Bay Of Saint-Brieuc Research Articles

The nocturnal life of the great scallops (Pecten maximus, L.): First description of their natural daily valve opening cycle.

Valvometry techniques used to monitor bivalve gaping activity have elucidated numerous relationships with environmental fluctuations, along with biological rhythms ranging from sub-daily to seasonal. Thus, a precise understanding of the natural activity of bivalves (i.e., not exposed to stressful environmental variations) is necessary as a baseline for detecting abnormal behaviors (deviations). This knowledge is also needed to reliably interpret observations of bivalve gaping behavior and associated biological processes (e.g., respiration, nutrition) acquired over time-limited periods. With this in mind, we investigated the natural daily gaping activity of the great scallop (Pecten maximus) by continuously monitoring 35 individuals in several individual tanks and in situ (Bay of Saint-Brieuc, Brittany, France) using fully autonomous Hall effect sensors. Our results revealed a circadian cycle (τ = 24.0h) in scallop gaping activity. Despite significant inter-individual variability in mean opening and cycle amplitude, almost all individuals (87.5%) exhibited nocturnal activity, with valves more open at night than during the day. A shift in light regime in the tanks triggered an instantaneous change in opening pattern, indicating that light levels strongly determine scallop activity. Based on the opening status of scallops, we also identified several gaping behaviors deviating from the regular daily pattern (lack of rhythmicity, high daytime opening), potentially reflecting physiological weakness. While further long-term studies are required to fully understand the natural activity of scallops, these findings pave the way for studies focused on the scallop response to external factors and introduce further research into the detection of abnormal behaviors. Coupling observations of diel valve gaping cycles with other daily variations in organismal and environmental parameters could help explain mechanisms driving the growth patterns of scallops observed in their shell striations. From a technical perspective, our field-based monitoring demonstrates the suitability of autonomous valvometry sensors for studying mobile subtidal bivalve activity in remote offshore environments.

Stomach content and stable isotope analyses provide complementary insights into the trophic ecology of coastal temperate bentho-demersal assemblages under environmental and anthropogenic pressures

Assessing organic matter fluxes and species interactions in food webs is of main interest to understand the ecological functioning in bays and estuaries characterised by a wide diversity of primary producers and consumers. Demersal fish and cephalopod assemblages were studied across a network of 24 shallow subtidal stations in the bay of Saint-Brieuc for their diversity, stable isotope compositions and stomach contents. The community was composed of 21 taxa, eight species accounting for 94.4% of the total abundance. Three different assemblages were identified along bathymetric gradient and spatial patterns in fish dredging. Marine POM and SOM were the most likely bases of food webs regarding δ13C range displayed by fish and cephalopod without differences among assemblages. Amphipoda was the main prey item in stomachs leading to significant diet overlaps among fish species, with some variations in additional items. Sepia officinalis was characterised by a singular diet and very low dietary overlap with other species. Contrasted stable isotope values and niche overlaps among species were evidenced in the δ13C/δ15N space. Callionymus lyra and Buglossidium luteum, characterised by the widest isotopic niches, encompassed those of other species, except the singular 13C-depleted Spondyliosoma cantharus. Coupling taxonomic assemblages, stomach contents and stable isotope analyses help disentangling the resources uses and evidencing trophic pathways. Contrasts in fish and cephalopod demersal assemblages occurring at different depths not necessarily imply differences in the trophic resources uses in such complex shallow coastal ecosystems under anthropogenic influences.

