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(IF 1.67; Q2); International audience; An overview is presented of the Non-Indigenous Species (NIS) of algae and invertebrates recorded in the marine and brackish coastal waters of Normandy in France. Out of the 152 NIS found, 86 have been introduced through shipping (ballast waters and fouling) and 66 through aquaculture activities. A total of 95 NIS are linked to a Pacific origin and 32 come from the northwestern region of the Atlantic. Among the 152 NIS identified, only nine show an invasive demography in Normandy waters. The first introductions occurred in the middle of the 19 th century and became frequent by the beginning of the 20 th century. However, over 50% of the NIS so far recorded were found only during the three last decades.

International audience; The fauna inhabiting the brown seaweed Sargassum muticum was studied on a spatial scale along the Normandy coast from the Normand-Breton Gulf to the Bay of Seine (English Channel) in both shallow sandy and rocky tidal pools during the springs 2018 and 2019. In this paper, we test the following hypothesis: do the areas with dense populations of S. muticum represent an appropriate habitat for dense motile fauna including other Non-Indigenous Species (NIS)? The ALEX (ALien biotic indEX) is used to ascertain whether or not S. muticum favours the establishment of other NIS in this new habitat. Results show that the epifaunal assemblage associated with S. muticum differs between the five sampling sites. However, the fauna at all five sites is dominated by arthropoda, especially the amphipods and isopods. In addition, five non indigenous species are observed inhabiting the brown seaweed (four amphipods: Aoroides longimerus, Aoroides semicurvatus, Monocorophium acherusicum, Monocorophium sextonae and one decapod: Hemigrapsus sanguineus). In spite of the presence of Non-Indigenous Species (NIS) associated with the invasive Sargassum, the ALEX yields a high Ecological Quality Status for all the sites. Nevertheless, the results suggest that S. muticum is a suitable habitat for many invertebrates especially amphipods and isopods, while also representing a potential source of food for several local fish and cephalopod species.

This study records the number of Peracarida (Cumacea, Isopoda, Mysida, Lophogastrida and Tanaidacea) from Algerian coastal waters. A total of 170 species are reported with the highest richness observed in the Isopoda (71 species), then the Cumacea with 43 species, the Mysida and Tanaidacea with 27 species each and the Lophogastrida with only two species. The diversity of Peracarida in Algeria is high, corresponding to 60% of the species recorded for the Mediterranean Sea. A geographical analysis of the distribution of the species shows that the Algerian fauna has a close similarity with taxa reported from both the European and African coasts of the Atlantic Ocean. This reflects the influence of Atlantic waters along the North African coasts extending from Morocco to Tunisia in the south of the Mediterranean Sea, which is related to the connection via the Strait of Gibraltar. For the Algerian coasts only five Peracarida species may be considered as Non-Indigenous Species.

This study from January to December 2018 was the first initiative of a Port Baseline Survey (PBS) aimed at assessing the impact of biological invasions in harbours of the Gulf of Gabès (GG). A total of 12 fishing and industrial harbours were seasonally prospected during 2018. A total of 174 macrobenthos taxa were recorded, belonging to eight zoological groups, with a dominance of crustaceans (32%), molluscs (31%) and polychaetes (20%). Among these taxa, 57 were Non-Indigenous Species (NIS) for Tunisian waters, while 27 species were recorded for the first time in GG harbours and three decapods ( Dyspanopeus sayi, Hippolyte prideauxiana and Pilumnus minutus ) and one amphipod ( Hamimaera hamigera ) were newly recorded from Tunisian waters. Two main categories of harbours are distinguished according to their macrobenthic communities and environmental features (essentially edaphic factors). The industrial harbours yield higher numbers of species and abundance of NIS than the fishing ports. The ALEX metric is used to evaluate the biological invasion status of the Gulf of Gabès harbours, showing that their status ranges from unaffected in fishing harbours to extremely affected in industrial harbours. Three biotic indices (AMBI, BO2A and BENTIX) are applied to assess the ecological status of harbours, which varies from moderate to good. ALEX and the other biotic indices are significantly correlated with harbour characteristics, maritime traffic and edaphic factors (organic matter and chemical contamination). The present study gives an overview of all available benthic data, the impact of biological invasions and the ecological quality status of harbours in the Gulf of Gabès. The results could be considered as providing important baseline data for the implementation of environmental policies and management plans in the future.

