Suchergebnisse

Lake Edward is one of the East African Rift lakes (surface 2325 km2, maximum depth 112 m), is located on the border between the Democratic Republic of Congo (DRC) and Uganda. It is connected to the smaller lake George (surface 250 km2, maximum depth 3m) through Kazinga Channel, and is part of the Nile watershed. On both sides of the border, Lake Edward is bordered by two major natural reserves, the Virunga National Park, Queen Elisabeth National Park. A collapse of the fisheries of Lake Edward was observed from the 1960's to 1980's that matched the reduction of the numbers of hippos observed from the 1960s and 1970s. The reason of this collapse is unknown, nor if fisheries continued to decline until present. The aim of HIPE was to test the causal relationship between the recent environmental changes and the drastic reduction of fisheries productivity. Our working hypothesis was that several environmental pressures in the watershed of Lake Edward have disrupted the biogeochemical, structural and functional links between the terrestrial and aquatic ecosystems, leading to a collapse of the main ecosystem service provided by Lake Edward. The fishing effort has dramatically increased since the 1960s. This in combination with a relaxed enforcement, resulted in an overexploitation of the fish stock and a spread of the use of damaging fishing techniques around the lake. Other potential causes are changes in the hydrological cycle, which could have also modified the transfer of nutrients from the watershed to the lake, and climate variability affecting nutrient cycling and availability in the Great Lakes. Shallow sediment cores from Lake Edward show a shift in stable carbon isotope composition in the upper 10 cm of the core (approximately last 40 yrs) that could be explained by (i) an increase in the delivery of C3-derived organic matter to the lake, and/or (ii) a decrease in phytoplankton productivity, which would increase isotope fractionation in phytoplankton due to alleviation of diffusive CO2 limitation. Museum-archived fish specimens confirm a shift in the baseline δ13C values in the lake, corresponding to a lower productivity or a change in the composition of terrestrial organic matter input to L. Edward over the past century. A range of bivalve shells analyzed for C and O isotope ratios along their growth lines indicate these are excellent tools to differentiate habitats, but this compromises their use as archives for paleo-environmental reconstruction in the area since exact provenance of museum collection specimens is typically not sufficiently well documented. The data from tooth enamel from Hippopotamus canines show a long-term trend towards decreasing δ13C values of the Hippopotamus diet in the region, although showing a high inter-individual variability in δ13C values, most pronounced in more recent specimens, indicating that dietary differences exist on small spatial scales. As Hippopotamus are thought to be rather indiscriminate grazers, this should reflect local differences in relative C3-C4 cover. The oxygen stable isotope data of Hippopotamus were shown to be likely good proxies for their lacustrine versus riverine habitat use. The phytoplankton community in Lake Edward was largely dominated cyanobacteria (60% of the phytoplankton biomass), followed by diatoms (25% of the phytoplankton biomass), and by green algae, chrysophytes and cryptophytes. 248 taxa phytoplankton were identified with clear prevalence of cyanobacteria (104 taxa), from the morphological groups of coccal and filamentous species (non-heterocytous and heterocytous). Compared to historical data from the 1930's it seems a shift in algal diversity (number of species) from diatoms to cyanobacteria. Lack of historical data does not allow to determine if a change in total phytoplankton biomass occurred. The primary production measured in Lake Edward during the three cruises was approximately 4 times lower than the single historical value (June 1960), but values seemed comparable in Lake George compared to those from the 1960's. This is consistent with an overall decrease of present phosphorus loading compared to historical data (1990's). Primary production rates were high, and in excess of community respiration, indicating a net autotrophic status leading to low values of dissolved CO2. Consequently, Lake George and the part of Lake Edward influenced by the outflow from Lake George acted as sinks for atmospheric CO2. This challenges the paradigm that inland waters are systematically sources of atmospheric CO2 that was derived from data mostly collected in boreal and temperate lakes. The sampled sites were in some cases very strong CH4 emitters to the atmosphere, although a very strong spatial variability was observed due to a combination of several factors such as the occurrence of anoxia in bottom waters and productivity, both related to depth (the shallowest systems being the most productive and devoid of bottom anoxia). Most systems were sinks of atmospheric N2O due to denitrification. Data on stable C, N and H isotope composition indicate that aquatic primary production is the dominant energy source at the basis of the foodweb, but the wide variability in consumer stable isotope signatures also indicates that a wider variety of