References of "Gobert, Sylvie"
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See detailPeut on repiquer les posidonies
Gobert, Sylvie ULg; Piet, Grégory ULg

Article for general public (2011)

Les posidonies qui colonisent les fonds marins et y sont indispensables sont malheureusement menacées par l'activité humaine. Les tentatives de transplantations ont abouti à des échecs. Cependant, on ... [more ▼]

Les posidonies qui colonisent les fonds marins et y sont indispensables sont malheureusement menacées par l'activité humaine. Les tentatives de transplantations ont abouti à des échecs. Cependant, on continue à avancer cette solution. Sylvie Gobert, spécialiste des écosystèmes marins nous explique cette controverse. [less ▲]

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See detailThe seascape as an indicator of environmental interest and quality of the Mediterranean benthos: the in situ development of a description index: the LIMA
Gobert, Sylvie ULg; Chéry, Aurélia; Volpon, Alexandre et al

Conference (2011, March)

The LIMA index conveys the environmental interest and quality of the landscape formed by the Mediterranean benthos, ranging from 0 to -40 m, in numerical format. The LIMA index allows a comparison ... [more ▼]

The LIMA index conveys the environmental interest and quality of the landscape formed by the Mediterranean benthos, ranging from 0 to -40 m, in numerical format. The LIMA index allows a comparison spatially and temporarily between sites. It is a comprehensive index which is easy to implement and is composed of two factors: a topographical description (classification of 15 typologies) and a biological description (the presence or absence of some thirty species or groups of structuring, remarkable and invasive species). The LIMA index has been validated in the Bay of Calvi (Corsica-France) where it varies between 0.31 and 0.79 on a scale of 0.00 to 1.00. [less ▲]

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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 detailPotential early indicators of anthropogenically derived nutrients : a multiscale stable isotope analysis
Vermeulen, Simon ULg; Sturaro, Nicolas ULg; Gobert, Sylvie ULg et al

in Marine Ecology. Progress Series (2011), 422

Increasing human pressure along Mediterranean coastlines raises the need to define sensitive bioindicators that provide an early response to nutrient enrichment. We performed multiscale carbon and ... [more ▼]

Increasing human pressure along Mediterranean coastlines raises the need to define sensitive bioindicators that provide an early response to nutrient enrichment. We performed multiscale carbon and nitrogen stable isotope analyses on the limpet Patella caerulea, the snail Monodonta turbinata, epilithic biofilms, and the macroalga Rissoella verruculosa inhabiting the rocky midlittoral zone. Samples were seasonally collected in 2006 from 5 sites exposed to a range of anthropogenic discharges in the Revellata Bay area and in Marseille harbour (France). All bioindicators exhibited strongly elevated δ15N values at impacted sites compared to pristine ones, which revealed the biological availability of anthropogenically derived nutrients. Only epilithic biofilms tended to show both the occurrence of nutrient pulses during the tourist season and a δ13C response at impacted sites. In contrast to macroalgae, which exhibited a somewhat equivocal signal, gastropods and especially M. turbinata provided the best time-integrated picture of the graduated exposure of the 5 sites to anthropogenic impact. Results also showed first evidence of large isotopic variability at a scale of tens of metres, close to that found at the kilometre scale. The intra- and interspecific isotopic variability in gastropods may be explained by the patchiness of resources and specific morphological and behavioural features, but these factors do not greatly hamper their potential as early bioindicators of wastewater disturbances. [less ▲]

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See detailDistribution patterns of Caprella tavolarensis (Crustacea: Amphipoda) in the Tavolara-Punta Coda Cavallo Marine Protected Area.
Sturaro, Nicolas ULg; Gobert, Sylvie ULg; Lepoint, Gilles ULg et al

in Biologia Marina Mediterranea (2011), 18(1), 290-291

Distribution patterns of Caprella tavolarensis was investigated at the tavolara-punta Coda Cavallo Marine protected area. results revealed that C. tavolarensis abundance may exhibit spatial patterns ... [more ▼]

Distribution patterns of Caprella tavolarensis was investigated at the tavolara-punta Coda Cavallo Marine protected area. results revealed that C. tavolarensis abundance may exhibit spatial patterns associated with the protection status of the zones, highlighting the importance of totally protected areas in species conservation and management. [less ▲]

