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The massive contamination of the environment by plastics is an increasing global scientific and societal concern. Knowing whether and how these pollutants affect the behaviour of keystone species is essential to identify environmental risks effectively. Here, we focus on the effect of plastic leachates on the behavioural response of the common blue mussel Mytilus edulis, an ecosystem engineer responsible for the creation of biogenic structures that modify the environment and provide numerous ecosystem functions and services. Specifically, we assess the effect of virgin polypropylene beads on mussels' chemotactic (i.e. a directional movement in response to a chemical stimulus) and chemokinetic (i.e. a non-directional change in movement properties such as speed, distance travelled or turning frequency in response to a chemical stimulus) responses to different chemical cues (i.e. conspecifics, injured conspecifics and a predator, the crab Hemigrapsus sanguineus). In the presence of predator cues, individual mussels reduced both their gross distance and speed, changes interpreted here as an avoidance behaviour. When exposed to polypropylene leachates, mussels moved less compared to control conditions, regardless of the cues tested. Additionally, in presence of crab cues with plastic leachates, mussels significantly changed the direction of movement suggesting a leachate-induced loss of their negative chemotaxis response. Taken together, our results indicate that the behavioural response of M. edulis is cue-specific and that its anti-predator behaviour as well as its mobility are impaired when exposed to microplastic leachates, potentially affecting the functioning of the ecosystem that the species supports. info:eu-repo/semantics/publishedVersion

(IF 1.70; Q1); International audience; In organic-rich shallow habitats, benthic macrofauna is known to play a major role in the geochemical functioning of surficial sediments through its metabolism, as well as its bioirrigation and/or bioturbation activity. In this paper, the effects of benthic macrofauna on metabolic fluxes at the sediment-water interface were studied at four dates, from winter to late summer, on two major macrobenthic communities of the eastern English Channel (macrotidal system): the fine sand Abra alba community (2 stations) and the sandy gravel Ophiothrix fragilis community (1 station). Oxygen and ammonium fluxes showed temporal changes that could be attributed to the variation of sea water temperature. Once the effect of temperature removed (using Q10 = 2.5), the average fauna mediated fluxes (FFauna) represented respectively 77% and 76% of average total fluxes. Considering the whole dataset, species number and biomass showed a significant correlation with fauna mediated fluxes of O2 and NH4+, while the relationships with abundance were not significant. The species composition of the community might influence ecosystem functioning, but in the present study, functional groups have a very poor relationship with FFauna (O2) and FFauna (NH4+). Despite the presence of engineer species, establishing general and simple rules to link macrofaunal parameters to functional attributes remains very difficult, suggesting that communities rather followed the idiosyncrasy and rivet hypothesis.

International audience; This study aimed to explore the spatial and temporal variability of benthic metabolism in a temperate mesotidal lagoon. This was achieved by measuring fluxes of CO2 in static chambers during emersion, both under light and dark conditions. Three sample sites were selected according to their tidal level (upper or mid), their sediment type (sand or mud) and the presence/absence of the seagrass Zostera noltei. The three sites were investigated at three seasons (end of winter, spring and beginning of autumn). At each site and each season, three benthic chambers were used simultaneously in successive incubations over the emersion period. The sediment chlorophyll-a content varied seasonally in the upper sands (reaching 283 mg.m− 2 in spring) but not in the mid muds (averaging 142 mg m− 2 in bare muds and 186 mg m− 2 in muds covered by seagrass). The maximum sediment CO2-uptake under light was 9.89 mmol m− 2 h− 1 in the mid bare muds, in early autumn. The maximum sediment CO2-release under darkness was 6.97 mmol m− 2 h− 1 in the mid muds covered by seagrass, in spring. Both CO2-fluxes measured in the light and in the dark increased over periods of emersion. This increase, not related to light nor temperature variations, could be explained by changes in the amount and chemistry of pore water during the air exposure of sediments. The benthic trophic state index, based on the maximum light CO2-flux versus maximum dark CO2-flux ratio, assigned to each site at each season indicated that the sediments were net autotrophic in spring in upper sands and in mid muds covered by seagrass and highly autotrophic in other cases. The most autotrophic sediments were the mid-level bare muds whatever the season. The relevance of this index is discussed compared to carbon annual budget.

Since sediments have the potential to form associations with several classes of pollutants, they have been recognized as a possible and significant source of contamination for the benthic environment. Flatfish maintain a close association with sediments for food and cover, and are therefore more likely to be exposed to contaminated sediments, especially in coastal areas (e.g. nursery grounds). The assessment of these potential biological effects involves the use of adapted biomonitoring tools. The main objective of this study was to assess and compare the response of several physiological biomarkers measured on juvenile turbot (Scophthalmus maximus) exposed to contaminated sediments. Sediments were collected from three stations in a harbour in northern France (Boulogne-sur-Mer), in an anthropogenic French estuary (the Seine), and in a reference site (exposed sandy beach of Wimereux). Unexposed lab-reared juvenile turbots were exposed to sediments for 7 and 21 days in laboratory conditions. Sediments were analysed for metals, PAH and PCB contamination. Several fish growth and condition indices were individually analysed in fish according to the chemical contaminant availability in sediment, the metal concentrations in gills and the estimation of PAH metabolites in their bile. Significant decreases in growth rates, morphometric index, RNA:DNA ratio and the lipid storage index, based on the ratio of the quantity of triacylglycerols on sterols (TAG:ST), were observed with increasing level of chemical contamination. This decrease in the fish's physiological status could be related to the significant increase of several metal concentrations in contaminated fish gills and the significant increase of PAH metabolites in bile. In a field situation, such a reduction in growth and energetic status of juvenile fish could dramatically decrease their over-winter survival in contaminated nursery grounds.

