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The reduction of body size with warming has been proposed as the third universal response to global warming, besides geographical and phenological shifts. Observed body size shifts in ectotherms are mostly attributed to the temperature size rule (TSR) stating that warming speeds up initial growth rate but leads to smaller size when food availability does not limit growth. Nevertheless, climate warming can decrease food availability by modifying biochemical cycles and primary production. Food availability can also influence growth, fecundity and survival and thus potentially modulate the effect of temperature on life history strategies and fitness. However, the interactive effects of temperature and food availability on life history traits have been mostly studied in small invertebrate species where life history traits have been mainly considered in isolation. In contrast, we have limited information on (1) how temperature and food availability jointly influence life history traits in vertebrate predators and (2) how changes in different life history traits combines to influence fitness and population growth. To fill this gap, we investigated under laboratory conditions the independent and interactive effects of temperature (20 or 30 °C) and food availability (restricted or ad libitum) on the growth, fecundity and survival of the medaka fish Oryzias latipes. We next used our empirical estimates of vital rates as input parameters of an Integral Projection model (IPM) to predict how modifications in vital rates translate into generation time and population growth rate (i.e. mean fitness). Our results confirm that warming leads to a higher initial growth rate and lower size leading to crossed growth curves between the two temperatures. Food-restricted fish were smaller than ad libitum fed fish throughout the experiment, leading to nested growth curves. Fish reared at 30 °C matured younger, had smaller size at maturity, had a higher fecundity but had a shorter life span than fish reared at 20 °C. Food restriction increased survival probabilities under both temperature conditions corresponding to a "eat little die old" strategy. According to the IPM, warming reduces generation time and increases mean fitness in comparison to the cold treatments. Food restriction increased generation time and fitness in the cold treatment but had no effect in the warm treatment. Our results highlight the importance of accounting for the interaction between temperature and food availability to understand how body size shifts can affects vital rates and population demography. This is of importance in the context of global warming as resources (e.g., phytoplankton and zooplankton communities in aquatic ecosystems) are predicted to change in size structure and total abundance with increasing temperatures. Interestingly, our results suggest that food restriction has a weaker effect on fish mean fitness under warming.

The reduction of body size with warming has been proposed as the third universal response to global warming, besides geographical and phenological shifts. Observed body size shifts in ectotherms are mostly attributed to the temperature size rule (TSR) stating that warming speeds up initial growth rate but leads to smaller adult size when food availability does not limit growth. Nevertheless, climate warming can decrease food availability by modifying biochemical cycles and primary production. The interactive effects of temperature and food availability on life history traits have been studied in small invertebrate species, but we have limited information on how temperature and food availability jointly influence life history traits in vertebrate predators, despite the observation that TS responses are amplified in larger species. Food availability can also influence growth, fecundity and survival and thus potentially modulate the effect of temperature on life history strategies. In this paper, we filled this gap by investigating under laboratory conditions the independent and interactive effects of temperature (20 or 30 °C) and food availability (restricted or ad libitum) on the growth, fecundity and survival of the medaka fish Oryzias latipes. Our results confirm that warming leads to a higher initial growth rate and lower adult size leading to crossed growth curves between the two temperatures. Food-restricted fish were smaller than ad libitum fed fish throughout the experiment, leading to nested growth curves. In addition, food restriction appears to amplify TSR by decreasing initial growth rate in the cold treatment. Fish reared at 30 °C matured younger, had smaller size at maturity, had a higher fecundity but had a shorter life span than fish reared at 20 °C, suggesting a "live fast die young" strategy under warming. Food restriction increased the survival probability under both temperature conditions corresponding to a "eat little die old" strategy. Finally, food restriction appeared to be advantageous as food restriction largely increased survival while have a weaker negative effect on growth and fecundity and no impact on age and size at maturity. Our results highlight the importance of accounting for the interaction between temperature and food availability to understand body size shifts. This is of importance in the context of global warming as resources (e.g., phytoplankton and zooplankton communities in aquatic ecosystems) are predicted to change in size structure and total abundance with increasing temperatures. Furthermore, we highlight the importance of considering ontogeny when investigating the effects of temperature-induced body size shifts on trophic interactions and community dynamics since thermal effects depend on the life stage of the organisms.