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See detailEffects of shading and sediment alterations on Posidonia oceanica meadows: in situ experiments
Pete, Dorothée ULg; Velimirov, Branko; Lepoint, Gilles ULg et al

Conference (2010, November 24)

In the Mediterranean Sea, the seagrass Posidonia oceanica is affected by many threats from anthropogenic sources. One of them is the increasing development of fish farming, which is responsible of the ... [more ▼]

In the Mediterranean Sea, the seagrass Posidonia oceanica is affected by many threats from anthropogenic sources. One of them is the increasing development of fish farming, which is responsible of the destruction of some meadows. Within troubles cause by those fish farms on the surrounding environment, the increase of phytoplankton biomass in the water column (leading to a shading effect) and a modification of the sediment are often cited as a reason of seagrass disappearance. To understand how those troubles are affecting P. oceanica and its sedimentary compartment, in situ experiments were led during three months, from the end of May til the end of August 2009, in STARESO (STAtion de REcherches Sous-marines et Océanographiques, Corsica, France), at a depth of 10 meters. The shading was mimicked by three replicated shading frames (3 x 1 m), which stopped around 50 % of the incident light. To modify the sedimentary compartment, some sediment was taken from under the fish farm of Calvi (Corsica, France) and added once a week on marked zones in the seagrass meadow. Those sites were compared with a control site, situated in the same meadow. Samples were taken once a month and consisted in pore water, sediment cores and shoots of P. oceanica. An estimation of the density of the meadow in every sampling zones was also performed. Measured parameters are the concentration of nutrients in pore water, grain size, redox potential discontinuity (RPD), biomass of bacteria, organic matter, meiofauna and microphytobenthos within the sediment, total carbon and nitrogen in the sediment and leaves, the length, width and biomass of leaves and shoots, the biomass of epiphytes and the content of chlorophyll a in leaves. During those experiments, Posidonia oceanica was not very affected. However, some parameters of the sedimentary compartment were modified (RPD, biomass of bacteria, organic matter, nutrients in pore water,…), suggesting a modification in the functioning of the ecosystem. These results are important because they show that the sedimentary compartment reacts more rapidly to threats then the seagrass itself. So, it could be an interesting tool in quality assessments. [less ▲]

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See detailImpact of grazing by amphipods on the epiphytic cover of the Posidonia oceanica leaves: an in situ experiment.
Michel, Loïc ULg; Dupont, Alessandra; Gobert, Sylvie ULg et al

Poster (2010, October 22)

It is now established that several species of amphipods associated to Mediterranean Posidonia oceanica meadows consume the macro-epiphytes present on the leaves of the seagrass. Moreover, under controlled ... [more ▼]

It is now established that several species of amphipods associated to Mediterranean Posidonia oceanica meadows consume the macro-epiphytes present on the leaves of the seagrass. Moreover, under controlled in vitro conditions, three amphipod taxa (Apherusa chiereghinii,Dexamine spiniventris and Gammarus spp.) are able to drastically deplete the biomass of erected algae, thus influencing the epiphytic cover in both a quantitative and a qualitative way. Here, we tried to assess whether this strong and complex trophic interaction was realized in the field. We designed an in situ experiment that used microcosms placed directly in the meadow, at a depth of 10m, to estimate the impact of grazing by the aforementioned amphipod taxa on the dynamics of the epiphytic cover. Both Gammarus spp. and Dexamine spiniventris caused a significant decrease of the biomass of erected algae and erected animals (bryozoans and hydrozoans). Impact of grazing by Apherusa chiereghinii on these two epiphytic groups was less important, although strong but marginally non-significant (0,1>p>0,05) trends to lower biomasses were present. None of the considered taxa seemed to consume encrusting macro-epiphytes. In addition, assimilation of epiphyte-derived carbon and nitrogen by grazers was monitored using stable isotopes (13C and 15N), and epiphyte elemental content (C & N) was measured. Our results shed light on trophic interactions between the amphipods from Posidonia oceanica meadows and the seagrass epiphytic cover, and thus enhance our understanding of the role of these grazers in the functioning of the meadow as an ecosystem. [less ▲]

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See detailTop-down role of fish predators in structuring amphipod community associated to Posidonia oceanica seagrass meadows
Sturaro, Nicolas ULg; Lepoint, Gilles ULg; Panzalis, Pier et al