International audience; Distributions of microphytobenthos are highly heterogeneous at scales as small as a few centimetres. However, the sampling protocols currently used for the absolute determination of microphytobenthos biomass through chlorophyll a concentration measurements in surface sediments are too limited to take this variability into account, typically relying on 3-5 samples taken within a randomly located 1 m2 quadrat in a given environment. We address this issue by objectively and quantitatively inferring the minimum number of samples required to obtain reliable estimates of microphytobenthos biomass on the basis of high-resolution sub-sampling (225 regularly spaced samples) within each of nine 1 m2 quadrats at an unvegetated sheltered intertidal sandbank of the Gold Coast (Queensland, Australia). The results were generalised using data obtained in previous studies on an exposed sandy shore and on sheltered estuarine sandy muds of the Eastern English Channel. Estimates of chlorophyll a concentration exhibited a high degree of heterogeneity, both between and within quadrats. The number of samples needed to estimate the average chlorophyll a concentration, and hence mean microphytobenthos biomass with 95% confidence intervals, ranged from 15 to 115, and mainly depended on the presence of global and local gradients within the quadrats. These results have major implications for intertidal ecology by implying a possible systematic bias in the measurement of both microphytobenthos biomass and production of up to 40%. Finally, we emphasise that this issue can be circumvented using field spectrometry or PAM fluorescence measurements coupled with traditional sediment sampling techniques, and urge for unified protocols to be adopted for the routine use of these combined methods

Photosynthetic microphytobenthic activity has increasingly been examined using pulse-amplitude-modulated (PAM) fluorescence techniques. Nevertheless, estimating carbon production rates from fluorescence measurements implies the establishment of reliable relationships. The aim of this study was to determine such a relationship from field measurements of both PAM fluorescence and CO2 fluxes. Three study sites of varying sedimentary features were investigated in different seasons. Both linear and with plateau relationships were obtained between the fluorescence parameter (relative electron transport rate [rETR]) and the community-level carbon-fixation rate (gross community primary production rate [GCP] in mg C · m−2 · h−1). The correlation calculated from the whole data set (i.e., all sites and all seasons) was very strong (n = 106; r = 0.928). Significant correlations were also obtained for light-curve parameters assessed with the two methods: Pm (n = 8; r = 0.920) and Ik (n = 8; r = 0.818). Total community-level carbon fixation for the emersion period was calculated from fluorescence measurements according to the relationship established between GCP and rETR, and between light-curve parameters, and the results were compared to the estimation obtained directly from GCP measurements. The agreement between the two estimations was quite good for both ways of calculation (with a mean discrepancy of 30% for the first one and −2% for the second one). These results suggest the potential application of PAM measurements to calculate carbon-fixation rates at large spatial and temporal scales, provided that a set of experiments coupled with CO2-flux measurements are performed.

International audience; In a context of intensifying anthropogenic pressures on sandy shores, the mapping of benthic habitat appears as an essential first step and a fundamental baseline for marine spatial planning, ecosystem-based management and conservation efforts of soft-sediment intertidal areas. Mapping allows representing intertidal habitats that are basically characterised by abiotic (e.g sediments, exposure to waves…) and biotic factors such as macrobenthic communities. Macrobenthic communities are known to show zonation patterns across sandy beaches and many studies highlighted the existence of three biological zones. We tested this general model of a tripartite biological division of the shore at a geographical scale of policy, conservation and management decisions (i.e. Northern France coastline), using multivariate analyses combined with the Direct Field Observation (DFO) method. From the upper to the lower shores, the majority of the beaches exhibited three macrobenthic communities confirming the existence of the tripartite biological division of the shore. Nevertheless, in some cases, two or four zones were found: (1) two zones when the drying zone located on the upper shore was replaced by littoral rock or engineering constructions and (2) four zones on beaches and estuaries where a muddy-sand community occurred from the drift line to the mid shore. The correspondence between this zonation pattern of macrobenthic communities and the EUNIS habitat classification was investigated and the results were mapped to provide a reference state of intertidal soft-sediment beaches and estuaries. Our results showed evidence of the applicability of this EUNIS typology for the beaches and estuaries at a regional scale (Northern France coastline) with a macroecological approach. In order to fulfil the requirements of the European Directives (WFD and MFSD), this mapping appears as a practical tool for any functional study on these coastal ecosystems, for the monitoring of anthropogenic activities and for the implementation of management plans concerning effective conservation strategies.

International audience; The photosynthetic activity and productivity of four dominant canopy intertidal macroalgae were measured under emersion and immersion, at saturating light levels (PAR > 300 μmol photons m−2 s−1), and compared at two sites (eastern and western English Channel) in spring and summer. The photosynthetic activity of thalli was measured by the electron transport rate (ETR) using pulse-amplitude modulated (PAM) fluorescence and the productivity of individuals and of communities was measured by carbon fluxes in closed chambers. Under emersion, when thalli were still hydrated, the uppermost species Pelvetia canaliculata had higher photosynthetic activity (mean ETR between 327 and 460 μmol e− m−2 s−1) and individual gross productivity (between 60 and 212 μmol C gDW−1 h−1) than the lowermost species Laminaria digitata (mean ETR between 24 and 53 μmol e− m−2 s−1 and gross productivity between 2 and 38 μmol C gDW−1 h−1), whatever the site and season. P. canaliculata had higher ETR in air than underwater (averaged 146 μmol e− m−2 s−1) and L. digitata had lower ETR in air than underwater (averaged 112 μmol e− m−2 s−1), while they exhibited respectively 3 and 5 times higher gross productivity underwater. At the community scale, the low mid-shore zone of Fucus serratus had the highest mean gross productivity under emersion (47 mmol C m−2 h−1) while rates were higher for the uppermost than lowermost zone at the eastern site (average 20 and 6 mmol C m−2 h−1 respectively) and of the same order of magnitude for both zones at the western site (about 30 mmol C m−2 h−1). Finally, the variability of under emersion primary productivity among sites and seasons was reduced when the measurements were performed on entire communities compared to isolated individuals of the dominant species.

