Arcachon Bay Research Articles

A new threat to the European marine environment: The exotic polyclad flatworm Postenterogonia orbicularis (Schmarda, 1859)

Harbours and marinas are optimal places for the detection of the arrival of Non-Indigenous Species (NIS) in the early stages of introduction. Marine traffic serves as a route for species movement among different regions, while the species settlement in the ports is facilitated due to habitat degradation. Among NIS, polyclads flatworms are active hunters of bivalves, posing a threat to recipient environments and aquaculture. They can either use their pharynx and mucus to penetrate the mussels and oysters, or enter molluscs while they filter, making the management of the species difficult. In this regard, this work aims to report the first morphological and molecular identification of a new NIS polyclad native to the Pacific Ocean in Europe, specifically in the Ría de Avilés and the Gijón Port (North of Spain, Cantabrian Sea, Bay of Biscay). The occurrence of mature ovigerous specimens and the collection of specimens of various sizes from different times of the year, evidence a reproductively-active population in the area. The external morphological characters, as the ruffled pharynx and the cephalic eyes, and the internal ones, as the male copulatory apparatus, fit with the description of Postenterogonia orbicularis. The phylogenetic analysis based on the mitochondrial COI marker, placed the studied specimens from Avilés and Gijón (Spain) and the recently described species Idiostylochus tortuosus from Arcachon Bay (France) within the P. orbicularis clade (Ilyplanidae family). Therefore, our results suggest that I. tortuosus may be a synonym of the New Zealander P. orbicularis. Finally, we discuss the possible ecological impacts of its introduction and provide some management recommendations for controlling its influx in the recipient environments.

Simple approaches for evaluation of OTU quality based on dissimilarity arrays

An accurate and complete taxonomic description of the diversity present in an environmental sample is out of reach at this time. Instead, metabarcoding is used today and it is expected that OTUs represent a category relevant for biodiversity inventories on a molecular basis. However, artefacts in the production of OTUs can occur at different stages and may impact ecological conclusions. We propose to evaluate the quality of OTUs in a sample by characterising the deviation of each OTU’s dissimilarity array from that of an ideal OTU where all sequences are at distances smaller than the barcoding gap. We consider two deviations: the creation of composed OTUs, corresponding to the artificial merging of several OTUs and the creation of noisy OTUs that contain some sequences that are loosely associated with the core sequence of the OTUs and that do not form a compact subgroup. We propose a simple and automatic 2-step method that successively categorises the OTUs of a sample as composed or single and then identifies OTUs with noise amongst the single ones. The associated code is available at https://forgemia.inra.fr/alain.franc/otu_shape. We applied the method on 32 samples of diatoms from Arcachon Bay (France) that represent contrasted environmental conditions and we obtained good agreement with expert categorisation of OTUs. We suggest that single OTUs without noise can be used as such for further ecological studies. Composed OTUs should be post-treated with classical clustering or community detection tools. The quality of single OTUs with noise remains to be further tested via supplementary studies on a diversity of organisms.

Co-infection of two eukaryotic pathogens within clam populations in Arcachon Bay.