sources is used, with contributions of terrestrial and possibly CH4-derived carbon. The basin of Lake Edward has a fish fauna that is typical for East Africa and consists of two components: a species-rich assemblage of Haplochromis species and a relatively species-poor assemblage of non-Haplochromis species. A total of 34 non-Haplochromis species belonging to 10 families and 21 genera are recorded from the system. These include six species of major importance to the fisheries. Three non-Haplochromis species are endemic to the system and two others have been introduced in the region. Six species are new records for the Lake Edward system. The Haplochromis species diversity was seriously underreported and went from 27 species known to 56, of which 13 new ones have been or are being described. We have currently no indication that species have disappeared from the system in the last few decades, though one catfish species known from historical records, H. longifillis, could not be retrieved during the recent expeditions. Substantial dietary niche overlaps were found between several commercially important fish species, while niche overlaps between Haplochromis species were small, which suggests that they display a high trophic differentiation in accordance with their specialised morphologies. We did not find indications that different stocks exist for the commercial species. However, we found that the populations in the lakes were separated from those inhabiting the rivers. We did find intraspecific differences in morphology and ecology between populations from Lake Edward and Lake George (including the Kazinga Channel) of some Haplochromis species. No signs of large-scale hybridization were found between the two important tilapias. Recent reports on the state of the fisheries of the Lake Edward system remain scarce. Lakes Edward and George are almost completely within protected areas. However, occupied land area, the number of inhabitants and the number of boats has risen substantially during the last decades. Total annual yields have been increasing in the last ten years, but Catch Per Unit Effort (CPUE) appears to be continuously decreasing. Tilapias, which were traditionally dominant in the catches, seem to have crashed in the eighties and their share in the catches keeps decreasing. Recent estimates showed poor stock status for most commercially important species with most stocks defined as either collapsed, recruitment impaired or overfished. Higher catches could be obtained under sustainable management. The immediate target of management should be rebuilding biomass to the biomass at maximum sustainable yield (Bmsy). A survey was conducted at the different landing sites along lakes Edward and George. This revealed that fishers were aware of the changes in the state of the fishery. Fishers attributed declining catches to excessive effort, fishing malpractices, destruction of breeding grounds, and pollution. Communities reported large-scale non-compliance with fisheries regulation, especially at Lake George.

During this study, we focused on the biogeochemical cycles of carbon and nitrogen in two tropical lakes, Lake Kivu and one of its bays, Kabuno Bay, located on the border between the Democratic Republic of the Congo and Rwanda, and a small temperate lake located in a limestone quarry in Belgium (Lake Dendre). Seasonal and inter-annual variations in methane (CH4) and nitrous oxide (N2O) fluxes to the atmosphere in Lake Kivu were calculated based on the concentrations of these two elements measured monthly for almost two consecutive years. These data show that Lake Kivu is a low CH4 emitter throughout the year (mean of 86 µmol m-2 d-1), in proportion to the high levels of CH4 present in its deep waters, and alternates between a source and a sink of N2O. The oxidation of CH4 has been proposed to explain these low emissions to the atmosphere. This study concentrated particularly on the detection of the anaerobic oxidation of CH4 (AOM) within the water column and on the identification of the potential electron acceptors: nitrate (NO3-), nitrite (NO2-), sulfate (SO42-), iron (Fe) and manganese (Mn). Significant levels of AOM, up to 16 and 75 μmol m-2 d-1, were found in the water column of Lake Kivu and Kabuno Bay, respectively, but the identification of the potential electron acceptors is not so obvious. At Kabuno Bay, which is considered as a ferruginous basin, Fe seems to be the most likely electron acceptor, since NO3-, NO2- and Mn concentrations are very low, and the sulfur cycle seems to be not really developed. Despite the high concentrations of SO42- measured in oxic waters (up to 600 μmol L-1), concentrations of sulfide (HS-) remained very low in anoxic waters (<1 μmol L- 1), suggesting a poor occurrence of SO42- reduction. In Lake Kivu, the main electron acceptor is most likely SO42- in view of the high concentrations recorded (up to 225 μmol L-1) compared to the concentrations of the other elements (NO3-: <10 μmol L-1, NO2- <1.5 μmol L-1, Mn and Fe total <15 μmol L-1), and high HS- concentrations (up to 120 µmol L-1 at 80 m depth) suggesting the occurrence of significant SO42- reduction. However, some vertical profiles observed in the rainy season, which showed that AOM levels were higher in the NO3- accumulation