International audience; Shorebird populations are declining worldwide due to the combined effect of climate change and anthropogenic forcing, the ongoing coastal urbanisation amplifying the alteration of their habitat in both rate and magnitude. By focusing on a highly anthropogenically-influenced region in Northern France, we studied the impact of a seawall construction on wintering shorebird populations through potential alterations in the abundance and availability of their food resources. We concurrently investigated changes in the spatial distribution of muddy-sand beach macrobenthic communities between two periods of contrasting anthropogenic impacts and examined year-to-year trends of wintering shorebirds. Our study reveals that the seawall construction led to a major spatial reorganisation of the macrobenthic communities with a drastic reduction of the muddy-sand community. However, no relation between macrobenthic changes and shorebird abundances was detected. Fluctuations in shorebird abundances appeared to be congruent with flyway population trends. This result suggests that the response of shorebirds to human-induced perturbations is much more complex than expected. While an assessment of potential disturbances induced by coastal engineering constructions is needed, the pathways by which alterations could propagate through an ecosystem are not linear and as such difficult to determine. Ecosystems appear as complex adaptive systems in which macroscopic dynamics emerge from non-linear interactions at entangled smaller/larger scales. Our results confirm that an in-depth knowledge of the local, regional and global factors that influence trends of shorebirds and their habitat use is essential for accurate and effective management and conservation strategies.

Varunid crabs Hemigrapsus sanguineus and Hemigrapsus takanoi are species native from intertidal coastal areas in North-western Pacific and have become invasive along the Atlantic European coasts. To gain insights into population genetic features, we developed and characterized 16 (H. sanguineus) and 11 (H. takanoi) novel polymorphic microsatellite loci from next-generation sequencing. The number of alleles ranged from 2 to 20 for H. sanguineus, and from 8 to 21 for H. takanoi. Expected heterozygosity ranged from 0.470 to 0.947 and from 0.313 to 0.781, with mean multilocus F is estimates suggesting rapid turnover of populations. Overall, these microsatellite markers showed very high levels of polymorphism that will facilitate population genetic studies devoted to track down the most likely sources of introduction.

International audience; We investigated whether individuals of the intertidal snail Littorina littorea may be attracted by water-borne and air-borne pheromones from conspecifics. The potential relative role of water-borne and air-borne pheromone in the behavioural and reproductive biology of L. littorea was assessed through chemotactic assays. These involved a series of choice experiments with snails, snail smell and snail mucus as stimuli in a T-maze under conditions of immersion and emersion, and during the nonmating and mating seasons. During the nonmating season, L. littorea did not choose the snail-conditioned side of the T-maze significantly more frequently than the control side under conditions of both immersion and emersion. During the mating season, under condition of immersion both males and females chose the side of the T-maze conditioned with individual of the opposite sex significantly more frequently than the control side, and did not show any preference for the side conditioned with individuals of the same sex. Under conditions of emersion, only males were significantly more attracted by cues from the opposite sex than by the control. These results indicate that L. littorea are not attracted by conspecifics during the nonmating season; the cues of conspecifics are then unlikely to play a role in the orientation or the aggregation behaviour of this species. The results also suggest that males and females are attracted by the odour of conspecifics of the opposite sex, which contains both water-borne and air-borne pheromones in females and only water-borne pheromones in males. Also the similar behaviours observed with snails, water-borne and air-borne snail smell, and snail mucus, as stimuli indicate that male and female sex pheromones are both present in mucus. Temperature manipulations conducted during both seasons did not affect any of the observed behavioural changes, hence suggesting that the chemoreceptive abilities of L. littorea may be driven by exogenous and/or endogenous factors that are decoupled from direct control by temperature. This is in sharp contrast to the locomotor activity of L. littorea, which consistently increased with temperature. We also report the possibility of mate-tracking in females, a behaviour that has yet to be reported in gastropods, since males are typically believed to be the active sex that searches for females. Our results build on previous evidence of the function played by mucus-trail following in the reproductive success of intertidal gastropods, through the ability of L. littorea to remotely detect the water-borne and air-borne sex-specific cues that are incorporated in their mucus.

The relationship between biodiversity and stability of marine benthic assemblages was investigated through meta-analyses using existing data sets (n = 28) covering various spatial (m-km) and temporal (1973-2006; ranging from 5 to >250 months) scales in different benthic habitats (emergent rock, rock pools and sedimentary habitats) over different European marine systems (North Atlantic and western Mediterranean). Stability was measured by a lower variability in time, and variability was estimated as temporal variance of species richness, total abundance (density or % cover) and community structure (using Bray-Curtis dissimilarities on species composition and abundance). Stability generally decreased with species richness. Temporal variability in species richness increased with the number of species at both quadrat (