Poster (2010, October)

Despite the major ecological importance of Posidonia oceanica seagrass meadows in the Mediterranean Sea, little attention has been given to community structuring forces by predators in this ecosystem. To ... [more ▼]

Despite the major ecological importance of Posidonia oceanica seagrass meadows in the Mediterranean Sea, little attention has been given to community structuring forces by predators in this ecosystem. To better understand the mechanisms by which fishes affect amphipod community structure associated to P. oceanica beds, experimental manipulations of predation intensity (enclosure and exclusion cages) were set up in the Tavolara-Punta Coda Cavallo Marine Protected Area (Sardinia, NW Mediterranean). In totally protected area, where high abundance of predatory fishes is recorded, we have performed exclusion experiment. Total amphipod abundance increased at the end of the experiment, but diversity and specific composition were unaffected. At the species taxonomic level, significant increase in abundance between treatments appeared only for Caprella acanthifera. In partially protected area, where fish abundance is lower and amphipod abundance higher, individuals of the carnivorous fish Coris julis (Labridae) were enclosed in cages to provide an estimate of the potential for this species to impact on amphipod community. There was a small but measurable effect on amphipod abundance between enclosures and unmanipulated controls. A few dominant amphipod species responded to fish predation by significant decrease in abundance. These results suggest that fish predation may determine the relative abundances in the community of some amphipod species and to some degree, through an untested link with habitat complexity, determine the spatial distribution of amphipod abundance within P. oceanica beds. Moreover, patterns observed at the species level, suggest parallel complex interactions probably mainly related to ecological behaviour of amphipod species. [less ▲]

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See detailShading and alterations of the sediment: in situ experiments to mimic impacts of fish farms on a Mediterranean coastal ecosystem
Pete, Dorothée ULg; Velimirov, Branko; Lepoint, Gilles ULg et al

Poster (2010, October)

In the Mediterranean coastal zone, the seagrass Posidonia oceanica forms underwater meadows which sustain a high biodiversity and has many important roles (production of oxygen, protection of coasts ... [more ▼]

In the Mediterranean coastal zone, the seagrass Posidonia oceanica forms underwater meadows which sustain a high biodiversity and has many important roles (production of oxygen, protection of coasts, ...). Unfortunately, they are more and more threaten, notably by the increasing development of aquaculture. Indeed, fish farms increase the biomass of phytoplankton organisms in the water column (leading to a shading effect) and modify the sediment, which entail the disappearance of the seagrass. To understand the impact of those troubles on P. oceanica and the ecosystem, in situ experiments were led during three months, in STARESO (STAtion de Recherches Sous- marines et Océanographiques; Calvi, Corsica), at a depth of 10 meters. The shading was mimicked by shading frames, which stopped around 50 % of the incident light. To modify the sedimentary compartment, sediment was taken from under the aquaculture of Calvi and added once a week on marked zones in the meadow. Those sites were compared with a control site, situated near them. Measured parameters are: the concentration of nutrients in pore water, grain size, redox potential discontinuity, biomasses of bacteria, organic matter, meiofauna and microphytobenthos within the sediment, the length, width, biomass and chlorophyll a content of P. oceanica leaves and the biomass of epiphytes. During those experiments, P. oceanica was not very affected although some parameters of the sedimentary compartment were modified. These results show that the sedimentary compartment reacts more rapidly to threats then the seagrass itself. So, it could be an interesting tool in quality assessments. [less ▲]

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See detailImpact of grazing by amphipods on the dynamics of the epiphytic cover of the Posidonia oceanica leaves : an in vitro experiment.
Michel, Loïc ULg; Gobert, Sylvie ULg; Dauby, Patrick ULg et al

Conference (2010, September 17)

It is now established that several species of amphipods associated to Mediterranean Posidonia oceanica meadows consume the epiphytes present on the leaves of the seagrass. However, little or no work has ... [more ▼]