zone, suggest that NO3- could be an electron acceptor for AOM, but at a low extent. NO3- concentrations were mostly too low to explain the AOM rates observed, and competition with other processes is most likely too high. Indeed, during this study, we also highlighted the occurrence of denitrification, the dissimilatory reduction of NO3- to ammonium (NH4+) (DNRA) and the anaerobic oxidation of NH4+ (Anammox), which compete for substrates. Finally, since Lake Dendre shares some characteristics with Lake Kivu (ie mainly they are both meromictic and have high CH4 concentrations in their anoxic waters), we also measured CH4 oxidation within the water column and put in evidence AOM rates up to 14 μmol L-1 d-1. Despite these high oxidation rates, Lake Dendre was a large emitter of CH4 for the atmosphere. SO42- was likely the primary electron acceptor, but high concentrations of NO3- (up to 80 μmol L-1) suggest that they could also be used for AOM, since AOM coupled to denitrification is thermodynamically much more favorable than the AOM coupled to the reduction of SO42-.

The Meuse is an international river that has been used by man for centuries and it is still the main source of drinking water for large cities in Belgium and the Netherlands. In fact, water quantity and quality have been a major issue between the various riparian countries and political regions. Many kinds of data have been generated in the past decades on various aspects of the river: (a) hydrology for the need of predicting and controlling floods; (b) water chemistry in the context of water pollution assessment and control; and (c) biology and ecology for water quality assessment and studies on aquatic biodiversity community dynamics and ecosystem function. ; Peer reviewed

La popularisation de l'activité de plongée sous-marine s'est accrue ces dernières années ajoutant une nouvelle dimension aux impacts humains sur les systèmes aquatiques (Spalding et al., 2017). Bien que des impacts au niveau individuel aient été identifiés (Chung et al., 2013, Au et al., 2014), les causes de ces comportements et les réponses à l'échelle de la communauté ichytologique méditérranéenne ne sont pas clairs (Di Franco et al., 2013, Rouanet et al. 2017). La présente étude vise à étudier, durant deux années consécutives (2019 et 2020) (i) la fréquentation du site de plongée de la Revellata (baie de Calvi, Corse, France) grâce à l'intégralité des feuilles de palanquées des structures de plongée locales mais aussi avec la prise de photographies (ii), le comportement des plongeurs grâce à l'observation de leur pratique en plongée, par tranche de 10 minutes, afin de déterminer le nombre de contacts qu'ils ont avec le milieu, le type de contact (volontaire/involontaire) et la partie du corps ou l'instrument concerné et enfin (iii) la composition de la communauté ichtyologique (i.e. richesse spécifique, abondance, structure démographique) grâce à des comptages visuels de poissons réalisés en plongée avant et après l'arrivée des plongeurs sur le site. En complément, une attention particulière a été portée sur l'espèce patrimoniale qu'est le mérou brun (Epinephelus marginatus), en relevant la taille et la réaction des individus observés face aux plongeurs, selon 5 typologies comportementales : « Fuite proche 10 m », « Attraction », « Indifférence » et « Changement de position, observation du plongeur ». Les résultats montrent que le site de plongée suivi est particulièrement fréquenté avec en moyenne 82 plongeurs par jour en saison. Les plongeurs sont peu sensibilisés aux impacts de la plongée et plus de 80 % des plongeurs ont un contact avec le milieu durant leur plongée, avec une moyenne de 9 contacts/10 min. La majorité des contacts involontaires est effectuée par les palmes et le reste des contacts est très diversifié, aussi bien avec le corps qu'avec des équipements (octopus, bloc, manomètre, parachute etc). De plus, le plongeur ayant un appareil photo est plus susceptible d'avoir des contacts volontaires avec le substrat. L'expérience des plongeurs est également un facteur prépondérant et ainsi la gestion de leur flottabilité influe sur les types de contacts observés. Les populations de poissons répondent différemment en fonction de l'espèce concernée. Les corbs (Sciaena umbra) et les mérous bruns (Epinephelus marginatus) semblent être les plus dérangés par la présence de plongeurs. Leurs biomasses diminuent significativement après le passage de plongeurs ce qui traduit une fuite des grands individus ou une volonté de se cacher. En complément, il apparaît que plus les mérous sont gros, plus ils ont tendance à fuir loin. Au contraire, les petits individus sont curieux et sont plus susceptibles de montrer une attraction envers le plongeur. Finalement, il apparaît que la fréquentation des sites de plongée, la sensibilité environnementale et les connaissances du plongeur, sa technicité ainsi que son type de pratique conditionnent son impact sur le milieu marin. La combinaison de suivis complémentaires permet d'avoir une vision d'ensemble des processus en action dans le cadre de cette activité. Ces résultats permettront finalement de proposer des recommandations, d'aider à éclairer la décision publique, notamment pour orienter plus efficacement les politiques de gestion et de conservation.