The parasitic species Perkinsus olseni (= atlanticus) (Perkinsea, Alveolata) infects a wide range of mollusc species and is responsible for mortality events and economic losses in the aquaculture industry and fisheries worldwide. Thus far, most studies conducted in this field have approached the problem from a "one parasite-one disease" perspective, notably with regards to commercially relevant clam species, while the impact of other Perkinsus species should also be considered as it could play a key role in the disease phenotype and dynamics. Co-infection of P. olseni and P. chesapeaki has already been sporadically described in Manila clam populations in Europe. Here, we describe for the first time the parasitic distribution of two Perkinsus species, P. olseni and P. chesapeaki, in individual clam organs and in five different locations across Arcachon Bay (France), using simultaneous in situ detection by quantitative PCR (qPCR) duplex methodology. We show that P. olseni single-infection largely dominated prevalence (46-84%) with high intensities of infection (7.2 to 8.5 log-nb of copies. g-1of wet tissue of Manila clam) depending on location, suggesting that infection is driven by the abiotic characteristics of stations and physiological states of the host. Conversely, single P. chesapeaki infections were observed in only two sampling stations, Ile aux Oiseaux and Gujan, with low prevalences 2 and 14%, respectively. Interestingly, the co-infection by both Perkinsus spp., ranging in prevalence from 12 to 34%, was distributed across four stations of Arcachon Bay, and was detected in one or two organs maximum. Within these co-infected organs, P. olseni largely dominated the global parasitic load. Hence, the co-infection dynamics between P. olseni and P. chesapeaki may rely on a facilitating role of P. olseni in developing a primary infection which in turn may help P. chesapeaki infect R. philippinarum as a reservoir for a preferred host. This ecological study demonstrates that the detection and quantification of both parasitic species, P. olseni and P. chesapeaki, is essential and timely in resolving cryptic infections and their consequences on individual hosts and clam populations.

Seasonal and Interannual Variability in the Phenolic Content of the Seagrass Nanozostera noltei: Characterization of Suitable Candidates for the Monitoring of Seagrass Health

Developing early warning indicators to accurately detect ecosystem disturbances is vital for enhancing ecosystem management. The seasonal and interannual variability of the phenolic content of Nanozostera noltei from Arcachon Bay, France, was explored over 47 consecutive months to identify suitable early indicators of the state of seagrass beds. Five phenolic acid derivatives and eight flavonoids were fully characterized using chromatographic and spectroscopic techniques; a caffeic tetramer was described for the first time as a metabolite of N. noltei and of the genus Nanozostera. The individual phenolic concentrations in each of the 47 collections were determined by quantitative HPLC and analyzed as a function of year and season. The variability of the phenolic content in the rhizomes of N. noltei from Arcachon Bay was also determined over one year, as well as rhizomes of N. noltei from three other locations in the Atlantic and Mediterranean for comparison purposes. In addition, the phenolic fingerprints of Z. marina rhizomes were also characterized for the first time. The results show that leaf phenolic chemistry could be used to signify changes in the ecological health of N. noltei. In particular, it appears that diosmetin 7-sulfate, rosmarinic acid and zosteranoic acid could be reliable and easy-to-use indicators for monitoring N. noltei meadows. From a phytochemical point of view, this work is the first report of zosteranoic acid in the leaves and the rhizomes of N. noltei and in the rhizomes of Z. marina.

Is part-night lighting a suitable mitigation strategy to limit Artificial Light at Night effects on the biological rhythm at the behavioral and molecular scales of the oyster Crassostrea gigas?

Artificial Light at Night (ALAN) is a fast-spreading threat to organisms, especially in coastal environments, where night lighting is increasing due to constant anthropization. Considering that ALAN affects a large diversity of coastal organisms, finding efficient solutions to limit these effects is of great importance but poorly investigated. The potential benefit of one strategy, in particular, should be studied since its use is growing: part-night lighting (PNL), which consists in switching off the lights for a few hours during nighttime. The aim of this study is to investigate the positive potential of the PNL strategy on the daily rhythm of the oyster Crassostrea gigas, a key species of coastal areas of ecological and commercial interest. Oysters were exposed to a control condition and three different ALAN modalities. A realistic PNL condition is applied, recreating a strategy of city policy in a coastal city boarding an urbanized bay (Lanton, Arcachon Bay, France). The PNL modality consists in switching off ALAN direct sources (5 lx) for 4 h (23−3 h) during which oysters are in darkness. Then, a PNL + skyglow (PNL + S) modality reproduces the previous one mimicking a skyglow (0.1 lx), an indirect ALAN source, during the direct lighting switch off, to get as close as possible to realistic conditions. Finally, the third ALAN condition mimics full-night direct lighting (FNL). Results revealed that PNL reduces some adverse effects of FNL on the behavioral daily rhythm. But, counterintuitively, PNL + S appears more harmful than FNL for some parameters of the behavioral daily rhythm. PNL + S modality is also the only one that affect oysters' clock and melatonin synthesis gene expression, suggesting physiological consequences. Thus, in realistic conditions, the PNL mitigation strategy might not be beneficial in the presence of skyglow, seeing worse for a coastal organism such as the oysters.