The reduction of body size with warming has been proposed as the third universal response to global warming, besides geographical and phenological shifts. Observed body size shifts in ectotherms are mostly attributed to the temperature size rule (TSR) stating that warming speeds up initial growth rate but leads to smaller adult size when resource availability is not limiting growth. Nevertheless, climate warming can decrease resource availability by modifying biochemical cycles and primary production and it remains unclear if, and how, the TSR pattern holds under resource restriction. Resource availability can also influence growth and survival and thus potentially modulate the effect of temperature on the growth survival trade-off, although this remains untested. In this paper, we filled this gap by investigating under laboratory conditions the independent and interactive effects of temperature (20 or 30 °C) and resource availability (restricted or ad libitum) on the growth and survival of the medaka fish Oryzias latipes. Our results confirm that warming leads to a higher initial growth rate and lower adult size leading to crossed growth curves between the two temperatures. Resource restriction modulated this temperature effect, particularly by decreasing initial growth rate at 20 °C. Restricted fish were smaller than ad libitum fed fish throughout the experiment leading to nested growth curves. Resource restriction appears to amplify TSR by decreasing initial growth rate in the cold treatment and shrinking adult size in the warm treatment. The survival probability of fish was lower at 30 °C compared to 20 °C suggesting a "live fast die young" strategy where accelerated growth trades of with increased mortality. Resource restriction increased the survival probability under both temperature conditions corresponding to a "eat little die old" strategy when resource restriction decreases growth but increases longevity. Our results highlight the importance of accounting for the interaction between temperature and resource availability to understand body size shifts. This is of importance in the context of global warming as resources (e.g., phytoplankton and zooplankton communities in aquatic ecosystems) are predicted to change in size structure and total abundance with increasing temperatures. Furthermore, we highlight the importance of considering ontogeny when investigating the effects of temperature-induced body size shifts on trophic interactions and community dynamics since thermal effects depend on the life stage of the organisms.

Initialement, l’étude des courbes de croissance en fonction de facteurs biotiques et abiotiques devait être réalisée sur des espèces piscicoles et zooplanctoniques. Les données concernant les poissons permettaient d’ajuster ces courbes de croissance soit à différentes conditions d’élevage (medaka en expérimental) soit à différentes cohortes (corégone in situ). En revanche, les données disponibles concernant les espèces zooplanctoniques ne permettaient pas d’obtenir une taille à un stade donné de l’ontogenèse, empêchant alors l’ajustement des courbes de croissance à différentes cohortes. En effet, l’échantillonnage réalisé en amont était trop diffus, mélangeant plusieurs générations de daphnies par date de prélèvement. Ainsi, dans cette étude, seul le modèle poisson a été utilisé.Par ailleurs, ce projet a été réalisé dans un contexte exceptionnel en raison de la présence du coronavirus, provoquant un confinement total du 17 mars 2020 au 11 mai 2020. Le télétravail était ensuite privilégié pour limiter au maximum les contacts physiques et la circulation du virus. Ainsi, la totalité de ce projet (analyses des données, interprétations des résultats et rédaction du rapport) a été réalisée à distance, impliquant quelques difficultés de communication entre collaborateurs

Response of a cold water species – the Arctic charr (Salvelinus alpinus) – to climate warming . Séminaire ACCAF "Recherche et Adaptation au Changement Climatique"

International audience; Developing efficient indicators of ecosystem functioning is becoming a priority within the context of increasing anthropogenic pressures and the need to preserve ecosystem services

International audience

Le développement d'indicateurs fonctionnels doit permettre une évaluation des trajectoires écologiques des écosystèmes dans le cadre des changements globaux et de la restauration écologique des milieux aquatiques