Samples were collected from 45 sites along the Walloon river network in 2007, in accordance with the Water Framework Directive (WFD, European Union, 2000), used to define the overall ecological status of rivers. Within each collected sample, macrophyte data were gathered at species level and the main water quality parameters were analyzed. This involved the use of two approaches: firstly, methods of ordination and classification (Principal Component Analysis and Multiple Factorial Analysis) and secondly, aquatic macrophyte community indexes. The Macrophyte Biological Index for Rivers (MBIR) was used to define the ecological status of the macrophyte community in response to eutrophication pressure. Four trophic qualities were detected in all the monitored stations: 56% of the sites showed a good trophic quality, with the Ardennes region in the leading position and only 2% of the sites showed a poor trophic quality. A Multiple Factorial Analysis (MFA) made it possible to regroup the species according to their ecological affinities and to specify their indicator values in relation to some abiotic parameters. As a result, a rivers typology was outlined based on this analysis. The dendrogram of the Hierarchical Cluster Analysis (HCA) gave three clusters determined by active variables of each compartment that defined functional parts of the Walloon network: Chiloscyphus polyanthos (L.) Corda, Rhynchostegium riparioides(Hedw.)C.Jens., Fontinalis squamosa(Hedw) and Ranunculus penicillatus (Dum.)Bb. showed an oligotrophic status and low mineralization in the Ardennes (GI), while P. pectinatus(Linne), Cladophora glomerata(Linnaeus)proved to be found more often in eutrophicated waters in the Region limoneuse (GIII). Pellia endvifolia (Dicks.)Dum, Fissidens crassipes(Br.Eur);Cinclidotus riparius (Web. & Mohr.) appeared in the Condroz and Famenne, rivers characterized by a high concentration of nitrogen (N-35. NO3-) (GII).

Pelagic habitats are a policy priority below Descriptor 1 (Biodiversity) of the Marine Strategy Framework Directive (MSFD). They are addressed under the D1C6 criterion, stating "the condition of the habitat type, including its biotic and abiotic structure and its functions…, is not adversely affected due to anthropogenic pressures". The evaluation of pelagic habitats status is challenged by the functional and structural characteristics of pelagic habitat diversity and processes. To date, pelagic habitats assessments are lacking in common criteria and methodologies that characterize the habitat while accounting for the effects of anthropogenic pressures to achieve the Good Environmental Status (GES). It is therefore necessary to prioritise communication between scientific and policy communities and frame pelagic research to agree on common methods and approaches at regional or EU scale. This is key for achieving harmonised and comparable pelagic assessments for the MSFD. This report summarizes the outcomes on the assessment workflow of pelagic habitats of the JRC "MSFD pelagic habitats" workshop (9th and 10th March 2021), and the need for coordinated evaluations of the scientific challenges of policy relevance. Recommendations on the MSFD implementation of D1C6, that were generated from the experts during the workshop, will be communicated to the MSFD policy groups and the EU Member States competent authorities to support future harmonised assessment of pelagic habitats. ; Publications Office of the European Union