International audience; The French coast of the Atlantic and English Channel (EC) is promising for the development of Marine Renewable Energy (MRE), including wind, wave, and tidal stream, due to the high velocity of currents in some parts of the area. This paper, focusing on wind and tidal energy, discusses how the implementation of MRE converters influences biodiversity, and vice versa, through biofouling and reef effects. The understanding of these interactions requires the knowledge of the hydro-sedimentary conditions and the macrofauna. The research on these topics, performed at the Continental and Coastal Morphodynamic laboratory (M2C) (UNICAEN, France), is presented through a multi-disciplinary approach by i) studying the hydrodynamic conditions and the macrofauna in Alderney Race, ii) studying the biofouling effects on tidal turbines and their influence on the turbulent wake, iii) assessing the hydro-sedimentary impacts induced by the offshore wind farm, like scouring, and iv) taking an ecosystem approach on MRE, such as the reef effect. From an ecological perspective, the reef effect can be responsible for changes in the structure and function of the ecosystem. Although several studies have analyzed this effect at the species-or community-scale, the propagation of the reef effect at the ecosystem-scale remains unclear. Thus, understanding these ecosystem-scale effects is urgent for future research. From an engineering perspective, biofouling changes the structural characteristics (i.e., supplementary mass) of the converters and thus, affects their performance.

International audience; From collected data analyzed to produce an inventory of all polychaetes in Algerian waters, the diversity of this group was estimated as 534 species. The largest families are Syllidae (66 species), Spionidae (37 species) and Terebellidae (27 species). The presence of those listed species along the Algerian coast was compared with their occurrence in nine other areas of the Mediter-ranean Sea, in the Black Sea and in four other more distant seas around the world. Comparisons are also made with respect to the biogeographical origin for each species. The polychaete fauna of the Algerian coast is among the richest of the Mediterranean Sea and comparable to the diversity reported for the French Mediterranean continental shelf and that in the Aegean Sea, but higher that that found in the nearby coastlines of Morocco and Tunisia. Most of the species found have an Atlantic origin and are present in the western Mediterranean Sea. This current inventory includes eight non-indigenous polychaete species found in the Algerian waters.

The Bay of Seine (Normandy coast of the English Channel) is a highly impacted ecosystem concerned by numerous human activities. It is subjected to heavy historic anthropogenic pressures and the emergence of new human activities: fishing, harbour extension, aggregate extraction, deposition of dredged sediment, and offshore wind farms. By contrast, this area shows a high level of protection of its natural heritage, mainly owing to the Natural Reserve and Natura 2000 sites. Moreover, an accumulation of research projects has ensured the acquisition of a high level of scientific knowledge and high-quality ecological data in this area. However, there is a lack of a systematic approach taking into account the available data. By building maps of benthic habitats, food-web modelling and calculating ecological indicators, we are able to take the first steps towards an ecosystem-based management. These integrative approaches allow us to assess the ecological quality status of the Bay of Seine and the Seine estuary. Trophic models based on the quantification of energy and matter fluxes in ecosystems, as well as indices derived from ecological network analysis, are used to describe the interaction between species across all trophic levels. When applied to spatial models, ecological functioning and ecosystem health can be assessed in different areas of the ecosystem. In the Bay of Seine, benthic habitats display high resilience while pelagic, fish and bird compartments have been shown to be highly modified, due to hydrological and climatic changes. The North Channel and the Navigation Channel of the Seine estuary appear to be far more intensely stressed, while the South Channel and marine areas of the Bay show a more mature functioning. Our conclusions reveal the need to consider the influence of human pressures on the functioning of complex ecosystems, thus providing an integrated approach that can be used to study a social-ecological system affected by global changes and investigate the cumulative impacts of human activities.

