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Engineer species, such as gorgonians, provide several ecosystem services and play a significant role in the maintenance of biodiversity, which is why it is important to identify optimal strategies for their conservation. We aimed to test an ecological niche modelling approach in the marine shallow environment and identify the ecological niche of various species of gorgonians in order to lay the scientific foundation for future conservation actions. We analyzed a unique dataset of spatialized inventories on a regular grid (< 800 m) along 450 km of coastline of five gorgonian species commonly found in the Mediterranean shallow habitats (10-50 m deep). We replicated data collection in 2013 and 2020. Fourteen environmental predictors derived from the most advanced geomorphological and hydrological data were tested to assess the ecological niche of the five species using maximum entropy (MaxENT). We tested the sensitivity of the model fit to sampling bias by reducing the number of occurrences and their geographic extent. Our results showed that there was a difference in the spatial distribution of the five gorgonian species in the Gulf of Lion: Eunicella singularis and Leptogorgia sarmentosa were widely distributed while the occurrence of Paramuricea clavata, Corallium rubrum and Eunicella cavolini was limited. The model confirmed that depth, rugosity, slope, sea surface temperature, current and turbidity can be significant drivers for gorgonians distribution, but in different associations, enabling one to differentiate the niche of four of the five species. Moreover, the model did not always identify the species specific drivers suggested in previous studies. Despite the model identifying a similar niche for E. singularis and E. cavolini (based on the environmental predictors tested), the two species, in fact, displayed very different spatial distributions in the area. For all the species, except E. cavolini, the predicted suitable habitat distribution from our model matched the observed spatial distribution. The reduction of the number of presence observations did not alter the quality of the ecological niche models as long as the observation points were spread over the entire variability range of predictors. The latter can be achieved by only including presence observations from highly protected zones of the marine protected areas of the region. Our results provide a greater understanding of the factors shaping the distribution of five gorgonian species commonly found in Mediterranean shallow areas. This is an essential step in the development of spatial planning for marine biodiversity conservation aimed at these key engineering species and their resilience to climate change.

The natural mechanism for sessile species resilience after major population disturbance is larval dispersal during reproduction. Modelling larval dispersal when processes controlling dispersal are accounted for, is a powerful tool to anticipate connectivity patterns among populations. However, simulations performance might be altered considerably by either flow representation in the underlying hydrodynamical simulations or the inclusion of larval traits. Here, we assessed how behaviour, ocean model resolution and temporal variability in the ocean dynamics influence connectivity patterns among coastal rocky locations, some of them being designated as MPAs. We combined a fine (0.3 km) and coarser (1.5 km) resolution ocean model, with or without the negatively buoyant behaviour of Paramuricea clavata larvae, with different turbulence intensity, in three years and for pelagic larval duration (PLD) ranging from 1 to 28 days. Ocean model resolution was the most influential factor on the resulting connectivity levels. The results were also equally influenced by buoyancy, PLD and temporal variability, in the fine resolution configuration, while turbulence could be neglected. Based on these results, guidelines for coastal biophysical modelling are proposed.

Habitat-forming species sustain biodiversity and ecosystem functioning in harsh environments through the amelioration of physical stress. Nonetheless, their role in shaping patterns of species distribution under future climate scenarios is generally overlooked. Focusing on coastal systems, we assess how habitat-forming species can influence the ability of stress-sensitive species to exhibit plastic responses, adapt to novel environmental conditions, or track suitable climates. Here, we argue that habitat-former populations could be managed as a nature-based solution against climate-driven loss of biodiversity. Drawing from different ecological and biological disciplines, we identify a series of actions to sustain the resilience of marine habitat-forming species to climate change, as well as their effectiveness and reliability in rescuing stress-sensitive species from increasingly adverse environmental conditions.

In shallow environments, common unsteady flows, such as tides, waves or wind-driven currents modulate the diffusive boundary layer thickness that controls the exchange of electron acceptors for mineralization and oxidation processes in surficial sediment. This study demonstrated the ability of an oscillating grid mesocosm to (1) produce homogenous turbulence at the sediment-water interface of multiple sediment cores (between-core variability

