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En plus d’un hymne à la biodiversité marine, cet ouvrage a pour objectif d’aider les décideurs à mieux comprendre le rôle de la planète bleue dans le climat et l’importance de la prendre en considération dans chacune des décisions politiques de ce XXIème siècle. Le chapitre concerne plus spécifiquement le rôle fondamental des herbiers de magnoliophytes marines dans la séquestration du carbone

International audience

International audience; The ability of Posidonia oceanica to concentrate contaminants has been used to evaluate trace- metal contamination in 84 sites, around the entire Mediterranean basin. Based on these measurements, evaluation scales have been established for seven metals (As, Ag, Cd, Cu, Hg, Ni and Pb), based on the calculation of the mean value of each quintile as class limit, allows the ranking of all sites and their classification in five classes between 'very low" until "very high" contamination. The application of these preliminary scales to bibliographic data demonstrated a good accuracy with the previous classification of these sites as "non contaminated" or "contaminated" sites, and allowed to propose a first map of contamination for different trace- metals at the sub regional level (e.g. Western Mediterranean basin, Adriatic basin). These maps will be very useful in the framework of the monitoring of the reduction of trace-metal contaminations (e.g. Horizon 2020 goals).

International audience; Les herbiers à Posidonia oceanica présentent plusieurs types morpho-structuraux généralement conditionnés par les conditions de milieu (profondeur, hydrodynamisme, substrat, pente, turbidité, sédimentation). Du fait de leur rareté, deux structures particulières, les récifs barrière et les herbiers tigrés, sont considérées depuis une vingtaine d'années comme des paysages marins menacés. Initialement décrits dans le golfe de Gabés, à proximité des îles Kerkennah, les herbiers tigrés se présentent sous forme " de rubans assez étroits qui se développent entre 0.5 et 3 m de profondeur sur matte ". La mise en place de nouveaux programmes d'études sur les herbiers à Posidonia oceanica et l'optimisation de l'imagerie satellitaire (accessibilité, résolution, coût) ont permis d'acquérir de nombreuses données dans plusieurs secteurs de Méditerranée et d'actualiser notre connaissance de ces structures. Il apparaît ainsi que les herbiers tigrés sont mieux représentés au niveau de la rive Sud du bassin (Golfe de Gabès, littoral de Zarzis en Tunisie, lagune de Farwa et littoral à l'Est de Tripoli en Libye) et dans des îles méditerranéennes (Marsala-Stagnone en Sicile et Porto-Vecchio en Corse). D'autre part la présence d'herbiers tigrés sur roche a été observée pour la première fois en Libye sur un platier rocheux à l'Est de Tripoli. Compte tenu de leur rareté et des pressions qu'elles subissent, il apparaît urgent de classer ces structures comme " monuments naturels " et mettre en œuvre une politique efficace pour assurer leur conservation

International audience; Seagrasses appear relevant bioindicators of metallic contamination in coastal waters. Posidonia oceanica leaves were collected at six locations along the north and east coast of the Adriatic Sea selected on the basis of the presence of different types and levels of human-induced pressures. Concentration of seven trace-metals (Ag, As, Cd, Cu, Hg, Ni and Pb), as well as the Methyl-Mercury content, were determined. The level of contamination is low at the pristine site of Lavdara (Cu: 4.73 ± 0.01 μg/g; Hg: 0.054 ± 0.003 μg/g; Met-Hg: 0.015 ± 0.000 μg/g; Ni: 21.40 ± 0.63 μg/g; Pb: 0.90 ± 0.10 μg/g) and higher along the Slovenian coast (Cu: 11.83 ± 0.22 μg/g, Hg : 0.092 ± 0.004 μg/g ; Met-Hg: 0.027 ± 0.004 μg/g; Ni: 40.07 ± 2.08 μg/g, Pb: 1.50 ± 0.06 μg/g). Generally, Mercury and the associated trace metals contents are relatively high in P. oceanica collected in the Northern Adriatic region. This is due not only to the strong anthropogenic impact (ports of Trieste and Koper, former chloralkaline plant - PVC near Seget Donji) but also to the geological characteristics of the hinterland (former cinnabar ore in Slovenia). This preliminary study confirms the capability of P. oceanica to record trace metal in relation with humaninduced pressures, as well as with geological background of the coast.

