Evolution of Posidonia oceanica meadows in Calvi Bay (Corsica, France) and anchoring effects in Alga Bay

In the framework of the STARE-CAPMED program we studied the impact of human activities on Posidonia oceanica meadows in Calvi Bay (Corsica, France). We mostly focused on the consequences of boats anchoring in Alga Bay. The map of the marine habitats realized during this study shows that P. oceanica meadows cover a surface of 4.94 km2 in 2010 and have declined of 26 % since 1997. Advances in the data acquisition techniques allow a better identification of the habitats and a map reliability improvement. In several places in the bay, especially near the waste waters rejection site, the lower limit of the meadow is shallower than in the past. The diminution of the meadow surface in the 21-30 m bathymetric section is more important in the Alga site than in the rest of Calvi Bay. The ecological state of the water surrounding the meadow in Alga was assessed as "good" with a PREI index of 0.685. However, big units anchoring in this area lead to the creation of dead “mattes” whose compactness are medium. In this area, the generation of dead mattes seems to favor the settlement of the invasive Chlorobionta Caulerpa racemosa var. cylindracea, of which anchoring is known to be one of the introduction vectors.Dans le cadre du programme STARE-CAPMED, l’impact des activités anthropiques sur les herbiers à Posidonia oceanica a été étudié dans la baie de Calvi (Corse, France), en se focalisant sur l’ancrage dans la baie de l’Alga. La cartographie des habitats marins, réalisée dans le cadre de cette étude, montre que, occupant une surface de 4.94 km2, les herbiers à P. oceanica ont régressé de 26 % depuis 1997. L’évolution des techniques d’acquisition des données permet une meilleure identification des habitats, améliorant ainsi la fiabilité des cartes. Une régression de la limite inférieure a été observée en plusieurs endroits de la baie, notamment au niveau de l’émissaire de rejets d’eaux usées. L’étude de la surface couverte par l’herbier au niveau de l’Alga montre une régression plus importante que celle visible sur l’ensemble de la baie pour la tranche bathymétrique 21-30 m. L’état écologique de la masse d’eau environnant l’herbier à l’Alga a été estimé comme "bon" avec un indice PREI de 0.685. Cependant, l’ancrage de grosses unités dans cette zone entraîne la formation de tâches de matte morte dont la compacité est moyenne. La création de matte morte favorise l’implantation dans cette zone de la Chlorobionte invasive Caulerpa racemosa var. cylindracea dont l’ancrage pourrait être l’un des vecteurs d’introduction.STARE-CAPME

Natural patches in Posidonia oceanica meadows: the seasonal biogeochemical pore water characteristics of two edge types

peer reviewedSeagrass meadows can be assimilated to seascape matrixes encompassing a mosaic of natural and anthropogenic patches. Natural patches within the Mediterranean Posidonia oceanica meadows show a structural particularity which consist in a duality of their edge types. One edge is eroded by bottom currents, while the adjacent meadow colonizes the bare sediments. This study aims to study the dynamics of these two edges through the investigation of the biogeochemistry (pH, total alkalinity, dissolved inorganic carbon, CO2, CH4, N2O, H2S, dissolved inorganic nitrogen, PO4 3−) within vegetated and unvegetated sediments. These observations are compared with the adjacent meadow to have a better understanding of the colonization processes. Our results reveal that the P. oceanica matrix shows differences from the vegetated edges of sand patches, especially with regard to nutrient availability, which is generally more important at the colonized edge (dissolved inorganic nitrogen up to 65.39 μM in June). A clear disparity also occurs between the eroded and colonized edge with both a seasonal and bathymetrical variation of leaf biomass with higher disparities at 10 m in June (colonized edge 1415 gDW m−2; eroded edge 1133 gDW m−2). Themost important contrasts during this study were assessed in June, suggesting that the warm period of the year is more suitable for sampling to highlight disparate characteristics in temperate seagrass meadows. These findings put into light the potential importance of biogeochemical processes in the dynamics of natural patch edges. We hypothesize that they may influence the structural dynamics of P. oceanica seascapes

Magnetic manipulation with several mobile coils towards gastrointestinal capsular endoscopy.

Traditional techniques of endoscopy based on flexible endoscopes are fairly reliable but poorly tolerated by patients and do not give access to the small bowel. It has been demonstrated that magnetic fields are usable for manipulating an untethered magnet, either using fixed coils or mobile permanent magnets.We introduce a novel approach for magnetic manipulation and present the preliminary results obtained by simulating a planar manipulation system including multiple mobile coils

From mechanical to chemical impact of anchoring in seagrasses: the premises of anthropogenic patch generation in Posidonia oceanica meadows

Intensive anchoring of leisure boats in seagrass meadows leads to mechanical damages. This anthropogenic impact creates bare mat patches that are not easily recolonized by the plant. Several tools are used to study human impacts on the structure of seagrass meadows but they are not able to assess the indirect and long term implication of mechanical destruction. We chose to investigate the possible changes in the substrate chemistry given contrasted boat impacts. Our observations show that hydrogen sulfide concentrations remain high at 15 and 20 m depth (42.6 µM and 18.8 µM) several months after the highest period of anchoring during the summer. Moreover, our multidisciplinary study reveals that anchoring impacts of large boats at 15 and 20 m depth can potentially change the seascape structure. By taking into account both structural and chemical assessments, different managing strategies must be applied for coastal areas under anthropogenic pressures.STARE-CAPME

Geometric analysis of the singularities of a magnetic manipulation system with several mobile coils.

