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See detailAn overview of the microbenthic loop in Posidonia oceanica meadows: the good, the bad and the ugly
Pete, Dorothée ULg; Quattrocchi, Loïc; Velimirov, Branko et al

in Creed, J.C.; Oigman-Pszczol, S.S. (Eds.) Proceedings of the 10th International Seagrass Biology Workshop (ISBW10), 25- 30 November 2012, Armação dos Búzios, Brazil (2012, November)

Posidonia oceanica is an endemic seagrass of the Mediterranean Sea. The ecosystem based on this plant is essential from an ecological and economical point of view (commercial species, touristic activities ... [more ▼]

Posidonia oceanica is an endemic seagrass of the Mediterranean Sea. The ecosystem based on this plant is essential from an ecological and economical point of view (commercial species, touristic activities, oxygen production), though very sensitive to environmental perturbations. To detect those perturbations, scientists are trying to find more efficient ecological indicators. Most of the time, those indicators are based on the plant itself. Unfortunately, this seagrass does not react very quickly to perturbations so, when a reaction is noticed, it is often too late to prevent irremediable damages to the ecosystem. The sedimentary compartment of P. oceanica meadows has been less studied than the canopy level. However, it could be a good source of ecological indicators because it is the final container of all the pollution. In this framework, the microbenthic loop has been studied. It is a major subsystem of those meadows and encompasses organic matter, bacteria, microphytobenthos and meiofauna. As those organisms have a rapid turnover and stay almost all their life inside the sediment, they seemed good potential indicators. This presentation will show what is useful or not inside the sediment and more specifically inside the microbenthic loop. Results of a comparison between a fish farm and a reference location will be used, as well as in situ experiments (shading and sediment loading) and small spatial scale variations. At the end of this presentation, you will know what are the good, the bad and the ugly in the sedimentary compartment of a P. oceanica meadow. [less ▲]

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See detailThe use of Eco-Exergy in Oceanology: Application to Posidonia oceanica meadows
Pete, Dorothée ULg; Velimirov, Branko; Gobert, Sylvie ULg

Conference (2011, June 17)

In classic thermodynamics, exergy is defined as the useful work a system can perform when brought into equilibrium with its environment. It represents a measure of the distance from thermodynamic ... [more ▼]

In classic thermodynamics, exergy is defined as the useful work a system can perform when brought into equilibrium with its environment. It represents a measure of the distance from thermodynamic equilibrium. From that definition, some researchers (S.E. Jørgensen) have decided to apply this theory to ecosystems and called this expression of exergy “Eco-exergy”. According to this theory, a developing ecosytem trends to go far from its thermodynamic equilibrium and its exergy content trends to increase. Thus, the Laboratory of Oceanology of the University of Liege has decided to apply this quite new theory to Posidonia oceanica meadows, an endemic ecosystem of the Mediterranean coastal zone. This ecosystem is known as a good environmental quality indicator. So it was choosen to test the relevance of eco-exergy index as a quality indicator in the Mediterranean Sea. As this ecosystem is complex, this study focuses on the sedimentary compartment and the microbenthic loop (organic matter, bacteria, microphytobenthos and meiofauna). Some estimations of this eco-exergy index in the sedimentary compartment of a P. oceanica meadow are presented here. According to them, it seems that the eco-exergy index is not sensitive enough to catch effects of perturbations in this ecosystem. [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 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 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 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 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 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 detailImportance of the microbenthic loop of Posidonia oceanica meadows to detect anthropogenic perturbations early: first results
Pete, Dorothée ULg; Velimirov, Branko; Bouquegneau, Jean-Marie ULg et al

Conference (2008, August)

It was demonstrated that Posidonia oceanica, the marine magnoliophyte endemic to the Mediterranean Sea, is a valuable tool to assess environmental qualities of the coastal zones. However, only few studies ... [more ▼]