International audience

International audience; Background: Plant defense strategy is usually a result of trade-offs between growth and differentiation (i.e. Optimal Defense Theory - ODT, Growth Differentiation Balance hypothesis -GDB, Plant Apparency Theory - PAT). Interaction between the introduced green alga Caulerpa taxifolia and the endemic seagrass Posidonia oceanica in the Mediterranean Sea offers the opportunity to investigate the plausibility of these theories. We have accordingly investigated defense metabolite content and growth year-round, on the basis of an interaction gradient. Results: When in competition with P. oceanica, C. taxifolia exhibits increased frond length and decreased Caulerpenyne - CYN content (major terpene compound). In contrast, the length of P. oceanica leaves decreases when in competition with C. taxifolia. However, the turnover is faster, resulting in a reduction of leaf longevity and an increase on the number of leaves produced per year. The primary production is therefore enhanced by the presence of C. taxifolia. While the overall concentration of phenolic compounds does not decline, there is an increase in some phenolic compounds (including ferulic acid and a methyl 12-acetoxyricinoleate) and the density of tannin cells. Conclusion: Interference between these two species determines the reaction of both, confirming that they compete for space and/or resources. C. taxifolia invests in growth rather than in chemical defense, more or less matching the assumptions of the ODT and/or PAT theories. In contrast, P. oceanica apparently invests in defense rather than growth, as predicted by the GDB hypothesis. However, on the basis of closer scrutiny of our results, the possibility that P. oceanica is successful in finding a compromise between more growth and more defense cannot be ruled out.

7 páginas, 5 figuras, 5 tablas., The pervasive use of ecological indices is increasingly requiring actions of harmonisation. Specifically, within the EU Water Framework Directive, an important effort in methods intercalibration is being done. However, a significant limitation in comparability assessment arises from the datasets used, which have different geographic origins. The purpose of our study was to perform an experimental intercalibration, where data were collected specifically on a set of common sites and following all the requirements of the methods being assessed. Three indices based on the marine angiosperm Posidonia oceanica, the POMI, the BiPo and the PoSte, were applied to sites in three different geographical areas of the western Mediterranean: Catalonia, Corsica and Southern Italy (Ischia), distant between hundreds and more than thousands of kilometers. Two indices, POMI and BiPo, showed not only a very good relationship with human pressures (measured on a common scale for all sites) but also a high comparability, in all aspects investigated. The differences found for the third one (PoSte) are hypothesised as being due to a different rationale used to define reference conditions, the different metrics used in the index, and in particular to a different definition of ecological status in relation to the time scale of the response to anthropogenic pressures. Our study demonstrates that indices with very different approaches can provide fully reliable and comparable results., This study was supported by the POSIDONIA Project, set up within the framework of the Interreg IIIB–MEDOCC Convention. The laboratory of benthic ecology of the Stazione Zoologica di Napoli was supported by a research contract of the Italian Environmental Protection Agency (APAT), for the “Development of methods and analysis of P. oceanica, according to the Water Framework Directive” (APAT, 2005–2006). We are indebted to Mian Vich

The coastal vegetation, and in particular the seagrasses, plays a major role in the fixation of carbon. Posidonia oceanica, a species endemic to the Mediterranean, is of particular interest because of the constitution of a particular structure, the matte, which enables the sequestration of carbon over long periods of time. An initial assessment of the stocks of carbon sequestrated within the matte has been undertaken in two sectors of the NATURA 2000 site “Grand Herbier de la Plaine Orientale”, Biguglia in the north and Aléria in the south. The surface area of the meadow has been measured by means of the combined use of aerial remote sensing (shallow zone) and side-scan sonar (deep zone). The thickness of the matte has been assessed by means of seismic reflection using a 2.5 KHz sediment probe and a sparker. The calibration of the seismic data was performed by scuba diving at the level of intermatte cliffs, clearly visible on the seismic profiles. The seagrass meadow at the NATURA 2000 site extends from 3 to 41 m depth and covers an estimated total area of 22 667 ha, or 52.4% of the bottom between 0 and 50 m depth. The speed of propagation within the matte (celerity), estimated by comparison of the field data (intermatte) and the seismic profiles, ranges from 1 600 to 1 700 m.s-1. The thickness of the matte, estimated on the basis of the mean celerity, is on average 2.7 m for the Biguglia zone where it may locally exceed 8 m; it is on average 3.2 m for the Aléria zone where it may exceed 13 m, in particular off the mouth of the coastal river Tavignano. The presence of matte beneath the sediment should also be noted in patches of sand within the meadow and also beyond the lower limit. The quantity of carbon sequestered at this NATURA 2000 site may exceed 60 million tons. However, it would be necessary to carry out coring within the matte, in several representative sectors, in order to assess more accurately the amounts of carbon sequestered at this site.