In the Mediterranean Sea, the seagrass Posidonia oceanica plays a key ecological role, and is protected by a range of legislation. Standard Posidonia monitoring programmes generally focus on the plant at different spatial and short temporal scales, without considering the organisms dependent on the ecosystem. Passive acoustic monitoring (PAM) has a high potential to non-intrusively monitor biological activities and biodiversity at high temporal resolution, and to assess ecosystem health. This is particularly relevant considering that Posidonia meadows host numerous sound-producing fish species. In this study, bottommoored hydrophones were deployed in nine Western Mediterranean meadows covering a distance of more than 200 km to identify acoustic features potentially relevant to monitor this critical habitat. Among eight identified fish sound categories, we found a single type of sound (that we will refer to as /kwa/) dominating the soundscape of Posidonia meadows over a time span of 7 months. Compared to other low-frequency sounds, the /kwa/ presented unique characteristics that suggest it is produced by a fish via fast contracting muscles. The /kwa/ was the only sound detectable under anthropogenic noise conditions, and little affected by it. Cluster analyses performed on 13 acoustic features revealed a high degree of call diversity. /Kwa/ diversity, combined with its large-scale (all meadows), long-term (7 months) occurrence and low noise interference, make the /kwa/ a promising candidate for PAM of Posidonia meadows. Furthermore, variability in acoustic features suggests a central role of the /kwa/ in communication. Overall, this work sets the basis for establishing the relevance of the /kwa/ in monitoring P. oceanica meadows and developing PAM techniques for this critical habitat. ; Peer reviewed

La gestion collective des équipements de la recherche scientifique, que l'on désigne communément par le terme de « gestion des plates-formes », constitue à la fois un objet de la politique scientifique en sciences de la vie, un domaine de gestion spécifique pour les organismes de recherche et les laboratoires et un lieu d'expérimentation et de coopération avec des équipes de recherche et des concepteurs d'équipements. Comme le notent justement Keating et Cambrosio (2003), les dimensions techniques et politiques sont indissociables dans la notion de plate-forme.L'intérêt des pouvoirs publics et des acteurs de la recherche en génomique pour les plates-formes rejoint les travaux d'histoire et de sociologie des sciences et d'économie qui mettent le rôle déterminant de la question de l'instrumentation dans l'émergence de nouveaux régimes de production des connaissances scientifiques et les conditions permettant d'accroître les rendements économiques et sociaux de la recherche. Gaudillière (Gaudillière, 2000) souligne que le recours accru à l'instrumentation dans les sciences de la vie s'inscrit dans une évolution historique vers de nouvelles logiques instrumentales, recourant de manière très lourde à l'équipement, l'automatisation et aux nouvelles technologies de l'information pour générer, stocker, analyser et représenter de vastes quantités de données. Joerges et Shinn (2001) soulignent le rôle joué par le développement d'une recherche instrumentale - par la création d'une lingua franca - dans l'intégration de champs disciplinaires de plus en plus spécialisés Plusieurs auteurs notent les effets d'une division croissante du travail de recherche qui requiert des compétences spécifiques (Hackett, 2004, Mangematin et Peerbaye, 2005, Arora et Gambardella, 1994)) ou encore l'importance de la localisation géographique de ces équipements, d'une part afin de tirer parti de capacités de recherche distribuées et difficilement transportables, d'autre part, afin de susciter des dynamiques d'innovation et de coopération entre équipes scientifiques. Il faut également noter que l'instrumentation de la génomique ne cadre pas avec les conceptions traditionnelles, héritées des sciences physiques : il s'agit moins ici d'infrastructures uniques, construites sur des sites stratégiquement choisis, que de réseaux d'instruments de taille réduite, dispersés sur le territoire autour de certains pôles locaux de spécialisation, dont le coût n'est pas comparable à celui d'un accélérateur à particules ou d'un synchrotron (Mangematin et Peerbaye, 2005).

