The amphipod Incisocalliope aestuarius was recently collected since 2015 in the mesohaline part of the Gironde Estuary (SW France) with a van Veen grab and in the lower intertidal part in oyster bed by hand-picking. A look back at past studies showed that this species was present in this estuary since 1976, whereas the original description of this amphipod comes from Watling and Maurer in 1973, from the East coast of America. The validity of the Incisocalliope genus is herein questioned, and it is proposed to transfer species of the genus Inciscalliope to Parapleustes genus.

Biological invasions are one of the main global threats to biodiversity in terrestrial, freshwater and marine ecosystems worldwide, requiring effective inventorying and monitoring programs. Here, we present an updated list of non-indigenous species in French marine and transitional waters. Focused on eukaryote pluricellular species found throughout the three metropolitan French marine regions (Western Mediterranean Sea, Bay of Biscay and the Northern Seas), a total of 342 non-indigenous, including 42 cryptogenic, species are listed as having been introduced since the 13th century. The majority of the species originated from the temperate Northern Pacific. They mainly arrived through both ballast and hull fouling and also are associated with shellfish farming activities. Most of them have been introduced since the 1970s, a time when maritime and aquaculture trade intensified. Despite important human-aided opportunities for species transfer between the three marine regions (for instance, via recreational boating or aquaculture transfers), only a third of these NIS are common to all regions, as expected due to their environmental specificities.

Celtodoryx ciocalyptoides is a Pacific sponge recorded for the first time as invasive in Europe (south Brittany, France) in 1996, then in 2005 (The Netherlands) and 2014 (eastern English Channel), likely in relation with aquaculture activities. It was observed by amateur divers in Arcachon Bay, Hossegor Lake (SW coast of France) and Thau Lagoon (French Mediterranean), but our study formally confirms its presence in the former two locations. Among the associated species, there was another non-indigenous species in both sites, the spionid polychaete Polydora colonia. Described from USA Atlantic coasts and later found in the Mediterranean, this worm seems to live exclusively in association with C. ciocalyptoides in our study sites. We suggest that this unlikely association between a Pacific sponge and a Western Atlantic worm, likely distributed along European coasts by oyster transfers, is probably more widespread than currently known.

At the interface between terrestrial and marine biomes, estuaries display high ecological productivity and provide goods and services to humans. Associated with many ecological functions, they are nursery, refuge, and growing areas for many species fish. These ecological functions and services depend on both their ecological production and trophic carrying capacity and the durability of food web functioning. These transitional key habitats undergo both strong anthropogenic pressures and climatic influences that impact the structure and dynamics of estuarine biodiversity. In this context, we explore, here, three decades of the Gironde estuary ecosystem history to detect the food web’s response to global changes-induced effect on biodiversity. At least two Ecological Abrupt Shifts associated with deep modifications in the biodiversity at most trophic levels have been documented for this particular ecosystem. Three food web models were thus calibrated, one for each of the three periods discriminated by the two shifts that occurred at the end of the 1980s and the beginning of the 2000s. Results highlighted that the ecotrophic efficiency estimate for subtidal macrofauna and shrimps reached the maximum possible values during the last period. This could mean that the Gironde estuary fully reached its trophic carrying capacity due to a food limitation especially for benthos demersal fish. We also observed a significant decrease in some food web indicators (such as Average Mutual Information, System Omnivory Index, and Average Path Length) usually associated with ecosystem stress, suggesting a significant impact of global change on the Gironde estuary ecosystem health and questioning the sustainability of the ecological functions associated with this ecosystem.

The spionid polychaete Boccardia proboscidea Hartman, 1940 is a tube-dweller and shell/stone-borer widely occurring in temperate waters across the world and considered invasive in many areas. It was originally described from California, USA, and later reported from Pacific Canada, the Asian Pacific, Australia, New Zealand, Argentina, South Africa, and northern Europe. The Bayesian inference analysis of sequence data of three gene fragments (836 bp in total) of the mitochondrial 16S rDNA, nuclear 28S rDNA, and Histone 3 has shown that individuals from the Pacific coasts of Canada and the USA, Argentina, Australia, South Africa, the United Kingdom, and Mediterranean France were genetically very similar (maximal average p-distance value, 0.49%, was between 16S rDNA sequences). We consider these individuals to be conspecific and report the earliest records of B. proboscidea from the UK and a possible first Mediterranean record in the Gulf of Lion. The high 16S haplotype diversity of B. proboscidea detected in the north-eastern Pacific suggests a native distribution for the species in the northern Pacific and subsequent introductions through human activities to other parts of the world. The histories of these introductions are reviewed and the hypotheses about times and places of introductions are updated.

