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Early detection of environmental disturbances affecting shellfish stock condition is highly desirable for aquaculture activities. In this article, a new biophysical model-based early warning system (EWS) is described, that assesses bivalve stock condition by diagnosing signs of persistent physiological dysfunctioning. The biophysical model represents valve gape dynamics, controlled by active contractions of the adductor muscle countering the passive action of the hinge ligament, the dynamics combine continuous convergence to a steady-state interspersed with discrete closing events. A null simulation was introduced to describe undisturbed conditions. The diagnostic compares valve gape measurements and simulations. Indicators are inferred from the model parameters, and disturbances are assessed when their estimates deviate from their null distribution. Instead of focusing only on discrete events, our EWS exploits the complete observed dynamics within successive time intervals defined by the variation scales. When applied to a valvometry data series, collected in controlled conditions from scallops (Pecten maximus), the EWS indicated that one among four individuals exhibited signs its physiological condition was degrading. This was detected neither during experiments nor during the initial data analysis, suggesting the utility of an approach that quantifies physiological mechanisms underlying functional responses. Practical implementations of biological-EWS at farming sites are then discussed.

Whale migrations are poorly understood. Two competing hypotheses dominate the literature: 1. moving between feeding and breeding grounds increases population fitness, 2. migration is driven by dynamic environmental gradients, without consideration of fitness. Other hypotheses invoke communication and learned behaviors. In this article, their migration was investigated with a minimal individual-based model at the scale of the Global Ocean. Our aim is to test if global migration patterns can emerge from only the local, individual perception of environmental change. The humpback whale (Megaptera novaeangliae) meta-population is used as a case study. This species reproduces in 14 zones spread across tropical latitudes. From these breeding areas, humpback whales are observed to move to higher latitudes seasonally, where they feed, storing energy in their blubber, before returning to lower latitudes. For the model, we developed a simplified ethogram that conditions the individual activity. Then trajectories of 420 whales (30 per DPS) were simulated in two oceanic configurations. The first is a homogeneous ocean basin without landmasses and a constant depth of −1000 m. The second configuration used the actual Earth topography and coastlines. Results show that a global migration pattern can emerge from the movements of a set of individuals which perceive their environment only locally and without a pre-determined destination. This emerging property is the conjunction of individual behaviors and the bathymetric configuration of the Earth’s oceanic basins. Topographic constraints also maintain a limited connectivity between the 14 DPSs. An important consequence of invoking a local perception of environmental change is that the predicted routes are loxodromic and not orthodromic. In an ocean without landmasses, ecophysiological processes tended to over-estimate individual weights. With the actual ocean configuration, the excess weight gain was mitigated and also produced increased heterogeneity among the individuals. Developing a model of individual whale dynamics has also highlighted where the understanding of whales’ individual behaviors and population dynamic processes is incomplete. Our new simulation framework is a step toward being able to anticipate migration events and trajectories to minimize negative interactions and could facilitate improved data collection on these movements.

Hall-Effect valvometry (HES) is being used to describe bivalve valve gape variations and infer environmental perturbations in a variety of aquatic environments. Surprisingly, the published calibrations in ecological literature ignore both the electromagnetic properties of HES and that the valves rotate around their hinge when they move. The high sensitivity of HES suggests these features should be accounted for explicitly to estimate measurement accurately. To address these issues, two calibration functions were developed based on the electromagnetic properties of the HES: one assumes that the HES and magnet are maintained on the same linear axis, and the second model accounts for the geometric properties of the system (i.e. variations of the angle between HES and the magnet during shell rotation). The great scallop (Pecten maximus) was used as biological model because of its large range of valve openings. HES were installed on the flat valve and magnets installed on the opposing rounded valve; 12 individuals of similar size (10 ± 1(SD) cm), were equipped and placed in controlled experimental conditions. A calibration was done for each individual once time series recordings were completed. The variability of parameter estimates was calculated with a bootstrap method. The second model (with rotatation) improves valve gape distance estimates for larger openings despite the decrease of sensor sensitivity. To infer valve gape dynamics, the reciprocal calculation of the calibration function was formalized and applied to the Hall voltage time series. Our analysis suggests that under controlled laboratory conditions, scallops are partially open most of the time (inter-valve distance equalca. 27 mm on average, or 45 % of the average maximum opening distance). Interspersed in this continuous regime, individual scallops performed closing events at a frequency ofca. 2.5 closings per hour. A closing event is a movement that is fast enough relative to the recording frequency (10 Hz) to qualify as discrete. We find that the inversed calibration model without rotation allows negative value estimates, which indicates that this calibration function is incorrect. In contrast, the inversed calibration model with valve rotation around the hinge constrains gape distance values in their domain of definition which automatically excludes sensor readings that produce negative values from estimated gape time series.

