Local and global anthropogenic pressures due to climate change and to local uses and activities are exerting significant cumulative impacts to greater extents of the oceans and seas. Coastal ecosystems are particularly threatened by the intensity and coexistence of several marine uses and pressures, including sewage and urban constructions, tourism, ship traffic, fisheries and aquaculture. Assessment of pressures and the identification of mitigation measures are key urgent actions, as already highlighted by the EU Marine Strategy Framework Directive and the United Nations Sustainable Development Goal 14. The aim of this work, developed within the Interreg-Med project SHAREMED, is to systematize existing knowledge on threats and pollution, including those of transboundary origin, for long term strategies and common action marine spatial planning, jointly developed with stakeholders. The quest is to assess coexisting environmental threats, and their propagation in space and time, at proper spatial and temporal scales, according to the type and action of each stressor (i.e. global vs. local). Cumulative pressures are tackled within a dedicated Atlas comprising three sub-basinsins of the Mediterranean Sea: the North Adriatic Sea, the Sicilian Channel and the North-Western region. The Atlas integrates information generated at the best available resolutions by 1) in-situ sampling, 2) remote observations, 3) numerical models, and 4) focusing on target ecosystems and habitat forming species. These sub-basins are subjected to multiple local and larger scale (e.g. climate) pressures that propagate in space and time, and across political boundaries, that need to be addressed through coordinated actions, based on evidence-rooted common understanding. Interactions with relevant Stakeholders, solicited through an online survey, and meetings, were used to select target ecosystems and to identify the key relevant pressures. The Atlas is based on open-access databases and portals, literature reviews and from ad-hoc model simulations concerning marine heatwaves, ship traffic, oil pollution, marine litter and fishing efforts. We will present the main preliminary results and needs and gaps in observations related to marine ecosystems threats.

Chronic hypoxia and anoxia have strong impacts on coastal ecosystems worldwide. In shallow coastal ecosystems, such situations are essentially driven by high benthic oxygen (O2) demand resulting from organic matter mineralization in surface sediment and amplified by a low mixing of the water column. However, the benthic O2 demand may greatly vary according to the O2 availability, sediment biogeochemical properties, and bioturbation by macrobenthic fauna. Here we examined how the sediment O2 demand varies in response to seasonal and long-lasting (pluri-decadal) hypoxia in the Berre lagoon, a coastal ecosystem impacted by chronic hypoxia events since 60 years. Oxygen penetration depth, diffusive and total O2 fluxes were measured in situ using a microelectrode autonomous profiler and benthic chamber deployments at three sites impacted by quite-permanent (PA), seasonal (PI) and occasional (PO) hypoxia in August 2016. They were seasonally repeated at site PI between August 2015 and August 2016. Additional physical and chemical characteristics were also measured in surface sediment. Sediment profile images and characteristics of benthic macrofauna communities enabled to estimate the quality of the benthic ecosystem. The highest benthic O2 demand was observed after seasonal anoxia in relation to the important accumulation of reduced chemical species in surface sediment. Interestingly, both pluri-decadal hypoxia and normoxia produced relatively high benthic O2 demand related to a higher accumulation of organic matter and to the presence of reduced chemical species at site dominated by hypoxia, and to the presence of fresher organic matter and active bioturbating macrofaunal communities in normoxic site. The low benthic O2 demand at site seasonally impacted by hypoxia likely resulted from the degraded state of the macrofaunal community and from the lower accumulation of reduced chemical species. The occurrence of hypoxia and anoxia situations in the Berre lagoon was predicted from the competition between kinetics of benthic O2 demand and water column reoxygenation events induced by strong wind. The good agreement between the measured and predicted hypoxia/anoxia occurrence clearly indicates that the chronic deoxygenation events in the Berre lagoon, and the resulting degraded ecological state of the benthic ecosystem are driven both by the benthic O2 demand and by the intensity and duration of the water column stratification.