Multi-criteria analysis to evaluate tidal energy potential in France

France benefits from an important tidal energy resource, with the second largest potential in Europe, and one of the biggest in the world. In addition, France has an important industrial and academic fabric, with several tidal developers, shipyards, and research centers, creating, theoretically, an attractive environment. However, though some tidal turbines already installed, such as Sabella demonstrator at Ouessant Island, or Guinard energy turbine in the Etel river, the sector still has a large development potential. One limitation of such a development is the lack of available data to assess the total potential. Previous studies mainly focused on the most energetic sites, such as the Alderney Race or the Fromveur Passage, while other sites are neglected. Yet, those sites, such has rivers or estuaries, offer softer conditions, lowering the risks. Moreover, although identifying a suitable area for tidal array implementation requires technical criteria (maximum current velocity, water depth, installable potential, etc.), it should also consider other aspects such as ecological indicators (migratory fishes, specific habitats, etc.), regulation specificities (Natura 2000, ZNIEFF, etc.) or human activities conflicts (fishery, UXO, etc.). On top of that, socioeconomic indicators, such as potential local content or partnerships with relevant academic stakeholders, are encouraged by authorities, and must be accounted for.
 Hence, this study proposes an extensive multi-criteria analysis methodology, to assess tidal energy potential of ten sites in France, including five nearshore locations (Alderney race, Fromveur passage, Raz-de-Sein, Raz-Barfleur, Paimpol-Bréhat), and five estuaries, river or similar (Gironde estuary, Gulf of Morbihan, Adour river, Etel river, Arcachon Bay). The analysis is limited to ten sites, selected based on a pre-screening analysis, which will be detailed in the study.
 The different criteria used will be presented, including their weight to the final score which reflect their importance during project development, and the 3-level grading system used to discriminate sites. The methodology developed to assess full-time equivalent employments created by a tidal array, using world input-output tables and other economic parameters will also be detailed. A specific focus will be proposed on methodology used to assess the installable capacity, relying on data from MARS 2D model for nearshore sites and public data for the others.
 First analysis shows that Raz-de-Sein and Paimpol-Bréhat are the two most suitable sites for tidal arrays implementation, while the Alderney Race is the most energetic one. Those results are driven by high scores obtained by these sites in categories such as ecological or human activities. Direct, indirect, and induced employments created during construction and operational phase by each project are also calculated, as well as potential growth value added. Hypothesis and sensitivity to them will be discussed.
 This research was funded by the H2020 projet ELEMENT, grant number 815180.

Spatial distribution of anthropogenic particles and microplastics in a meso-tidal lagoon (Arcachon Bay, France): A multi-compartment approach

Assessment of microplastic (MP) contamination is still needed to evaluate this threat correctly and tackle this issue. Here, MP contamination was assessed for a meso-tidal lagoon of the Atlantic coast (Arcachon Bay, France). Sea surface, water column, intertidal sediments and wild oysters were sampled. Five different stations were studied to assess the spatial distribution of the contamination. Two were outside of the bay and three were inside the bay (from the inlet to the back). A distinction was made between all anthropogenic particles (AP, i.e. visually sorted) and MP (i.e. plastic polymer confirmed by ATR-FTIR spectroscopy). The length of particles recovered in this study ranged between 17 μm and 5 mm. Concentration and composition in sea surface and water column samples showed spatial variations while sediment and oyster samples did not. At outside stations, the sea surface and the water column presented a blended composition regarding shapes and polymers and low to high concentrations (e.g. 0.16 ± 0.08 MP.m−3 and 561.7 ± 68.5 MP.m−3, respectively for sea surface and water column), which can be due to coastal processes and nearby input sources. The inlet station displayed a well-marked pattern only at the sea surface. High AP and MP concentrations were recorded, and fragments along with polyethylene overwhelmed (respectively 76.0 % and 73.2 %). Higher surface currents could explain this pattern. At the bay back, AP and MP concentrations were lower and fibers were mainly recorded. Weaker hydrodynamics in this area was suspected to drive this contamination profile. Overall, fragments and buoyant particles were mainly detected at the sea surface while fibers and negatively buoyant particles prevailed in other compartments. Most of the studied samples presented an important contribution of fiber-shaped particles (from 31.5 % to 94.2 %). Finally, contamination was ubiquitous as AP and MP were found at all stations in all sample types.