Commercial cuttlefish exposed to noise from offshore windmill construction show short-range acoustic trauma

The installation of marine renewable energy devices (MREDs, wind turbines and converters of wave, tidal and ocean thermal energy) has increased quickly in the last decade. There is a lack of knowledge concerning the effects of MREDs on benthic invertebrates that live in contact with the seabed. The European common cuttlefish (Sepia officinalis) is the most abundant cephalopod in the Northeast Atlantic and one of the three most valuable resources for English Channel fisheries. A project to build an offshore wind farm in the French bay of Saint-Brieuc, near the English Channel, raised concern about the possible acoustic impact on local cuttlefish communities. In this study, consisting of six exposure experiments, three types of noise were considered: 3 levels of pile-driving and 3 levels of drilling. The objectives were to assess possible associated changes in hatching and larva survival, and behavioural and ultrastructural effects on sensory organs of all life stages of S. officinalis populations. After exposure, damage was observed in the statocyst sensory epithelia (hair cell extrusion) in adults compared to controls, and no anti-predator reaction was observed. The exposed larvae showed a decreased survival rate with an increasing received sound level when they were exposed to maximum pile-driving and drilling sound levels (170 dB re 1 μPa2 and 167 dB re 1 μPa2, respectively). However, sound pressure levels's lower than 163 dB re 1 μPa2 were not found to elicit severe damage. Simulating a scenario of immobile organisms, eggs were exposed to a combination of both pile driving and drilling as they would be exposed to all operations without a chance to escape. In this scenario a decrease of hatching success was observed with increasing received sound levels.

Spatio-temporal patterns in stable isotope composition of a benthic intertidal food web reveal limited influence from salt marsh vegetation and green tide

Assessing fluxes of matter and energy in food webs within and across benthic habitats is important to understand the ecological functioning in bays and estuaries, where the productivity is favoured by a wide diversity of primary producers. The temporal variability (March vs September 2019) in the carbon and nitrogen stable isotope composition of primary food sources and benthic invertebrates consumers was investigated in a large intertidal area (Western English-Channel, France). The study area is influenced by megatidal conditions and characterised by salt marshes in the sheltered part, and seasonal Ulva spp. blooms. The spatio-temporal variability in the structure of the benthic food web was analysed at the scales of both the whole bay and the different assemblages, which constitute the mosaic of habitats. Inferences on potential sources fuelling the food web were supported by spatio-temporal patterns based on covariations and stable isotope trajectory analysis. Results highlighted that phytoplankton, microphytobenthos and SOM were, most likely, the main food sources. The trophic connectivity between salt marsh and benthic habitats within the bay was limited to some macrofauna species inhabiting muddy creeks within the salt marsh. Unexpectedly, the influence of Ulva spp. blooms appeared also limited. Spatial patterns illustrates the constancy of the spatial variability in the benthic pelagic coupling, with a higher influence of microphytobenthos in the upper shore compared to low shore assemblages. This first attempt to characterize intertidal benthic food web constitutes a relevant baseline for the conservation of the bay of Saint-Brieuc where a national Nature Reserve has been created in 1998 for the conservation of overwintering birds. The spatial and temporal patterns of the benthic food web observed in this study (1) confirm the importance to consider food web variability at spatial and temporal scales from sampling designs to data analysis, and (2) demonstrate the ability of the stable isotope trajectory analysis framework to highlight food web dynamics.

Optimal impulsive harvesting strategy of a stochastic Gompertz model in periodic environments

This research focuses on optimal impulsive harvesting strategy of a stochastic Gompertz model with periodic coefficients. By investigating the associated Hamilton function, the explicit expressions of the optimal impulsive effort, the maximum annual yield and the expectation of the optimal population level are provided. The theoretical results are also utilized to investigate the optimal impulsive harvesting strategy of scallop (Pecten maximus) fishery in the Saint Brieuc Bay, France.

Characterizing spatio-temporal changes in benthic communities: Taxonomic and functional trajectories of intertidal assemblages in the bay of Saint-Brieuc (English Channel)

