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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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See detailLes vigies de l'environnement côtier
Gobert, Sylvie ULg; Moreau, Didier ULg

Article for general public (2009)

S’ils ne recouvrent qu’une faible partie des fonds marins, les herbiers de posidonies constituent un écosystème complexe et jouent un rôle fondamental dans l’équilibre écologique des zones côtières. A ... [more ▼]

S’ils ne recouvrent qu’une faible partie des fonds marins, les herbiers de posidonies constituent un écosystème complexe et jouent un rôle fondamental dans l’équilibre écologique des zones côtières. A partir de la Station de Recherches Sous-Marines et Océanographiques (STARESO) de l’ULg à Calvi (Haute-Corse), en bordure de la pointe de La Revellata, Sylvie Gobert observe en permanence l’état de l’herbier, cette « forêt » qui tapisse le sol marin côtier. La baie de Calvi étant plutôt épargnée par les pollutions d’origine anthropique, les données récoltées par Sylvie Gobert permettent de garder un œil attentif sur les premières conséquences qui pourraient être provoquées par les changements climatiques sur cet écosystème essentiel mais fragile. [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 detailRecent threats on coastal ecosystems by new pollutants: a multiple trace element study
Richir, Jonathan ULg; Gobert, Sylvie ULg; Bouquegneau, Jean-Marie ULg

Poster (2009, January)

The Mediterranean Sea is an enclosed basin, highly submitted to anthropogenic pressures. Chemical pollution from coastal urban centres and industries, or carried by air and rivers, primarily affects its ... [more ▼]

The Mediterranean Sea is an enclosed basin, highly submitted to anthropogenic pressures. Chemical pollution from coastal urban centres and industries, or carried by air and rivers, primarily affects its coastal ecosystems. Pollution by trace elements is rapidly evolving further to the recent modifications of their production and industrial uses by men. As a result, certain trace elements can now be considered as new environmental pollutants. Appropriate bioindicators are useful tools for the early warning of marine pollution. We presently investigate the use of the purple sea urchin Paracentrotus lividus and the marine phanerogam Posidonia oceanica as bioindicators to monitor the Mediterranean coastal pollution by new trace pollutants (Be, V, Mo, Mn, PGEs, Ag, Al, As, Se, Sb and Bi). Classic trace metals (Cd, Cr, Cu, Zn, Ni, Sn, Pb, Co and Fe) are also studied. Organisms were seasonally collected in 2008 in a reference site and a polluted one, respectively Calvi bay (Corsica) and Marseille (France). Their tissular trace element concentrations were determined by ICP-MS. All the investigated trace elements were chosen for their potential toxic effects. [less ▲]

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See detailFish farm impacts on Posidonia oceanica meadows: interest of the microbenthic loop.
Pete, Dorothée ULg; Velimirov, Branko; Bouquegneau, Jean-Marie ULg et al

Poster (2009, January)

Posidonia oceanica, the seagrass endemic to the Mediterranean Sea, is a valuable tool to assess the environmental quality in coastal zones. However, only few studies have attempted to use characteristics ... [more ▼]

Posidonia oceanica, the seagrass endemic to the Mediterranean Sea, is a valuable tool to assess the environmental quality in coastal zones. However, only few studies have attempted to use characteristics of its sediment compartment as an indicator of environmental perturbations. In this study, the impact of a fish farm on the microbenthic loop (organic matter, bacteria, microphytobenthos and meiofauna) of P. oceanica meadows will be described. Samples were taken under an aquaculture situated in Calvi Bay (Corsica, France) at a depth of 22 m, in March and June 2008. The control site was the meadow situated in front of the research station STARESO (Calvi Bay, Corsica, France), sampled at the same periods and depth. Results concerning bacteria, microphytobenthos and organic matter will be presented here. For both seasons, differences between sites exist. For example, biomasses of organic matter, microphytobenthos and bacteria are higher in the fish farm than in the control site, indicating that the microbenthic loop has potential to be a good early indicator of pollution in this sea. [less ▲]

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See detailEvidence for wastewater influence in a low impacted area throughout stable isotope analyses of the limpet Patella caerulea and epilithic biofilms
Vermeulen, Simon ULg; Lepoint, Gilles ULg; Gobert, Sylvie ULg