Coastal ecosystems are highly complex and driven by multiple environmental factors. To date we lack scientific evidence for the relative contribution of natural and anthropogenic drivers for the majority of marine habitats in order to adequately assess the role of different stressors across the European seas. Such relationship can be investigated by analysing the correlation between environmental variables and biotic patterns in multivariate space and taking into account non-linearities. Within the framework of the EMBOS (European Marine Biodiversity Observatory System) programme, hard bottom intertidal communities were sampled in a standardized way across European seas. Links between key natural and anthropogenic drivers and hard bottom communities were analysed using Boosted Regression Trees modelling. The study identified strong interregional variability and showed that patterns of hard bottom macroalgal and invertebrate communities were primarily a function of tidal regime, nutrient loading and water temperature (anomalies). The strength and shape of functional form relationships varied widely however among types of organisms (understorey algae composing mostly filamentous species, canopy-forming algae or sessile invertebrates) and aggregated community variables (cover or richness). Tidal regime significantly modulated the effect of nutrient load on the cover and richness of understorey algae and sessile invertebrates. In contrast, hydroclimate was more important for canopy algae and temperature anomalies and hydroclimate separately or interactively contributed to the observed patterns. The analyses also suggested that climate-induced shifts in weather patterns may result in the loss of algal richness and thereby in the loss of functional diversity in European hard bottom intertidal areas.

Within the COST action EMBOS (European Marine Biodiversity Observatory System) the degree and variation of the diversity and densities of soft-bottom communities from the lower intertidal or the shallow subtidal was measured at 28 marine sites along the European coastline (Baltic, Atlantic, Mediterranean) using jointly agreed and harmonized protocols, tools and indicators. The hypothesis tested was that the diversity for all taxonomic groups would decrease with increasing latitude. The EMBOS system delivered accurate and comparable data on the diversity and densities of the soft sediment macrozoobenthic community over a large-scale gradient along the European coastline. In contrast to general biogeographic theory, species diversity showed no linear relationship with latitude, yet a bell-shaped relation was found. The diversity and densities of benthos were mostly positively correlated with environmental factors such as temperature, salinity, mud and organic matter content in sediment, or wave height, and related with location characteristics such as system type (lagoons, estuaries, open coast) or stratum (intertidal, subtidal). For some relationships, a maximum (e.g. temperature from 15–20°C; mud content of sediment around 40%) or bimodal curve (e.g. salinity) was found. In lagoons the densities were twice higher than in other locations, and at open coasts the diversity was much lower than in other locations. We conclude that latitudinal trends and regional differences in diversity and densities are strongly influenced by, i.e. merely the result of, particular sets and ranges of environmental factors and location characteristics specific to certain areas, such as the Baltic, with typical salinity clines (favouring insects) and the Mediterranean, with higher temperatures (favouring crustaceans). Therefore, eventual trends with latitude are primarily indirect and so can be overcome by local variation of environmental factors.

This study aims to describe the patterns of soft bottom macrozoobenthic richness along French coasts. It is based on a collaborative database developed by the “Réseau des Stations et Observatoires Marins” (RESOMAR). We investigated patterns of species richness in sublittoral soft bottom habitats (EUNIS level 3) at two different spatial scales: 1) seaboards: English Channel, Bay of Biscay and Mediterranean Sea and 2) 0.5° latitudinal and longitudinal grid. Total observed richness, rarefaction curves and three incidence-based richness estimators (Chao2, ICE and Jacknife1) were used to compare soft bottom habitats species richness in each seaboard. Overall, the Mediterranean Sea has the highest richness and despite higher sampling effort, the English Channel hosts the lowest number of species. The distribution of species occurrence within and between seaboards was assessed for each major phylum using constrained rarefaction curves. The Mediterranean Sea hosts the highest number of exclusive species. In pairwise comparisons, it also shares a lower proportion of taxa with the Bay of Biscay (34.1%) or the English Channel (27.6%) than that shared between these two seaboards (49.7%). Latitudinal species richness patterns along the Atlantic and English Channel coasts were investigated for each major phylum using partial LOESS regression controlling for sampling effort. This showed the existence of a bell-shaped latitudinal pattern, highlighting Brittany as a hotspot for macrobenthic richness at the confluence of two biogeographic provinces.