International audienceIt has been demonstrated that magnetic fields are relevant for manipulating an untethered magnet, either using fixed coils or mobile permanent magnets. This paper shows however, that any magnetic manipulation method is prone to singular configurations and that the simple numerical analysis of the rank of the "manipulation matrix" is not enough to detect them. Alternatively, we propose a geometrical analysis to interpret and detect the singularities as well as to decide on the acceptability of a reference trajectory. Then, we present results obtained by simulating a planar manipulation system including a multiple mobile coils and a Helmholtz like set-up

Seascape ecology in Posidonia oceanica seagrass meadows: Linking structure and ecological processes for management

Seagrass meadows constitute marine habitats in shallow water temperate and tropical coastal areas worldwide that have a high ecological and economic importance. Amongst the 60 or so seagrass species, the endemic Mediterranean species Posidonia oceanica forms meadows that are arguably the most important shallow water coastal habitat in the region but which are subjected to high anthropogenic pressures. Because of the relatively large size of the plant, the meadows formed by this seagrass have high architectural and morphological complexity, which results in different morphotypes or seascapes. While numerous studies of P. oceanica architectural characteristics for continuous meadows of the seagrass are available, few works have addressed seascape ecological features and the influence of environmental factors (natural and anthropogenic) thereon. In the present review, we give an overview of P. oceanica meadow architectural and morphological characteristics and how these contribute to Mediterranean landscapes and seascapes. Studies addressing the influence of natural and anthropogenic factors on morphometric features of different meadow types and landscape ecological characteristics of P. oceanica habitat are also reviewed, as well as their influence on ecosystem processes. Finally, by considering the available data and tools for seascape studies, we present a discussion on methods to assess seagrass seascapes within the framework of coastal management. Our review highlights several gaps in P. oceanica seascape ecology knowledge such as the lack of data on the spatial distribution of this engineer species, and the possibility to use modern techniques and procedures for analysing structural and ecosystemic data

Advocacy for Multi Mobile Coil Magnetic Manipulation in Active Digestive Endoscopy.

International audienceTraditional techniques of endoscopy based on flexible endoscopes are fairly reliable but poorly tolerated by patients and do not give access to the small bowel. Magnetic fields have been shown usable for manipulating endoscopic capsules, either using static coils with varying currents or mobile permanent magnets. In this short paper, we propose a novel approach which combines electromagnetic and kinematic effects and outline our research

Original hybrid control for robotic structures using magnetic shape memory alloys actuators.

International audienceMagnetic Shape Memory Alloys (MSMA) are relatively new active materials but at this time they are not actually very used as actuators despite a high strain and a small response time. This is probably due in part to a large hysteresis and a strong non-linear behaviour. In this paper, an original hybrid control is designed taking into account dynamical effects and hysteretic behaviour in order to increase static gain of the system. After a short presentation of MSMA behaviour, a modelling is proposed to obtain two different control strategies. Some experimental results are also given

Conversion d'énergie magnéto-thermo-mécanique dans les alliages à mémoire de forme magnétiques.

National audienceLes matériaux actifs sont de plus en plus utilisés en tant qu'actionneurs dans les systèmes mécatroniques et micro-mécatroniques. Les matériaux piézoélectriques et les alliages à mémoire de forme sont les deux exemples les plus représentatifs à l'heure actuelle dans ces domaines. Les alliages à mémoire de forme magnétiques sont des matériaux relativement récents et ils apparaissent très intéressants de par leur rapidité d'actionnement et leur grande déformation ; cependant, leur comportement fortement non-linéaire reste un frein à leur développement et les méthodes de conception et de commande les concernant se doivent d'évoluer

Multistable actuator based on magnetic shape memory alloy..

International audienceMagnetic Shape Memory Alloys (MSMs) are attractive smart materials because they exhibit, at the same time, a large strain (10 %) and a short time response (100 microns s). In this paper, we propose a novel MSM based actuator exploiting the characteristics of MSMs. This device is a push-pull actuator where two pieces of MSM act in an opposite way. The magnetic fields are created by two magnetic coils supplied by current pulses. The hysteretic behaviour of the MSM permits to keep a stable position when no current is applied and so limits heat losses in the coils. A model of this actuator is proposed and validated by experiments. A precise position feedback control of the actuator is then achieved using a displacement laser sensor