La gestion collective des équipements de la recherche scientifique, que l'on désigne communément par le terme de « gestion des plates-formes », constitue à la fois un objet de la politique scientifique en sciences de la vie, un domaine de gestion spécifique pour les organismes de recherche et les laboratoires et un lieu d'expérimentation et de coopération avec des équipes de recherche et des concepteurs d'équipements. Comme le notent justement Keating et Cambrosio (2003), les dimensions techniques et politiques sont indissociables dans la notion de plate-forme.L'intérêt des pouvoirs publics et des acteurs de la recherche en génomique pour les plates-formes rejoint les travaux d'histoire et de sociologie des sciences et d'économie qui mettent le rôle déterminant de la question de l'instrumentation dans l'émergence de nouveaux régimes de production des connaissances scientifiques et les conditions permettant d'accroître les rendements économiques et sociaux de la recherche. Gaudillière (Gaudillière, 2000) souligne que le recours accru à l'instrumentation dans les sciences de la vie s'inscrit dans une évolution historique vers de nouvelles logiques instrumentales, recourant de manière très lourde à l'équipement, l'automatisation et aux nouvelles technologies de l'information pour générer, stocker, analyser et représenter de vastes quantités de données. Joerges et Shinn (2001) soulignent le rôle joué par le développement d'une recherche instrumentale - par la création d'une lingua franca - dans l'intégration de champs disciplinaires de plus en plus spécialisés Plusieurs auteurs notent les effets d'une division croissante du travail de recherche qui requiert des compétences spécifiques (Hackett, 2004, Mangematin et Peerbaye, 2005, Arora et Gambardella, 1994)) ou encore l'importance de la localisation géographique de ces équipements, d'une part afin de tirer parti de capacités de recherche distribuées et difficilement transportables, d'autre part, afin de susciter des dynamiques d'innovation et de coopération entre équipes scientifiques. Il faut également noter que l'instrumentation de la génomique ne cadre pas avec les conceptions traditionnelles, héritées des sciences physiques : il s'agit moins ici d'infrastructures uniques, construites sur des sites stratégiquement choisis, que de réseaux d'instruments de taille réduite, dispersés sur le territoire autour de certains pôles locaux de spécialisation, dont le coût n'est pas comparable à celui d'un accélérateur à particules ou d'un synchrotron (Mangematin et Peerbaye, 2005).

La gestion collective des équipements de la recherche scientifique, que l'on désigne communément par le terme de « gestion des plates-formes », constitue à la fois un objet de la politique scientifique en sciences de la vie, un domaine de gestion spécifique pour les organismes de recherche et les laboratoires et un lieu d'expérimentation et de coopération avec des équipes de recherche et des concepteurs d'équipements. Comme le notent justement Keating et Cambrosio (2003), les dimensions techniques et politiques sont indissociables dans la notion de plate-forme.L'intérêt des pouvoirs publics et des acteurs de la recherche en génomique pour les plates-formes rejoint les travaux d'histoire et de sociologie des sciences et d'économie qui mettent le rôle déterminant de la question de l'instrumentation dans l'émergence de nouveaux régimes de production des connaissances scientifiques et les conditions permettant d'accroître les rendements économiques et sociaux de la recherche. Gaudillière (Gaudillière, 2000) souligne que le recours accru à l'instrumentation dans les sciences de la vie s'inscrit dans une évolution historique vers de nouvelles logiques instrumentales, recourant de manière très lourde à l'équipement, l'automatisation et aux nouvelles technologies de l'information pour générer, stocker, analyser et représenter de vastes quantités de données. Joerges et Shinn (2001) soulignent le rôle joué par le développement d'une recherche instrumentale - par la création d'une lingua franca - dans l'intégration de champs disciplinaires de plus en plus spécialisés Plusieurs auteurs notent les effets d'une division croissante du travail de recherche qui requiert des compétences spécifiques (Hackett, 2004, Mangematin et Peerbaye, 2005, Arora et Gambardella, 1994)) ou encore l'importance de la localisation géographique de ces équipements, d'une part afin de tirer parti de capacités de recherche distribuées et difficilement transportables, d'autre part, afin de susciter des dynamiques d'innovation et de coopération entre équipes scientifiques. Il faut également noter que l'instrumentation de la génomique ne cadre pas avec les conceptions traditionnelles, héritées des sciences physiques : il s'agit moins ici d'infrastructures uniques, construites sur des sites stratégiquement choisis, que de réseaux d'instruments de taille réduite, dispersés sur le territoire autour de certains pôles locaux de spécialisation, dont le coût n'est pas comparable à celui d'un accélérateur à particules ou d'un synchrotron (Mangematin et Peerbaye, 2005).