It was demonstrated that Posidonia oceanica, the marine magnoliophyte endemic to the Mediterranean Sea, is a valuable tool to assess environmental qualities of the coastal zones. However, only few studies have attempted to use characteristics of its sediment compartment as an indicator of the environment state of health. Yet, organisms living in this compartment have a turnover which is faster than for canopy-organisms which makes them useful as valid early descriptors of pollution. The study described here takes place in a project which aims to find an early holistic indicator of anthropogenic perturbations in the Mediterranean coastal zones. The investigation is based on the microbenthic loop (organic matter, bacteria, microphytobenthos and meiofauna) and was led in two different sites of Calvi Bay (Corsica, France), at 10 m depth, in March and June 2007. Only results about bacteria (abundance, biomass, morphotypes), microphytobenthos (biomass) and organic matter (biomass) will be presented. For both seasons, significant differences between sites are found, irrespective on whether variables are treated separately or together, thus indicating that the microbenthic loop has potential to be a good early indicator of pollution. [less ▲]

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See detailSmall scale variations in the microbenthic loop of Posidonia oceanica meadows: an experimental interpolation design.
Pete, Dorothée ULg; Lenartz, Fabian ULg; Velimirov, Branko et al

Poster (2008, August)

In the sediment compartment of Posidonia oceanica meadows, there is a severe lack of information on small scale variations. In an attempt to understand spatial variations of the microbenthic loop ... [more ▼]

In the sediment compartment of Posidonia oceanica meadows, there is a severe lack of information on small scale variations. In an attempt to understand spatial variations of the microbenthic loop (bacteria, organic matter, microphytobenthos and meiofauna), an experiment based on interpolation methods 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 square, 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 P. oceanica, concentration in nutrients in the pore water, bacteria (biomass, abundance, morphotypes), organic matter (biomass), microphytobenthos (biomass), roots and rhizomes (biomass) and meiofauna (biomass). Results and distribution maps of the respective sediment parameters will be presented for the first time. [less ▲]

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See detailDirective Cadre Eau: Mise en oeuvre du contrôle de surveillance - résultats de la campagne 2006 - district Corse
Boissery, Pierre; Andral, Bruno; Belin, Catherine et al

Report (2007)

Les programmes de surveillance liés à la mise en oeuvre de la DCE sont coordonnés par le Ministère de l’Ecologie et de l’Aménagement durable (MEDAD) et dans chaque bassin hydrographique ce sont les ... [more ▼]

Les programmes de surveillance liés à la mise en oeuvre de la DCE sont coordonnés par le Ministère de l’Ecologie et de l’Aménagement durable (MEDAD) et dans chaque bassin hydrographique ce sont les Agences de l’eau qui, avec l’Etat, prennent en charge l’application, la mise en oeuvre de ces réseaux. Sur la façade méditerranéenne, Ifremer a assuré pour le compte du Schéma Directeur des Données sur l’Eau la maîtrise d’ouvrage de la première campagne du contrôle de surveillance, en coordonnant l’ensemble de l’acquisition des données et de leur synthèse en collaboration avec de nombreux partenaires : Universités, bureaux d’études, structures locales de gestion et services de l’Etat. La mobilisation des différents acteurs autour d’un objectif commun a permis de faire face à la pluridisciplinarité et à la complexité des aspects logistiques de ce programme. Les résultats de cette première campagne du contrôle de surveillance (2006) permettent d’ores et déjà d’avoir une bonne vision d’ensemble de la qualité des eaux littorales à l’échelle du district. Ils confortent les évaluations faites « à dire d’expert » lors de l’état des lieux du district avec des informations nouvelles concernant plus particulièrement la biologie, notamment le benthos de substrat meuble. En eaux côtières, les eaux sont de bonne qualité. En eau de transition, essentiellement lagunaires, il existe une plus grande hétérogénéité des résultats avec des paramètres déclassant relevant plutôt de la biologie, mais sur un nombre important d’indicateurs. [less ▲]

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See detailUtilisation de l'exergie pour mesurer et détecter les perturbations affectant le compartiment sédimentaire des herbiers à Posidonia oceanica (L.) Delile: Etude préliminaire.
Pete, Dorothée ULg

