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International audience; Intertidal marshes and mudflats of estuaries support a wide range of ecological functions and ecosystem services, including provision of food and refuge to nekton organisms. Habitat destruction, in particular reduction of intertidal areas, is one of the main anthropogenic causes of the erosion of biodiversity in coastal and estuarine ecosystems. However, although a growing number of tidal restoration projects have been implemented to counteract the loss of intertidal wetlands, few studies have so far described nekton assemblages of restoring sites in Europe. In addition, the attraction of tidally restored sites for nekton has rarely, if ever, been compared with a set of alternative habitats on a whole-estuary scale. This paper aims to describe nekton assemblages and their main abiotic drivers on a range of dyked, restored and natural habitats. Nekton assemblages were sampled during five seasons (2011e2012) in the Gironde estuary (France) among a set of 13 dyked and intertidal habitats including two marshes, tidally restored one and 12 years ago. Nekton assemblage structure and taxonomic composition clearly differentiated tidally restricted marshes from natural intertidal habitats. Nekton assemblages of natural intertidal habitats were shaped by position along the longitudinal gradient (i.e. salinity gradient) of the estuary, with a steep change in assemblage composition around a salinity of 10. The two tidally restored marshes were highly similar to natural intertidal habitats and greatly departed from tidally restricted marshes. A slower rate of community change was observed in a post-breach ponding area of the 1-year-old restored marsh. The study shows some original features of the restored marshes, including high occurrence and biomass of the limno-benthofagous Liza ramada. Furthermore, based on our feedback from the Gironde estuary, storm-breach tide restoration proved to be a valuable means to control the exotic freshwater species that thrived in dyked marshes.

[Departement_IRSTEA]Eaux [ADD1_IRSTEA]Dynamique et fonctionnement des écosystèmes; International audience; Functional trait theory provides a mechanistic framework to understand change in community composition and community assembly through time and space. Despite this, trait-based approaches have seldom been used in ecological restoration. Succession theory predicts that habitat complexity and resource availability will increase with restoration time, leading to increased functional dissimilarity among coexisting species. However, in the case of tidal marsh restoration, it is not clear whether reestablishing the harsh abiotic conditions typical of estuaries will initiate successional trajectories. We investigated monotonic changes in the functional structure of fish communities and shifts in assembly mechanisms, with tidal restoration time. A five-level gradient of 'intertidal habitat naturalness' was constructed from a set of artificialized (dyked), restored (with different ages) and natural intertidal sites, and used as a surrogate for restoration progress. The fish ecophases were described using ten functional traits related to food acquisition and swimming ability. The trends in six functional dimensions (identity, richness, evenness, dispersion, originality and specialization) were investigated along the naturalness gradient. Consistenly with succession theory, functional specialization, dispersion and, less markedly, richness increased with intertidal naturalness meaning that restored and natural intertidal habitats supplied fish with specific foraging and dwelling conditions absent from dyked marshes. Community assembly patterns varied with respect to traits and differed at both ends of the naturalness gradient. Dyked marshes were more affected by trait convergence possibly due to limiting resources. Environmental filtering was detected all along the naturalness gradient although the traits affected varied depending on the naturalness level of habitats. Environmental filtering tended to decrease in restored and natural intertidal habitats. Increased naturalness restored the attractivity of benthic habitats as feeding or settling grounds, promoted shelter-seeking vs. free-swimming strategists and favoured ecophases with carnivorous diets, feeding on microinvertebrates and benthic low-mobility macroinvertebrates. Approaches based on functional trait diversity have the potential to question and refine the theoretical frame of ecological restoration and to assist managers in their efforts to restore tidal wetlands.

International audience; Although land management policies have improved the overall control of rivers, they have also resulted in considerable disturbance and deterioration in a range of different environments. New approaches to the restoration of wetlands are now being tried in south-western France, on the Garonne River and in the Gironde estuary. Such changes primarily involve allowing storm-induced flooding of marshlands (depolderisation). Further upstream, in the mid-Garonne-Toulouse region, consideration is currently being given to restoring areas of standing water or creating flood expansion zones. Our article uses a multidisciplinary approach to analyze the emergence of this new paradigm from a geo-historical, geochemical, ecological and sociological perspective.; Bien que les politiques aménagistes aient permis d’améliorer la maîtrise globale des fleuves, elles ont également généré de nombreuses perturbations et altérations. Aujourd’hui, la restauration des cours d’eau fait l’objet de nouvelles expérimentations. Dans le sud-ouest de la France, sur le fleuve Garonne et dans l’estuaire de la Gironde, elles se traduisent notamment par des remises en eau des marais, liées au passage de tempêtes (dynamique de dépoldérisation). Plus en amont, dans la moyenne Garonne toulousaine, les réflexions en cours concernent la réouverture de bras morts ou la création de zones d’expansion de crues. Nous proposons d’examiner l’émergence de ce nouveau paradigme, dans une perspective pluridisciplinaire, par une évaluation géohistorique, géochimique, écologique et sociologique.

Bien que les politiques aménagistes aient permis d’améliorer la maîtrise globale des fleuves, elles ont également généré de nombreuses perturbations et altérations. Aujourd’hui, la restauration des cours d’eau fait l’objet de nouvelles expérimentations. Dans le sud-ouest de la France, sur le fleuve Garonne et dans l’estuaire de la Gironde, elles se traduisent notamment par des remises en eau des marais, liées au passage de tempêtes (dynamique de dépoldérisation). Plus en amont, dans la moyenne Garonne toulousaine, les réflexions en cours concernent la réouverture de bras morts ou la création de zones d’expansion de crues. Nous proposons d’examiner l’émergence de ce nouveau paradigme, dans une perspective pluridisciplinaire, par une évaluation géohistorique, géochimique, écologique et sociologique., Although land management policies have improved the overall control of rivers, they have also resulted in considerable disturbance and deterioration in a range of different environments. New approaches to the restoration of wetlands are now being tried in south-western France, on the Garonne River and in the Gironde estuary. Such changes primarily involve allowing storm-induced flooding of marshlands (depolderisation). Further upstream, in the mid-Garonne-Toulouse region, consideration is currently being given to restoring areas of standing water or creating flood expansion zones. Our article uses a multidisciplinary approach to analyze the emergence of this new paradigm from a geo-historical, geochemical, ecological and sociological perspective., Si las políticas de planificación han permitido mejorar el control global de los ríos, también han generado numerosas perturbaciones y alteraciones. Hoy en día, la restauración de los cursos de agua es objeto de nuevas experimentaciones. En el Sud-oeste de Francia, sobre el rio Garona y el estuario de la Gironda, tales experimentaciones consisten en el restablecimiento en agua de pantanos inherentes al paso de tempestades (dinámica de dépolderización). Rio arriba, en Garona tolosana media, las reflexiones actuales conciernen la reapertura de meandros abandonados o la creación de zonas de expansión de crecidas. Nos proponemos cuestionar la emergencia de ese nuevo paradigma, en una perspectiva pluridisciplinaria, a través de una evaluación geohistórica, geoquímica, ecológica y sociológica.