Cet ouvrage a pour objectif d’aider les décideurs à mieux comprendre le rôle de la planète bleue dans le climat et l’importance de la prendre en considération dans chacune des décisions politiques de ce XXIème siècle. Le chapitre s'intéresse aux conséquences possibles du changement climatique sur les herbiers de magnoliophytes marines

The availability of maps of the main habitats and types of bottom constitutes a priority for managers of the marine environment. For several years, a number of studies have been undertaken in order to meet this requirement, but they generally only cover limited areas and the methods used, as well as their accuracy, vary widely from one site to another. An original approach has been initiated for this purpose along the coast of Corsica (1 000 km of coastline); it has involved (i) surveying all the available data (293 identified maps), (ii) selecting and extracting the most relevant data (date and method of acquisition, accuracy), (iii) updating the data on surface habitats (e.g. upper limits of the Posidonia oceanica meadows) by means of remote sensing of recent images, (iv) homogenizing all the available data (typology of benthic biocenoses in the Mediterranean), (v) assembling the full set of data within an easily incrementable Geographical Information System (GIS), and (v) proposing a scale of reliability making it possible to associate a degree of confidence to each point on the map. This approach has resulted in the production of a map covering the whole of the Corsican coastline down to 50 to 150 m depth (depending on the sector considered), including, where there is an overlap, only the data with the highest degree of reliability. The surface area mapped is estimated at more than 299 700 ha, which makes it one of the largest recent maps ever produced for the Mediterranean. The P. oceanica meadow covers a surface area of about 57 500 ha, or 45.3% of the seabed between 0 and 50 m depth. In relation to the earlier data collected in the 1990s (potential surface area of seagrass beds), the extension of P. oceanica has remained relatively stable, and the differences observed may be explained mainly by the accuracy of this new map which possesses a greater degree of reliability.

International audience

International audience; Neogoniolithon brassica-florida (encrusting rhodobionta) is generally reported as a veneering coral community along the wave-beaten rocky coast of the Mediterranean Sea. Its presence in the hyperhaline lagoon of Bahiret el Bibane, situated in SE Tunisia, takes on particular importance because of its extension. It constitutes a reef formation 14 km long developing on both sides of the sea inlet. The building of this ''natural monument'' seems to be the result of an evolutionary series. The aim of this study was to investigate the current status of this reef, comparing it to 30 years ago. The current extension of the Neogoniolithon brassica-florida reef appears to be much reduced from that reported 30 years ago, indicating a regression of 26%. Four different phases leading to the reef building were also identified

International audience

International audience; The seagrass Posidonia oceanica is extensively monitored in Mediterranean coastal waters and is an ideal candidate for an eco-regional assessment of the coastal ecosystem. The aim of this study is to evaluate the potential of P. oceanica as eco-regional indicator for its assessment at the scale of Mediterranean basin. For this purpose, regional and national P. oceanica monitoring programmes are identified, and their data and metadata are collected and compared in terms of objectives, strategies, sampling designs and sampling methods. The analysis identifies a number of issues concerning data quality, reliability and comparability. In particular, the adoption of different sampling designs and methods may introduce relevant errors when comparing data. The results of this study stress the necessity of carefully planning monitoring programmes. Moreover, it highlights that the adoption of a number of common tools would facilitate all Mediterranean monitoring activities and allows an optimisation of management efforts at an eco-regional scale.

International audience; The development of ecologically based indices that respond to disturbances in a predictable manner has been stressed by the EU Water Framework Directive. The seagrass Posidonia oceanica, given its ecological indicator characteristics, has been identified as one of the elements to determine ecological status under the EU Water Framework Directive. The purpose of this study is therefore to develop a biotic index based on P. oceanica (BiPo), focussing on: (i) the necessity of an index that may be applied over the larges geographical extent possible, (ii) the necessity of a tool for a baseline evaluation of P. oceanica status in the Mediterranean, (iii) the compliance with WFD requirements, (iv) the efficiency of the method in terms of reliability and cost. The BiPo index is developed on the basis of all P. oceanica monitoring data available in the western Mediterranean and on a standard assessment of anthropogenic pressures. The index metrics are selected and evaluated on the basis of this pressures assessment, and are subsequently integrated for the evaluation of ecological status. The index is then tested on 15 sites around Corsica (France). The results show that the BiPo well reflects meadow health status and ecological status. Furthermore it is reliable, standard and cost-effective, and can be applied to a wide array of management and conservation purposes.