It is now established that several species of amphipods associated to Mediterranean Posidonia oceanica meadows consume the epiphytes present on the leaves of the seagrass. However, little or no work has been undertaken to quantify this interaction. Here, we present the results of an in vitro experiment that used seagrass mimics to estimate the impact of grazing by the amphipods Apherusa chiereghinii, Dexamine spiniventris and Gammarus spp on the dynamics of the epiphytic cover. All species reduced epiphyte biomass in a significant way, and grazers preferentially fed on erected algae. Assimilation of epiphyte-derived carbon and nitrogen was monitored using stable isotopes (13C and 15N) labelling, and was obvious in the three taxa. Moreover, grazing activity of amphipods seemed to influence epiphyte physiology, notably by increasing nitrogen uptake by the erected algae. These results shed light on trophic interactions between the amphipods from Posidonia oceanica meadows and the seagrass epiphytic cover, and thus enhance our understanding of the role of these grazers in the functioning of the meadow as an ecosystem. [less ▲]

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See detailThe role of fish predation in the structure of amphipod community associated with Posidonia oceanica seagrass meadows
Sturaro, Nicolas ULg; Lepoint, Gilles ULg; Panzalis, Pier et al

Conference (2010, September)

Despite the major ecological importance of Posidonia oceanica seagrass meadows in the Mediterranean Sea, little attention has been given to community structuring forces by predators in this ecosystem. To ... [more ▼]

Despite the major ecological importance of Posidonia oceanica seagrass meadows in the Mediterranean Sea, little attention has been given to community structuring forces by predators in this ecosystem. To better understand the mechanisms by which fishes affect amphipod community structure associated to P. oceanica beds, experimental manipulations of predation intensity (enclosure and exclusion cages) were set up in the Tavolara-Punta Coda Cavallo Marine Protected Area (Sardinia, NW Mediterranean). In totally protected area, where high abundance of predatory fishes is recorded, we have performed exclusion experiment. Total amphipod abundance increased at the end of the experiment, but diversity and specific composition were unaffected. At the species taxonomic level, significant increase in abundance between treatments appeared only for Caprella acanthifera. In partially protected area, where fish abundance is lower and amphipod abundance higher, individuals of the carnivorous fish Coris julis (Labridae) were enclosed in cages to provide an estimate of the potential for this species to impact on amphipod community. There was a small but measurable effect on amphipod abundance between enclosures and unmanipulated controls. A few dominant amphipod species responded to fish predation by significant decrease in abundance. These results suggest that fish predation may determine the relative abundances in the community of some amphipod species and to some degree, through an untested link with habitat complexity, determine the spatial distribution of amphipod abundance within P. oceanica beds. Moreover, patterns observed at the species level, suggest parallel complex interactions probably mainly related to ecological behaviour of amphipod species. [less ▲]

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See detailFish farm impacts on meiofauna and the microbenthic loop in Posidonia oceanica meadows
Pete, Dorothée ULg; Mannard, Jennifer ULg; Velimirov, Branko et al

in Hendrik, Gheerardyn; Nara Bezerra, Tania; Cnudde, Clio (Eds.) et al Fourteenth International Meiofauna Conference, Aula Academia, Ghent, 11-16 July 2010. (2010, July)

For about ten years, fish farming has been expanding all over the world. Even if this way of producing fishes is presented as a solution against overfishing, its impact on the surrounding environment can ... [more ▼]

For about ten years, fish farming has been expanding all over the world. Even if this way of producing fishes is presented as a solution against overfishing, its impact on the surrounding environment can be important. For example, meadows of Posidonia oceanica, the endemic seagrass of the Mediterranean coastal zone, are fading close to those aquaculture, showing negative impacts on this hot spot of biodiversity. This seagrass is used as an indicator of perturbations, although it does not react quickly, mainly because of its low turnover rate (1,5 y-1). So, it is proposed here to use meiofauna and the microbenthic loop (organic matter, bacteria, microphytobenthos and meiofauna) of this ecosystem to detect earlier perturbations due to fish farms. Moreover, the exergy index, measuring the distance between an ecosystem and its optimum state (climax), is also calculated on the microbenthic loop in order to show its interrest in ecological studies. Study sites are both situated in the Gulf of Calvi (Corsica, France), in P. oceanica meadows, at a depth of 22 m. The studied fish farm is small (10 cages), situated offshore in front of Calvi and produces 40 tons of seabass (Dicentrarchus labrax) per year. The reference site is located in front of the research station STARESO (STation de REcherches Sous-marine et Oceanographiques). Sediment cores (diameter: 4,7 cm) were taken in November 2008 at both sites and sliced in four layers (0-1 cm, 1-2 cm, 2-5 cm and 5-10 cm), according to the expected abundance of meiofauna organisms. Biomass and abundance of every parts of the microbenthic loop were thus analysed. Results concerning abundance, biomass and diversity of meiofauna organisms are presented here and compared with the rest of the microbenthic loop. Values of biomasses are also integrated in the calculation of the exergy index. Finally, this study evaluate the interest of meiofauna and the microbenthic loop to detect perturbations due to an aquaculture. [less ▲]