Poster (2009, January)

Eutrophication is considered to be one of the main threats to marine environments leading to changes in trophic status of ecosystems and alteration of biological diversity. Carbon and Nitrogen stable ... [more ▼]

Eutrophication is considered to be one of the main threats to marine environments leading to changes in trophic status of ecosystems and alteration of biological diversity. Carbon and Nitrogen stable isotopes analyses were performed on the limpet Patella caerulea and one of its food sources (epilithic biofilms) to assess their potential as early indicators of eutrophication. Samples were seasonally collected in 2005-2006 on five locations gradually exposed to urban sewage in the Calvi Bay and in the Marseilles harbour. Stable isotope signatures of Patella caerulea muscles exhibited steady site - specific values over seasons. In contrast to this time – integrated signal, wide variations in biofilm values show that either composition or isotopic ratios of food sources may vary greatly in time and space. Elevated δ15N values of limpets and biofilms, typical of wastewater influence but unrelated to nitrogen loads, indicate the biological availability of sewage-derived nitrogen in the Calvi Bay and the Marseilles harbour. A reference level of δ15N values is rapidly reached with increasing depth that indicates the limited vertical extent of pollution in the Calvi Bay. [less ▲]

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See detailSeed nutrient content and nutritional status of Posidonia oceanica seedlings in the northwestern Mediterranean Sea
Balestri, Elena; Gobert, Sylvie ULg; Lepoint, Gilles ULg et al

in Marine Ecology. Progress Series (2009), 388

Successful seedling establishment is rare in Posidonia oceanica. The first year after germination is likely to be the most critical phase in the recruitment process, but little is still known on the ... [more ▼]

Successful seedling establishment is rare in Posidonia oceanica. The first year after germination is likely to be the most critical phase in the recruitment process, but little is still known on the factors affecting seedling survival. Mature fruits of P. oceanica released from a meadow of the north-western Mediterranean were deposited by currents on the adjacent beach in May 2004. In May and December 2005, some seedlings established in the previous summer were uprooted by storms and deposited on the beach. This material provided the opportunity to examine seed mass and nutrient content, and the nutritional status of seedlings. Our findings support the hypothesis that growth limitation may be an important cause of mortality for seedlings during the first year of establishment in poor-nutrient sites. [less ▲]

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See detailAssessment of the ecological status of Mediterranean French coastal waters as required by the Water Framework Directive using the Posidonia oceanica Rapid Easy Index: PREI
Gobert, Sylvie ULg; Sartoretto, Stéphane; Rico-Raimondino, Valérie et al

in Marine Pollution Bulletin (2009), 58

This paper describes the PREI (Posidonia oceanica Rapid Easy Index), a method used to assess the ecological status of seawater along Mediterranean French coasts. The PREI was drawn up according to the ... [more ▼]

This paper describes the PREI (Posidonia oceanica Rapid Easy Index), a method used to assess the ecological status of seawater along Mediterranean French coasts. The PREI was drawn up according to the requirements of the Water Framework Directive (WFD 2000/60/EC) and was tested on 24 and 18 stations in PACA (Provence-Alpes-Côtes d’Azur) and Corsica respectively. The PREI is based on five metrics: shoot density, shoot leaf surface area, E/L ratio (Epiphytic biomass/leaf biomass), depth of lower limit, and type of this lower limit. The 42 studied stations were classified in the first four levels of status: high, good, moderate and poor. The PREI values ranged between 0.280 and 0.847; this classification is in accordance with our field knowledge and with our knowledge of the literature. The PREI was validated regarding human pressure levels (r²= 0.74). (http://eurex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2000:327:0001:0072:EN:PDF) [less ▲]

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See detailMulti-scale spatial variability of amphipod assemblages from the foliar stratum of the Posidonia oceanica (L.) Delile meadow
Sturaro, Nicolas ULg; Lepoint, Gilles ULg; Michel, Loïc ULg et al

Conference (2008, October 31)

Studying spatial patterns is of ecological importance in order to understand the causes of the distribution and abundance of organisms, and it also provides valuable basis for management and conservation ... [more ▼]