[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASARE; International audience; 1. Climate change could be one of the main threats faced by aquatic ecosystems and freshwater biodiversity. Improved understanding, monitoring and forecasting of its effects are thus crucial for researchers, policy makers and biodiversity managers. 2. Here, we provide a review and some meta-analyses of the literature reporting both observed and predicted climate-induced effects on the distribution of freshwater fish. After reviewing three decades of research, we summarise how methods in assessing the effects of climate change have evolved, and whether current knowledge is geographically or taxonomically biased. We conducted multispecies qualitative and quantitative analyses to find out whether the observed responses of freshwater fish to recent changes in climate are consistent with those predicted under future climate scenarios. 3. We highlight the fact that, in recent years, freshwater fish distributions have already been affected by contemporary climate change in ways consistent with anticipated responses under future climate change scenarios: the range of most cold-water species could be reduced or shift to higher altitude or latitude, whereas that of cool- and warm-water species could expand or contract. 4. Most evidence about the effects of climate change is underpinned by the large number of studies devoted to cold-water fish species (mainly salmonids). Our knowledge is still incomplete, however, particularly due to taxonomic and geographic biases. 5. Observed and expected responses are well correlated among families, suggesting that model predictions are supported by empirical evidence. The observed effects are of greater magnitude and show higher variability than the predicted effects, however, indicating that other drivers of changes may be interacting with climate and seriously affecting freshwater fish. 6. Finally, we suggest avenues of research required to address current gaps in what we know about the climate-induced effects on freshwater fish distribution, including (i) the need for more long-term data analyses, (ii) the assessment of climate-induced effects at higher levels of organisation (e.g. assemblages), (iii) methodological improvements (e.g. accounting for uncertainty among projections and species' dispersal abilities, combining both distributional and empirical approaches and including multiple non-climatic stressors) and (iv) systematic confrontation of observed versus predicted effects across multi-species assemblages and at several levels of biological organisation (i.e. populations and assemblages).

1. Climate change could be one of the main threats faced by aquatic ecosystems and freshwater biodiversity. Improved understanding, monitoring and forecasting of its effects are thus crucial for researchers, policy makers and biodiversity managers. 2. Here, we provide a review and some meta-analyses of the literature reporting both observed and predicted climate-induced effects on the distribution of freshwater fish. After reviewing three decades of research, we summarise how methods in assessing the effects of climate change have evolved, and whether current knowledge is geographically or taxonomically biased. We conducted multispecies qualitative and quantitative analyses to find out whether the observed responses of freshwater fish to recent changes in climate are consistent with those predicted under future climate scenarios. 3. We highlight the fact that, in recent years, freshwater fish distributions have already been affected by contemporary climate change in ways consistent with anticipated responses under future climate change scenarios: the range of most cold-water species could be reduced or shift to higher altitude or latitude, whereas that of cool- and warm-water species could expand or contract. 4. Most evidence about the effects of climate change is underpinned by the large number of studies devoted to cold-water fish species (mainly salmonids). Our knowledge is still incomplete, however, particularly due to taxonomic and geographic biases. 5. Observed and expected responses are well correlated among families, suggesting that model predictions are supported by empirical evidence. The observed effects are of greater magnitude and show higher variability than the predicted effects, however, indicating that other drivers of changes may be interacting with climate and seriously affecting freshwater fish. 6. Finally, we suggest avenues of research required to address current gaps in what we know about the climate-induced effects on freshwater fish distribution, including (i) the need for more long-term data analyses, (ii) the assessment of climate-induced effects at higher levels of organisation (e.g. assemblages), (iii) methodological improvements (e.g. accounting for uncertainty among projections and species’ dispersal abilities, combining both distributional and empirical approaches and including multiple non-climatic stressors) and (iv) systematic confrontation of observed versus predicted effects across multi-species assemblages and at several levels of biological organisation (i.e. populations and assemblages).