Woody debris is found in all habitats of the land-sea continuum. While isolated experimental studies of wood degradation exist, few programs have observed the dynamics of wood degradation, in situ across this gradient. Since 2014, we have been conducting a series of long-term observations of wood decay in three characteristic areas of a Mediterranean Sea coastal watershed: forest leaf litter ('Forest'), river bed ('River') and the near-shore marine environment ('Sea'). The study sites are within the Massane River watershed (France) whose headwaters are in a protected beech tree (Fagus sylvatica) dominated forest. Branch sections from a recently fallen beech tree and standardized blocks of Norway spruce (Picea abies) were installed in all three environments. The proportion of remaining mass and volumetric mass of the individual wood samples were determined periodically over 4.2 years. Regardless of wood type, there were marked differences in the decay dynamics. Mass losses at the Forest and River sites were well-described by continuous negative exponential models. At the Sea site, there was a short latency period followed by rapid degradation for the wood fraction exploited by shipworms; in this case, a Weibull-type function was fitted to the data. Integrated mass loss rates at the coastal location were 6 to 20 times faster than in the other two environments. Our study suggests that the early dynamics of wood degradation in a land-sea meta-ecosystem are dominated by the marine invertebrate community. This means woody debris, once it reaches the sea, is likely to break down rapidly within near shore coastal habitats. These results highlight the need to quantify the mass transport dynamics between local ecosystems.

In this review, the use of environmental DNA (eDNA) within Environmental Impact Assessment (EIA) is evaluated. EIA documents provide information required by regulators to evaluate the potential impact of a development project. Currently eDNA is being incorporated into biodiversity assessments as a complementary method for detecting rare, endangered or invasive species. However, questions have been raised regarding the maturity of the field and the suitability of eDNA information as evidence for EIA. Several key issues are identified for eDNA information within a generic EIA framework for marine environments. First, it is challenging to define the sampling unit and optimal sampling strategy for eDNA with respect to the project area and potential impact receptor. Second, eDNA assay validation protocols are preliminary at this time. Third, there are statistical issues around the probability of obtaining both false positives (identification of taxa that are not present) and false negatives (non-detection of taxa that are present) in results. At a minimum, an EIA must quantify the uncertainty in presence/absence estimates by combining series of Bernoulli trials with ad hoc occupancy models. Finally, the fate and transport of DNA fragments is largely unknown in environmental systems. Shedding dynamics, biogeochemical and physical processes that influence DNA fragments must be better understood to be able to link an eDNA signal with the receptor’s state. The biggest challenge is that eDNA is a proxy for the receptor and not a direct measure of presence. Nonetheless, as more actors enter the field, technological solutions are likely to emerge for these issues. Environmental DNA already shows great promise for baseline descriptions of the presence of species surrounding a project and can aid in the identification of potential receptors for EIA monitoring using other methods.

The technical difficulties of performing underwater observation mean that marine ecologists have long relied on behavioural experiments to study reactions of marine organisms. In this article, we examine the underlying complexity of assumptions made in raceway experiments and we propose a statistical inference procedure tailored to this type of experimental protocol. As an example, experiments were performed to test if light of two different intensities affects the proximal behaviour (i.e. direct, local and immediate) of two species of crustaceans, the hermit crab (Pagurus bernhardus), and the green crab (Carcinus maenas). Individuals were collected in the vicinity of the Sven Loven Marine Center in Tjarnö (Sweden). Their movements in raceways were recorded and the statistical distance between the resulting experimental distribution and a simulated null distribution was used to compare their behaviour in two situations: dim (when they were expected to feed) and bright light (when they were expected to shelter). Initial tests indicated no differences of behaviour between dim and bright light for the two species. However, when compared with the reference state (here, a null distribution) the behaviour in dim light deviates significantly from the null distribution suggesting non-random behaviour. Our results suggest that efforts should be made to understand the behaviours of the individuals of these two species to establish a comprehensive reference state as a basis for comparison. This fundamental information should be a prerequisite before implementing experiments testing how potential disturbances affect individual organisms in behavioural ecology.