Master of advanced studies dissertation (2007)

La mise en place de la Directive Cadre Eau (WFD 2000/60/EC) par l’Union Européenne préconise la recherche de nouveaux outils permettant de détecter et de quantifier les perturbations des écosystèmes, afin ... [more ▼]

La mise en place de la Directive Cadre Eau (WFD 2000/60/EC) par l’Union Européenne préconise la recherche de nouveaux outils permettant de détecter et de quantifier les perturbations des écosystèmes, afin d’aboutir à une gestion durable de ceux-ci. Dans ce contexte, il est proposé d’étudier l’intérêt des orienteurs thermodynamiques que sont l’exergie et l’exergie spécifique. Ceux-ci se basent sur la mesure de la distance qui sépare un écosystème de son équilibre thermodynamique. Pour cela, une attention particulière a été portée à la boucle microbenthique (matière organique, bactéries, microphytobenthos, méiofaune) d’un des écosystèmes dominant et climacique de la zone côtière méditerranéenne, l’herbier à P. oceanica. Cette boucle est un sous-système important de cet écosystème et présente l’avantage de réagir plus rapidement que la posidonie aux perturbations environnementales. Il semble donc être une portion d’écosystème de choix pour notre étude. Ainsi, les objectifs de ce travail sont de quantifier les différents paramètres intervenant dans le calcul de l’exergie, de comprendre les interactions qu’ils peuvent avoir entre eux et avec leur environnement ainsi que de déterminer les variations potentielles du calcul de l’exergie entre deux sites différents, pour deux saisons différentes. Dans ce travail, il est ainsi montré, que l’estimation de l’indice d’exergie, réalisée à partir de trois des quatre parties de la boucle microbenthique, variait entre les deux sites et entre les deux saisons. Cependant, pour ce qui est de la différence entre site, il est difficile d’attribuer la différence observée à l’un ou l’autre facteur, étant donné le comportement particulier des différents paramètres au site de l’Alga. Par contre, la même variation est observée entre les deux saisons pour les deux sites, ce qui suggère que l’indice d’exergie est sensible aux variations saisonnières. Cela présente une importance considérable pour ce qui est de la comparaison de l’état de santé d’écosystèmes. [less ▲]

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See detailEarly colonization of Posidonia oceanica (L.) Delile by epiphytes: Comparison between natural and artificial seagrass leaves
Pete, Dorothée ULg; Gobert, Sylvie ULg; Lepoint, Gilles ULg et al

in Pergent-Martini, Christine; El Asmi, Souha; Le Ravallec, Célia (Eds.) Proceedings of the third Mediterranean symposium on marine vegetation (2007, March)

Posidonia oceanica is an important marine Magnoliophyta of the Mediterranean coastal zone that can form dense meadows. The leaves of this seagrass are colonized by a lot of organisms, from bacteria to ... [more ▼]

Posidonia oceanica is an important marine Magnoliophyta of the Mediterranean coastal zone that can form dense meadows. The leaves of this seagrass are colonized by a lot of organisms, from bacteria to polychaetes and algae. However, the early stages of colonization are not well known. A preliminary is proposed to examine the nine first days of colonization by epiphytes on natural leaves and on Artificial Seagrass Units (ASUs). Aims of this work were to understand which species are the first to set up, to compare colonization on both leaves and to determine the interest of ASUs in ecological studies. It was shown that the setting up of epiphytes on the bases of both leaves is rapid (first algae on the second day) but the number of organisms increases quicker on ASUs than on natural leaves and on the smooth faces than the rough ones. Shannon-Wiener diversity and evenness were higher for the P. oceanica leaves and the use of Bray-Curtis similarity index showed that colonisation is not similar (between 20 and 30 % similarity) on both leaves for the same day. It can be explained by the lower colonization rate of natural leaves. This lower rate is probably due to a less developed biofilm on natural leaves than on ASUs, to a difficult access to the bases of P. oceanica leaves for epiphytes and microoganisms, and the production of phenol compounds by the plant. Even if ASUs used here do not seem to be similar to natural leaves in early stages of colonization, they could be used in ecological studies thanks to their rapid covering by epiphytes. [less ▲]