A survey of benthic primary production during periods of emersion was performed in a muddy-sand station of the Bay of Somme. Primary production and respiration were estimated by in situ measurements of carbon dioxide fluxes using infra-red analysis. Photosynthetic response of the community to incident light and temperature was analysed at different periods of the year. Seasonal variations of the photosynthetic parameters were estimated using the photosynthesis versus irradiance ( P–I ) curves constructed in February, April, July, August and October. The rate of maximum gross community primary production ( P m ), highly correlated to sediment chlorophyll a (Chl a ) content, was low in February (6.7 mg C m −2 h −1 ) and high in July (97.7 mg C m −2 h −1 ). Photosynthetic efficiency at low light intensity ( α ) was positively correlated to P m . The very high production ( P m =126.8 mg C m −2 h −1 ) and productivity (ratio of P m and sediment Chl a content) measured in March may be related to the set down of active planktonic microalgae. At five dates, the effects of temperature on primary production seemed to overshadow the role of light. The Q 10 for primary production varied from 1.2 in August to 3.0 in December. Daily potential primary production was calculated as a function of theoretical and measured irradiance for the period of superimposition of day and emersion. At the annual scale, the potential gross community primary production was 147 g C m −2 with theoretical irradiance and 110 g C m −2 with measured irradiances. The annual community respiration was 188 g C m −2 , leading to a heterotrophic annual budget. The annual pattern of daily production can be largely explained by changes in day length. It is also characterized by a fortnightly variability due to the variation of the total daily irradiance available for photosynthesis caused by the superimposition of the tidal and day/night cycles. Finally, sharp variations occurring with nebulosity can overshadow this fortnightly variability.

A 2D distribution of microphytobenthic biomass is determined from a superficial sediment sampling on an exposed sandy shore. The distribution undergoes a very structured pattern, displaying a few dense patches over a wide range of low density patches. We perform a statistical analysis of this 2D patterns using statistical tools developed in the field of fractal theory. It is shown that the patch pattern belongs to fractal and multifractal structures, and exhibits specific power-law in the probability space, involving the appearance of a self-organized critical state. To our knowledge, this is the first experimental study of self-organized criticality in benthic ecology. Some theoretical consequences are outlined, and their practical applications to improve our understanding of intertidal ecosystems structures and functions are discussed.

International audience; Comprehending marine invasions requires a better knowledge of the biological traits of invasive species, and the future spread of invasive species may be predicted through comprehensive overviews of their distribution. This study thus presents the current distribution of a non-indigenous species, the Asian shore crab Hemigrapsus takanoi, as well as the species population characteristics (size distribution and cohorts), based on a five-year survey (2008e2012) along the French coast of the English Channel. Two large populations were found near harbours: one on the Opal Coast (where density reached 61 ! 22 ind.m"2, mean ! s.d., in Dunkirk harbour) and one on the Calvados coast (density up to 26 ! 6 ind.m"2, mean ! s.d, in Honfleur harbour). H. takanoi exhibited a short life cycle, a rapid growth, an early sexual maturity and a high adult mortality. These features, combined with previously described high fecundity and high dispersal ability, endow this species with an 'r-selected strategy'. This strategy, which usually characterises species with a high colonisation ability, would explain the success of H. takanoi for colonising the French coast of the Channel. However, the species was found only in harbours and their vicinity; H. takanoi thus exhibited a discontinuous distribution along the 700 km of coastline. These results are discussed regarding sediment preference and potential introduction vectors. Hemigrapsus takanoi is now considered as established on the French coast and further studies are needed to evaluate the consequences of its introduction on the structure and functioning of the impacted shores

Funding provided by French National Centre for Scientific Research/INSU program EC2CO-MicroBien (Microbiologie Environnementale -BIOPOURPRE Project), European Community (ASSEMBLE grant agreement n° 227799), Region Pays de la Loire (France), Marine Alliance for Science and Technology for Scotland and the Scottish Funding Council and participating institutions. There is a relative absence of studies dealing with mats of purple sulphur bacteria in the intertidal zone. These bacteria display an array of metabolic pathways that allow them to disperse and develop under a wide variety of conditions, making these mats important in terms of ecosystem processes and functions. Mass blooms of purple sulphur bacteria develop during summer on sediments in the intertidal zone especially on macroalgal deposits. The microbial composition of different types of mats differentially affected by the development of purple sulphur bacteria was examined, at low tide, using a set of biochemical markers (fatty acids, pigments) and composition was assessed against their influence on ecosystem functions (sediment cohesiveness, CO2 fixation). We demonstrated that proliferation of purple sulphur bacteria has a major impact on intertidal mats diversity and functions. Indeed, assemblages dominated by purple sulphur bacteria (Chromatiaceae) were efficient exopolymer producers and their biostabilisation potential was significant. In addition, the massive growth of purple sulphur bacteria resulted in a net CO2 degassing whereas diatom dominated biofilms represented a net CO2 sink. Publisher PDF

International audience; A major challenge in ocean and coastal management is to find simple ways to evaluate the health of such complex ecosystems. This task may prove complicated as selection criteria needs to be established for choosing appropriate indicators and evaluation tools which do not mask or leave out inherent ecosystem properties and dynamics. Here, we review some empirical analyses and modelling techniques which can be used to derive environmental health indicators. With a series of case studies ranging from the combined use of structural and functional attributes of the system, to modelling outputs that integrate the biological and physical environments, we illustrate the usefulness and complementarities of these methods to assess ecosystem health. The choice of relevant indicators will depend on the ecological questions raised as well as the biological and habitat components considered which can range from a single level (individual or population) to multiple levels (community or ecosystem-based indicators) in the ecosystem. Each method has its own capabilities and limitations that may render it useful or insufficient in some cases. We suggest, however, that, whenever possible, the combination of ecological attributes and tools should be used to improve our knowledge and assessment of marine ecosystems for better management and conservation in the future.