In the frame of the COST ACTION EMBOS' (Development and implementation of a pan-European Marine Biodiversity Observatory System), coverage of intertidal macroalgae was estimated at a range of marine stations along the European coastline (Subarctic, Baltic, Atlantic, Mediterranean). Based on these data, we tested whether patterns in macroalgal diversity and distribution along European intertidal rocky shores could be explained by a set of meteo-oceanographic variables. The variables considered were salinity, sea surface temperature, photosynthetically active radiation, significant wave height and tidal range and were compiled from three different sources: remote sensing, reanalysis technique and in situ measurement. These variables were parameterized to represent average conditions (mean values), variability (standard deviation) and extreme events (minimum and maximum values). The results obtained in this study contribute to reinforce the EMBOS network approach and highlight the necessity of considering meteo-oceanographic variables in long-term assessments. The broad spatial distribution of pilot sites has allowed identification of latitudinal and longitudinal gradients manifested through species composition, diversity and dominance structure of intertidal macroalgae. These patterns follow a latitudinal gradient mainly explained by sea surface temperature, but also by photosynthetically active radiation, salinity and tidal range. Additionally, a longitudinal gradient was also detected and could be linked to wave height.

The non-native amphipod Melita nitida Smith, 1873 was collected between 2013 and 2016 in Arcachon Bay, Hossegor Lake and the Gironde Estuary (SW France) in intertidal oyster reefs and under stones. This species, native to the Atlantic coast of North America, is considered as a non-indigenous species on the Pacific coast of North America. Recently, the presence of M. nitida was reported in Europe, both in The Netherlands and in Germany. This species may have been accidentally introduced to Arcachon Bay with oyster transfers. An identification key for species belonging to the genus Melita and closely related species in European waters is also provided.

Estuarine ecosystems have been described as a mosaic of habitats exhibiting different physical, biological and chemical properties and processes. These habitats are of primary importance for fishes, providing refuges and/or food for juveniles. While it is well known that habitats contribute also to the structuration of meio- and macrobenthic assemblages, this concept of habitat has never been associated to zooplankton communities, a major food resource for many pelagic fishes during summer in North-European estuaries. The objective of this work was thus to assess if estuarine habitats, in addition to the salinity gradient, structured zooplankton communities as well. Sampling was conducted at high tide during summer in a highly turbid system, the Gironde estuary, for which primary production and thus food resource at the basis of the food web is strongly limited. The results showed that even if the upstream-downstream estuarine gradient was the main factor structuring zooplankton at the scale of the estuary, there was a significant difference of zooplankton assemblages between samples collected over subtidal areas and those collected over intertidal areas. More particularly, the estuarine gradient was associated to the distribution pattern of species while difference between subtidal and intertidal samples were mainly due to difference in the level of abundance of species. Stable isotope analysis revealed that these zooplanktonic omnivorous species may be attracted to intertidal mudflats by microphytobenthos availability and that some planktivorous fishes, in particular Alosa fallax, preferentially fed on this zone. The role of intertidal habitats in structuring zooplankton assemblages suggests that this habitat strongly participates to the production of planktivorous species and that it represents a biotic vector of carbon resources toward subtidal areas. The loss of tidal flats habitats could thus have consequences on the functioning of pelagic system as well.

Examining how variability in population abundance and distribution is allotted among different spatial scales can inform of processes that are likely to generate that variability. Results of studies dealing with scale issues in marine benthic communities suggest that variability is concentrated at small spatial scales (from tens of centimetres to few metres) and that spatial patterns of variation are consistent across ecosystems characterized by contrasting physical and biotic conditions, but this has not been formally tested. Here we quantified the variability in the distribution of intertidal rocky shore communities at a range of spatial scales, from tens of centimetres to thousands of kilometres, both in the NE Atlantic and the Mediterranean, and tested whether the observed patterns differed between the two basins. We focused on canopy-forming macroalgae and associated understorey assemblages in the low intertidal, and on the distribution of Patella limpets at mid intertidal levels. Our results highlight that patterns of spatial variation, at each scale investigated, were consistent between the Atlantic and the Mediterranean, suggesting that similar ecological processes operate in these regions. In contrast with former studies, variability in canopy cover, species richness and limpet abundance was equally distributed among spatial scales, possibly reflecting the fingerprint of multiple processes. Variability in community structure of low intertidal assemblages, instead, peaked at the largest scale, suggesting that oceanographic processes and climatic gradients may be important. We conclude that formal comparisons of variability across scales nested in contrasting systems are needed, before any generalization on patterns and processes can be made.