This report presents the specifications followed during the test phase to test the feasibility of a network of thermal measurements in water level nationally. This document is intended as a support for the realization of fountain solution temperature recorders (protocol, assembly, cost ...). In the second part, the conceptual diagram of the pre-processing of data is exposed: storage of raw data archiving in a specific database. In addition, a graph of raw data collected on Lake Sainte Croix (04/83) is presented. The last section focuses on exposing potential prospects this testing phase to a short-term maturity (balance equipment, interval adjustment measures and the position of the probes along the moorings, launch the network on a large scale).; Ce rapport présente le cahier des charges suivi lors de la phase de test de la faisabilité d’un réseau de mesures thermiques en plan d’eau à l’échelle nationale. Ce document est dans sa première partie un support technique pour la réalisation de solutions de mouillage d’enregistreurs de température (protocole, montage, coût…). Dans une seconde partie, le schéma conceptuel du pré-traitement des données est exposé : du stockage des données brutes à l’archivage dans une base spécifique. De plus, un graphique des premières données recueillies sur le lac de Sainte Croix (04/83) y est présenté. La dernière partie expose des propositions de perspectives à cette phase de test à une échéance à court terme (bilan du matériel, ajustement des intervalles de mesures et de la position des sondes le long des mouillages, lancement du réseau à large échelle).

A family of empirically based ecological 'rules', collectively known as temperature-size rules, predicts larger body size in colder environments. This prediction is based on studies demonstrating that a wide range of ectotherms show increased body size, cell size or genome size in low-temperature habitats, or that individuals raised at low temperature become larger than conspecifics raised at higher temperature. There is thus a potential for reduction in size with global warming, affecting all levels from cell volume to body size, community composition and food webs. Increased body size may be obtained either by increasing the size or number of cells. Processes leading to changed cell size are of great interest from an ecological, physiological and evolutionary perspective. Cell size scales with fundamental properties such as genome size, growth rate, protein synthesis rates and metabolic activity, although the causal directions of these correlations are not clear. Changes in genome size will thus, in many cases, not only affect cell or body size, but also life-cycle strategies. Symmetrically, evolutionary drivers of life-history strategies may impact growth rate and thus cell size, genome size and metabolic rates. Although this goes to the core of many ecological processes, it is hard to move from correlations to causations. To the extent that temperature-driven changes in genome size result in significant differences among populations in body size, allometry or life-cycle events such as mating season, it could serve as a fast route to speciation. We offer here a novel perspective on the temperature-size rules from a 'bottom-up' perspective: how temperature may induce changes in genome size, and thus implicitly in cell size and body size of metazoans. Alternatively: how temperature-driven enlargement of cells also dictates genome-size expansion to maintain the genome-size to cell-volume ratio. We then discuss the different evolutionary drivers in aquatic versus terrestrial systems, and whether it is possible to arrive at a unifying theory that also may serve as a predictive tool related to temperature changes. This, we believe, will offer an updated review of a basic concept in ecology, and novel perspectives on the basic biological responses to temperature changes from a genomic perspective.

Aquatic ecosystems undergo various local or regional anthropogenic pressures that managers try to understand and to mitigate their consequences. Nowadays these local and regional pressures interact with climate change. To better manage these interactions, managers should be familiar with the thermal behaviour of aquatic ecosystems. For lakes, Onema wants to set up a perennial temperature monitoring network for national water bodies as it is being done for rivers. However, all French lakes cannot be surveyed. As a consequence, lake subsampling, reflecting the national diversity of thermal behaviour (and especially the intensity and the frequency of the mixing events), has to be defined. Since temperature of a large amount of lakes have never been measured, it is necessary to estimate first the thermal behaviour diversity of all lakes. To do this, we used in this study the Lewis typology of mixing behaviour which is based on thermal characteristics of the water column of lakes. However, all lakes in France were not thermally monitored continuously and therefore, for some of them, no information on their thermodynamic function is available. This lack of temperature data imposes to use empirical models in order to estimate their thermal behaviour from morphometric and climate data. These empirical models are based on classical environmental variables such as maximum depth, surface area or air temperature, and allow the estimation of several physical variables necessary to classify water bodies according to the Lewis scheme. The relevance of using specific empirical models was verified using the few actual data available. Finally, a lake classification according to the Lewis typology is proposed.; Les écosystèmes aquatiques sont soumis à diverses pressions anthropiques locales ou régionales dont les gestionnaires essayent de comprendre les conséquences pour mieux les contrôler. De nos jours, ces pressions interagissent avec la pression plus globale que représente le changement climatique. Afin de mieux gérer ces interactions, il convient de bien connaître les dynamiques thermiques des écosystèmes. Dans ce sens, l’Onema désire mettre en place un réseau pérenne de suivi de la température des plans d’eau nationaux. Tous les plans d’eau ne pouvant pas être équipés, il convient de sélectionner un sous-échantillon de plans d’eau représentatif de la diversité des fonctionnements thermiques à travers notamment l'intensité et la fréquence de leur mélange par retournement des lacs français. Un pré-requis nécessaire à ce choix consiste à connaître cette diversité de fonctionnement. Pour ce faire, nous nous sommes basés sur la typologie thermo-mictique proposée par Lewis (1983) qui regroupe les lacs en fonction de leur comportement physique. Couramment utilisée, elle s’applique à des situations très variables géographiquement (altitude/latitude) et morphologiquement (profondeur), et se base sur différentes caractéristiques thermiques des lacs (e.g. existence/absence d’une période de gel). Cependant, tous les lacs de France n’ont pas été thermiquement suivis en continu et donc, pour certains, aucune information sur leur fonctionnement thermodynamique n’est disponible. Ce manque de donnée thermique dans les plans d’eau français nous contraint à recourir à l’utilisation de modèles empiriques pour avoir une connaissance qualitative a priori de leur fonctionnement thermo-mictique. Ces modèles empiriques sont basés sur des variables environnementales classiques (e.g. profondeur maximale, surface, température de l’air…) et permettent d’estimer des critères nécessaires pour classer les plans d’eau selon les grands types de fonctionnement. Le choix des modèles empiriques a été vérifié à l’aide des lacs pour lesquels il existe un suivi, même partiel dans le temps et dans l'espace, de la température. Finalement, un classement des lacs français selon la typologie de Lewis est proposé.