International audience; The invasion process can be described as a succession of stages initiated by the transport of organisms from their native range to a new area where they persist, proliferate and spread. It is important to monitor the demographic development of invaders for management purposes. This study focuses on the different stages of population development during the invasion process and underlines the importance of understanding and monitoring the 'persistence phase'. The distribution of Hemigrapsus sanguineus (Asian shore crab) in the English Channel, along the French coast, was first undertaken in 2008. In 2010, 35 sites were surveyed and it appeared that the abundance of this species had already established a 2-5 fold increase since 2008. The present study presents the geographical distribution of H. sanguineus in 2011 and 2012 which includes a further 39 sites (72 sampling stations in 2012). All populations observed during previous years persisted in 2011 and 2012. In 2012, H. sanguineus was detected at 61 sites; 36 intensely colonised (including 3 newly colonised sites compared to 2011); 22 had trace numbers and 3 sites had 'proven presence'. In addition to males with carapaces up to 39 mm width (CW), abundances increased by a factor of 2 since 2010, which testifies for the naturalized status of the species along the French coast of the English Channel. Since 2008, La Hougue proved to be the most abundantly colonised site along the French coast. By 2011 it had an average density of 101±19 ind.m-2, with an abundance of 258±54 individuals (under 30 boulders). Populations were subsequently halved in 2012. Increasing densities and abundances recorded between 2008 and 2011 at la Hougue suggest that H. sanguineus had reached the 'expansion phase', but the dynamics of H. sanguineus populations at the most colonised sites (12 sampling sites with abundance >200 individuals under 30 boulders), suggest that maximum values had already peaked and that the 'persistence phase' was probably reached. The implementation of pluri-annual surveys seems of prime importance to correctly evaluate population dynamics of alien species.

Carbon dioxide (CO2) exchanges between a tidal flat (Wadden Sea, Netherlands) and the atmosphere were measured during a three-year survey. CO2 exchanges were monitored during 1-2 days each month between September 2006 and September 2009 using a flux chamber. The flux of CO2 was separated into two fluxes: the dark flux and the gross light flux, with the dark flux representing the flux during darkness and the gross light flux the difference between the net CO2 flux (measured under light) and the dark flux. It was argued that dark and light fluxes may deviate from respiration and photosynthesis, as the fluxes between wet tidal sediment and the atmosphere are affected by the partial pressure of CO2 in pore water, which is only gradually changed by sources and sinks of CO2 in the sediment. Light and dark fluxes were empirically related to environmental parameters in order to interpolate between succeeding measurements. The dark flux appeared to increase with temperature and the light flux became more intense with increasing irradiance with signs of saturation at high light levels on many but not all measurement days. These relations with environmental parameters showed seasonal and inter-annual variability. Fluxes were negligible just after the site was emersed and it took up to 3 h of emersion until fluxes were adapted to environmental conditions. Dark and light fluxes both showed strong seasonality with high values in summer and low values in winter. The tidal flat appeared as a source of atmospheric CO2 in the first year of measurement (+0.35 mol CO2 m(-2) yr(-1)) and a sink in the following two years (-1.59 and -0.72 mol CO2 m(-2) yr(-1)). Since the source of CO2 was observed during an extremely warm year, we suggest that climate warming might influence the carbon budget of tidal flats. (C) 2011 Elsevier Ltd. All rights reserved.

International audience; The European Marine Strategy Framework Directive (MSFD 2008/56/EC-17/06/2008) will be implemented in regions/subregions determined by their hydrology, oceanographic and biogeographic features. In this framework, Dauvin (2012) claimed that the English Channel (EC) is characterized by hydrologic, oceanographic and biogeographic features that support its division in two main ecosystems: the Western Basin (WBEC) and the Eastern Basin (EBEC). We think that this statement is controversial and that the conclusions drawn by Dauvin (2012) were not supported by the data presented, especially regarding the use of the term 'ecosystem'. We therefore re-evaluated this viewpoint with regard to the data and terminology used....

International audience; In situ measurements of both community metabolism (primary production and respiration) and PAM fluorometry were conducted during emersion on intertidal sediments in the Mont Saint-Michel Bay, in areas where oysters and mussels were cultivated. Results highlighted a low benthic metabolism compared to other intertidal areas previously investigated with the same methods. Comparisons between gross community primary production and relative electron transport rates confirmed this statement. More specifically, primary productivity remained very low all over the year, whereas the associated microalgal biomass was estimated to be high. We suggest that the microphytobenthic community studied was characterized by a self-limitation of its primary productivity by its own biomass, as previously shown in Marennes-Oléron Bay for example. The almost permanent high biomass would represent a limiting factor for micromigration processes within the first millimetres of the sediment. This could be explained by very low resuspension processes occurring in the western part of the bay, enhanced by the occurrence of numerous aquaculture structures that could decrease tidal currents in the benthic boundary layer

The eastern English Channel, the narrow channel of water separating northern France and southeast England is an area of intense human use of the array of resources concentrated into its relative small area. The vulnerability of living resources and their habitats brought together French and British maritime experts within a common project (called CHARM): to create an atlas of marine resource habitats in the eastern English Channel so as to provide planners and decision-makers with the necessary information to help managing the use of its living and non-living resources. This multidisciplinary and richly illustrated atlas provides abundant information on the legal framework and physical environment; benthic invertebrates, fish and their habitats; fishing activities; and a first attempt at developing a trophic network model (using ECOPATH software) and a marine conservation planning exercise (using MARXAN software, at a spatial resolution of 25 km(2)). Although most of the data used were collected elsewhere, some were collected especially for the project. Similarly, most of the analyses performed on the data where entirely original for this geographical area. The CHARM atlas has significantly improved the knowledge about the eastern Channel while contributing to the recognition that such holistic or multidisciplinary approaches to exploited marine systems are necessary to efficiently and durably manage their resources use., La Manche orientale, ce bras de mer qui sépare l’Angleterre de la France, est une zone très riche d’un point de vue écologique et soumise à une forte utilisation anthropique d’une gamme de ressources concentrées sur une superficie relativement faible. La fragilité des ressources marines vivantes et leurs habitats a rassemblé des experts maritimes français et britanniques autour d’un projet commun (nommé CHARM) dans le but de réaliser un atlas des habitats des ressources marines de laManche orientale. Cet atlas contient les informations nécessaires aux planificateurs et décideurs pour une meilleure gestion des ressources marines, vivantes ou non. Dans ce document pluridisciplinaire, richement illustré, on peut trouver des informations sur le cadre juridique et l’environnement, les invertébrés benthiques, les poissons et leurs habitats ; les activités de pêche ; et également sur le développement d’un modèle de réseau trophique (utilisant le logiciel ECOPATH) et un premier exercice de planification spatiale de la conservation (utilisant le logiciel MARXAN, à une résolution spatiale de 25 km2). Bien que la plupart des données aient été collectées en dehors du projet, certaines l’ont été spécialement pour le projet. De même, la plupart des analyses faites sur ces données sont entièrement inédites pour cette zone géographique. L’atlas CHARM contribue de façon significative à une meilleure connaissance de la Manche orientale tout en démontrant la nécessité de développer ce genre d’approche intégrée ou pluridisciplinaire sur les milieux marins exploités, afin de fournir les connaissances scientifiques nécessaires pour gérer efficacement et de manière durable l’utilisation de leur ressources.

