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

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

Une méthode d'intercalibration des indicateurs poissons de la Directive Européenne sur l'Eau, basé sur l'utilisation d'un indice commun de pression anthropique

International audienceMost of the EU member states along the Northeast Atlantic coastline have developed different fish-based indices to assess the ecological status of transitional waters due to the Water Framework Directive. To be valid, each method should show a good correlation with a gradient of human pressures. In order to define a comparable view of what should be “good ecological status”, we performed an intercalibration of seven fish-based indices according to a common pressure index. Anthropogenic pressures were assessed by expert knowledge and best available pressure data. Nearly 170 estuaries from Portugal to Germany and Northern Ireland, where fish data existed, were qualified with 15 candidate pressure indicators. Only the indicators that showed a good regression to the biological assessment were selected. A set of 8 indicators assessing habitat degradation, contamination and dissolved oxygen composed the final common pressure index. The biological response is expressed as an Ecological Quality Ratio (EQR: score ranging between 0 and 1) divided into five quality classes. However, the seven methods differ regarding the boundary setting between these classes. Linear regressions were used to show the correlation between the common pressure index and the EQR obtained for each estuary. All the seven fish-based indices displayed a significant pressure-response relationship. A harmonisation band for the class boundaries was defined using the bias to the median value for all methods obtained on the common pressure index scale. A multi-rater Kappa analysis controlled the agreements between all methods in the attribution of a quality class. All methods showed significant trend in EQR values decrease with an increasing pressure value. All methods were able to discriminate between good or better and moderate or worst status. This intercalibration process enabled the comparison of EQR values despite very different ecological assessment strategies, monitoring regime and type of estuary