Studying spatial patterns is of ecological importance in order to understand the causes of the distribution and abundance of organisms, and it also provides valuable basis for management and conservation. In the Mediterranean coastal zone, the Posidonia oceanica seagrass meadows constitute one of the dominant ecosystems and are an important habitat for vagile invertebrates. Among these, amphipods comprise a large number of species, with considerable abundance and biomass, as well as being an important trophic resource for fish populations. Until now, little attention has been given to the horizontal variability at different spatial scales of amphipod assemblages associated with P. oceanica meadows. A hierarchical sampling design, spanning three orders of magnitude (from 1 to 100s of metres) was elaborated. Sampling was undertaken in March 2007 in the meadows of Calvi Bay (NW Corsica), at depths ranging from 10 to 13 m, using a suction sampler. Our results indicated an important horizontal variability of the studied assemblage, and this at different spatial scales. In addition, these results tend to show that the small scale (~ 1 m and ~ 10 m) influenced abundance, while the medium-scale (~ 100 m) influenced diversity. Some potential causes of the observed patterns are discussed. These results emphasize the importance of considering different spatial scales in the study of the vagile invertebrates associated with P. oceanica meadows. [less ▲]

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See detailTrophic diversity among amphipod crustaceans from Posidonia oceanica meadows : A stable isotope assessment
Michel, Loïc ULg; Lepoint, Gilles ULg; Gobert, Sylvie ULg et al

Conference (2008, October 31)

Vagile invertebrates are regarded as key-components of Posidonia oceanica meadow ecosystems, particularly in organic matter transfers from primary producers to higher level consumers. Among these ... [more ▼]

Vagile invertebrates are regarded as key-components of Posidonia oceanica meadow ecosystems, particularly in organic matter transfers from primary producers to higher level consumers. Among these invertebrates, amphipod crustaceans are one of the most abundant and diverse groups, and probably play an important role in meadow ecosystem functioning. However, their trophic ecology is poorly known, and these crustaceans are generally regarded as vegetal epiphytes consumers or generalist detritivores, due to the lack of accurate studies. Here, we focused on the study of the interspecific trophic diversity, and on the importance of other food sources (Posidonia leaves and litter, animal epiphytes, suspended particular organic matter, …) in those amphipods’ diet. To assess these phenomena, we used stable isotopes ratios of carbon and nitrogen as trophic tracers. It appears that, while some species (such as Apherusa chiereghinii and Aora spinicornis) seem to feed mainly on epiphytes, others, like Dexamine spiniventris, exploit different food sources. These results thus tend to show that amphipod trophic diversity could have been underestimated in the past. Moreover, they enhance the comprehension of the feeding ecology of these animals, and therefore of the way they interact with the Posidonia meadow ecosystem. [less ▲]

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See detailPotential use of Paracentrotus lividus as bioindicator for recent trace element pollution monitoring
Richir, Jonathan ULg; Gobert, Sylvie ULg; Bouquegneau, Jean-Marie ULg

Poster (2008, October)

The Mediterranean Sea is an enclosed basin, highly submitted to anthropogenic pressures. Chemical pollution originating from coastal urban centres and industries, or carried by air and rivers, will ... [more ▼]

The Mediterranean Sea is an enclosed basin, highly submitted to anthropogenic pressures. Chemical pollution originating from coastal urban centres and industries, or carried by air and rivers, will primarily affect its coastal ecosystems. The pollution by trace elements into the marine environment is rapidly evolving further to the recent modifications of their production and industrial uses by men. As a result, some trace elements that were previously poorly studied can be considered now as environmental pollutants, whose concentrations can sometimes be way above their natural baseline levels. The purple sea urchin Paracentrotus lividus is a well know bioindicator used for metal pollution monitoring (Fe, Cd, Cr, Pb, Zn and Cu) along the Mediterranean and Atlantic coasts. This sedentary organism successfully concentrates the pollutants diluted in its environment, and the measured concentrations reflect properly the health status of the ecosystem. This study is a first approach on the use of P. lividus as bioindicator for some less investigated trace elements (Al, V, Mn, Co, Ni, Se, Mo and Ag), chosen for their potential toxic effects. We have compared the element concentrations of the digestive tract tissues and gonads of female and male sea urchins. The organisms were frozen prior to dissection, or they were dissected alive, the two experimental procedures being compared afterwards. The existence of an eventual relationship between their gonadic index or their test diameter and the measured pollutant concentrations was also investigated. [less ▲]