The establishment of benthic marine habitat maps plays an important role in the conservation and management of coastal ecosystems faced with the increasing impacts of human activities. The Bay of Seine, bordering the eastern part of the English Channel, is an area undergoing considerable cumulative impacts, and which consequently requires a synthesis of our knowledge of the ecological status of its benthic habitats. Fortunately, numerous benthic sampling campaigns have been carried out over the last two decades, mainly in the eastern and western shallow parts of the bay. These campaigns have led to the construction of a database, allowing statistical analyses at the scale of the whole area which are then used to produce maps. Nevertheless, it appears that maps constructed using existing Natura 2000, EUNIS (European Nature Information System), and French MNHN (Museum National d’Histoire Naturelle) typologies are not enough detailed to distinguish the mosaic of habitats of the Seine estuary. It is indispensable to add expert judgements concerning local areas to updated maps of the benthic communities in the Bay of Seine. Several Natural Zones of Interest for Ecology in terms of Flora and Fauna named ‘ZNIEFF-Marine’ areas have been identified, which could be useful in the future in the context of marine Natura 2000 sites for the management and conservation of endangered marine habitats in this maritime zone subject to highly conflicting interests.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASARE [ADD1_IRSTEA]Dynamique et fonctionnement des écosystèmes(IF 4.49 [2018]; Q1); International audience; A combination of modelling tools was applied to simulate the impacts of the future Courseulles-sur-mer offshore wind farm (OWF) construction (Bay of Seine, English Channel) on the ecosystem structure and functioning. To do so, food-web models of the ecosystem under three scenarios were constructed to investigate the effect caused by the OWF of added substrate (reef effect), fishing restriction (reserve effect), and their combined effect. Further, Ecological Network Analysis indices and Mean Trophic Level were derived to investigate their suitability for detecting changes in the ecosystem state. Our analysis suggests changes in the ecosystem structure and functioning after the OWF construction, the ecosystem maturity was predicted to increase, but no alterations in its overall resilience capacity.

(IF 0.78 [2018]; Q3); International audience; Two galatheoid anomurans, Gastrosacus raboeufi n. sp. and G. sp., the earliest members of the genus Gastrosacus von Meyer, 1851 known to date, are recorded from upper Bathonian strata in Calvados (Normandy, France). In this respect, we consider the enigmatic Palaeomunidopsis moutieri Van Straelen, 1925 from the middle Bathonian of Giberville (Normandy) to be a nomen dubium. As far as carapace morphology of G. raboeufi n. sp. is concerned, we note that it reveals a number of primitive characters that are indicative of a close relationship with the Gastrodoridae amongst paguroid anomurans.

(IF 1.74 [2018]; Q2); International audience; The mysid Neomysis americana (S.I. Smith, 1873), which originates from North-American estuaries, was reported for the first time in 2017 in the Seine estuary (English Channel, France). This sighting represents the second reported occurrence of this species in Europe, following the record of two individuals in 2010 in the Wadden Sea (Netherlands). Its appearance seems recent since no individuals were recorded in previous intensive sampling carried out in the navigational channel and North Channel of the Seine estuary since the middle of the 1990s. In 2017, a total of 2674 individuals of N. americana were sampled, showing the rapid establishment of a reproductive population which was favorised by the decline of the autochthonous population of Neomysis integer (Leach, 1814).