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See detailMultiparametric observations and analysis in the Bay of Calvi (Corsica), an ideal site for studying the human activity effects and climate changes in the Mediterranean Sea; STARESO
Gobert, Sylvie ULg; Alvera Azcarate, Aïda ULg; Barth, Alexander ULg et al

Conference (2010, May)

STARESO (Station de REcherche Sous marine et Océanographique) is the marine and oceanographic research station of the University of Liège (Belgium) managed by the French company STARESO S.A.. Constructed ... [more ▼]

STARESO (Station de REcherche Sous marine et Océanographique) is the marine and oceanographic research station of the University of Liège (Belgium) managed by the French company STARESO S.A.. Constructed in 1969, it is located near Calvi (Corsica, Western Mediterranean Sea) in an oligotrophic area chosen for the exceptional quality of its coastal waters STARESO offers to the oceanographers, by diving or with boats, a direct access to the sea. The variety of the accessible ecosystems is remarkable and unique in the Mediterranean basin: -the Bay of Calvi is characterized by healthy and very diverse biocenosis (e.g. Posidonia meadows, rocky and sandy communities, -a steep submarine canyon, with depths greater than 1 000 meters, is accessible in 15 minutes of navigation; -the Liguro-Provençal front, a major hydrologic structure, is situated between 10 and 15 miles of the coast. STARESO is accessible all the year for everybody and is functioning like an oceanographic research vessel. The Station is a platform for all oceanographic disciplines with a scientific expertise widely based on a long tradition of interdisciplinary work, and a direct access to time series of physical, chemical and biological data registered with automated systems and variety of sensors deployed in the Bay of Calvi since 30 years. This platform provides the opportunity to reach coastal, pelagic, benthic, deep systems with a manageable cost and ship requirements in a pristine zone. [less ▲]

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See detailTrophic diversity of idoteids (Crustacea, Isopoda) inhabiting the Posidonia oceanica litter
Sturaro, Nicolas ULg; Caut, Stéphane; Gobert, Sylvie ULg et al

in Marine Biology (2010), 157(2), 237-247

The coexistence of three idoteid species in Posidonia oceanica litter raises the question of trophic diversity and their role in the litter degradation process. Hence, diet composition of Idotea balthica ... [more ▼]

The coexistence of three idoteid species in Posidonia oceanica litter raises the question of trophic diversity and their role in the litter degradation process. Hence, diet composition of Idotea balthica, Idotea hectica and Cleantis prismatica was studied using a combination of gut contents and stable isotopes analysis. Gut content observations indicate that P. oceanica dead leaves are an important part of the ingested food for the three species, although their tissues are constituted of only a small to medium fraction of P. oceanica carbon. Our results also underlined the potential role of these species in the degradation of P. oceanica litter by mechanically fragmenting the litter and by assimilating a small to medium fraction of carbon. Moreover, we showed that there were considerable inter- and intra-specific differences in diet composition. Diet differed between juveniles and adults for I. balthica. Crustaceans are an important food source for adults of I. balthica, while I. hectica indicated a major contribution of algal material. C. prismatica showed an intermediate diet. This trophic diversity is probably one of the factors allowing these species to coexist in the same biotope. [less ▲]

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See detailChemical contamination in fish species from rivers in the North of Luxembourg: Potential impact on the Eurasian otter (Lutra lutra).
Boscher, Aurore; Gobert, Sylvie ULg; Guignard, C. et al

in Chemosphere (2010), 78

Contamination levels of PCBs, and of the heavy metals cadmium (Cd), lead (Pb) and mercury (Hg) were analyzed in four fish species from seven rivers in the North of Luxembourg. During August and September ... [more ▼]