Changes in (1) main sediment characteristics, and (2) benthic bacterial and macrofaunal communities were simultaneously addressed along an inner–outer transect within the West Gironde Mud Patch (Bay of Biscay, NE Atlantic), through the sampling of three stations (E: inner part, C: central part and W: outer part) during July 2010. Except in the top centimetre where a sandy layer was found at station E, all sediments were muddy and tended to be coarser and richer in photosynthetic pigments and particulate organic carbon and nitrogen at stations C and W than at station E. Maximum oxygen penetration depth was also lower at station E than at stations C and W. These results are consistent with: (1) the occurrence of strong hydrodynamics precluding current sedimentation in the inner part of the WGMP, and (2) conversely, inputs of particles originating from the Gironde Estuary in its central and outer part. Prokaryotic cell abundances were lower at station E than at stations C and W. Bacterial community composition also differed more clearly at station E as compared to stations C and W. Conversely, macrofaunal abundances and species richness decreased monotonously from station E to station W (i.e., along the inner–outer gradient). Macrofaunal composition strongly differed at station E on one side, and stations C and W on the other side. These results are consistent with the current paradigm regarding the long term effect of major rivers on benthic macrofauna given that strong hydrodynamics at station E precludes the sedimentation of fine particles originating from the Gironde Estuary. At last, we found no overall correlation between benthic bacterial and macrofaunal compositions, which may however clearly result from limitations in our sampling design.

The mysid Heteromysis (Heteromysis) microps is reported for the first time in the Bay of Biscay. During surveys carried out between March and September 2015 in Arcachon Bay, mysid specimens were fortuitously collected from Upogebia pusilla burrows.

The European cockle (Cerastoderma edule) is an exploited bivalve along the North-Eastern Atlantic semi-sheltered ecosystems. Its population dynamics are driven by numerous environmental factors, including parasitism, particularly by trematodes. The complex life cycle of trematodes includes a free living stage (cercaria) between the first (a mollusk) and the second (an invertebrate or a vertebrate) intermediate hosts. Taking the example of Himasthla quissetensis, a dominant trematode in Arcachon Bay (France) utilizing Nassarius reticulatus as first intermediate host and the cockle as second intermediate host, we investigated the correlation between cockle infection and cercariae emergence by N. reticulatus, including the role of water temperature and light. Experimental and field data provided evidence that cercariae emergence from N. reticulatus took place during the night and for water temperature comprised between 15 °C and 22 °C (optimum at 20 °C). The lifespan of cercariae did not exceed 48 h and 50% of them were no more infectious after 7 h. A model was designed (emergence = f(water temperature)) in order to calculate an average monthly cercarial emergence rate according to water temperature that was daily recorded for 5 years (1998–2002). Concomitantly, non-infected cockles were transplanted each of these years in order to assess the infection rate by H. quissetensis. Infection occurred strictly for the same water temperatures (and dates) as those expected for cercariae emergence. Within each year, there was often (but not always) a good correlation between the predicted number of emerging cercariae and the observed number of cercariae transformed into metacercariae in cockles. However, the among-years variability of cockle infection (× 4.4 range) was not explained by the predicted annual number of emerging cercariae. This study highlights the importance of water temperature and light in stimulating cercariae emergence which is closely related to the occurrence of cockle infection. Accordingly, climate change would be expected to alter certain parasite transmission traits. Conversely, the lack of correlation between the total number of metacercariae in cockles and the expected number of cercariae suggests that other factors contribute to infestation variability.

The amphipod genus Aoroides is reported for the first time in European marine waters. Specimens of Aoroides semicurvatus and Aoroides curvipes were collected in oyster reefs in Arcachon Bay between 2009 and 2014 and in Hossegor Lake in 2014 ( SW France). Specimens of Aoroides longimerus were collected in 2013 and 2014 in subtidal slipper limpet beds and Zostera marina meadows in Arcachon Bay and in 2014 on floating pontoons in the Bay of Brest (W France). These species, native to Asia, may have been accidentally introduced in Arcachon Bay and Hossegor Lake with oyster transfers and in the Bay of Brest through both oyster transfers and shipping.

Sandy beaches exposed to tide and waves are characterized by low abundance and diversity of benthic macrofauna, because of high-energy conditions. This is the reason why there are few studies on benthic communities living in such highly dynamic environments. It has been shown recently that tidal sandy beaches may act as biogeochemical reactors. Marine organic matter that is supplied in the sand during each flood tide is efficiently mineralized through aerobic respiration. In order to quantify the role of macrofauna in the whole beach benthic respiration, we studied the macrofauna and the pore water oxygen content of an exposed sandy beach (Truc Vert, SW of France) during four seasons in 2011. The results showed that macrofauna was characterised by a low number of species of specialized organisms such as the crustaceans Eurydice naylori and Gastrosaccus spp. and the polychaetes Ophelia bicornis and Scolelepis squamata. The distribution and abundance of macrofauna were clearly affected by exposure degree and emersion time. The combined monitoring of benthic macrofauna and pore waters chemistry allowed us to estimate (1) the macrofauna oxygen uptake, calculated with a standard allometric relationship using biomass data, and (2) the total benthic oxygen uptake, calculated from the oxygen deficit measured in pore waters. This revealed that benthic macrofauna respiration represented a variable but low (<10%) contribution to the total benthic oxygen consumption. This suggests that oxygen was mainly consumed by microbial respiration.