International audience; Since the beginning of the 2000’, the French government ambition was to have an offshore wind production formed 40% of the renewable electricity in 2030. Three calls tenders of Offshore Wind Farms (OWFs) construction have been pronounced since 2011. However, no offshore wind farm (OWF) had been constructed at the end of 2017 due to long administrative procedures and numerous appeals in justice, at French and European levels. Nevertheless, several studies have been enterprised to identify the environmental conditions and ecosystem functioning in selected sites before OWF implantations. However, these studies are generally focused on the conservation of some species or groups of species, and there is no holistic study on the effects of the construction and operation of OWF on an ecosystem taken as a whole. In 2017, a complete and integrated view of the ecosystem of two future OWF sites of the eastern English Channel (Courseulles-sur-Mer and Dieppe-Le Tréport) was developed to model the marine ecosystems before OWF implementation and to simulate reef effects due to new spatial occupation of maritime territory. Results contribute to a better knowledge of the impacts of the OWFs on the functioning of marine ecosystems. They also allow to define recommendations for environmental managers and industry in terms of monitoring the effects of marine renewable energy (MRE), not only locally but also on other sites, at national and European levels.

International audience; Offshore Wind Farms (OWFs) in the English Channel and along the coast of Normandy (France) will be installed on coarse sediments, which cover about 80% of the seabed of the English Channel. A BACI (Before After Control Impact) approach has been recommended by the French State for each of these OWFs. This provides the opportunity to acquire macrofauna data and assess the Ecological Quality Status in areas that are poorly sampled. In the case of the Dieppe-Le Tréport (DLT) OWF, for that, a sampling strategy was developed in 2014–2016 to establish a ‘Before’ state for the sediment and macrofauna. Results highlight that the DLT OWF project site includes three different sediment type: sandy Gravel (sG), gravelly Sand (gS) and medium Sand (mS). Taxonomic Richness and abundances are dominated by Annelids in all three habitats, followed by Arthropods and Molluscs. In terms of biomass, Molluscs (bivalves) are predominant in sG and gS, while Echinoderms and Polychaetes along with bivalves represent a high fraction of the biomass in mS. Surface Deposit Feeders are the most important group in terms of abundance, while Filter feeders largely dominate the biomass. The benthic indices based on abundances reveal a high Ecological Quality Status for the three sediment types. However, due to the predominant contribution of the bivalve Glycymeris glycymeris to the biomass, the habitat quality appears to vary from moderate to bad. In comparison with other similar habitats, the Taxonomic Richness and Abundances of coarse sediments and medium sand are in the same order of magnitude as other sites. However, the biomasses are among the highest so far recorded, reflecting the importance of this area as a hotspot of biomass in the English Channel.

The European seas are known to be the recipient of several hundreds of Non-Native Species (NNS) due two main origins: shipping and aquaculture. More than 160 NNS had been recorded along the Normandy coast, which remains low in comparison with the number of marine invertebrate species known in the English Channel (> 3,000). The main sites of introduction are the harbours, especially Le Havre and the oyster cultivation zones. Among these NNS, 56 are present in Normandy and considered invasive along the European coasts, but only ten (one macro-algae and nine invertebrates) are invasive in Normandy. Six examples are illustrate, the molluscs Magallana gigas, Crepidula fornicata, Ensis leei, and Ruditapes philippinarum, the polychaete Ficopomatus enigmaticus and the crab Hemigrapsus sanguineus. The two first species have changed the dynamics and functioning of the coastal ecosystems, while the others have lower impact. In fact, the oyster and the manila clam are now key species for the French economy, while the rapid expansion of the other species change biodiversity in the more colonised sites. The ALEX (ALien Biotic IndEX) proposed by Cinar and Bakir in 2014 for the Mediterranean Sea is used for the first time in Atlantic waters.

The Gulf of Gabès on the southern coasts of Tunisia in the central part of the Mediterranean is a very shallow basin, characterized by semidiurnal tides, attaining a range of 2.3 m during spring tides. The intertidal zone was covered by extended Zostera (Zosterella) noltei Hornemann, 1832 beds mainly developed around the Kneiss Islands while tidal channels ensured the water circulation in this sub-tropical environment with very low freshwater input and high summer temperature. In spite of protected conventions, the area remained under high human pressures: overfishing, and the impact of the pollution of the phosphate industry. Intensive sampling in both intertidal and shallow subtidal zones during annual cycles permitted to identify a rich macrofauna which increase considerably the species known in this eastern part of the Mediterranean Sea. More than 50 species are added for the Tunisian fauna. Moreover, patterns of diversity are analysed with the sediment types, presence or absence of Zostera noltei seagrass bed, and human pressures. The list of the collected species are compared with those of surrounding areas in both Western and Eastern Mediterranean Sea.