Aquatic ecosystems undergo various local or regional anthropogenic pressures that managers try to understand and to mitigate their consequences. Nowadays these local and regional pressures interact with climate change. To better manage these interactions, managers should be familiar with the thermal behaviour of aquatic ecosystems. For lakes, Onema wants to set up a perennial temperature monitoring network for national water bodies as it is being done for rivers. However, all French lakes cannot be surveyed. As a consequence, lake subsampling, reflecting the national diversity of thermal behaviour (and especially the intensity and the frequency of the mixing events), has to be defined. Since temperature of a large amount of lakes have never been measured, it is necessary to estimate first the thermal behaviour diversity of all lakes. To do this, we used in this study the Lewis typology of mixing behaviour which is based on thermal characteristics of the water column of lakes. However, all lakes in France were not thermally monitored continuously and therefore, for some of them, no information on their thermodynamic function is available. This lack of temperature data imposes to use empirical models in order to estimate their thermal behaviour from morphometric and climate data. These empirical models are based on classical environmental variables such as maximum depth, surface area or air temperature, and allow the estimation of several physical variables necessary to classify water bodies according to the Lewis scheme. The relevance of using specific empirical models was verified using the few actual data available. Finally, a lake classification according to the Lewis typology is proposed.; Les écosystèmes aquatiques sont soumis à diverses pressions anthropiques locales ou régionales dont les gestionnaires essayent de comprendre les conséquences pour mieux les contrôler. De nos jours, ces pressions interagissent avec la pression plus globale que représente le changement climatique. Afin de mieux gérer ces interactions, il convient de bien connaître les dynamiques thermiques des écosystèmes. Dans ce sens, l’Onema désire mettre en place un réseau pérenne de suivi de la température des plans d’eau nationaux. Tous les plans d’eau ne pouvant pas être équipés, il convient de sélectionner un sous-échantillon de plans d’eau représentatif de la diversité des fonctionnements thermiques à travers notamment l'intensité et la fréquence de leur mélange par retournement des lacs français. Un pré-requis nécessaire à ce choix consiste à connaître cette diversité de fonctionnement. Pour ce faire, nous nous sommes basés sur la typologie thermo-mictique proposée par Lewis (1983) qui regroupe les lacs en fonction de leur comportement physique. Couramment utilisée, elle s’applique à des situations très variables géographiquement (altitude/latitude) et morphologiquement (profondeur), et se base sur différentes caractéristiques thermiques des lacs (e.g. existence/absence d’une période de gel). Cependant, tous les lacs de France n’ont pas été thermiquement suivis en continu et donc, pour certains, aucune information sur leur fonctionnement thermodynamique n’est disponible. Ce manque de donnée thermique dans les plans d’eau français nous contraint à recourir à l’utilisation de modèles empiriques pour avoir une connaissance qualitative a priori de leur fonctionnement thermo-mictique. Ces modèles empiriques sont basés sur des variables environnementales classiques (e.g. profondeur maximale, surface, température de l’air…) et permettent d’estimer des critères nécessaires pour classer les plans d’eau selon les grands types de fonctionnement. Le choix des modèles empiriques a été vérifié à l’aide des lacs pour lesquels il existe un suivi, même partiel dans le temps et dans l'espace, de la température. Finalement, un classement des lacs français selon la typologie de Lewis est proposé.