Tracking and quantifying ecological changes at large and long-term scales is a central point for monitoring and conservation issues. The Community Trajectory Analysis Framework was used in complement with classical methods to analyse and represent long-term changes in marine habitats at 42 stations in the bay of Saint-Brieuc (western English Channel), sampled in 1987, 2001 and 2019. The taxonomic and functional trajectories of intertidal benthic assemblages were studied at local and assemblage scales. Whatever the perennial contribution of dominant prevalent species at the site scale, some species were highly variable over time and space, influencing the structuration of assemblages. Taxonomic changes were not systematically associated with significant changes in the functional properties at local and community scale. The consideration of local changes and variations at the species level explained the differences in composition observed at the scale of assemblages. Observed changes mainly reflected random population dynamics of structuring prevalent species in habitat under strong natural pressures, rather than specific changes of the community. Few species reveal the long-term effect of green tides in some assemblages. Overall, this study confirms the complexity to disentangle factors of changes in the absence of a monitoring strategy specifically devoted the measurement of environmental factors and anthropogenic pressures. The study also highlights the need for the development of benthic monitoring strategies at multiple spatial and temporal scales.

Evolution of a Holocene banner bank controlled by morphodynamics and structural setting of a macrotidal coast: Saint-Brieuc Bay (NW-Europe)

The morphology and internal structure of the Horaine Bank (Bay of Saint-Brieuc, NW France) are described based on multibeam echosounder and high-resolution seismic datasets coupled with vibro-core data. The Horaine Bank shows large-scale bedforms in the lee of a submerged rocky shoal, which allowed defining it as a Banner Bank. The internal structure of the sandbank reveals four seismic units (U1–U4) on a Cambrian basement (U0). The basal unit U1 is interpreted as reworked lowstand fluvial sediments those infilled micro incised valleys during a rise in sea level. This unit is overlain by paleo-coastal barrier sand-spit (U2) whose development was controlled by swell in the context of a rapid rise in sea level. The successive prograding unit (U3) is interpreted as flooding deposits in continuity with unit U2. The unit U4 is characterized by oblique reflectors oriented in two opposite directions. This last unit, dated post 3500 yr BP, corresponds to migrating dunes superimposed on the bank and observable in the high-resolution bathymetric data. The strong correlation between tidal currents and the apparent clockwise migration of dune crests suggests the presence of a tidal gyre controlling the present-day dynamics of most of the Horaine bank dunes. This study proposes a new model for the construction of banner banks characterized by the gradual transition of a sand spit to a banner bank during marine transgression and ensuing hydrodynamic variability.

Total vulnerability of the littoral zone to climate change-driven natural hazards in north Brittany, France

Current worldwide projections of sea-level rise show a staggering increase in water level of up to 2 m by 2100 owing to global warming exacerbated by anthropogenically induced climate change. While amplified rates of sea-level rise is an immense hazard to coastal communities, storm surges are expected to increase in intensity and frequency making it an equally significant threat to coastal populations. In France, these hazards are not uncommon with records of extreme tempests every thousand years in the Holocene. Despite these recurring devastating events, in the Bay of Saint-Brieuc, Brittany, legislated laws for coastal management do not entirely focus on protecting littoral zones from such calamities. 130,739 people are concentrated in 21 municipalities with major cities located at close proximity to the shoreline with numerous socio-economic activities, which increases the vulnerability of the coastal population and infrastructures; thus, affirming the indispensable need of a thorough vulnerability assessment. Here, we conduct a mechanistic appraisal of the vulnerability of the bay considering thirteen parameters within three governing sub-systems that demonstrate the multidimensional dynamics in these municipalities. In the occasion of an extreme climatic event, our results of total vulnerability show risks in the sub-systems highlighting erosional processes due to augmented hydrodynamics, socio-economic and administrative vulnerabilities associated with anthropogenic development. Eight municipalities of the bay portray moderate to very high vulnerability and the remaining exhibits a lower risk; however, not devoid of high vulnerabilities for certain sub-systems. We posit that a more accurate fit for predicting the total vulnerability of the region can be achieved by exclusively integrating physical-natural and administrative sub-system vulnerabilities. We propose generic but requisite recommendations for Integrated Coastal Zone Management such as surveillance of urban development along the coast, implementation of coastal defense systems and appropriate industrial corridors to attenuate and dispose hazardous refuse.