Benthic community impacts from sediment dredging and disposal: A comparison of sampling gear

The effect of sediment dredging and disposal work on benthic communities was compared according to two sampling strategies, grab (1-mm mesh) and dredge (1-cm mesh). Nine subtidal, sandy sites were selected in Arcachon Bay (French Atlantic coast), where these operations were performed during winter. Fauna was sampled several months before and one year after the dredging or disposal work. The sediments were fine to medium sands and their characteristics were not modified. In dredging sites, abundance, diversity and community structure of grab sampled fauna were minimally affected by the activities, while abundance and community structure displayed significant changes for dredge sampled fauna. In disposal sites, there was no work effect on fauna, although environmental conditions changed, especially when initial sediments were covered by mussels or seagrass. This study suggests that dredge sampling can be an alternative to grab sampling for monitoring changes related to dredging in sandy shallow channels.

Investigation of the possible valorization of dredged sediments in compressed earth blocks

The construction sector is currently facing an environmental challenge and construction materials with low CO₂ emissions are needed. In view of this ecological transition, earth constructions are an interesting solution given their low environmental impact and their hygrothermal properties. On the other hand, the ports must be regularly maintained by dredging operations in order to provide the necessary water depth for navigation. This induces huge amounts of sediments that should be valorized as they cannot be discharged in the sea with the evolution of dredging practices laws. This study investigates the potential use of “Arcachon Bay” dredged sediments in South West France in Compressed Earth Blocks (CEB). Several sediment samples were collected from eight different locations along the bay to take into consideration their variability. The characterization of the sediments has been conducted in a cross way by laboratory and field tests to provide a feedback on the limitations and the complementarity of the two approaches and improve the current practices. The correlation between geotechnical and field tests has been also analysed. The field tests allow the characterization of sediments through sensory and cohesion tests such as appearance, smell, plasticity, clay content, cigar, pellet, shine, hand washing and adhesion. The conducted laboratory tests were wet sieving granulometry, sedimentation, Atterberg limits, Organic Matter (OM) content and Methylene Blue Value (MBV). The GTR classification has been also determined and the results showed that most of the sediments are silty clay of class A2 or A3. Based on those data, the compliance of these sediments with the CEB manufacturing recommendations is analysed. Several mix optimization techniques have been proposed to improve the mechanical properties such as adapting the granulometry by adding sand or opting for a chemical stabilization. In addition, a machine learning model based on a dataset collected from the literature has been developed to predict the compressive strength of CEB and optimize the mix and fabrication conditions.

How sustainable are daily medicine consumption practices? The case of a fragile coastal area, Arcachon Bay (SW,France)