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See detailUse of exergy to detect and measure perturbations affecting Posidonia oceanica (L.) Delile meadows: Characterization in the sedimentary compartment
Pete, Dorothée ULg; Bouquegneau, Jean-Marie ULg; Gobert, Sylvie ULg

Poster (2007, March)

Within the scope of the European Water Framework Directive, it seems important to characterize state and evolution of marine ecosystems in a global way. So, it is proposed to use both thermodynamic ... [more ▼]

Within the scope of the European Water Framework Directive, it seems important to characterize state and evolution of marine ecosystems in a global way. So, it is proposed to use both thermodynamic indicators called exergy (Ex) and specific exergy (Exsp) in Posidonia oceanica meadows. Aims of this project are to detect and measure perturbations owed to nutrients loading and mechanical spoiling in the Mediterranean coastal zone. It will be led in the Bay of Calvi, on the microbenthic loop (organic matter, bacteria, microphytobenthos and meiofauna) and will be divided in two parts: sampling in different zone of the meadow and in situ experiments. In the end of this study, it will be possible to give a diagnostic on the health of P. oceanica meadow and to determine how this health will evolve, thanks to the introduction of the exergy in a model. [less ▲]

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See detailColonisation épiphyte de Posidonia oceanica (L.) Delile: Comparaison entre des feuilles artificielles et des feuilles naturelles.
Pete, Dorothée ULg

Master's dissertation (2005)

Face aux importantes perturbations, principalement d’origines anthropiques, qui affectent l’écosystème côtier méditerranéen, il est nécessaire de mettre en place des outils de diagnostic rapides de ces ... [more ▼]

Face aux importantes perturbations, principalement d’origines anthropiques, qui affectent l’écosystème côtier méditerranéen, il est nécessaire de mettre en place des outils de diagnostic rapides de ces perturbations. Posidonia oceanica (L.) Delile, qui est un des piliers de cet écosystème, a souvent été utilisée pour évaluer l’état de santé du milieu côtier méditerranéen. Cependant, comme son turnover est relativement lent et que cette plante peut accumuler des réserves qui lui permettent, durant des périodes relativement longues, du garder une phénologie stationnaire, malgré des changement environnementaux, il est parfois trop tard lorsqu’elle montre les effets d’une perturbation. Dans ce contexte, il devient nécessaire de trouver des outils de diagnostic précoces de ces perturbations. Dans ce cadre, les modifications des populations épiphytes, qui ont un turnover plus rapide que la plante, apparaissent comme des marqueurs plus précoces de la pollution. Dans ce cadre, nous avons tenté de déterminer si les communautés épiphytes se développant sur des feuilles artificielles imitant les feuilles de posidonies étaient semblables à celles s’installant sur les feuilles naturelles, et ce afin de voir si les feuilles artificielles pouvaient être utilisées comme modèle de feuilles de posidonies dans le cadre d’études d’impact. Les résultats obtenus ont montrés que la colonisation des deux types de feuilles n’était pas similaire. En effet, la densité des épiphytes était beaucoup plus importante à la base des feuilles artificielles qu’à la base des feuilles de posidonies mais la diversité et l’équitabilité calculées pour les grands taxa était plus élevée sur les feuilles naturelles. Cependant, l’étude de la colonisation par les épiphytes réalisée sur toute la longueur de la feuille artificielle a montré une zonation proche de celle normalement rencontrée sur les feuilles matures de posidonies. Ainsi, au début de la colonisation et pour la base des feuilles, les feuilles artificielles ne sont pas de bons modèles des feuilles de posidonies et ne peuvent pas être utilisées dans le cadre d’études d’impact. Cependant, au vu des résultats obtenus pour toute la longueur des feuilles artificielles et des données de la littérature, on ne peut pas exclure que, pour des stades plus avancés de la colonisation, la feuille artificielle soit un bon modèle de la feuille naturelle. [less ▲]

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