Previous studies have demonstrated that male European lobsters (Homarus gammarus) use chemical and visual signals as a means of intra-specific communication during agonistic encounters. In this study, we show that they also produce buzzing sounds during these encounters. This result was missed in earlier studies because low frequency buzzing sounds are highly attenuated in tanks, and are thus difficult to detect with hydrophones. To address this issue, we designed a behavioural tank experiment with hydrophones, and accelerometers placed on the lobsters to directly detect their carapace vibrations (i.e. the sources of the buzzing sounds). While we found that both dominant and submissive individuals produced carapace vibrations during every agonistic encounter, very few of the associated buzzing sounds (15 %) were recorded by the hydrophones. This difference is explained by their high attenuations in tanks. We then used the method of algorithmic complexity to analyze the carapace vibration sequences as call-and-response signals between dominant and submissive individuals. Even if some intriguing patterns appeared for closely size-matched pairs (< 5 mm carapace length difference), the results of the analysis did not permit to conclude that the processes underlying these sequences could be differentiated from random ones. Thus, such results prevented any conclusion about acoustic communication at this time. This concurs with both the high attenuation of the buzzing sounds during the experiments and the poor understanding of acoustic perception by lobsters. New approaches that circumvent tank acoustic issues are now required to validate the existence of acoustic communication in lobsters.

International audience; Spiny lobsters (Palinurus elephas) have been overfished in European waters, and adult breeders are now scarce. Our recent study highlighted the high acoustic potential of this species, which can emit loud broadband pulse trains, called “antennal rasps,” with peak-to-peak source levels (estimated at 1 m from the source) above 160 dB re 1 μPa² [Jézéquel et al., Marine Ecology Progress Series 615 (2019)]. These acoustic properties imply that these sounds could be detected during in situ passive acoustic monitoring. However, before using a such tool, we need to understand how antennal rasps propagate in situ and at what distance they could be detected above the ambient noise. To answer these questions, we recorded spiny lobster antennal rasps in the Iroise Sea (Brittany, France). We used a linear array of 8 hydrophones, with distances between animals and receivers ranging from 0.5 m to 100 m. We recorded antennal rasps from 38 individuals of various sizes. Our results demonstrate that large spiny lobsters can be detected at 100 m, and that sound properties might be directly influenced by the size of the individuals.

Previous studies have demonstrated that male European lobsters (

International audience; Spiny lobsters (Palinuridae) are capable of emitting sounds called antennal rasps. In the bioacoustics literature, such broadband sounds have mostly been characterized from tank recordings where reverberation and resonant frequencies might strongly distort their features. Hence, in this study, we compared antennal rasps produced by European spiny lobsters Palinurus elephas in both tank and in situ conditions. We found significant differences in all sound features (temporal, intensity and spectral features) between tank and in situ recordings, confirming that antennal rasps-and broadband sounds generally -cannot be accurately characterized in tanks if sound reverberation is ignored. In recordings of antennal rasps made in situ, we show that the main acoustic power is located in the low frequency band (below 1 kHz), which was missed by all earlier studies done in tanks where such low frequencies cannot be properly measured. The hearing capacities of crustaceans suggest roles for intra-specific communication of these sounds, and their high levels indicate they could be heard above noise. Indeed, we outline that antennal rasps are among the loudest sounds known in the marine animal kingdom, with peak-to-peak sound pressure levels (calculated at 20 cm from the source) above 175.7 dB re 1 mu Pa-2, and peak-to-peak source levels (estimated at 1 m from the source) ranging from 154.2 to 160.6 dB re 1 mu Pa-2. These acoustic properties imply they could be detected in situ during passive acoustic monitoring. This study also highlights the importance of using appropriate measurement methods when characterizing sounds produced by marine invertebrates.