Contamination levels of PCBs, and of the heavy metals cadmium (Cd), lead (Pb) and mercury (Hg) were analyzed in four fish species from seven rivers in the North of Luxembourg. During August and September 2007, 85 samples of fish were collected belonging to four species: the stone loach (Barbatula barbatula, n = 12 pools), the chub (Squalius cephalus, n = 36), the barbel (Barbus barbus, n = 23) and eel (Anguilla anguilla, n = 14). The concentration of seven indicator PCBs (P7PCBs) reached a mean of 39 ng g􏰀1 and varied between 4.0 and 346.2 ng g􏰀1 (wet wt) depending on the site and species. Fish collected at Wal- lendorf on the Our River and sites on the Wiltz and the Clerve rivers showed the highest concentrations for PCBs. In comparison with 1994, PCB levels in fish decreased strongly during the last decade in these rivers. Lead was detected at low levels (0–181.4 ng g􏰀1 wet wt). Mercury concentrations ranged between 10.3 and 534.5ngg􏰀1 (wet wt) exceeding maximum tolerable levels for human consumption of 500 ng g􏰀1 in two fish out of 85. Chubs and eels from the Sûre River were the most contaminated by mer- cury. Cadmium levels varied between 4.0 and 103.9 ng g􏰀1 (wet wt). In addition to mercury in fish, cad- mium was the most problematic pollutant on the Our, the Wiltz, the Clerve and the Troine Rivers, because values found in 20% of fish exceeded the threshold of about 10–50 ng g􏰀1 (wet wt) recommended for human health. The total PCB level predicted to accumulate in livers from otter potentially feeding on these fish based on a previously published mathematical model is 37.7 lg g􏰀1 (lipid wt), which is between a proposed ‘‘safe level” and a ‘‘critical level” for otters. Rivers in the North of Luxembourg are thus to some extent polluted, and the establishment of otter populations could be affected by current levels of contamination. [less ▲]

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See detailPosidonia oceanica (L.) Delile, a usefull tool for the biomonitoring of chemical contamination along the Mediterranean coast: a multiple trace element study
Richir, Jonathan ULg; Gobert, Sylvie ULg; Sartoretto, Stéphane et al

in 4th Mediterranean Symposium on Marine Vegetation (2010)

The concentrations of 19 trace elements (TE): Be, Al, V, Mn, Co, As, Se, Mo, Ag, Sn, Sb and Bi as well as Cr, Fe, Ni, Cu, Zn, Cd and Pb, were analyzed by DRC ICP-MS in Posidonia oceanica (L.) Delile ... [more ▼]

The concentrations of 19 trace elements (TE): Be, Al, V, Mn, Co, As, Se, Mo, Ag, Sn, Sb and Bi as well as Cr, Fe, Ni, Cu, Zn, Cd and Pb, were analyzed by DRC ICP-MS in Posidonia oceanica (L.) Delile leaves from the Mediterranean French coast. The first 12 TE have little been studied nowadays. Except for Al, Cr, Fe, Cu and Ag, TE were preferentially accumulated in photosynthetic part of leaves. Moreover, trace element concentrations of the third intermediate leaf are representative of the integral shoot, and could be used alone in biomonitoring. Environmental background concentrations of the 12 little studied TE were determined, and spatial variations were related to anthropic activities. Compared to previous publications, concentrations of the 7 other TE classically investigated present a diminution or a stabilization, reflecting the change of anthropogenic inflows. In conclusion, P. oceanica is a sensitive bioindicator for chemical contamination, even for the twelve little studied TE. [less ▲]

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See detailMultidisciplinary study of the trophic diversity and functional role of amphipod crustaceans associated to Posidonia oceanica meadows
Michel, Loïc ULg; Lepoint, Gilles ULg; Gobert, Sylvie ULg et al

Poster (2009, November 27)

Posidonia oceanica is a seagrass endemic to the Mediterranean Sea, and is able to form large monospecific areas, called meadows. These meadows are critical features of the Mediterranean coastal zones, and ... [more ▼]