The present paper is specifically focused on enclosed or semi-enclosed basins where the wind is the dominant driver of water surface tilting, leading to the so-called wind tide contributing to water levels rise. Wind-induced free surface tilting is studied using the 1-D steady form of the depth-averaged shallow water (Saint-Venant) momentum equation which reflects the depth-averaged local balance between surface slope and wind stress. Two contrasted field sites, the Berre and Vaccarès lagoons, have been monitored providing water level data along a reference axis. This study highlighted the occurrence of wind tides at the two field sites. The bimodal wind exposure ensured the robustness of the observations, with non-linear but symmetric behaviors patterns observed in winds from opposite directions. It is observed that the higher the wind speed, the steeper the slope of the free surface in accordance with the well known basic trend. In addition, a significant effect of depth is observed, with greater surface tilting in the shallower lagoon. The data analysis confirmed the robustness of such a simple approach in the present context. Using the additional assumption of constant, i.e. wind-independent, drag coefficients (CD) allowed a good match with the observations for moderate wind speeds for both sites. However, the depth effect required the CD to be increased in the shallower basin. Classical empirical wind-dependent CD parameterizations provide better wind-tide predictions than the constant-CD approach in very strong wind conditions but totally failed in predicting surface tilting in the shallower site, suggesting that physical parameters other than wind speed should be taken into account for the CD parameterization in very shallow lagoons.

En Méditerranée, le marnage est faible, et les effets barométriques, liées aux régimes dépressionnaires, contribuent de façon prépondérante aux surcotes.Dans les bassins semi-fermés, des phénomènes de basculement des plans d'eau peuvent s'ajouter aux variations du niveau, du fait de la contrainte du vent sur la surface.Dans l'étang de Berre, le manque de données continues de niveau sur le long terme ne permettait pas d'avoir une appréciation quantitative des phénomènes contribuant aux variations du niveau d'eau.Le réseau d'instrumentation HTM-NET, composé actuellement de 16 stations de mesure en Provence dont deux sur l'étang de Berre, dans les ports du Jaï et de Saint-Chamas, permet d'acquérir des données de niveau.Une station du réseau est également installée dans le port de Carro au cap Couronne en méditerranée.Nous pouvons observer d'une part une évolution du niveau d'eau dans l'étang forcée par les variations du niveau de la mer qui se transmettent par le canal de Caronte : l'effet de la marée astronomique est perceptible avec un marnage d'environ 5cm, et le niveau moyen suit de façon systématique les évolutions du niveau de la mer associées aux effets barométriques, inférieurs à 45cm.A ce forçage par la mer, s'ajoute un basculement du plan d'eau, du même ordre de grandeur, entre le nord et le sud de l'étang, par des conditions de vent fort.Des ondes de seiches dans les ports du Jaï et Saint-Chamas sont mises en évidence : une seiche d'environ 100 min est retrouvée dans les deux sites, correspondant à la résonance selon le grand axe de l'étang.D'autres seiches sont en revanche propres à des phénomènes de résonance selon le grand étang d'une part et dans l'étang de Vaïne d'autre part.Les évènements de seiches sont corrélés à la présence de vent fort et la création d'un basculement dans l'axe du bassin.

The invasive ctenophore, Mnemiopsis leidyi has been proliferating in lagoons and coastal areas around Europe for almost 20 years but the role and the impact of its presence in sink ecosystems is still not completely understood. In France, Mnemiopsis leidyi is present in Mediterranean lagoons and estuaries along La Manche Sea. Mnemiopsis was first recorded in the Berre Lagoon in early 2000. This lagoon has been highly perturbated for years, with a large volume of freshwater inflow through natural rivers and a succession of large hydroelectric power plants, inducing important eutrophication. Legislation has been implemented to improve the health status of the lagoon since 1994. A long-term study was undertaken in 2010 to measure Mnemiopsis population dynamics, and to identify the main drivers of its persistence in this highly anthropogenic lagoon. In 2011 and 2012, during extreme winter conditions, populations of this ctenophore were not observed for months. Its re-appearance later in year could be linked to either a new introduction from the Mediterranean Sea or the existence of retention areas where individuals sought refugia. Following measurement of biochemical conditions (i.e. chlorophyll a), plankton biomass and Mnemiopsis populations structure (eggs, cydippid larvae/transitional phase and adult) in different areas of the lagoon, as well as the lagrangian modelling of "particles" distribution (i.e. Ichthyop), we highlighted the seasonal patterns in the population structure, the level of available carbon always above the minimal for the survival of Mnemiopsis (24 mu gC L-1) and the potential refugia area role the Vaine sub-basin could play. Populations from the Vaine sub-basin probably serve as source populations for the rest of the lagoon by advective transport in spring. (C) 2020 Elsevier B.V. All rights reserved.