In this paper, we describe the aims and specifications of the setting up of a water temperature monitoring network in French water bodies. We also propose a set of technological solutions to be tested.; Ce document s’intéresse à la faisabilité d’un réseau de suivi thermique en plans d’eau par l’étude des objectifs de suivi et d’un cahier des charges. Il propose également de tester quelques solutions technologiques.

Fish body size is crucial biological trait. Understanding how temperature affects individuals allow us to predict the impact of global warming on ecosystems. This multiple-scale and eco-physiological framework offers news perspectives in order to understand and quantify the ecological consequences of the global warming.

40 espèces de poissons d'eau douce parmi les plus communs ou les plus remarquables.

The mollusc fauna of the Ognon river, one of the main tributaries of the Saône, surveyed for the first time in 1977, was re-sampled in 2007 to assess long-term changes. Overall, the total species richness remained stable during the period (40 vs 39 species) although there was considerable species turnover: 8 disappearances offset by 7 appearances including that of the invasive Corbicula fluminea which accounted for 30.4% of the total number of individuals in 2007. However, we observed radical changes in the structure of mollusc communities between years which mainly occurred in downstream area. The chronology of the changes observed strongly suggest that competition for food following the proliferation of C. fluminea and the 2003 heatwave may be, responsible for the dramatic decline of native bivalves (Unionidae and Sphaeriidae, respectively). Given the magnitude of these changes, a return to a state prior to the disturbance of the malacological structure is hardly conceivable. However, the evolution towards a new relatively stable state is an alternative hypothesis., Les mollusques de l'Ognon, un des principaux affluents de la Saône, inventorié une première fois en 1977 ont été ré-échantillonnés en 2007 afin d'évaluer les changements intervenus. Globalement la richesse spécifique totale est restée stable entre ces années (40 vs 39 species) grâce à un important turnover des espèces : 8 disparitions compensées par 7 apparitions dont celle de Corbicula fluminea qui, en 2007, représente 30,4% du nombre total d'individus. Cependant, entre 1997 et 2007 de profonds changements sont intervenus dans la structure des communautés de mollusques particulièrement dans la partie aval du cours d'eau. La chronologie des changements observés suggère fortement que la compétition pour la nourriture, suite à la prolifération de C. fluminea d'une part et la canicule de 2003 d'autre part, est responsable du dramatique déclin des bivalves autochtones Unionidae et Sphaeriidae, respectivement. Compte tenu de l'ampleur des changements intervenus dans la structure des communautés un retour à l'état antérieur est peu probable. En revanche l'évolution vers un nouvel état relativement stable est envisageable.

Understanding the ecological impacts of climate change is a crucial challenge of the twenty-first century. There is a clear lack of general rules regarding the impacts of global warming on biota. Here, we present a meta-analysis of the effect of climate change on body size of ectothermic aquatic organisms (bacteria, phyto-, zooplankton and fish) from the community to the individual level. Using long term surveys, experimental data and published results, we show a significant increase in the proportion of small-sized species and young age-classes, and a decrease in size-at-age. These results are in accordance with the ecological rules dealing with the temperature-size relationships (i.e. Bergmann's rule, James' rule and Temperature-Size Rule). Nevertheless, the effect of confounding factors are discussed. We especially consider these results within the context of disturbance theory. Our study provides evidence that reduced body size may be the third universal ecological response to global warming in aquatic systems besides the shift of species ranges towards higher altitudes and latitudes and the seasonal shifts in life-cycle events.

