistent with data obtained from other species. [less ▲]

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See detailExperimental determination of the feeding rate for some Antarctic amphipod species
Dauby, Patrick ULg; Nyssen, Fabienne ULg; Scailteur, Yves et al

Poster (2003, April)

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See detailAmphipods: the second food source for top-predators in the Southern Ocean?
Dauby, Patrick ULg; Nyssen, Fabienne ULg; De Broyer, Claude

Poster (2003, April)

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See detailAmphipods as food sources for higher trophic levels in the Southern Ocean: a synthesis
Dauby, Patrick ULg; Nyssen, Fabienne ULg; de Broyer, Claude

in Antarctic biology in a global context (2003)

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See detailStructural and ecofunctional biodiversity of the amphipod crustacean benthic taxocoenoses in the Southern Ocean
De Broyer, Claude; Chapelle, Gauthier; Duchesne, Paul-André et al

in Belgian Scientific Research Programme on the Antarctic-Phase 4. Vol 1. Marine Biota and Global Change (2003)

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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)

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See detailAmphipod as food sources for higher trophic levels in the Southern Ocean
Dauby, Patrick ULg; Nyssen, Fabienne ULg; De Broyer, Claude

Poster (2001, July)

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