(IF 2.87; Q1); International audience; As part of the energy transition, the French government is planning the construction of Offshore Wind Farms (OWFs) in Normandy. These OWFs will be integrated into an ecosystem already facing multiple anthropogenic disturbances. A holistic view of cumulated impacts (OWF construction, global warming and fisheries) were developed on the Courseulles-sur-Mer’ ecosystem through the use of a qualitative mathematical modelling approach. This modelling approach provides the mean to consider alternative hypotheses about how the ecosystem structure and function affects its dynamics. Alternative models were constructed to address the different hypotheses regarding the behaviour of top predator (whether the top predators will be scared away by the OWF or attracted by the reef effect), impacts of global warming and changes in fisheries activities. Key findings from these analyses are that the OWF construction could lead to an increase in benthos species and fish benthos feeders whatever the perturbation scenario, while the predicted response of top predators was ambiguous across all perturbation scenario. Qualitative modelling results can play a vital role in decision making by improving long term planning for the marine environment but also as a tool for communication with the public and so contribute to a better acceptability of the Marine Renewable Energy (MRE) project.

(IF 1.74; Q2); International audience; Asthenognathus atlanticus Monod, 1932, is reported here for the first time in the area around Dieppe-Le Tréport (Normandy coast in the eastern part of the English Channel). A total of 26 specimens were collected in 2015–2016 from fine and coarse sands at water depths between 12 and 25 m. Two specimens were found in the stomach of two thornback rays Raja clavata. The eastward progression of A. atlanticus is consistent with tidal residual currents in the English Channel. The period of global warming is likely favorable for this easterly progression, and the species could reach the southern part of the North Sea in a few years. Our observations in the eastern part of the English Channel also illustrate a new commensal association between the tubicolous polychaete C. variopedatus and the crab A. atlanticus, the latter being found in a variety of soft-bottom sediments ranging from muddy to coarse sands, in agreement with reports of its presence in the Rade de Cherbourg and the Bay of Seine.

Background Finding of a single female specimen of the African mangrove crab Perisesarma alberti Rathbun, Bull Am Mus Nat Hist 43: 379–474, 1921, in the intertidal zone of the eastern part of the Bay of Seine, English Channel, France. Result Identification and description of the recorded crab, photographs and measurements of the single specimen. Comparison with reports from West African mangroves. Conclusion It is unlikely to assume an African origin of the collected species. It is more likely a species escaped from an aqua-terrarium, even if the common species in the French aquarium trade have an Australasian origin.

International audience; In the Gulf of Gabès (South-eastern Tunisia), polychaete bait digging is widely practiced for recreational and commercial fishing and is an economically significant activity. The present study aims to assess the short-term effects of intertidal bait digging on macrobenthic communities from the Kneiss Islands. Following a protocol with a control station (not impacted) and three impacted stations for polychaete collection, the study was conducted during March and April 2015 at spring tides. After digging, immediate significant decreases were observed in the abundance of total macrofauna as well in numerous families of polychaetes. Control of this activity should be proposed for the future to protect the biodiversity of this intertidal area of high heritage interest.