International audience; The oceans and seas receive coarse woody debris since the Devonian, but the kinetics of wood degradation remains one of many unanswered questions about the fate of driftwood in the marine environment. A simple gravimetric experiment was carried out at a monitoring station located at the exit of a steep, forested Mediterranean watershed in the Eastern Pyrenees. The objective was to describe and quantify, with standardized logs (in shape, structure and constitution), natural degradation of wood in the sea. Results show that the mass decrease of wood logs over time can be described by a sigmoidal curve. The primary process of wood decay observed at the monitoring station was due to the arrival and installation of wood-boring species that consumed more than half of the total wood mass in six months. Surprisingly, in a region where there is little remaining wood marine infrastructure, “shipworms”, i.e. xylophagous bivalves, are responsible for an important part of this wood decay. This suggests that these communities are maintained probably by a frequent supply of a large quantity of riparian wood entering the marine environment adjacent to the watershed. By exploring this direct link between terrestrial and marine ecosystems, our long term objective is to determine how these supplies of terrestrial organic carbon can sustain wood-based marine communities as it is observed in the Mediterranean Sea.

00000 ăWOS:000388003500012; International audience; The ecological process of community assembly is described as the succession of three phases: colonization, regulation and segregation. Early colonization remains the least studied and quantified phase of assembly. In order to fill this gap, an approach combining in situ experiments and modelling was proposed to study colonization by a benthic macrofauna community in open microcosms containing a single, non-limiting resource. The experiment was three months long. A total of 51 taxa were observed in the microcosms, but data analyses of the species composition and abundances revealed that five species, Capitella spp., Gammaropsis maculata, Erichtionus punctatus, Nereiphylla paretti and Harmothoe mariannae, explained most of the observed variation in the assembly process. The population dynamics of these species were simulated taking into account functional traits that govern individual interactions. The dynamic model simulated a demographic stochasticity due to low population densities that result from the small size of the experimental microcosms. Using this combined approach of experiments and modelling, we showed that predation interactions alone can account for the abundances and species composition of primary consumers during the transient phase of early colonization.

International audience; The SPA (“Savoir, Pouvoir, Avoir”) project (CNRS, 2017-2019) presented in this article focuses on the ways French society deals with the issue of environmental impact – from the vast question of impact in the context of global change and the issue of the measurement of impact in science, to the specific case of the public policy instrument known as “environmental impact assessment”. Impact is considered as a boundary object at the intersection of several fields of inquiry which captures both the architecture and the dynamics of relationships between “savoir” (scientific and lay knowledge), “pouvoir” (power and decision) and “avoir” (economy/appropriation), that aggregate different interests around the sustainable management of coastal socio-ecological systems. Three sites were selected along a north-south gradient of Long-Term Ecological Research sites: the Bay of Brest and the Iroise Sea, the National Nature Reserve of the French islands in the Southern Ocean and the overseas collectivity of Saint Pierre and Miquelon. The approach of the SPA project is to link concretely social sciences, natural sciences and engineering sciences on these study sites, in an interdisciplinary, multi-site and multi-scale methodology that makes it possible to reveal the conditions for the possible – or impossible – implementation of sustainable management of coastal socio-ecological systems.; Le projet SPA (Savoir, Pouvoir, Avoir) (CNRS, 2017-2019) présenté dans cet article se concentre sur la manière dont la société française aborde la question de lʼimpact environnemental – de son évaluation et sa mesure à son traitement. Le processus réglementaire de lʼ « étude dʼimpact environnemental » qui consiste en lʼanalyse préalable des impacts potentiels prévisibles dʼune activité donnée sur lʼenvironnement est donc placé ici au cœur de nos préoccupations dans ce projet qui considère lʼimpact comme un objet frontière, à lʼintersection de plusieurs champs, permettant de saisir lʼarchitecture et la dynamique des relations entre savoir (savoir scientifique et profane), pouvoir (pouvoir et décision) et avoir (économie/appropriation). Pour ce faire, nous proposons de saisir les différents intérêts qui sʼagrègent autour de la gestion durable des socio-écosystèmes côtiers. Trois sites ont été choisis selon un gradient nord-sud dans des sites de recherche écologique à long terme : la rade de Brest et la mer dʼIroise, la réserve naturelle nationale des îles françaises de lʼocéan Austral et la collectivité dʼoutre-mer de Saint-Pierre-et-Miquelon. Lʼapproche du projet SPA consiste à lier concrètement les sciences sociales, les sciences naturelles et les sciences de lʼingénieur sur ces sites dʼétude, dans une approche interdisciplinaire multi-sites et multi-échelles qui permet de mettre au jour les conditions de possibilité (ou dʼimpossibilité) de mise en œuvre dʼune gestion soutenable des socio-écosystèmes côtiers.

