A Bayesian framework to objectively combine metrics when developing stressor specific multimetric indicator

In the context of the European Water Framework Directive (WFD), monitoring programs and related indicators have been developed to assess anthropogenic impacts on various components of aquatic ecosystems. While great precautions are usually taken when selecting and calculating relevant core metrics, little attention is generally paid to the generation of the multimetric indicator, i.e. the combination of the different core metrics. Indeed, most multimetric indicators are generated by simply averaging or summing metrics, without taking into account their sensitivity and their variability. Moreover, few indicators provide a rigorous estimate of the uncertainty of the assessments, while this estimation is essential for managers. In this context, we developed a Bayesian framework to build multimetric indicators aiming at improving those two weaknesses. This framework is based on two phases. First, pressure-impact statistical models are developed to quantify the impact of pressure on various fish metrics. Then the Bayesian theorem is applied to estimate probabilities of being at a certain anthropogenic pressure level from fish observation and pressure-impact models outputs. The Bayesian theorem allows to combine objectively the different core metrics, taking into account their sensitivity and their variability, and to provide rigorous uncertainty quantification, which is especially valuable in the WFD context. The method is applied as illustrative example on transitional French water bodies to demonstrate its relevance, especially in the Water Framework Directive context though the method is generic enough to be applied in various contexts

Des détritus à l'homme : diversité et stabilité d'un réseau trophique estuarien

International audienceEstuarine areas provide highly valuable ecosystem benefits for human populations despite being particularly exposed to demographic, economic and ecological pressures. Hence, an understanding of the structure and function of estuarine ecosystems is essential for understanding the persistence and stability of these ecosystems and their response to perturbations. This paper synthesises available data and knowledge about the Gironde estuary (SW France) in a mass-balance trophic model to illustrate potential key patterns in the functioning of the estuarine ecosystem and key elements of its stability. In order to evaluate the total direct and indirect impact on the whole community of the two main sources of anthropogenic perturbations in the estuarine area, mortalities induced by fishing and the Blayais nuclear power plant were included in the model. The results suggest that in the Gironde, a typical heterotrophic estuary, there is an asymmetrical flow between distinct and complementary energy channels that enhances the stability of the food web. This dynamic process is illustrated by differential trophic flows in the water column according to the seasons. The succession of the species in the environment indicates an optimisation of the use of the available carbon resources over one typical year by the estuarine biological communities. Finally, it seems that an increase of human impacts could significantly affect the topology and functioning of the food web by impacting stabilizing elements of the network and decreasing the diversity of trophic flows that insures resilience of the trophic structure

Réserve Naturelle Nationale des prés salés d'Arès et de Lège-Cap Ferret (33) : connaissance et suivi des peuplements benthiques, supra-benthiques, ichtyologiques et des fonctions écologiques du compartiment tidal (programme de recherche Biamar 2012)

National audienceLes objectifs de cette étude étaient : • Le développement et l’expérimentation de méthodes réplicables pour l’étude du «couple» benthos/poissons, dans une optique à la fois de connaissance, de suivi et de gestion/conservation • La caractérisation des peuplements étudiés, en termes de richesses spécifiques, d’abondances relatives et de biomasses • L’étude de la dynamique spatio-temporelle (habitats/saisons) des peuplements étudiés • L’identification et la caractérisation des fonctions écologiques jouées par ces marais maritimes pour les poissons amphihalins

Assimilation of Allochthonous Matter by Estuarine Consumers During the 2015 El Niño Event

International audienceThe El Niño phenomenon refers to a warming of the tropical Pacific basin whose meteorological effects influence the dynamics of aquatic ecosystems around the world. Prior studies have shown that strong El Niño events are highly correlated with high rainfall episodes and high freshwater discharge into subtropical estuaries, with subsequent changes in species composition, abundance, and diversity of their biota. In this work, we evaluated the hypothesis that riverine allochthonous matter associated with the strong 2015 El Niño event is assimilated by decapod crustaceans and fishes of a southwestern Atlantic estuary. We analyzed carbon (δ13C) and nitrogen (δ15N) stable isotope ratios of primary food sources and consumers in the estuary and of riverine allochthonous matter. Our findings revealed that higher water surplus and lower salinity associated with the 2015 El Niño coincided with an increase in the number of freshwater fish species and a decrease in the number of marine- and estuarine-dependent fishes inside the estuary. In addition, most estuarine consumers had lower average δ13C values during the wet period associated with the 2015 El Niño. This seemed to reflect the assimilation of 13C-depleted riverine matter, which according to Bayesian isotope mixing models ranged from 11% (adult resident decapod crustaceans) to 60% (adult resident fishes) during the wet season. Further studies are needed to evaluate the role of El Niño events on structuring food web organization in estuaries under the influence of this climatic phenomenon, which may become more frequent and intense in a global warming scenario