Among the polychaetes, the Syllidae comprise numerous species whose study over many years has benefitted from valuable revisions and descriptions of new species in Europe. This abundant literature proves very useful for revisiting the taxonomy and distribution of the Syllidae in the English Channel (EC), mainly as regards existing studies on coarse sediment communities in the eastern part of the Channel. This habitat is one of the most widespread in the EC and is known as favourable for the small polychaete fauna including Syllidae. A 2-year survey (winter and summer sampling periods) covering 19 stations, associated with theBranchiostoma lanceolatumcoarse sand community offshore Dieppe-Le Tréport, led to the identification of 6537 individuals from 29 taxa including 27 species. Six fine sand stations were also sampled in which only 12 individuals were collected. Among these species, seven are new for the EC polychaete fauna and six others are observed for the first time in the eastern part of the EC. All the new species for the EC are warm temperate species previously only known south of the Bay of Biscay. The Syllidae list given in Dauvinet al. (2003) has been re-analysed and amended with our list and that of the Chausey Archipelago study (Olivieret al., 2012). To date, 91 Syllidae species have been recorded in the EC and are established mostly in coarse sediments.

International audience; An experimental study was conducted to assess the physical and biological impacts of muddy fine sand 3 dredged material dumped on a medium sand site MACHU offshore the Seine Estuary. Complementary 4 trophic web modelling tools were applied to the MACHU ecosystem to analyse the effects of dumping 5 operations. Results show that, after the dumping operations, the biomass of fish increased while 6 invertebrate biomass remained relatively stable through time. Nevertheless, the biomasses of benthic 7 invertebrates, omnivores/scavengers and predators showed some increases, while non-selective 8 deposit feeders and filter feeders decreased. At the ecosystem level, results show that the total 9 ecosystem activity, the ascendency and the overall omnivorous character of the food-web structure 10 increased after dumping operations, whereas recycling subsequently decreased. Finally, the fine and 11 medium sand habitat offshore from the Seine estuary, which undergoes regular natural physical 12 perturbations, shows a high resilience after a short dumping phase. 13

A Before/During/After Control-Impact approach is used to assess the effects of Port 2000 on the suprabenthos in the North Channel (NC) of the Seine estuary during the period from September 2001 to October 2015. Since the beginning of Port 2000 construction (2002-2005), the NC is affected by an increase of salinity (marine influence) and input of sand. The suprabenthos changes are mainly characterised by an increase in species richness in the upper part of the NC and a decrease in species density and biomass of the dominant mysid species over time. Multiple stressors (natural and anthropogenic) have been operating simultaneously (hydrological changes, construction of Port 2000, supplementary dredging) rendering the interpretation of the biological changes difficult. Thus, the present results evidenced a combination of changes in the Seine Estuary not only attributed to the impact of the Port 2000 construction.

International audience; This study aims to identify the composition and the distribution of macrobenthic communities in the Rade de Cherbourg (RdC), on the north coast of the Cotentin Peninsula (Normandy, France). The results show the presence of six main benthic communities: (1) Crepidula fornicata banks in coarse mixed sediment, (2) Amphipholis squamata and Apseudopsis latreillii in mixed sediment, (3) Melinna palmata in muddy sand, (4) Melinna palmata in mixed muddy fine sand, (5) Spio decoratus in fine sand and (6) Spio decoratus and Apseudopsis latreillii in very fine and fine sand (from EUNIS classification). The RdC appears as a rich soft bottom macrobenthic habitat in a semi-enclosed bay, surrounded by hard-bottom environments. However, current and future projects related to human activities (harbour extension, salmon farming) could impact the benthic communities. Moreover, the structure and composition of the muddy fine sand and fine sand communities, which are dominant within the area of the RdC, show similarities with comparable communities found in the western English Channel under the influence of Atlantic waters.