International audience

From 1999 to 2005, studies carried out in the frame of regional and national French programs aimed to determine whether the Phaeocystis globosa bloom affected the intertidal benthic communities of the French coast of the eastern English Channel in terms of composition and/or functioning. Study sites were chosen to cover most of the typical shore types encountered on this coast (a rocky shore, an exposed sandy beach and a small estuary). Both the presence of active Phaeocystis cells and their degradation product (foam) did have a significant impact on the studied shores. The primary production and growth rates of the kelp Saccharina latissima decreased during the bloom because of a shortage of fight and nutrient for the macroalgae. On sandy sediments, the benthic metabolism (community respiration and community primary production), as well as the nitrification rate, were enhanced during foam deposits, in relation with the presence of bacteria and active pelagic cells within the decaying colonies. In estuarine sediments, the most impressive impact was the formation of a crust at the sediment surface due to drying foam. This led to anoxic conditions in the surface sediment and resulted in a high mortality among the benthic community. Some organisms also tended to migrate upward and were then directly accessible to the higher trophic level represented by birds. Phaeocystis then created a shortcut in the estuarine trophic network. Most of these modifications lasted shortly and all the systems considered came back to their regular properties and activities a few weeks after the end of the bloom, except for the most impacted estuarine area. (C) 2008 Elsevier Ltd. All rights reserved.

International audience; In order to provide an accurate annual rate of net benthic community production, community photosynthetic response to incident irradiance and respiration were measured at different times of the year, at mid-tide level on the muddiest part of the Mont Saint-Michel Bay. As the water turbidity prevented any photosynthesis by the microphytobenthos during immersion periods, primary production was measured only during emersion periods. In contrast respiration was expected to vary according to the tidal cycle and was measured during both emersion and immersion periods. Primary production and respiration rates under emersion were assessed using in situ infra-red gas analysis of CO(2) exchange measured in a benthic chamber. Respiration rates under immersion were assessed through total CO(2) concentration variations in incubated cores. When respiration rate was considered constant over a day and equal to the rate measured under emerged conditions, the community respiration was 54.56 gC m(-2) yr(-1). Taking into account the variations of respiration during the emersion/immersion cycle, community respiration increased to 101.76 gC m(-2) yr(-1) (86% increase). Assuming that community primary production varied as a function of irradiance from the time of exposure until flooding, GCP was 53.22 gC m(-2) yr(-1) when calculated with theoretical irradiance and 45.86 gC m(-2) yr(-1) after correction for cloudiness (14% decrease). Then, by integrating the effect of vertical migration of microphytobenthos, the rate was adjusted to 23.49 gC m(-2) yr(-1) (49% decrease). The net community production budget, calculated as the difference between the GCP and the CR budgets taking into account the corrections described above, was -78.27 gC m(-2) yr(-1). This example of annual budget calculation highlights the need to integrate several processes occurring over various time scales to accurately reflect the metabolic balance of a system The results also confirmed the heterotrophic status generally suggested for intertidal muddy sediments. (C) 2009 Elsevier Ltd. All rights reserved.

International audience; Fatty acids (FAs) profiles and stable isotope signatures of the ghost shrimp, Trypaea australiensis and the soldier crab, Mictyris longicarpus were determined at an unvegetated sandbank of Southport (Gold Coast, Queensland, Australia), in November 2005 and February 2006. Additionally, the FAs composition of the faeces and feeding pellets of M. longicarpus and the surface sediment at the study site were also analysed. Trypaea australiensis was found to selectively feed principally on benthic diatoms, as revealed by the high contribution of the marker lipid (20:5 (n-3)) to tissue total FAs and the delta 13C and delta 15N isotopic signatures of shrimp tissues. Although the diet of T. australiensis did not change between the two sampling periods, the shrimps appeared to reduce their feeding activity in summer, presumably in relation to a restricted metabolism, as revealed by a decrease in the contribution of the microalgal markers in their tissues. The FAs composition of the tissues of the soldier crab indicated that bacteria and diatoms constituted the base of its diet (contributions of branched 15:0 and 17:0, 18:1 (n-7) and 20:5 (n-3)). However, the isotopic signatures of the crabs suggested that meiofauna may represent an intermediate link between the crab and these micro-organisms

International audience

Short-term variability in benthic community primary production was studied during the course of emersion on a study site located in the Bay of Somme (eastern English Channel, France). Primary production was estimated at the community level through in situ measurements of carbon dioxide fluxes (infra-red analysis) in benthic chambers. Throughout the emersion period, gross com- munity production (GCP) exhibited strong variations that were strongly correlated with natural vari- ations in light. Light response curves explained the variations in GCP during the greater part of the emersion period, and vertical migrations of the microphytobenthos were suggested to explain the remaining variations (i.e. just before or just after immersion of the study site). A time lag was observed between the start of emersion and the maximum GCP, which was positively correlated with the time lag between emersion and local noon. The introduction of this time lag within the annual budget calculation enhanced production variability at a 2 wk time scale (i.e. tidal cycle), but light variability at the small time scale (i.e. cloudiness) remained the major factor inducing production vari- ability. Results highlighted that omitting the time lag between emersion time and the maximum GCP within annual budget calculations led to large overestimations of annual GCP, since the annual bud- get for the study site was recalculated as being 67 g C m -2 yr -1 compared to 110 g C m -2 yr -1 when the short-term variability was not taken into account.