Assessment of freshwater discharge into a coastal bay through multi-basin ensemble hydrological modelling

Coastal basins of the Brittany peninsula (France) are hydrological hot spots. A high level of nutrient pollution affects many of these basins and causes algal blooms in several coastal bays; nine have been a specific focus of the European Commission since 2007. The flux of each contributing basin flowing into these bays must be examined to assess the conditions and explore mitigation options. However, this task encounters a large lack of data since most of the basins are ungauged. In this context, this study developed a method which facilitates transposition of hydrographs from gauged basins to ungauged neighbouring basins of interest. Inverting a simple geomorphology-based transfer function of the gauged basin which describes travel time through channels enables the net rainfall time-series to be estimated from the discharge time-series of donor basins. To estimate the net rainfall of a given ungauged catchment, several net rainfall time series of gauged catchments are averaged. The resulting net rainfall is then transposed onto the ungauged target basin and convoluted by its own transfer function to estimate the hydrograph. This allows the transposition of as many hydrographs as there are different donor basins. This ensemble prediction enables the proportion of prediction uncertainty that is due to the heterogeneity in hydrological behaviour to be estimated. Moreover, the time-series of the donor basins are combined to estimate the ungauged net rainfall time-series. This provides a discharge prediction which values all available measurements. The method was applied to the highly controversial Saint Brieuc Bay, where it was possible to quantify the contribution of each coastal basin, even those influenced by dams, and ultimately the entire volume of fresh water entering the bay at an hourly time step. This work opens perspectives to additionally refine estimation of the associated nutrient fluxes.

New insights into the reproductive cycle of two Great Scallop populations in Brittany (France) using a DEB modelling approach

The present study aimed to improve understanding of the environmental conditions influencing the reproductive cycle of the great scallop Pecten maximus in two locations in Brittany (France). We also evaluated potential consequences of future climate change for reproductive success in each site.We simulated reproductive traits (spawning occurrences and synchronicity among individuals) of P. maximus, using an existing Dynamic Energy Budget (DEB) model. To validate and test the model, we used biological and environmental datasets available for the Bay of Brest (West Brittany, France) between 1998 and 2003. We also applied the scallop DEB model in the Bay of Saint-Brieuc (North Brittany, France) for the same period (1998–2003) to compare the reproductive cycle in different environmental conditions. In order to accurately model the P. maximus reproductive cycle we improved the scallop DEB model in two ways: through (1) energy acquisition, by incorporating microphytobenthos as a new food source; and (2) the reproductive process, by adding a new state variable dedicated to the gamete production. Finally, we explored the effects of two contrasting IPCC climate scenarios (RCP2.6 and RCP8.5) on the reproductive cycle of P. maximus in these two areas at the 2100 horizon.In the Bay of Brest, the simulated reproductive cycle was in agreement with field observations. The model reproduced three main spawning events every year (between May and September) and asynchronicity in the timing of spawning between individuals. In the Bay of Saint-Brieuc, only two summer spawning events (in July and August) were simulated, with a higher synchronicity between individuals. Environmental conditions (temperature and food sources) were sufficient to explain this well-known geographic difference in the reproductive strategy of P. maximus. Regarding the forecasting approach, the model showed that, under a warm scenario (RCP8.5), autumnal spawning would be enhanced at the 2100 horizon with an increase of seawater temperature in the Bay of Brest, whatever the food source conditions. In the Bay of Saint-Brieuc, warmer temperatures may impact reproductive phenology through an earlier onset of spawning by 20 to 44 days depending on the year.

Influence of Green Tides in Coastal Nursery Grounds on the Habitat Selection and Individual Performance of Juvenile Fish.