National audience; The Mediterranean Sea is known as a biodiversity hot spot in terms of species, as well as at the ecosystem level with varied and rich benthic habitats. If this high biological diversity can be mainly explained by environmental conditions (interface between tropical an temperate regions, hydrology, climate, habitat heterogeneity), the historical factors also played a major role (remnant of the Tethys Ocean, Messinian crisis, Atlantic Ocean connection, opening of the Suez Canal). The diversity of Mediterranean benthic habitats is the basis of biological diversity. Among these habitats, seagrass meadows and coralligenous assemblages appear as key habitats, and have been taken into account in two action plans of the Regional Activity Centre for Specially Protected Area and Biodiversity (UNEP, MAP, RAC/SPA). If the extension of seagrass meadows in the Mediterranean basin has been estimated at 30,000 to 40,000 km2, with considerable amounts of data concerning the location of main meadows, there are important gaps in knowledge concerning the composition and distribution of coralligenous assemblages and maërl beds. Data concerning coralligenous assemblages are sparse and most of the information is based on data obtained in the northwestern Mediterranean, with some data additionally available in southern Italy and the Alboran Sea. The northern Adriatic constitutes a particular biogeographical sector due to its northern location, superficial depth, and important nutrient discharges from rivers. Extensive seagrass meadows, composed of four of the five species present in the Mediterranean basin, have been observed in this region; the lack of rocky substrate and the high sedimentation, however, seem to be unable to support extensive coralligenous assemblages.

International audience; Metal concentrations have been measured in blades of the endemic Mediterranean seagrass Posidonia oceanica, along transects from three different contaminant point sources (the former asbestos mine of Canari - Corsica, France; the chemical plant of Solvay/Rosignano - Livorno, Italy; and the industrial harbour of Porto-Torres - Sardinia, Italy). The aim of this study was to evaluate the spatial extent of the impact of these sources in terms of metal contamination. The results showed that metal contamination from the former mine of Canari (cobalt - Co, chromium - Cr and nickel - Ni) extends at least 5 km to the north and south. The impact of this mine, which closed in 1965, seems to be lingering still. Mercury (Hg) contamination in the Livorno location was difficult to evaluate due to the presence of others potential sources of mercury in the area (e.g. industrialized city of Livorno, natural cinnabar deposits, intense tectonic activity of the area). At any rate, mercury concentration decreased strongly with distance from the plant. Lead (Pb) contamination at the Porto- Torres harbour was very low and disappeared with distance from the harbour. However, as the Porto-Torres harbour does not appear as a substantial point source of Pb contamination and because of the ubiquitous characteristic of the Pb element, it is difficult to draw any general conclusions concerning this element. The results presented in this study demonstrated the usefulness of the seagrass P. oceanica as a tool for the evaluation of the spatial extent of metal contaminations from point sources and could, therefore, contribute to on-going efforts to manage coastal environments.

International audience; The Biotic Index based on Posidonia oceanica (BiPo) is a classification system for evaluation of the ecological status in Mediterranean coastal waters, developed in accordance with the EU Water Framework requirements. The aim of this study is to verify the applicability and reliability of the BiPo index to different geographical areas of the north-western Mediterranean (France, Spain and Italy), to understand whether such a classification system may be applied more extensively, as so far it has only been applied to coastal waters in Corsica. The ecological status determined for sites is verified against pressures revealed from satellite imagery and from trace metal contamination of plants, to identify the sources of pressure that may be responsible for a low ecological status. The results of this study indicate that: (i) the BiPo index responds reliably to pressures, in different areas of the Mediterranean; (ii) sites with an ecological quality ratio (EQR) close to the good/moderate boundary require particular attention to identify and reduce causes of deterioration; (iii) the support of chemical indicators, in this case metal contamination, is relevant to identify potential sources of pressure.