The potentially negative environmental effects of pesticides and antibiotics are a source of concern for public health. Many studies in recent years have focused on so-called “emerging micropollutants” emanating from domestic activity and found primarily in cleaning products, cosmetics, and medicines. This awareness of potential risks to the natural environment has evolved considerably since the 1970s. Sustained population growth in urban areas has forced public policy makers to pay more attention to the links between health and the environment, and specifically to the complexity of medicine consumption. Using a practice theory approach, this article aims to identify how sustainable daily medicine consumption practices are. Our research is based on the analysis of medicine consumption in relation to four interdependent elements: prescription, treatment, unused medication, and representations of environmental issues. First, the background of practice theory and sustainable medicine consumption are discussed. This approach is then applied to quantitative data from a questionnaire survey on consumers that we conducted in a French coastal area subject to specific demographic pressure and micropollution of the water. A multivariate statistical exploratory analysis of the data set highlights the structure of the practices concerned, and the extent to which environmental issues are considered when unused medication is disposed of. We conclude by highlighting the relevance of our approach in understanding the complex nature of sustainable medicine consumption, which involves diverse communities of practice. We also underline the need for public policy to target all stakeholders in the medicine consumption process, from medical professionals to end users.

Assessment of size at first maturity for Ruditapes philippinarum from Arcachon Bay (French Atlantic coast): New insights for fishery management

Regarding fisheries, management strategies aim at regulating access to the resource and at enforcing resource conservation in order to achieve sustainable exploitation. In this context, Minimum Conservation Reference Size (MCRS) is a technical measure based on scientific knowledge of the species characteristics (sexual maturity, individual growth and natural mortality). Reproductive capacity is generally apprehended by using the size at first maturity SL50, the size at which 50% of the individuals are mature. The SL50 was unknown for the Arcachon Bay Manila clam population (Ruditapes philippinarum). This study provides a first estimate based on the histological analysis of a large sample of individuals (1420 clams ranging from 10 to 41 mm) from four distinct bay inner sites and collected when the majority of the individuals are mature (from June to August). Our methodological choice was made to allow comparison with other European R. philippinarum deposits but also to be recognized by the EU; an interest of practices harmonization was besides revealed for bivalves. Following a logistic regression analysis, the SL50 was estimated to be 26.7 mm for the totality of the samples considered, with moderate spatial variability. If only sexed individuals were taken into account in the estimation, the SL50 was 24.5 mm for females and 21.6 mm for males. All sites and hypsometric levels combined, it is estimated that SL50 is reached at an average age of 1.6 years, 32 mm at 2.3 years and 35 mm at 2.9 years with high variability at the scale of site-hypsometric level pairs. Considering the SL50 and the spawning activity usually observed intra-basin, at least half of the clam population would have spawned at least once before their potential catch if the MCRS was reduced from 35 mm (current regulations) to 32 mm (regulations under study). This information constitutes essential knowledge to be included in Joint Recommendations when considering a MCRS revision in a European context that recognizes a more important place dedicated to regionalization.

On-field high-resolution quantification of the cobalt fraction available for bio-uptake in natural waters using antifouling gel-integrated microelectrode arrays

We report the optimization, characterization, and validation of Adsorptive Square Wave Cathodic Stripping Voltammetry on antifouling gel-integrated microelectrode arrays for autonomous, direct monitoring of cobalt(II) metal species. Detection is accomplished by complexation with an added nioxime ligand. The limit of detection established for a 90 s accumulation time was 0.29 ± 0.01 nM in freshwater and 0.27 ± 0.06 nM in seawater. The microelectrode array was integrated in a submersible probe to automatically dose the complexing agent nioxime and realize an integrated sensing system. For the first time ever, the potentially bioavailable Co(II) fraction was determined in La Leyre River-Arcachon Bay continuum, enabling to evaluate the potential ecotoxicological impact of freshwater-carried Co(II) in the Arcachon Bay. The measured potentially bioavailable Co(II) concentrations were hazardous for aquatic biota along the continuum. The electrochemical Co(II) data were compared to ICP-MS data in various fractions to determine spatial Co(II) speciation.

A New Polyclad Flatworm, Idiostylochus tortuosus gen. nov., sp. nov. (Platyhelminthes, Polycladida) from France. Can this Foreign Flatworm be Responsible for the Deterioration of Oyster and Mussel Farms?