International audience; Resuspension of microphytobenthic biomass that builds up during low tide has been acknowledged as amajor driver of the highly productive food web of intertidal mudflats. Yet, little is known about the contributionto pelagic food web of the resuspension of other microorganisms such as viruses, picoeukaryotes,cyanobacteria, bacteria, nanoflagellates, and ciliates, living in biofilms associated with microphytobenthosand surficial sediment. In the present study, a novel approach that involves simultaneous Lagrangian andEulerian surveys enabled to disentangle the effects of resuspension and mixing with offshore waters on thedynamics of water column microorganisms during a rising tide in the presence of waves. Temporal changesin the concentration of microorganisms present in the water column were recorded along a 3 km cross-shoretransect and at a fixed subtidal location. In both surveys, physical and biological processes were separated bycomparing the time-evolution of sedimentary particles and microorganism concentrations. During a risingtide, sediment erosion under wave action occurred over the lower and upper parts of the mudflat, whereerodibility was highest. Although erosion was expected to enrich the water column with the most abundantbenthic microorganisms, such as diatoms, bacteria and viruses, enrichment was only observed fornanoflagellates and ciliates. Grazing probably overwhelmed erosion transfer for diatoms and bacteria,while adsorption on clayed particles may have masked the expected water column enrichment in free virusesdue to resuspension. Ciliate enrichment could not be attributed to resuspension as those organisms wereabsent from the sediment. Wave agitation during the water flow on the mudflat likely dispersed gregariousciliates over the entire water column. During the rising tide, offshore waters imported more autotrophic,mainly cyanobacteria genus Synechococcus sp. than heterotrophic microorganisms, but this import was alsoheavily grazed. Finally, the water column became a less heterotrophic structure in the subtidal part of thesemi-enclosed bay, where mixing with offshore waters occurs (50% decrease), compared to the intertidalmudflat, when resuspension occurs. The present study suggests that this differential evolution resulted predominantlyfrom dilution with offshore waters less rich in heterotrophic microorganisms. Indeed, any inputof microorganisms accompanying physical transfers due to bed erosion or offshore water mixing was immediatelybuffered, probably to the benefit of grazers.

International audience; Repeated use of Cu based fungicides (Bordeaux mixture: Ca(OH)2+CuSO4) to control vine downy hasled to signi!cant increase of Cu in vineyard soils. In Mediterranean catchments, brief and intense flood events can multiply stream discharge by up to 10 and are responsible for important soil leaching and therefore for high "uxes of Cu exported at the outlet of the catchment. In order to assess the origin and fate of Cu measured in the Baillaury catchment (South of France, combined sequential extraction (SCE) and isotopic Cu compositions (δ65Cu) approaches are proposed in this study.

International audience

Un modèle numérique de couche limite oscillante a été développé sur la base de la fermeture turbulente k-w transitionnelle de Wilcox (1992) permettant de décrire des couches limites transitionnelles et turbulentes (programme européen SEDMOC). En modifiant les constantes de diffusion et de transition du modèle de Wilcox et en introduisant une condition de décollement de couche limite sous l'effet d'un gradient de pression adverse, on a pu reproduire avec un bien meilleur accord que le modèle originel de Wilcox des simulations directes (Vittori et Verzicco, 1998) ainsi que les mesures de Jensen et al. (1989) d'écoulement oscillant sur fond plat lisse dans le régime turbulent intermittent (version 1DV, Guizien et al., 2003). Ce modèle décrit également mieux que le modèle originel de Wilcox les grandeurs turbulentes mesurées dans l'interaction houle-courant par Dohmen-Janssen (1999) sur fond plat dans le régime turbulent rugueux (version 1DV, Guizien et al., 2003). En particulier, le modèle reproduit les fluctuations turbulentes lors de la décélération de l'écoulement ainsi que le déphasage des contraintes turbulentes sur la verticale. Ces deux points d'achoppement des modèles jusqu'alors expliquait en partie les difficultés des modèles existants à reproduire correctement les concentrations sédimentaires en présence de sédiment (Davies et al, 1997). Cette fermeture turbulente est également implémentée dans une version 2DHV du modèle qui permet d'étudier l'écoulement sur des fonds présentant des macro-rugosités. Il a été en particulier utilisé dans le cadre du programme européen SANDPIT pour calculer des profils de concentration en présence de formes de fond sédimentaires (ride de sable) et pour investiguer la notion de rugosité hydo-sédimentaire équivalente. La contribution du LOBB dans cette action transversale prévoyait les actions suivantes: - caractériser mathématiquement des rugosités d'origine biogène - modéliser l'hydrodynamisme pour une variété d'interaction houle-courant sur ces rugosités et paramétriser la rugosité macroscopique résultante (question 8) - comparer ces résultats avec ceux d'autres modèles numériques - tester la validité des simulations hydrodynamiques face aux expériences de laboratoire menées dans le cadre de ce projet (exemple des fonds de crépidules) - modélisation de la suspension sédimentaire pour ces mêmes fonds de crépidules pour des distributions granulométriques a) réalistes et b) idéales.