International audience; The assessment of human-induced pressures on the coastal area is essential to target management plans effectively, and moreover is required by the EU Water Framework Directive. A simple and cost-effective assessment of human-induced pressures on the coastal zone is applied using two methodologies: a qualitative visual assessment which uses satellite images; and a quantitative assessment based on governmental census data. These methods are applied to defined areas (23 areas) of four Italian regions: Liguria, Tuscany, Latium and Sardinia. The results show a high agreement (83%) between these two methods, in which only four of the 23 areas are classified differently. These differences may mainly be ascribed to the qualitative or quantitative properties of the methods, and to the different geographical units adopted. These characteristics however provide complementary information, which suggests that the application of both proposed methods confirms reliability and allows fine-tuning of the assessment. The pressure assessment proposed is simple, time and cost-effective, and repeatable over time and space. It therefore can be applied in different contexts to respond to legislative requirements or to target management plans and remedial actions effectively.

International audience; Mapping marine biocenoses is an efficient method for providing useful data for the management and conservation of Mediterranean lagoons. Fused images from two satellites, SPOT 5 and IKONOS, were tested as management tools for identifying specific ecosystems in the El Bibane lagoon, situated in southern Tunisia near the Libyan border. The objectives of this study were to provide a precise map of the entire El Bibane lagoon using fused images from SPOT 5 and to compare fused images from SPOT 5 and IKONOS over a test-area. After applying a supervised classification, pixels are automatically classified in four classes: low seagrass cover, high seagrass cover, superficial mobile sediments and deep mobile sediments. The maps of the lagoon revealed and confirmed an extremely wide distribution of seagrass meadows within the lagoon (essentially Cymodocea nodosa; 19 546 ha) and a large area of mobile sediments more or less parallel to the shore (3 697 ha). A direct comparison of overall accuracy between SPOT 5 over the entire area, SPOT 5 over the test-area and IKONOS over the test-area revealed that these tools provided accurate mapping of the lagoon environment (83.25%, 85.91% and 73.41% accuracy, respectively). The SPOT 5 images provided greater overall accuracy than the IKONOS image, but did not take into account the heterogeneous spatial structure of the seagrasses and sediments present in the lagoon environment. Although IKONOS imagery provided lower overall accuracy than SPOT 5, it proved a very useful tool for the mapping of heterogeneous structures as it enabled the patchiness of formations to be better taken into account. The use of SPOT 5 and IKONOS fused images appears to be very promising for completing the mapping of lagoons in other regions and countries of the Mediterranean Sea.

International audience; The aim of this study is to assess the relevance and the potential of Posidonia oceanica as a tracer of past mercury contamination. Shoots were collected on two sites, an impacted site, Rosignano (Tuscany, Italy), and a pristine site, Tonnara (Corsica, France). Lepidochronology was used to measure mercury concentrations in living sheaths and in the corresponding dead sheaths. The results show that there is an overestimation of mercury concentrations in dead sheaths (because of the degradation of this tissue due to its ageing), overestimation which stabilizes itself from the third lepidochronological year onwards (trend significant only for Rosignano). Thus, it is possible to estimate previous mercury concentrations and to date a contamination, by measuring mercury concentration in the dead sheaths of a given lepidochronological year and by taking into account the degradation of the sheaths. Therefore, Posidonia oceanica can be used to reconstruct the evolution of the past mercury contamination

International audience; The aim of this study is to determine metal (Cd, Co, Cr, Hg, Ni, Pb) concentrations in Posidonia oceanica tissues along the Corsican coastline. The results show that except for Cr, all the metals are preferentially accumulated in the blades; this is particularly interesting as it means that future metal analyses may be carried out only on the blades avoiding thus the removal of the shoots. Moreover, they show that metal concentrations may reflect the ''background noise'' of the Mediterranean Sea. Station 15 (Canari) can however be distinguished from the others due to its high Co, Cr and Ni concentrations. This result may be related to the presence of a previous asbestos mine, located near this station. Therefore, this study reinforces the usefulness and the relevance of Posidonia oceanica as a tracer of spatial metal contamination and as an interesting tool for water quality evaluation.

International audience; Little doubt is left that climate change is underway, strongly affecting the Earth's biodiversity. Some of the greatest challenges ahead concern the marine realm, but it is unclear to what extent changes will affect marine ecosystems. The Mediterranean Sea could give us some of the answers. Data recovered from its shores and depths have shown that sea temperatures are steadily increasing, extreme climatic events and related disease outbreaks are becoming more frequent, faunas are shifting, and invasive species are spreading. This miniature ocean can serve as a giant mesocosm of the world's oceans, with various sources of disturbances interacting synergistically and therefore providing an insight into a major unknown: how resilient are marine ecosystems, and how will their current functioning be modified?