A new species of polyclad flatworm, Idiostylochus tortuosus gen. nov., sp. nov. (Polycladida, Idioplanidae), from Arcachon Bay (France) is described. This description is based on a morphological analysis and a molecular analysis using partial sequences of the 28S and cytochrome Oxidase I (COI) genes. After the molecular analysis Idiostylochus gen. nov. appears to be the second genus of the Family Idioplanidae and closely related to the family Latocestidae as well as the genera Leptostylochus and Mirostylochus. The molecular data revealed that the new species may belong to an Indonesian or Indo-Pacific family, closely related to genera with origins in South Pacific Ocean waters. This species was found feeding on the oysters and mussels of the Arcachon farms.

Assessment of the distribution of Ruditapes spp. in northern Mediterranean sites using morphological and genetic data

ABSTRACT In the 1970s, Ruditapes philippinarum was introduced to France at Arcachon Bay for aquaculture. At present, in Europe, R. philippinarum is often found in place of the native species Ruditapes decussatus. The aim of this study is to evaluate the distribution of these two species along the northern Mediterranean coastline using morphological and morphometric analysis. The sampling period was between June and December 2018. Among the 11 French sites, only 2 contained R. philippinarum, whereas only the indigenous species was present at the other sites. Genetic analyses were used to confirm species identity and to confirm this distribution. A site in Italy, Pialassa Baiona, was also added to the sample. This analysis of Ruditapes from multiple French sites and one Italian site highlights species-level differences in shell morphology between R. decussatus and R. philippinarum. The intraspecific morphometric analysis showed the presence of different groups depending on spatial scales (i.e. at the large scale, between the Mediterranean Sea and the Atlantic, and on the small scale, that is within the Berre lagoon in France. No relationship between morphometric and genetic variation was found. This suggests that the differences in the shell shape of Ruditapes are driven by local environmental conditions.

Trajectories of nutrients concentrations and ratios in the French coastal ecosystems: 20 years of changes in relation with large-scale and local drivers

Along with their important diversity, coastal ecosystems receive various amounts of nutrients, principally arising from the continent and from the related human activities (mainly industrial and agricultural activities). During the 20th century, nutrients loads have increased following the increase of both the global population and need of services. Alongside, climate change including temperature increase or atmospheric circulation change has occurred. These processes, Ecosystem state changes are hard to monitor and predict. To study the long-term changes of nutrients concentrations in coastal ecosystems, eleven French coastal ecosystems were studied over 20 years as they encompass large climatic and land pressures, representative of temperate ecosystems, over a rather small geographical area. Both univariate (time series decomposition) and multivariate (relationships between ecosystems and drivers) statistical analyses were used to determine ecosystem trajectories as well as typologies of ecosystem trajectories. It appeared that most of the French coastal ecosystems exhibited trajectories towards a decrease in nutrients concentrations. Differences in trajectories mainly depended on continental and human influences, as well as on climatic regimes. One single ecosystem exhibited very different trajectories, the Arcachon Bay with an increase in nutrients concentrations. Ecosystem trajectories based on ordination techniques were proven to be useful tools to monitor ecosystem changes. This study highlighted the importance of local environments and the need to couple uni- and multi-ecosystem studies. Although the studied ecosystems were influenced by both local and large-scale climate, by anthropogenic activities loads, and that their trajectories were mostly similar based on their continental influence, non-negligible variations resulted from their internal functioning.

Role of suspended particulate material on growth and metal bioaccumulation in oysters (Crassostrea gigas) from a French coastal semi-enclosed production area, Arcachon Bay