International audience; The polychaete Sabellaria alveolata (Linnaeus, 1767) is an important ecosystem engineer building reef structureswhich add to the topographic complexity in colonized areas. In Europe, the most extensive reef formation is located in the Bay of Mont-Saint-Michel (France). Since 2006, Sabellaria bio-constructions have developed on hard substrates along the west coast of the Cotentin Peninsula between Champeaux and Saint-Germain-sur-Ay on the northern part of the Bay of Mont-Saint-Michel. In this sector, two distinct types of bio-construction can be distinguished: platforms and reefs. The aim of this study is to analyse the patterns of the associated macrofauna on these platforms and reefs, as well as outside, and test for a correlation between the presence of Sabellaria bio-constructions and the richness of the benthic macrofauna. Univariate analyses are used to compare the macrofauna on four sites (Champeaux, Lingreville, Blainville-sur-Mer and Saint-Germain-sur-Ay). The results show a higher taxonomic richness on the platform-type than on the reef-type structures, and also a higher taxonomic richness outside the bio-construction areas. This suggests that, on the examined sites, the presence of S. alveolata bio-constructions does not contribute to higher levels of benthic macrofaunal richness on hard substrates. Temporary bio-constructions along this coast exhibit reefs of interest at some sites as well as in very small zones which merit special attention.

Along the French coast of the English Channel, Hemigrapsus sanguineus (De Haan, 1835) is abundant under boulders on exposed shores that have high-energy hydrodynamic conditions in the intertidal zone. However, small individuals (< 6 mm) are rare in the muddy gravel sediments under boulders and the settlement habitat for post-larvae is largely unknown. This study explored whether mussel beds could represent a settlement zone for H. sanguineus . At the end of the summer of 2013, there were many post-larvae and small crabs in some mussel beds, with up to 528 individuals/m². However, at one location, no juveniles of H. sanguineus were found in mussel bed habitat despite the presence of adults on the same shore. We conclude that mussel beds are an important habitat for the settlement of juvenile crabs. Key words: Asian shore crabs, invasive marine species, English Channel Introduction The introduction of alien shore crabs into coastal environments is mainly the result of human activities that are becoming more frequent with the ever-increasing maritime traffic levels (Williams 1984; Ng et al. 2008). Nevertheless, the introduction of invasive species is a complex phenomenon, and there is a pressing need to assess the risks linked to biological invasions. In some cases, the introduced species can have a strong negative, or even a positive, effect on native species and/or communities (Carlton 1989; Ruiz et al. 1997; Cohen and Carlton 1998; Occhipinti-Ambrogi 2007). The Asian shore crab

Recreational and professional clam fishing was an important activity on the extensive intertidal zone of the western Cotentin coast (western English Channel). A variety of fishing gear was used to harvest the target species: the European clam Ruditapes decussatus (Linnaeus, 1758) and the introduced Manila clam R. philippinarum (Adams and Reeve, 1850). In this study, we studied the effect of rake harvesting during the spring tides of February–March 2014, following an experimental design with a control station and three stations impacted by rake harvesting in three sediment types: sandy, gravelly, and mixed gravelly rocky habitats. No significant sediment and macrofauna changes occurred at the three sites after rake harvesting. Nevertheless, the number of clams decreased significantly after raking on the gravelly habitat, whereas in the other two habitats, sediment transport in this high-energy hydrodynamic environment was able to transfer clams and other macrofauna species across the fishing sites, thus minimizing the effects of rake harvesting. Therefore, although the effect of rake harvesting appeared limited during winter, the regional impact (high fishing pressure along 60 km of coast) and increase of recreational fishers during summer needed to be studied in the future.

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

International audience; The freshwater discharge into the Seine estuary decreased between 1996 and 2012 and no discharge N 1200 m3 s−1 has occurred after 2001. The suprabenthic community in the navigational channel ofthe Seine estuary was characterised in 1996 by high abundances and biomass of mysids and the decapod Palaemon longirostris, which were among the highest in the world for transitional waters during a period of high discharge of the Seine River. A recent sampling (2011-2012) of the suprabenthos in new hydrological conditions (i.e., lowriver discharge) showed subsequent changes of the quantitative composition of the community with both decreases of abundance and biomass. Such long-term changes were probably due to the combination of hydrological changes, and anthropogenic modifications of the entrance of the Estuary, the Port 2000 construction, and supplementary dredging in the navigational channel of the Rouen harbour. The changes of the suprabenthic community encompassed an important impact in the estuarine trophic chain, which was essential to fish juveniles, such as sea bass and flat fish.

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.