International audience; Passive acoustics is a useful non-invasive tool to collect behavioral information in marine species. This is the case for temperate crustaceans which are known to emit a large variety of sounds through diverse mechanisms. But despite numerous studies in tanks, little is known about their ecological meaning, particularly for decapods of high commercial interest. When stressed by handling, the European lobster (Homarus gammarus) vibrates its carapace and produces low frequency “buzzing sounds” that can be characterized in tanks. In this presentation, we discuss a straightforward experimental approach to investigating the role of these buzzing sounds in male European lobsters by combining passive acoustics and behavioral analysis (video and accelerometry). We recorded sound and video simultaneously during agonistic encounters. Based on the video, an ethogram was created with a total of 30 behaviors regrouped by agonistic levels. During agonistic encounters, European lobsters emitted buzzing sounds in association with stressful events such as claw grasping or tail flipping. Our results suggest that these sounds may be used by H. gammarus to maintain dominance around its shelter.

International audience; Experiments were done to investigate in situ colonization of pine wood blocks by marine wood borers at the mouth of a small mountain river in the foothills of the Eastern Pyrenees. Standardized blocks were recovered after remaining underwater for increasingly long durations, until the available resource was exhausted by the shipworms assemblage that developed. Computer-aided tomography (CT) was used for visualizing and quantifying biogenic structures into the wooden blocks. The biodiversity survey of the wood pieces colonized indicated that up to three species of shipworms shared the resource at the same time. The specific wood consumption rate of Nototeredo norvagica was estimated 185 mm 3 ind −1 day −1. The quantification of voids created by shipworm crowding indicated that total tunnelling represents, on average, 60% of the initial volume of a wood block, revising upward earlier estimates of wood destruction by 28%. CT analysis provides the quantitative measurements necessary to parameterize individual-based growth models linking wood consumption with the species diversity of shipworm assemblages.

International audience; A new probabilistic approach is proposed to assess muricid species population abundances at scales relevant to both Ancient and Modern coastal fisheries. Motivated by the long-term goal of reconstructing the dynamics of exploited murex populations during Antiquity, the objective was to estimate the population density of the banded dye-murex, Hexaplex trunculus (Linnaeus, 1758) from successive captures with baited traps, using a method similar to the technique employed in the Mediterranean purple dye industry. The stochastic model developed simulates cumulative captures while accounting for high variability. It was calibrated with data acquired during a field trapping experiment (Crete Island, Greece). Traps' catchability and Effective Area of Attraction (EAA) were estimated using the individual speed and behavioural response towards bait from laboratory experiments. Average density of H.trunculus was estimated as 2.2 +/- 1.4SE individuals per square metre, with no significant differences between seagrass and rocky habitats. The clearing time of successive capture experiments averaged 84 +/- 6SE hr. Clearing ca. 0.4ha of subtidal area would be necessary to produce ca. 1.0g of pure Tyrian purple pigment. The method described is generalizable to making population abundance estimates for similar groups, such as whelks, in modern fisheries.