Coastal ecosystems, which provide numerous essential ecological functions for fish, are threatened by the proliferation of green macroalgae that significantly modify habitat conditions in intertidal areas. Understanding the influence of green tides on the nursery function of these ecosystems is essential to determine their potential effects on fish recruitment success. In this study, the influence of green tides on juvenile fish was examined in an intertidal sandy beach area, the Bay of Saint-Brieuc (Northwestern France), during two annual cycles of green tides with varying levels of intensity. The responses of three nursery-dependent fish species, the pelagic Sprattus sprattus (L.), the demersal Dicentrarchus labrax (L.) and the benthic Pleuronectes platessa L., were analysed to determine the effects of green tides according to species-specific habitat niche and behaviour. The responses to this perturbation were investigated based on habitat selection and a comparison of individual performance between a control and an impacted site. Several indices on different integrative scales were examined to evaluate these responses (antioxidant defence capacity, muscle total lipid, morphometric condition and growth). Based on these analyses, green tides affect juvenile fish differently according to macroalgal density and species-specific tolerance, which is linked to their capacity to move and to their distribution in the water column. A decreasing gradient of sensitivity was observed from benthic to demersal and pelagic fish species. At low densities of green macroalgae, the three species stayed at the impacted site and the growth of plaice was reduced. At medium macroalgal densities, plaice disappeared from the impacted site and the growth of sea bass and the muscle total lipid content of sprat were reduced. Finally, when high macroalgal densities were reached, none of the studied species were captured at the impacted site. Hence, sites affected by green tides are less favourable nursery grounds for all the studied species, with species-specific effects related to macroalgal density.

Некоторые элементы социологии перевода: приручение морских гребешков и рыболовов бухты Сен-Бриё

Некоторые элементы социологии перевода: приручение морских гребешков и рыболовов бухты Сен-Бриё

Individual preferences regarding environmental offset and welfare compensation: a choice experiment application to an offshore wind farm project

This paper uses the choice experiment method to investigate the preferences of local communities with respect to various compensatory measures in connection with a development project. A survey was conducted among recreational users of the bay of Saint-Brieuc, where an offshore wind farm is currently planned. The goal is to identify the preferences of the bay's users with respect to various compensation possibilities: monetary compensation, investment in publicly owned assets, or the ecological restoration. Two multinomial logit (MNL) models and a latent class (LC) model are used to explore the preferences and some sources of heterogeneity within the community. The results of this study show that form of compensation is an important determinant of preferences and has an effect on the acceptability towards the compensation principle. More precisely, results shows that compensation is better accepted if it obeys the principle of strong sustainability, which includes ecological restoration for the gain of the population as a whole and which excludes monetary transactions, associated with the bribe effect. The study also highlights the naturalists' specific attitude for who compensation should be determined within a regulatory framework, one which imposes compensatory measures related to objectively determined ecological impacts.

Stakeholder Perceptions of Offshore Wind Power: A Fuzzy Cognitive Mapping Approach

ABSTRACTUsing the method of fuzzy cognitive mapping, this study explores stakeholder attitudes toward offshore wind energy. The survey was conducted with local communities of the Bay of Saint-Brieuc, where an offshore wind farm is under development. It was used to record the stakeholder perceptions of social, ecological, and economic impacts and the expression of expected compensation for negative impacts. Distribution and interaction among the data were analyzed through multiple correspondence analysis. Our study illustrates a gap between positive impacts associated with sustainable development perceived at the national level and more negative impacts perceived by local communities. The expression of expected compensation is dependent on the perceived impacts. This study highlights the place attachment of local stakeholders and thus suggests developing offshore wind farms with respect to territorial integrity and its heritage dimension in order to improve social acceptability.

Two decades of Pseudo-nitzschia spp. blooms and king scallop (Pecten maximus) contamination by domoic acid along the French Atlantic and English Channel coasts: Seasonal dynamics, spatial heterogeneity and interannual variability