Posidonia oceanica is a seagrass endemic to the Mediterranean Sea, and is able to form large monospecific areas, called meadows. These meadows are critical features of the Mediterranean coastal zones, and are of great ecologic and economic importance. Posidonia oceanica meadows shelter high biomasses and biodiversities of amphipod crustaceans. In other temperate meadows, such as Atlantic Zostera marina 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, due to the lack of precise studies, and little is known about the trophic ecology of amphipods. In this context, our research is structured in three main tasks. We chose the Calvi Bay (NW Corsica, France) as a study site, and sampling is undertaken from the STARESO research station (University of Liège, Belgium). First, we study the exact composition of the amphipod community, as well as its temporal variation at diel and seasonal scale. This task is based on in situ collection of samples using three methods: the hand-towed net, litter collection and light traps. Completion of this task will allow us to have accurate and reliable data, taken on our study site, concerning the abundance and specific diversity of amphipods associated with P. oceanica meadows. The second task is a reconstruction of the diet of the studied animals. Indeed, amphipods from P. oceanica meadows are usually regarded as vegetal epiphytes grazers, or generalist detritivores, but few studies focus on the interspecific trophy diversity, or on the importance of alternative food sources. Our approach relies on in situ sampling of amphipods and potential food items. The techniques used combine traditional methods (gut content observation) and use of trophic markers, such as measurements of C and N stable isotope rations and fatty acid composition analysis. Finally, we use in vitro and in situ microcosms experiments to evaluate the impact of amphipod feeding activity on the ecosystem functioning, and more precisely on the dynamics of the epiphyte cover. By quantifying this interaction, our purpose is to put back the results obtained in the first two parts into a wider context, the functioning of the Posidonia oceanica meadow as an ecosystem. Thus, by combining in situ sampling and in vitro experimentation, and by combining traditional and innovating techniques, we hope, at the end of this research, to enhance the knowledge of the trophic diversity and the functional role of amphipod crustaceans associated with Mediterranean Posidonia meadows. [less ▲]

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See detailCan we use exergy index and the microbenthic loop as indicators of perturbations in Posidonia oceanica (L.) Delile meadows?
Pete, Dorothée ULg; Lenartz, Fabian ULg; Velimirov, Branko et al

Poster (2009, November 27)

Nowadays, many anthropogenic perturbations threaten the Mediterranean Sea. Posidonia oceanica , its endemic phanerogam, is often used as a pollution descriptor. Unfortunately, it does not react very fast ... [more ▼]

Nowadays, many anthropogenic perturbations threaten the Mediterranean Sea. Posidonia oceanica , its endemic phanerogam, is often used as a pollution descriptor. Unfortunately, it does not react very fast because of its low turnover rate (i.e. 1.5y-1). To solve that problem, this project proposes to use the microbenthic loop (meiofauna, bacteria, microphytobenthos and organic matter) of this important coastal ecosystem to detect anthropogenic pollutions earlier, because its components may react more rapidly than the posidonia plant. Every components of the loop are investigated and characterized, in order to determine their reactions to perturbations and use them in the calculation of the exergy index. This index comes from the thermodynamic theory of ecosystems and expresses the distance of an ecosystem, at a given state, from its equilibrium. The higher this index, the closer from its optimum state (climax) the ecosystem is. To calculate it, the biomass of each part of the studied ecosystem, weighted by a factor called β, is needed. This factor is estimated on a genetic basis and given in Jørgensen et al. (2005). The final aim of this project is to show if the exergy index can be used in the Mediterranean Sea as a tool in monitoring strategies, specifically in the sedimentary compartment of P. oceanica meadows. To realise these goals, a reference meadow was chosen near the research station STARESO (STAtion de REcherches Sous-marines et Oceanographiques) in Calvi Bay (Corsica, France). This meadow is studied since the 80’s and its good state of health is proven. Seasonal, spatial (small scale) and bathymetric variations in the microbenthic loop are studied there since 2007, by sediment cores (diameter=4.7cm, length=10cm). Those results are compared for 2008 with the patterns observed in a supposed perturbed site, situated close to a fish farm, in Calvi Bay too. In situ experiments were also led in summer 2009. During three months, a shading experiment and an enrichment of the sediment with sediment coming from under the aquaculture (once a week) were performed. Those experiments aimed to understand reactions of the microbenthic loop to those kinds of perturbations, that are often occurring close to a fish farm. Up to now, that study has led to a better understanding of seasonal and bathymetric patterns in the microbenthic loop of P. oceanica. The most important result obtained is the existence of an important spatial heterogeneity at small scale in that ecosystem. This phenomenon must absolutely be taken into account in every study based on the sediment in P. oceanica meadows. [less ▲]

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