International audience; Experiments in marine behavioural ecology rely heavily on observations made in tanks. However, when studying acoustic behaviours of marine animals in confined volumes, the effects of reverberation must be characterized, something that has been overlooked in parts of the marine ecology literature. In this study, we characterized reverberation in tanks using an artificial sound source and examined the implications for bioacoustic studies using sounds emitted by the European lobster Homarus gammarus during feeding and in response to stress. Broadband and transient sounds commonly produced by crustaceans were severely impacted by reverberation such that their spectral characteristics and pulse width durations could not be assessed. In contrast, lowfrequency sounds could be characterized in tanks, but not their source level. Based on these observations, we describe a simple methodology to identify which sound characteristics can be measured in tanks. When feeding, the lobsters produced broadband and transient sounds called 'rattles', similar to sounds reported for tropical spiny lobsters Palinurus longipes and P. argus. When stressed, H. gammarus vibrated its carapace, producing a low-frequency sound analogous to the 'buzzing' sound of the American lobster H. americanus. The potential role of species-specific sound is discussed; however, although our observations represent the first bioacoustic characterization of H. gammarus, additional behavioural studies are necessary to understand their ecological meaning.

International audience; In this contribution, the evolution of the Bay of Brest ecosystem over the past 50 years is used to explore the construction of interdisciplinary knowledge and raise key questions that now need to be tackled at the science-policy-communities interface. The Bay of Brest is subject to a combination of several aspects of global change, including excessive nutrient inputs from watersheds and the proliferation of invasive species. These perturbations strongly interact, affecting positively or negatively the ecosystem functioning, with important impacts on human activities. We first relate a cascade of events over these five decades, linking farming activities, N and Si biogeochemical cycles, the proliferation of an exotic benthic suspension feeder, the Great scallop fishing and biodiversity in maerl beds. This cascade leads to today’s situation where toxic phytoplankton blooms become recurrent in the Bay, preventing the fishery of the great scallop and leading the fishermen community to switchpray and alter the maerl habitat and the benthic biodiversity it hosts, despite the many scientific alerts and the protection of this habitat, How is this possible despite decades of joint work between scientists and fishermen? Is adaptive co-management a sufficient condition for a sustainable management of an ecosystem? How do the different groups (farmers, fishermen, scientists, environmentalists…), with their diverse interests, take charge of this situation? What is the role of power in this difficult transformation to sustainability? Answering these questions requires an interdisciplinary approach, especially between natural sciences (NS) and human and social sciences (HSS). Here, we first show the importance of geographical proximity in the build-up of this interdisciplinary knowledge, first among biogeochemists and benthic biologists by the time the IUEM institute was built in the late 1990’s. We also confirm the importance of this proximity and the need for the establishment of boundary settings that allow for the crucially needed long-term interactions between the NS and HSS communities. Thecreation of the research group ApoliMer (for a political anthropology of the sea) in 2014 and the creation of a new axis on social-ecological systems (SES) within the LabexMer in 2015, are such examples of these boundary settings created recently. Combining natural sciences with political science, anthropology and the political sociology of science, we hope to improve the contribution of HSS to SES studies, creating the conditions to address these key questions at the science-policy interface. The ZABrI created in 2012 provides an ideal setting for inter- and trans-disciplinary studies through tight work with various stakeholders, hopefully improving the transformation towards sustainability.

A new statistical method based on a stochastic dynamic model is proposed to assess population abundances of murcid species at scales relevant to both Ancient and Modern artisanal, coastal fisheries. Motivated by the long-term goal of reconstructing the dynamics of exploited murex populations during Antiquity, the objective was to quantify the population density of the banded-dye murex, Hexaplex trunculus (Linnaeus, 1758) from successive captures with baited traps, using a method similar to the technique employed in the Mediterranean purple dye industry. A stochastic model simulating cumulative captures while taking into account high variability was developed and calibrated with data acquired during a field experiment conducted on Crete Island, near Heraklion. Sampling devices were deployed in two shallow water habitats. The traps’ catchability and the Effective Area of Attraction were estimated using the individual speed and behavioural response toward the bait observed during independent laboratory experiments. The average density of H. trunculus was estimated at 2.2 ± 1.4 SE individuals per square meter, with no significant differences between seagrass and rocky habitats, respectively. The clearing time (the time to catch all individuals within reach of the trap) of the successive experiments was 84 ± 6 SE hours, on average. This means that clearing ca. 0.4 ha of subtidal area would be necessary to produce ca. 1.0 g of pure dye pigment. While the method is discussed here with respect to a particular historical context, it is generalizable to making population abundance estimates for other species such as whelks, in modern fisheries.