King scallop contamination (Pecten maximus) by domoic acid, a neurotoxin produced by some species of the diatom Pseudo-nitzschia, is highly problematic because of its lengthy retention in the bivalve tissue, leading to prolonged fishery closures. Data collected within the French Phytoplankton and Phycotoxin monitoring network (REPHY) over the 1995–2012 period were used to characterize the seasonal dynamics and the interannual variability of P.-nitzschia spp. blooms as well as the contamination of king scallop fishing grounds, in six contrasted bays distributed along the French Atlantic coast and English Channel. Monitoring revealed that these toxic events have become more frequent since the year 2000, but with varying magnitudes, frequencies and timing depending on the bay. Two bays, located in southern Brittany, exhibited both recurrent contaminations and high P.-nitzschia abundances. The Brest bay and the Seine bay were intermittently affected. The Pertuis Breton exhibited only one major toxic event related to an exceptionally intense bloom of P.-nitzschia in 2010, and the Saint Brieuc bay neither showed significant contamination nor high P.-nitzschia abundance. While high P.-nitzschia abundance appeared to be correlated to scallop toxicity, this study highlights the difficulty in linking P.-nitzschia spp. blooms to king scallop contamination through monitoring. Indeed, P.-nitzschia was determined at the genus level and data regarding species abundances and their toxicity levels are an absolute prerequisite to further assess the environmental control of ASP events. As results describe distinct P.-nitzschia bloom dynamics along the French coast, this may suggest distinct controlling factors. They also revealed that major climatic events, such as the winter storm Xynthia in 2010, can trigger toxicity in P.-nitzschia over a large spatial scale and impact king scallop fisheries all along the coast.

Prediction of streamflow from the set of basins flowing into a coastal bay

Abstract. Many coastal basins of the Brittany peninsula (France) display a high level of nitrate pollution, nine of them highlighted by the European Commission since 2007, as causing algal blooms in several coastal bays. To precisely diagnose and solve this issue the fluxes of every contributing basin have to be considered. However, this faces a strong data-scarce situation as most of the basins are ungauged. In this context, we propose to transpose hydrological information from one gauged basin to neighbouring points of interest. The methodology uses a simple geomorphology-based transfer function on the gauged basin, which allows assessment of the net rainfall time series through the de-convolution of the gauged discharge series. This net rainfall is then transposed and convoluted on the ungauged basin using its own transfer function in order to estimate discharge. This approach enables the quantification of the whole volume of freshwater entering the controversial Saint-Brieuc Bay.

Exploitation of intertidal feeding resources by the red knot Calidris canutus under megatidal conditions (Bay of Saint-Brieuc, France)

The feeding ecology of the red knot has been widely studied across its wintering range. Red knots mainly select bivalves and gastropods, with differences between sites due to variation in prey availability. The shorebird's diet is also influenced or controlled by the tidal regime. The aim of this paper is to demonstrate the adaptation of foraging red knots to the megatidal environment. The variation in their diet during tidal cycles was studied in the bay of Saint-Brieuc, a functional unit for this species. The method used combined macrofauna, distribution of foraging birds and diet data. Comparative spatial analyses of macrofauna and distribution of foraging red knots have shown that the bay's four benthic assemblages are exploited by birds. By analysing droppings, we highlighted that bivalve molluscs are the main component of their diet, as shown in most overwintering sites. Fifteen types of prey were identified and Donax vittatus was discovered to be a significant prey item. The relative proportion of each main prey item differs significantly depending on the benthic assemblage used to forage. All available benthic assemblages and all potential feeding resources can be used during a single tidal cycle, reflecting an adaptation to megatidal conditions. This approach develops accurate knowledge about the feeding ecology of birds which managers need in order to identify optimal areas for the conservation of waders based on the areas and resources actually used by the birds.

Contrasting Benthos Communities and Prey Selection by Red KnotCalidris canutusin Three Nearby Bays on the Channel Coast

In this study, we describe food availability and diet selection of the Red Knot Calidris canutus islandica wintering in three estuarine bays on the French Channel coast. We examined whether the distribution of birds is related to the density and availability of high quality prey. Results indicate strong seasonal and inter-annual variation in the abundance of birds and considerable variation in prey-item abundance and diet selection depending upon site. At Mont Saint-Michel Bay, the prey community was dominated by Baltic Tellins, Macoma balthica. As expected from their high meat-to-shell ratio, Macoma contributed more than 90% of the diet. Most of the cockles, Cerastoderma edule were too large and their quality too low to be preyed upon. Less than 100 km away, in Saint-Brieuc Bay, Red Knots mainly selected the Thin Tellin Tellina tenuis. Although Tellina are a lower quality prey than Macoma, they occurred at a high density and in some winters might explain why the number of Red Knots exceeds those at Mont Saint-Michel Bay. At Bay des Veys, Normandy, Red Knots were restricted to a small intertidal area and fed on Abra tenuis, Macoma balthica and Hydrobia ulvae.