Habitat connectivity is central to several key evolutionary and ecological processes, having implications for the spatial structuring of marine populations. For benthic species that have no or little mobility as adults, connectivity is evaluated by analyzing the dispersal of propagules across the seascape. We investigate fine-scale connectivity of coralligenous habitats in Marseille Bay (located in the north-western Mediterranean Sea) using high-resolution cartography and a particle-tracking model ran over a range of parameters derived from the biological traits of potential target species. We present annual and seasonal means of various connectivity diagnostics measuring the retention and exchange of propagules among coralligenous patches. A synthetic view is obtained by clustering individual patches into "coralligenous provinces" (ensemble of patches tightly connected by ocean currents). When discussing our results against historical observations, we highlight some genetic breaks, sharp community changes and ecological clusters that fit well our simulated connectivity patterns. Consistent findings include reduced biodiversity along Cote Bleue, high biodiversity at Planier Island and the presence of various dispersal barriers, which evolve with dispersal durations and provide the backbone of habitat connectivity. Our results help to apprehend and test hypothesis on marine population structures, providing useful information for ecologists and conservationists.

Berre lagoon is a Mediterranean lagoon deeply impacted by industry and urban activities. Since 1966, a hydroelectric powerplant has discharged large quantities of freshwater and nutrients into the lagoon, inducing major ecosystemic changes. The lagoon ecosystem has declined to a eutrophic state with the loss of Zostera meadows and marine macrofauna. In 1994, an extensive monitoring network for Berre lagoon was set up. Different compartments of the ecosystem were measured: water quality, sediment quality, macrophytes (including Magnoliophyta), benthic macrofauna, fisheries, and ichthyofauna. Results show a pattern of change in the ecosystem linked to the different phases of eutrophication reduction. However, in 2018, a major ecological crisis occurred, inducing anoxia over more than 90 % of the lagoon surface area. Analysis of data from the monitoring network during and after this crisis, taking into account environmental and climatic factors, provides a basis for understanding the degradation of the different compartments of the ecosystem. The origin of this crisis is a `cocktail effect' of high spring nutrient inputs, high water temperature, strong water stratification, lack of wind, lack of Zostera meadows and high benthic biomass. This crisis highlights the extreme fragility of the Berre lagoon ecosystem and shows the importance of an ecosystemic approach for the monitoring network.

To clarify the formation process of the salinity minimum in the Kuroshio-Oyashio mixed water region and understand the mechanism of meridional heat transport between the subtropical and subpolar gyres, 16 profiling floats were deployed within a warm-core anticyclonic eddy off Hokkaido from June 2012 to December 2013. Then, the evolution of an anticyclonic eddy was examined using time series of the water properties. The largest fluctuations in water properties were observed in April and May 2013, when the anticyclonic eddy first moved south to interact with a warm front, then back north. Salinity in the salinity minimum layer increased during the interaction. After the eddy detached from the frontal structure, low-salinity water was again observed with small intrusive structures, which eventually converged to a smooth zigzag structure in the potential temperature-salinity diagram, suggesting that both vertical mixing and vertical heaving played a role in the temporal changes observed after the eddy detached from the front. Since the salinity variation during the interaction event was about half the total salinity change during the whole experimental period, the interaction of an eddy with a front might be important for modifying the water properties of the eddy, and, therefore, for the meridional transport of heat and fresh water.