A two year survey of benthic primary production during periods of emersion was performed on two stations of an intertidal mudflat (a muddy-sand station and a muddy station) in the Seine Estuary (English Channel, France). The goals of this study were to investigate the seasonal variations of metabolism, to estimate daily potential primary production variation at the annual scale and to estimate the annual potential primary production of the mudflat. Primary production and respiration were estimated by in situ measurements of carbon dioxide fluxes. Chlorophyll a concentration exhibited a great variability on both locations. Gross community production ranged from ca. 0 to 77 mg C m −2 h −1 at the muddy-sand location and from ca. 0 to 122 mg C m −2 h −1 at the muddy location. Community respiration showed a seasonal trend following temperature variations (up to 28.51 mg C m −2 h −1 in the muddy-sand and up to 23.40 mg C m −2 h −1 in the mud). Daily potential primary production was calculated, according to seasonal variations of photosynthetic parameters calculated using three photosynthesis versus irradiance curves obtained for the muddy location. The annual gross community primary production was 135 g C m −2 yr −1 , leading to a low autotrophic annual budget, considering an annual community respiration of 110 g C m −2 yr −1 .

Benthic community metabolism during emersion was measured in a three-year survey by monitoring CO2 fluxes in benthic chambers on an exposed sandy beach of the eastern English Channel (Wimereux, France). The three-year chronology of variations in benthic metabolism was characterised by a high variability around a low value for gross community primary production (GCP: 17.47 ± 40.85 mgC m−2 h−1, mean ± SD) and community respiration (CR: 1.66 ± 1.97 mgC m−2 h−1, mean ± SD). Although benthic metabolism remained low most of the time, some high values of primary production and respiration were occasionally detected. High primary production rates (up to 213.94 mgC m−2 h−1 measured at the end of summer) matched with the development of Euglena sp., together with the occurrence of phytoplanktonic species on the sediment, whereas high community respiration rates were detected at the end of spring on Phaeocystis sp. foam deposits. Community respiration was positively correlated with bacterial abundance, suggesting that CR was mainly supported by microfauna.

We compared 3 simple techniques for estimating the concentration of microphytoben- thos chlorophyll a at the sediment surface using high spectral-resolution field spectra. The tech- niques are based on relationships established between chlorophyll a (chl a) absorption at ~673 nm estimated from field reflectance spectra and chl a concentration in field samples. For ease of applica- tion, the best approach should provide an estimate that is independent of the physical properties of the sediment such as grain size, moisture content, etc. and of sediment type and illumination condi- tions. To achieve as comprehensive a picture as possible, tidal flats from the French shore of the east- ern English Channel that differed in sediment type and dynamics were studied at low tide and at var- ious times of the year in order to cover seasonal blooms and illumination variations. The preliminary results show that all 3 methods are fairly robust (R 2 > 0.8), with very little difference between them, indicating little influence of the measurement conditions on reflectance in the wavelength range used (570 to 720 nm) and great stability of the instrument (a portable field spectrometer) used in the field. Validation of the 3 approaches was made with further, more recently acquired data set, and a very close correlation (R 2 > 0.93, slope ~1) was found between measured and estimated chl a con- centrations for all 3 techniques at the range of chlorophyll concentrations encountered that time at the Baie de Somme site (50 to 200 mg m -2 ). The influence of sampling strategy and sediment optical properties with respect to spectral signatures must, however, be investigated in more detail. More measurements are required to fully validate the relationships found and to ensure that they are generally applicable to most intertidal flat environments.

This paper describes a closed-chamber method for measuring CO2 fluxes in intertidal soft sediments during periods of emersion. The method relies on closed-circuit incubations of undisturbed sediment and measurement of CO2 exchanges using an infrared gas analyser. The method was assessed during field experiments, both in light and dark conditions, on an exposed sandy beach and in an estuary. The rates of gross community production measured under moderate diance (4.2 mg C m(-2) h(-1) on the exposed sandy beach and 35 mg C m(-2) h(-1) in the estuary) are in good agreement with rates reported in the literature. In conjunction with appropriate sampling strategies, this method can be useful for estimating and comparing production of intertidal areas or for assessing factors that influence production.