International audience

International audience; The main objective of the Water Framework Directive (WFD) is to reach a good ecological status in all rivers and watersheds by 2015. The health of fish communities is considered to be one of the main environmental indicators to evaluate the status of a river. Lessons have been learned from the impacts of the 2003 heat wave, and a working group in hydrobiology and temperature has been created in France. One of the goals is the exploitation of long-term data (> 20 years) from biological monitoring programs set up in the vicinity of all French nuclear power stations. An initial meta-analysis assessing the effect of climate change on stream organisms was presented in 2005. The fish communities in French rivers, subject to various anthropogenic pressures, globally showed long-term changes that have paralleled the progressive rise in water temperature (+0.5 to +1.6 °C over the last ten years), consistent with the predicted effects of climate warming. This study provides evidence that the effects of climate change should not be ignored when analyzing long-term changes in community structures, even in highly disturbed sites. The authors also propose the questions and components for establishing a new research agenda, to make optimum use of the knowledge gained in the 70s and to build up new knowledge.

It is widely accepted that climate change constrains biota. Yet, because of the lack of consistent multisite and multitaxon surveys, few studies have addressed general rules about how climate change impacts on structure and diversity of animal communities. Especially, the relative influence of nonclimatic anthropogenic disturbances on this impact is fairly unknown. Here, we present for the first time a meta-analysis assessing the effect of global warming on stream organisms. Fish communities of large rivers in France undergoing various anthropogenic pressures showed significant increase in proportions of warm-water species and of specific richness during the last 1525 years. Conversely, the equitability decreased, indicating a gradual decrease of the number of dominant species. Finally, the total abundance increased, coupled with rejuvenation and changes in size-structure of the communities. Interestingly, most of these effects were not depressed by the strength of nonclimatic anthropogenic disturbances. Conversely, geographical location of communities and especially closeness of natural barriers to migration could influence their response to climate change. Indeed, increase in the proportion of southern species seemed hindered at sites located close to the southern limit of the European species' geographical ranges. This work provides new evidence that climate change have deep impacts on communities which, by overtaking the effects of nonclimatic anthropogenic disturbances, could be more substantial than previously thought. Overall, our results stress the importance of considering climate change impacts in studies addressing community dynamics, even in disturbed sites.

There is now increasing evidence that climate change strongly influences organisms at the individual, population and community scale. One of the most global patterns observed is a shift of the species' geographical ranges to higher latitude and/or altitude to track the shifiing climate. Thus, ecogeographical rules can be used to forecast the ecological impacts of global warming. One of the most widely studied patterns is the change in body size of animals with latitude. This rule, generally known as the "Bergman's rule", postulates that body size increases with latitude and, as a matter of fact, decreases with temperature. Using a large amount of experimental data and long term surveys, we checked that body sizes decrease with increasing temperature and/or with time (ie due to global warming) in aquatic ecosystem. We showed such pattern in bactena, phytoplankton and fish communities due to increase in proportions (in total abundance) of small species with temperature. At the population scale, this pattern was also observed because of a gradua1 increase in proportions of young organisms. Finally, at the individual scale, the decrease in size at age with temperature was not the rule but was observed for some zooplankton and fis6 species in the Baltic Sea. Our results hilighted an interesting mle which could help forecasting the ecological impact of climate change on aquatic ecosystems.

Pour répondre à la Directive cadre européenne sur l'Eau, il est nécessaire de définir les conditions de référence pour tous les éléments de qualité biologique. Les outils d'évaluation de l'état écologique des plans d'eau sont en cours de développement. Par conséquent cette étude porte uniquement sur la définition des conditions de référence pour le paramètre chlorophylle-a qui représente un estimateur de la biomasse de phytoplancton. A partir des données acquises sur les lacs naturels de référence, un modèle de prédiction de la concentration en chlorophylle-a est construit : la profondeur moyenne est identifiée comme variable explicative. Pour la déclinaison par type national de plan d'eau, la médiane des profondeurs moyennes est injectée dans le modèle dans le but de fournir une valeur de référence. Les résultats obtenus semblent cohérents, notamment en regard des conclusions des travaux européens. Outre ces résultats concernant la chlorophylle-a, ce document expose les bases d'une démarche générale pour la définition des conditions de référence, applicable à tous les éléments de qualité biologique.