Arcachon Bay is a prominent oyster production area on the coast of Western Europe, and is subject to chemical contamination including by trace metals. Recently, the national “mussel-watch” monitoring network – using local bivalves as semi-quantitative bioindicators of coastal chemical contamination – highlighted a significant increase in copper (Cu) concentrations in oysters from this bay. Here, we conducted a one-year multi-compartment and multi-parameter field study to investigate some aspects of the surrounding environment of oysters that could explain their metal bioaccumulation. Sediment, seawater (through punctual and passive sampling), particles (suspended particulate material of selected sizes, including trophic resources for oysters) and transplanted oysters were regularly collected at two contrasted sites of the bay (i.e. under continental versus more oceanic influence). These matrices were characterised for their total Cu, zinc (Zn), nickel (Ni), cadmium (Cd) and lead (Pb) concentrations. Several physico-chemical and biological parameters (e.g. salinity, particle loads, oyster growth rate and condition indices, carbon and nitrogen stable isotope compositions, etc.) were also analysed. Overall, sediment, particles and oysters from the outermost site had slightly lower δ 13 C values, confirming the more oceanic influence in this part of the bay. Among organic particles, although dinoflagellates tended to be more abundant at the outermost site while ciliates were more abundant at the innermost site of the bay, the two sites did not differ in mean total microphytoplankton and diatom densities. However, the variations observed for most of the other parameters studied show that oysters located near the continental shore are exposed to higher loads of particles in general, and to higher metal contents in the dissolved phase and “bulk” seawater (dissolved plus particulate phases) during the year. While fluvial inputs and continental/urban run-offs are suspected sources of anthropogenic metal inputs into the bay, (fine) sediment particle resuspension appears to be a likely major contributor to metal release and hence to the contamination of the bay including oysters. The decline of seagrass beds in the last two decades in the bay could also have decreased the potential of fine particle retention in the sedimentary stratum. Concomitantly, oysters presenting the highest metal concentrations were those with the lower growth rates and condition indices, which may be induced by physical constraints, high amounts of pseudo-faeces produced and/or reduced food and energy acquisition by oysters due to high particle loads in the water column. The findings of this study imply that using raw metal concentrations in bivalves to monitor marine coastal contamination can lead to misleading interpretations if potentially great spatial variations in bivalve growth rates or condition indices are not considered. Finally, peculiar trends were observed for Cu compared to other metals, highlighting the need of further studies to fully address the Cu contamination in this marine system (e.g. specific sources of contamination for this metal in the bay). This study more broadly raises the issue of potentially man-induced ecological changes (e.g. modification of natural habitats) and their consequences on metal transfer and physiological performance of marine biota. • A multi-compartment and multi-parameter study to unravel oyster metal contamination. • Higher contamination found in dissolved and particulate seawater phases inside the bay. • Contamination likely explained by river flows and tidal resuspension of sediments. • Higher particle loads observed with higher oyster metal concentrations and lower growth. • Differences in oyster bioaccumulation patterns for copper compared to other metals.

Guidelines for model adaptation: A study of the transferability of a general seagrass ecosystem Dynamic Bayesian Networks model.

In general, it is not feasible to collect enough empirical data to capture the entire range of processes that define a complex system, either intrinsically or when viewing the system from a different geographical or temporal perspective. In this context, an alternative approach is to consider model transferability, which is the act of translating a model built for one environment to another less well‐known situation. Model transferability and adaptability may be extremely beneficial—approaches that aid in the reuse and adaption of models, particularly for sites with limited data, would benefit from widespread model uptake. Besides the reduced effort required to develop a model, data collection can be simplified when transferring a model to a different application context. The research presented in this paper focused on a case study to identify and implement guidelines for model adaptation. Our study adapted a general Dynamic Bayesian Networks (DBN) of a seagrass ecosystem to a new location where nodes were similar, but the conditional probability tables varied. We focused on two species of seagrass (Zostera noltei and Zostera marina) located in Arcachon Bay, France. Expert knowledge was used to complement peer‐reviewed literature to identify which components needed adjustment including parameterization and quantification of the model and desired outcomes. We adopted both linguistic labels and scenario‐based elicitation to elicit from experts the conditional probabilities used to quantify the DBN. Following the proposed guidelines, the model structure of the general DBN was retained, but the conditional probability tables were adapted for nodes that characterized the growth dynamics in Zostera spp. population located in Arcachon Bay, as well as the seasonal variation on their reproduction. Particular attention was paid to the light variable as it is a crucial driver of growth and physiology for seagrasses. Our guidelines provide a way to adapt a general DBN to specific ecosystems to maximize model reuse and minimize re‐development effort. Especially important from a transferability perspective are guidelines for ecosystems with limited data, and how simulation and prior predictive approaches can be used in these contexts.