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See detailSpatial heterogeneity at small scale in the microbenthic loop of Posidonia oceanica meadows
Pete, Dorothée ULg; Lenartz, Fabian ULg; Velimirov, Branko et al

Conference (2008, October)

In the Mediterranean coastal zone, one the most important ecosystem is the Posidonia oceanica meadow. This seagrass is endemic of the Mediterranean Sea and plays many important ecological roles like ... [more ▼]

In the Mediterranean coastal zone, one the most important ecosystem is the Posidonia oceanica meadow. This seagrass is endemic of the Mediterranean Sea and plays many important ecological roles like oxygen production, nursery for numerous commercial species of fishes and protection of coastal zones by reducing the impact of waves. However, there is a severe lack of informations on small scale variations in its sediment compartment. In an attempt to understand spatial variations in the microbenthic loop (bacteria, organic matter, microphytobenthos and meiofauna) of this ecosystem, an experiment was led in Calvi Bay (Corsica, France), in March 2008, at 10 m depth. Twelve points were sampled randomly in a 125 x 125 cm grid, divided into twenty-five 25 x 25 cm squares, to assess and describe the spatial distribution and variations of different parameters of the sediment. Those parameters are granulometry, density of the P. oceanica meadow, nutrients concentration in pore water, bacteria (biomass, abundance, morphotypes), organic matter (biomass), microphytobenthos (biomass), roots and rhizomes (biomass) and meiofauna (biomass). Distribution maps were produced using the DIVA (Data-Interpolating Variational Analysis) method. Our results prove that the sediment compartment is highly heterogeneous at small scale, especially for bacteria and in the first centimeter of sediment cores. Moreover, a correlation has been established between microphytobenhtos variations and phosphate concentration in pore water. For the first time, such small scale variations are depicted in a P. oceanica meadow, which underlines the importance to take them into account in sampling strategies. [less ▲]

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See detailUnderwater Imagery, a Measuring Tool to Extend the Spatio-Temporal Understanding of Benthic Organisms Dynamics: Case Study of Codium elisabethae in the Azores.
Sirjacobs, Damien ULg; Tempera, Fernando; Cardigos, Frederico et al

Poster (2008, October)

Benthic habitat mapping studies have been increasingly exploiting the use of underwater images to collect information on substrate nature and biological coverage. Concurrently, research has been ongoing ... [more ▼]

Benthic habitat mapping studies have been increasingly exploiting the use of underwater images to collect information on substrate nature and biological coverage. Concurrently, research has been ongoing to develop methods that use the imagery collected to conduct regular quantitative monitoring studies of biological resources distributed over large areas. This study provides the first multi-annual monitoring information on the dynamics of a benthic macroalgae population derived from underwater imagery collected by scuba divers in the Monte da Guia Site of Community Importance /Natura 2000 network (Faial isl. Azores, NE Atlantic). The green alga Codium elisabethae - a long-living green alga that represents a potential good indicator of coastal environmental change - was chosen for the study. The analyses focus on using the underwater imagery to quantify seasonal fluctuations of density, percentage cover, biomass, growth rate and primary production of the species. Two study sites were investigated: one was located in a sheltered no-go reserve exhibiting a dense C. elisabethae population, and the other in a location experiencing more exposed conditions and holding a sparser population. Between August 2003 and November 2005, fifteen (15) photo coverages were collected by scuba-divers. Subsequent processing consisted of producing image mosaics and using automated and interactive change detection methods that recognized, measured and counted individuals present in photos of fixed quadrats and yielded dynamical parameters such as population structures, growth, recruitment, and mortality. Chi-square tests of image-derived estimates and in situ measurements confirmed the validity of a centimeter precision estimation of population structure for individuals above 4 cm diameter. Important variability of population structure and density were observed at small spatial scales. Population density showed a sharp reduction in autumn 2003 and did not show a full recovery in spring and summer 2004. During the following year, population of the protected site maintained density and biomass, while at the exposed site population density dropped. The production of information based on observations of thousands of individuals is mandatory in biological population statistics. The presented imagery approach made it possible, avoiding the need to collect all the measurements and quantitative information during time-constrained SCUBA diving operations. [less ▲]

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