Modelling green macroalgal blooms on the coasts of Brittany, France to enhance water quality management

First recorded in the 1970s, massive green macroalgal blooms have since become an annual recurrence in Brittany, France. Eutrophication (in particular to anthropogenic nitrogen input) has been identified as the main factor controlling Ulva ‘green tide’ events. In this study, we modelled Ulva proliferation using a two-dimensional model by coupling hydrodynamic and biological models (coined ‘MARS-Ulves’) for five sites along the Brittany coastline (La Fresnaye Bay, Saint-Brieuc Bay, Lannion Bay, Guissény Bay and Douarnenez Bay). Calibration of the biological model was mainly based on the seasonal variation of the maximum nitrogen uptake rate (VmaxN) and the half-saturation constant for nitrogen (KN) to reproduce the internal nutrient quotas measured in situ for each site. In each bay, model predictions were in agreement with observed algal coverage converted into biomass. A numerical tracking method was implemented to identify the contribution of the rivers that empty into the study bays, and scenarios of decreases in nitrate concentration in rivers were simulated. Results from numerical nitrogen tracking highlighted the main nitrogen sources of green tides and also showed that each river contributes locally to green tides. In addition, dynamic modelling showed that the nitrate concentrations in rivers must be limited to between 5 and 15mgl−1, depending on the bay, to reduce Ulva biomass by half on the coasts. The three-step methodology developed in this study (analysing total dissolved inorganic nitrogen flux from rivers, tracking nitrogen sources in Ulva and developing scenarios for reducing nitrogen) provides qualitative and quantitative guidelines for stakeholders to define specific nitrogen reduction targets for better environmental management of water quality.

Modelling larval dispersal of the king scallop (Pecten maximus) in the English Channel: examples from the bay of Saint-Brieuc and the bay of Seine

The king scallop (Pecten maximus) is one of the most important benthic species of the English Channel as it constitutes the first fishery in terms of landings in this area. To support strategies of spatial fishery management, we develop a high-resolution biophysical model to study scallop dispersal in two bays along the French coasts of the English Channel (i.e. the bay of Saint-Brieuc and the bay of Seine) and to quantify the relative roles of local hydrodynamic processes, temperature-dependent planktonic larval duration (PLD) and active swimming behaviour (SB). The two bays are chosen for three reasons: (1) the distribution of the scallop stocks in these areas is well known from annual scallop stock surveys, (2) these two bays harbour important fisheries and (3) scallops in these two areas present some differences in terms of reproductive cycle and spawning duration. The English Channel currents and temperature are simulated for 10 years (2000–2010) with the MARS-3D code and then used by the Lagrangian module of MARS-3D to model the transport. Results were analysed in terms of larval distribution at settlement and connectivity rates. While larval transport in the two bays depended both on the tidal residual circulation and the wind-induced currents, the relative role of these two hydrodynamic processes varied among bays. In the bay of Saint-Brieuc, the main patterns of larval dispersal were due to tides, the wind being only a source of variability in the extent of larval patch and the local retention rate. Conversely, in the bay of Seine, wind-induced currents altered both the direction and the extent of larval transport. The main effect of a variable PLD in relation to the thermal history of each larva was to reduce the spread of dispersal and consequently increase the local retention by about 10 % on average. Although swimming behaviour could influence larval dispersal during the first days of the PLD when larvae are mainly located in surface waters, it has a minor role on larval distribution at settlement and retention rates. The analysis of the connectivity between subpopulations within each bay allows identifying the main sources of larvae which depend on both the characteristics of local hydrodynamics and the spatial heterogeneity in the reproductive outputs.