Marine trematode parasites as indicators of environmental changes

Coastal ecosystems are threatened by growing pressures related to global change. The evaluation of an ecosystem’s biodiversity and status is by consequence of increasing importance to assess potentially undergone changes and predict their future trajectory for management and conservancy purposes. Biotic indicators sensitive to ecosystem changes are thus continuously sought for. Trematode parasite communities were examined as potential indicators of environmental changes, considering that the achievement of their complex life cycle is modulated by several factors. Indeed, the rule for trematode is that each species complete their cycle by a succession of three different host species and two free-living stages, thus depending on several biotic and abiotic factors. To this end, we examined the trematode community infecting the common cockle in Banc d’Arguin, Arcachon Bay, France. Monthly data extending over 16 years and sampled at a single station were compared to field book notes describing the changes of the closely surrounding landscape. In 2021, we also sampled cockles at 15 stations presenting different substrate features along the bank. Over time, seven out of nine changes of the trematode community structure presented concordances with changes in landscape. We hypothesize this was related to the environment heterogeneous substrate (i.e., temporal succession of oyster parks, bare sands and seagrass) with cascading effects on host populations. However, some changes could not solely be explained by changes in landscape. Our spatial study showed that the trematode communities exhibited intricate infection patterns with a complex interaction between substrate heterogeneity and larval dispersal ability of parasites. Thus, trematode communities might be potential indicators of subtle changes in the environment. However, it remains unclear which scale of environmental changes trematodes are actually sensitive to.

Redescription of Apocorophiumacutum (Crustacea, Amphipoda, Corophiidae) with material from type locality and key of world Apocorophium species.

Apocorophiumacutum (Chevreux, 1908), the type species of the genus, was originally but only partially described by Chevreux with female specimens from Bônes (Algeria); male specimens were later described from Brittany (France). Since then, the species has been recorded in different places of the world, some of them questionable. Herein, the species is entirely redescribed with material from the type locality and Brittany, and additional material from Arcachon Bay is studied to provide biological data. The known geographical distribution of this species is summarized, and a world identification key of Apocorophium species is also given.

Adapting a dynamic system model using life traits and local fishery knowledge — Application to a population of exploited marine bivalves (Ruditapes philippinarum) in a mesotidal coastal lagoon

Effective planning and management strategies of the Manila clam (Ruditapes philippinarum) stock in Arcachon Bay rely on a co-management approach, involving scientific advice and the fishing industry. In order to strengthen this management process, a specific compartmental single-species model has been developed to assess different management strategies. Based upon a size structure of the population and built from the dynamic systems paradigm, the modelling involves selected environmental and fishery-related parameters for their impact on the population dynamics. Integration of newly available life traits data regarding the local population and better knowledge of the fishing activity and its control parameters have enabled a revision of the existing version including model parameters and integration of new formulations. Effect of food availability and total suspended matter on the production of newly settled juveniles, natural mortality, growth rates, and price, accounted for the bulk of the undertaken improvements. Model performance was evaluated by comparing simulation outputs to observed data from stock assessments (2003, 2006, 2008, 2010, 2012, 2014 and 2018). In addition, a sensitivity analysis regarding uncertainty on parameters related to biological and environmental aspects was carried out to provide information about parameters that influence the outputs of the model the most. In particular, this highlighted that a deeper understanding of the processes related to the reproduction phase and its control parameters on biomass should be pursued. The improvements enable the calibration of the model with parameters that are as close as possible to the specificities of the stock considered. This adaptation permits use of the model to test various management strategies on the stock evolution and also to evaluate potential effects of environmental or market fluctuations. It encompasses ecological and socio-economic valuations of the measures of impact. As long as those objectives are shared by the different entities involved at the regional scale, communication and management decisions should be facilitated.