The Subarctic Front (SAF) of the North Pacific Ocean is important because it considerably affects the storm track in the troposphere, and mode water ocean mixed layer (OML) forms south of the front. However, processes controlling the sea surface temperature and salinity in the area of the SAF are not fully understood. Using Argo, satellite, and atmospheric reanalysis data, we investigate the OML heat budget seasonal cycle around the SAF in a domain defined by 150°–168°E and 40°–46°N. In summer, a large imbalance suggests a non-negligible cooling effect due to vertical mixing. In winter, we find that in the area of mode water OML, air–sea fluxes contribute to 60 % of heat dissipation. The remaining cooling is due to lateral advection and mixed layer base entrainment, while eddies warm the OML. North of the SAF, the geostrophic and Ekman flows have comparable cooling effects. Entrainment also cools the OML in fall, but vanishes in winter. In March, entrainment warming due to a temperature inversion below the OML is found to be negligible. We also estimate the salinity budget of the OML. In winter, entrainment contributes to a salinity increase north of the SAF, but it is negligible in the mode water OML area. The contribution of salinity to buoyancy loss during fall and winter OML deepening is relatively small, especially south of the front where it accounts for only 6 % of total buoyancy loss.

The Rhone River provides the largest inputs of terrestrial freshwater and nutrients into the Mediterranean Sea. The Rhone River diluted water intrusions into the Bay of Marseille were investigated, examining their physical generation processes and associated biogeochemical impact by using in situ observations, remote sensing data, and a three-dimensional physical/biogeochemical coupled model. During our study period from 2007 to 2011, Rhone River intrusions occurred on average 7.6 times per year and affected more frequently the northern part of the bay. A classification of intrusion events in three categories is proposed (short lived, big, and small) as a function of their duration and spatial extent. The intrusions appeared to be driven by: (i) wind forcing, (ii) the presence of a mesoscale eddy, (iii) the Rhone River discharge volume, and (iv) the variation in thermocline depth. Typically, a combination of these favorable factors was necessary to induce an intrusion. An intrusion strongly impacts the biogeochemical functioning of the Bay of Marseille by bringing large quantities of nutrients into the bay. Mass balances were computed allowing us to quantify this impact on the Bay of Marseille. The results show that the ecological impact depends very much on the type of intrusion, with big intrusions having the highest impact.

In the present work, a biophysical dispersal model is used to understand the role of the physical environment in determining reef fish larval dispersal patterns in the South-West Lagoon of New Caledonia. We focus on a reef fish species, the humbug damselfish Dascyllus aruanus, to investigate seasonal variability of simulated larval retention at the scale of a reef patch and at the scale of the lagoon, and to explore links between larval retention and wind variability. The model shows that retention exhibits considerable temporal variability and periodically reaches values much larger than anticipated. Non-zero larval settlement occurs over a large part of the lagoon. Nevertheless, settlement values decrease quickly away from the natal reef and mean dispersal distances are of order 25-35 km. Cross-correlation analyses indicate that weather conditions characterized by strong south east trade winds lead to low retention rates at both local (reef) and regional (lagoon) scales. By contrast, subtropical weather conditions characterized by weak winds result in high retention rates. These results suggest that large-scale weather regimes can be used as proxies for larval retention of the humbug damselfish in the South-West Lagoon of New Caledonia. Nevertheless, relatively small mean dispersal distances suggest that metapopulation dynamics occur on relatively small spatial scales. (C) 2013 Elsevier Ltd. All rights reserved.

Depuis 2008, l’Ifremer a developpe un modele hydrodynamique a petite echelle de la grande rade de Toulon, utilise dans le cadre du projet Girac pour la representation des panaches bacteriologiques en mer. Ce modele, construit sur la base du code numerique MARS3D, genere toutes les demiheures les composantes du courant ainsi que les valeurs de temperature et de salinite dans une grille horizontale de resolution 25 m, etendue sur 30 niveaux en profondeur suivant une echelle d’epaisseur variable en fonction de la bathymetrie. La calibration/validation d’un modele de cette precision necessite le deploiement de different appareils de mesure : sondes CTD donnant des profils de temperature et de salinite, thermosalinographe donnant des cartes de repartition en surface, courantometres Doppler (ADCP) permettant d’obtenir des profils verticaux de courant le long d’une trajectoire navire avec une precision dans notre cas de 1 a 4 metres, courantometres Doppler en station fixe permettant d’enregistrer sur une longue duree l’evolution de la colonne d’eau en un point donne, bouees derivantes donnant la trajectoire des courants maritimes en frontiere des modeles. On montrera dans cette etude l’interet particulier de chaque type de mesure et la methode utilisee pour affiner les parameters du modele et approcher progressivement la realite observable. Au terme de ce processus de validation, le modele est apte a reproduire avec un indice de confiance acceptable les ecoulements d’eau douce en sortie des exutoires. Par couplage avec le module complementaire MARS3D/MET&OR, il permet ensuite de realiser des simulations de dispersion d’ Escherichia coli plus fines tenant compte des variations d’intensite lumineuse lors des cycles diurnes/nocturnes, afin de predire le degree de contamination des panaches susceptible d’atteindre les zones de baignade dans les 24 heures consecutives a l’evenement pluvieux.