Coarse particulate organic matter (CPOM) represents a small portion of the inner shelf sediments but occurs across all river outlets. To consider the ecogeochemical fate of CPOM in such an environment, we examined both the infauna community and secondary evidence of geochemical reactions preserved in the surface sediments of the Rhone prodelta. ICP-AES, scanning electron microscopy and energy dispersive X-ray spectrometry of the CPOM showed that the fate of organic matter in this environment is driven by sulphate reduction and geochemical reactions resulting from the precipitation of sulfide due to the presence of large amounts of iron-bearing minerals. Leaf litter debris contained such high quantities of iron that after dry ashing the remaining material is easily attracted by a magnet. The observed geochemical trade-off was proposed as a mechanism that helps to maintain a bioturbating animal community that in turn contributes to the mineralization of organic matter within this suboxic environment. This study showed that the accumulation of refractory organic carbon in sediments was intimately associated with the sequestering of iron and sulphur by providing a nucleation point for mineral deposition and also that the extent of decomposition of the organic materials did not necessarily increase progressively from coarser to finer particles.

A new roadmap for quantitative methodologies of Environmental Impact Assessment (EIA) is proposed, using an ecosystem-based approach. EIA recommendations are currently based on case-by-case rankings, distant from statistical methodologies, and ecological ideas that lack proof of generality or predictive capacities. These qualitative approaches ignore process dynamics, scales of variations and interdependencies and are unable to address societal demands to link socio-economic and ecological processes (e.g. population dynamics). We propose to re-focus EIA around the systemic formulation of interactions between organisms (organized in populations and communities) and their environments but inserted within a strict statistical framework. A systemic formulation allows scenarios to be built that simulate impacts on chosen receptors. To illustrate the approach, we design a minimum ecosystem model that demonstrates nontrivial effects and complex responses to environmental changes and validated with case study. We suggest that an Ecosystem-Based EIA—in which the socio-economic system is an evolving driver of the ecological one—is more promising than a socio-economic-ecological system where all variables are treated as equal. This refocuses the debate on cause-and-effect, processes, identification of essential portable variables, and allows for quantitative comparisons between projects, which is critical in cumulative effects determinations.

WOS:000419146600029; International audience; This viewpoint article examines Environmental Impact Assessment (EIA) practices in developed and transitioning nations, identifies weaknesses, and proposes a new quantitative approach. The literature indicates that there exists little to no standardization in EIA practice, transitioning nations rely on weak scientific impact analyses, and the establishment of baseline conditions is generally missing. The more fundamental issue is that the "receptor"- based approach leads to a qualitative and subjective EIA, as it does not adequately integrate the full measure of the complexity of ecosystems, ongoing project risks, and cumulative impacts. We propose the application of a new framework that aims to ensure full life cycle assessment of impacts applicable to any EIA process, within any jurisdictional context. System-Based EIA (SBEIA) is based on modeling to predict changes and rests on data analysis with a statistically rigorous approach to assess impacts. This global approach uses technologies and methodologies that are typically applied to characterize ecosystem structure and functioning, including remote sensing, modeling, and in situ monitoring. The aim of this approach is to provide a method that can produce quantifiable reproducible values of impact and risk and move EIA towards its substantive goal of sustainable development. The adoption of this approach would provide a better evaluation of economic costs and benefits for all stakeholders.

International audience; The terminal lobe complex of the Congo River submarine fan sits on the abyssal Atlantic plain, at 5000 m water depth, 760 km offshore from the river mouth estuarine area. While most rivers deliver particulate material to the continental shelf, particulate matter from the Congo River largely bypasses the shelf and is transported by turbidity currents through the Congo submarine canyon system. We determined the quantity and quality of the organic matter reaching the terminal lobe complex at five sites with marked morphological differences that may influence the distribution of organic matter. A suite of bulk geochemical (% OC, δ13Corg, δ15N, C: N), 137Cs and palynofacies analyses were done on cores collected from the terminal lobe area. These results were also compared to the composition of sediments collected upstream at the Malebo Pool (Congo River).Distal lobe complex sediments contain high amounts of terrestrial organic carbon (3–5 wt.%) that is homogeneously distributed in surficial (22 cm) and deeper sediments (580 cm) silty–clay facies. Strongly altered soil-derived organic matter with well-preserved land plant detritus from the Congo River predominates. A terrestrial soil origin for the particulate load was confirmed by the elevated 137Cs activity in lobe sediments. The vertical distribution of the 137Cs signal suggests that there has been a massive arrival of terrestrial sediments since 1963, consistent with a turbiditic origin. From the locations surveyed, we estimate a maximum accumulation of terrestrial organic carbon of ca. 1 kg OC m− 2 y− 1 for the distal lobe. However, transport modifies the organic matter both in terms of quantity and quality. Observed differences were attributed to preferential degradation of nitrogenous matter during diagenesis and to the addition of highly remineralized marine organic matter.Results from our temporal reference site (E) suggest that organic matter may be preserved in turbidite facies for thousands of years. The good preservation state of the accumulated organic matter shows that turbiditic lobe complexes should be considered as a sink for terrestrial organic carbon in the deep ocean.