Ce rapport compte 4 lots regroupant une synthèse de données thermiques, physico-chimiques et biologiques (macroinvertébrés benthiques et poissons) collectées sur le Rhône français. Le résumé indiqué ci-dessous est général pour l'ensemble des travaux réalisés. L'étude thermique globale du Rhône, lancée en 2000 à l'initiative de la DRIRE Rhône-Alpes en partenariat avec la DIREN, l'Agence de l'Eau Rhône Méditerranée et Corse, le Service de la Navigation et EDF a pour objectif de déterminer l'incidence des rejets de chaleur cumulés sur le régime thermique du fleuve et les effets hydrobiologiques qu'ils engendrent. Après une description du régime thermique du Rhône (phase 1), et une évaluation de l'échauffement apporté par les CNPE (Centres Nucléaires de Production d'Electricité) en phase 2, la phase 3 concerne l'impact hydrobiologique de ces échauffements cumulés de l'amont vers l'aval. Dans sa partie française, le Rhône est équipé d'aménagements hydroélectriques et de navigation qui engendrent des conditions hydro-morphologiques très différentes entre des écoulements semi-naturels rapides, des retenues à écoulements plus lents, des canaux, des tronçons court-circuités à débit régulé qu'empruntait le lit original du fleuve. A ces facteurs hydro-morphologiques qui structurent les habitats, se superposent depuis la fin des années 70 des changements dans la qualité chimique de l'eau (réduction de la pollution organique et de certaines pollutions toxiques), et le développement d'espèces exogènes qui influent sur la structure biologique et le fonctionnement de l'écosystème rhodanien. Par ailleurs, au cours des trois dernières décennies, le régime thermique du Rhône a été principalement affecté par le changement climatique qui s'est traduit par un échauffement moyen d'environ 1,5°C sur le Haut-Rhône et 3,0°C sur le bas Rhône. Dans cette dérive générale des températures, la part des échauffements cumulés causés par les rejets thermiques des CNPE est estimée à environ 0,5°C sur le haut Rhône et 1,0°C à Aramon sur le bas Rhône (valeurs médianes sur les quinze dernières années). Des traitements statistiques effectués sur les données de la surveillance hydro-écologique à long terme des CNPE indiquent que les modifications constatées sur les peuplements de macro-invertébrés et de poissons s'expliquent en premier lieu par les effets du changement climatique. En réponse à l'élévation de température, une modification générale dans la structure des peuplements de macro-invertébrés et de poissons est observée sur le haut Rhône au cours des 25 dernières années et particulièrement au cours de la dernière décennie: les espèces thermophiles et lénitophiles sont favorisées alors que les espèces sténothermes d'eau froide et rhéophiles montrent une tendance à la régression. Ces évolutions sont plus nettement visibles aux stations à l'aval proche du CNPE de Bugey qui sont exposées en permanence à des échauffements plus élevés (environ + 5°C et + 9°C) que ceux réalisés après mélange du rejet du CNPE. Sur le bas Rhône, où les peuplements étaient déjà dominés par des taxons thermophiles et lénitophiles, cette dérive est également observée mais elle est moins marquée. Dans les tronçons court-circuités et les annexes hydrauliques, le régime thermique est en grande partie indépendant de la température du Rhône en période estivale; dans les conditions actuelles ces milieux à haute valeur écologique ne sont pas affectés par les rejets thermiques des CNPE. Enfin, quelques recommandations sont formulées. Elles portent sur des ajustements des programmes de surveillance hydro-écologique des CNPE et du programme de surveillance renforcé en cas de crise climatique ainsi que sur des actions de recherche. Dans ce domaine, il est préconisé de développer des modèles hydrodynamiques d'habitat sur les secteurs à fort enjeu écologique couplant les conditions hydrologiques et thermiques.