Intertidal organisms inhabit highly variable and complex environments and are submitted to a large range of stimuli and stresses. Recently, new insights into the sensory abilities of intertidal gastropods and their subsequent ability to navigate through topographically complex landscapes demonstrated that the behavioural repertoire of intertidal gastropods is much wider than previously thought. In this context, the present thesis first aimed to ameliorate our knowledge in the thigmotactic behaviour of Littorina littorea. Specifically, thigmotactic behaviour was tested in experimental containers of different sizes and shapes. This approach allowed individuals to encounter two-dimensional and three-dimensional discontinuities in order to understand how the topographical complexity of their environment can modify this behaviour. Thigmotaxis was further tested under decreasing salinity concentrations to understand how salinity can modify gastropods behaviour, since they are typically submitted to large salinity variations during emersion periods. During emersion, intertidal organisms are also submitted to large temperature variations (up to 20°C). Thus, this work also investigated the thermal behaviour of intertidal gastropods by studying body temperature of L. littorea and Patella vulgata and their microhabitat temperature on a rocky platform on the French coasts of the eastern English Channel. Temperatures were investigated on four sunny days from June to December to test the microhabitat choice of these two intertidal gastropods species under temperature conditions typically experienced through a seasonal cycle on the Opal Coast. Aggregation behaviour in L. littorea and the associated thermal benefits previously found in gastropods literature were also investigated, (i) in situ under a moderate heat wave and (ii) ex situ under an extreme heat wave simulated under laboratory-controlled conditions. Specifically, the body temperature of individuals inside and at the edge of aggregates were investigated to assess the importance of the position within aggregates.Taken together, the results of this thesis suggest that the thigmotactic behaviour can be one of the major taxes involved in intertidal gastropods orientation. Indeed, even under unfavourable conditions (e.g. low salinity conditions), the thigmotactic behaviour is still observed in L. littorea. This work also highlighted macrohabitat preference in L. littorea and P. vulgata for biogenic structures which allow to reduce both desiccation and thermal stresses. Within a macrohabitat, intertidal organisms are able to take advantage of the thermal mosaic encountered in intertidal environment and select microhabitat. This microhabitat selection in gastropods, is species- temperature- and habitat-dependent and allows individuals to maintain their body into their optimal range of temperatures. Finally, this work stressed the absence of thermal benefits of being aggregated in L. littorea under heat stress conditions. Specifically, under extreme heat wave, body temperature of individuals inside the aggregate is higher than for individuals at the edge of the aggregate. This result raised the rather unexpected and still unresolved question to understand the mechanisms driving aggregation behaviour in L. littorea. These results nevertheless contribute to the growing evidence that studying behaviour in intertidal gastropods is critical to understand how they move, how they perceive their environment and how they cope with raising temperature under global warming. This work also highlighted the importance of a better understanding of the thermoregulatory behaviour in intertidal organisms, for a better estimation of the impact of global warming in their ecology.; Les organismes intertidaux vivent dans un environnement variable et complexe et sont soumis à de nombreux stimulus et stress. Récemment, de nouvelles études sur les capacités sensorielles de ces gastéropodes et sur leur capacité à se déplacer dans leur environnement, ont démontrées que leur répertoire comportemental était plus large que prévu. Dans ce contexte, cette thèse a pour but d’améliorer nos connaissances sur le comportement de thigmotaxie chez Littorina littorea. La thigmotaxie a donc été testée dans des dispositifs expérimentaux de différentes tailles et de différentes formes. Cette approche permet aux individus de rencontrer des discontinuités en 2-dimension ou en 3-dimension et a pour but d’aider à comprendre comment la complexité topographique de leur environnement peut modifier le comportement thigmotactique chez les gastéropodes. La thigmotaxie a aussi été testée sous différentes conditions de salinité pour comprendre comment ces variations de salinité peuvent altérer leur comportement. En effet, les organismes intertidaux sont soumis à de larges variations de salinité pendant les périodes d’émersion. Pendant ces périodes d’émersion, ils sont aussi soumis à de grandes variations de température (jusqu’à 20°C). Ce travail s’intéresse aussi au comportement thermique des gastéropodes intertidaux via l’étude de la température du corps de L. littorea et de Patella vulgata et celle de leur microhabitat. Ces températures sont étudiées durant 4 jours ensoleillés, de Juin à Décembre, afin de tester le choix d’un microhabitat par ces 2 espèces de gastéropodes sous des conditions de températures auxquelles ils peuvent être soumis au cours d’un cycle saisonnier sur la Côte d’Opale. Le comportement d’agrégation chez L. littorea et les bénéfices thermiques associés précédemment étudiés dans la littérature sont aussi examinés, (i) in situ sous des conditions de vague de chaleur modérée et (ii) ex situ sous des conditions extrêmes de vague de chaleur simulée au laboratoire. En particulier, la température du corps des individus à l’intérieur et de ceux à l’extérieur des agrégats est étudiée pour comprendre l’importance de la position des individus au sein des agrégats.Ces résultats suggèrent que la thigmotaxie semble être l’une des taxies majeures impliquée dans l’orientation des gastéropodes. En effet, même sous des conditions défavorables (i.e. salinité basse), le comportement thigmotactique est observé chez L. littorea. Ce travail souligne également une préférence pour les macrohabitats biogéniques chez L. littorea et P. vulgata, qui permettent de réduire les stress thermique et de dessiccation. Au sein d’un macrohabitat, les organismes intertidaux sont capables de tirer avantage de la mosaïque thermique rencontrée dans leurs environnements et de sélectionner un microhabitat. Chez les gastéropodes, cette sélection de microhabitat est espèce-, température- et habitat-dépendante et leur permet de se maintenir dans leur optimum de températures. Pour finir, ce travail souligne l’absence de bénéfice thermique à être agrégé chez L. littorea sous des conditions de stress thermique. En particulier, sous des conditions de vague de chaleur extrême, la température du corps des individus à l’intérieur de l’agrégat est supérieure à celle des individus à l’extérieur de l’agrégat. Ce résultat pose la question, encore irrésolue, des mécanismes qui entrainent le comportement d’agrégation chez L. littorea.Ces résultats contribuent néanmoins à la preuve croissante qu’étudier le comportement chez les gastéropodes intertidaux est crucial pour comprendre comment ils se déplacent, perçoivent leur environnement et peuvent réagir à l’augmentation des températures dans le cadre du réchauffement global. Ce travail souligne également l’importance d’une meilleure compréhension de la thermorégulation chez les organismes intertidaux, pour permettre une meilleure estimation de l’impact du réchauffement global sur leur écologie.