In the framework of climate change, the increase in ocean heat wave frequency is expected to impact marine life. Large-scale positive temperature anomalies already occurred in the northwestern Mediterranean Sea in 1999, 2003 and 2006. These anomalies were associated with mass mortality events of macrobenthic species in coastal areas (0–40 m in depth). The anomalies were particularly severe in 1999 and 2003 when thousands of kilometres of coasts and about 30 species were affected. The aim of this study was to develop a methodology to assess the current risk of mass mortality associated with temperature increase along NW Mediterranean continental coasts. A 3D regional ocean model was used to obtain the temperature conditions for the period 2001–2010, for which the model outputs were validated by comparing them with in situ observations in affected areas. The model was globally satisfactory, although extremes were underestimated and required correction. Combined with information on the thermo-tolerance of a key species (the red gorgonian P. clavata ) as well as its spatial distribution, the modelled temperature conditions were then used to assess the risk of mass mortality associated with thermal stress for the first time. Most of the known areas of observed mass mortality were found using the model, although the degree of risk in certain areas was underestimated. Using climatic IPCC scenarios, the methodology could be applied to explore the impacts of expected climate change in the NW Mediterranean. This is a key issue for the development of sound management and conservation plans to protect Mediterranean marine biodiversity in the face of climate change.

Modelling of the Bay of Marseille: Impact of the Anthropogenic Supply on the marine coastal ecosystem Christel PINAZO1, Andrea DOGLIOLI1, Vincent FAURE1, Marion FRAYSSE1,2, Ivane PAIRAUD2, Anne PETRENKO1, Benedicte THOUVENIN3, Jacek TRONCZYNSKI4, Romaric VERNEY3, Christophe YOHIA1 1Aix-Marseille Universite; UM110 CNRS IRD, Mediterranean Institute of Oceanography, OSU Institut Pytheas, Station Marine d'Endoume, Ch. de la Batterie des Lions 13007 Marseille 2 Laboratoire Environnement Ressources Provence Azur Corse, IFREMER Mediterranee, Zone portuaire de Bregaillon BP 330, 83507 La Seyne/Mer Cedex 3 Laboratoire Physique Hydrodynamique et Sedimentaire, Departement Dynamiques de l'Environnement Cotier, Centre de Brest BP 7

Terrestrial inputs (natural and anthropogenic) from rivers, the atmosphere and physical processes strongly impact the functioning of coastal pelagic ecosystems. The objective of this study was to develop a tool for the examination of these impacts on the Marseille coastal area, which experiences inputs from the Rhone River and high rates of atmospheric deposition. Therefore, a new 3D coupled physical/biogeochemical model was developed. Two versions of the biogeochemical model were tested, one model considering only the carbon (C) and nitrogen (N) cycles and a second model that also considers the phosphorus (P) cycle. Realistic simulations were performed for a period of 5 years (2007-2011). The model accuracy assessment showed that both versions of the model were able of capturing the seasonal changes and spatial characteristics of the ecosystem. The model also reproduced upwelling events and the intrusion of Rhone River water into the Bay of Marseille well. Those processes appeared to greatly impact this coastal oligotrophic area because they induced strong increases in chlorophyll-a concentrations in the surface layer. The model with the C, N and P cycles better reproduced the chlorophyll-a concentrations at the surface than did the model without the P cycle, especially for the Rhone River water. Nevertheless, the chlorophyll-a concentrations at depth were better represented by the model without the P cycle. Therefore, the complexity of the biogeochemical model introduced errors into the model results, but it also improved model results during specific events. Finally, this study suggested that in coastal oligotrophic areas, improvements in the description and quantification of the hydrodynamics and the terrestrial inputs should be preferred over increasing the complexity of the biogeochemical model.