International audience; Major rivers transfer high loads of continental particulate organic matter to deltaic environments, where the impact on the biogeochemistry and productivity of coastal sediments depends on the sources and lability of these inputs. Our aims are to provide new insights into the reactivity of riverine inputs in coastal environments and to delineate the parameters controlling their fate in these dynamic systems. Sediment cores were collected from a Mediterranean deltaic system (the Rhône prodelta and its adjacent shelf) during a period of moderate river discharge (Spring 2007) and analyzed for their fatty acid composition. Sediment properties were also described using biochemical bulk analyses (organic carbon and lipids), granulometry and profiles of redox potential. Based on the bulk compositional changes and hierarchical clustering of the fatty acid biomarkers, we determined the principal sources of organic matter and their spatial distribution. Fatty acids were primarily of continental origin in the prodelta, shifting to a higher contribution from marine sources in the shelf area. Fatty acids derived from both continental and marine sources were efficiently degraded in the sediments by microbial decay processes in the upper oxic layer. Degradation rate constants calculated from the down-core decreases in concentrations indicate that fatty acid degradation was enhanced in sediments influenced by the Rhône River. The most important parameters affecting fatty acid preservation were the inherent stability of individual molecular components and their physical association with mineral matrices, the source and freshness of the inputs, and the depositional environment (redox condition, accumulation rates).

The PAH contamination level and biochemical composition of sinking particles and surficial sediments (0-0.5 cm layer) were assessed at a rural coastal site in the northwestern Mediterranean Sea. Surficial sediment contamination (≈20 ng g(-1)) was considerably lower than at other Mediterranean sites, yet particles collected in sediment traps had 6-8 times more PAH. Contaminated particles were mostly marine in origin. Temporal variation of contamination levels correlated with organic content of the particles, but some of the observed variability could be attributed to seasonal changes in pyrolytic PAH production. Sinking organic particles were potentially as readily digestible as surficial sediments for prospective consumers however, transfer of PAHs along the benthic food chain is probably enhanced because of the particles' higher nutritional value.

International audience; Generally, growth rates of living organisms are considered to be at steady state, varying only under environmental forcing factors. For example, these rates may be described as a function of light for plants or organic food resources for animals and these could be regulated (or not) by temperature or other conditions. But, what are the consequences for an individual's growth (and also for the population growth) if growth rate variations are themselves dynamic and not steady state? For organisms presenting phases of dormancy or long periods of stress, this is a crucial question. A dynamic perspective for quantifying short-term growth was explored using the daily growth record of the scallop Pecten maximus (L.). This species is a good biological model for ectotherm growth because the shell records growth striae daily. Independently, a generic mathematical function representing the dynamics of mean daily growth rate (MDGR) was implemented to simulate a diverse set of growth patterns. Once the function was calibrated with the striae patterns, the growth rate dynamics appeared as a forced damped oscillation during the growth period having a basic periodicity during two transitory phases (mean duration 43 days) and appearing at both growth start and growth end. This phase is most likely due to the internal dynamics of energy transfer within the organism rather than to external forcing factors. After growth restart, the transitory regime represents successive phases of over-growth and regulation. This pattern corresponds to a typical representation of compensatory growth, which from an evolutionary perspective can be interpreted as an adaptive strategy to coping with a fluctuating environment.