Analyse comparative de l'ecologie trophique des juveniles de poissons plats dans differents systemes hydrologiques cotiers

Les sources de matières organiques, à la base des réseaux trophiques des juvéniles de poissons plats, diffèrent selon le système hydrique considéré. Au sein des nourriceries estuariennes, le réseau trophique repose principalement sur la matière organique particulaire d'origine terrigène. En revanche, dans les zones non estuariennes et notamment les baies, les sources de matière organique sont peu connues. La baie du Mont-Saint-Michel (BMSM), importante nourricerie de la Manche ouest pour les juvéniles de sole et de plie, se distingue des autres nourriceries côtières par ses apports en eau douce limités. Des analyses ont montré le rôle prépondérant joué par le microphytobenthos, à la base du réseau trophique de cette nourricerie. Les isotopes stables du carbone et de l'azote ont été utilisés pour comparer la ligne basale de huit nourriceries ouest européennes de sole afin d'analyser les contrastes dans les sources de matière organiques des juvéniles de sole. Le modèle de mélange SIAR a été utilisé afin de quantifier les contributions de toutes les sources trophiques potentielles au sein de chaque écosystème et d'effectuer une analyse de sensibilité de l'impact des facteurs d'enrichissement trophique sur les sorties du modèle. Alors que dans les estuaires, des études antérieures ont démontré la dépendance des juvéniles vis-à-vis de la matière organique d'origine terrigène, la présente étude souligne que, dans le cas de nourriceries non estuariennes, la production primaire locale peut être prépondérante. En outre, le rôle important joué par la production primaire locale dans les estuaires, en complément des apports fluviaux, a été mis en avant

Sources of organic matter for flatfish juveniles in coastal and estuarine nursery grounds: A meta-analysis for the common sole (Solea solea) in contrasted systems of Western Europe

Document Type : Proceedings Paper Conference Date : NOV 05-11, 2011 Conference Location : Ijmuiden, NETHERLANDSShallow and productive areas provide the high food supply that allows maximizing juvenile growth and survival in most flatfish species. However, the main organic matter sources at the basis of benthic food webs might differ drastically between estuarine nursery grounds under strong freshwater influences, where food webs are mainly supported by continental organic matter, and coastal ecosystems under limited freshwater influence, where the local marine primary production is the main source of carbon for the benthos. To better understand the links between continental inputs to the coastal zone and stock maintenance in the highly prized common sole, Solea solea (L.), we investigated the variability in the organic matter sources supporting the growth of its young-of-the-year (YoY) in five contrasted estuarine and coastal nursery grounds under varying freshwater influence. Stable isotopes of carbon and nitrogen allowed tracing the origin of the organic matter exploited by YoY soles in the very first months following their benthic settlement, i.e. when most of the juvenile mortality occurs in the species. A mixing model was run to unravel and quantify the contribution of all major potential sources of organic matter to sole food webs, with a sensitivity analysis allowing assessment of the impact of various trophic enrichment factors on model outputs. Thismeta-analysis demonstrated a relative robustness of the estimation of the respective contributions of the various organic matter sources. At the nursery scale, the upstream increase in freshwater organic matter exploitation by YoY soles and its positive correlation with inter-annual variations in the river flow confirmed previous conclusions about the importance of organic matter from continental origin for juvenile production. However, inter-site differences in the organic matter sources exploited for growth showed that, although freshwater organic matter use is significant in all nursery sites, it is never dominant, with especially high contributions of local primary production by microphytobenthos or saltmarsh macrophytes to juvenile sole growth in tidal nursery ecosystems. These patterns stress the need for maintaining both the intensity of freshwater inputs to the coastal zone and of local autochthonous primary production (especially that of the intertidal microphytobenthos) to preserve the nursery function of coastal and estuarine ecosystems