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Highlights • ECO-MARS3D model is described for the French continental shelf pelagic ecosystem. • It provides descriptors for the WFD and MSFD assessment of eutrophication status. • Validation is made on the 2000–2010 decade for descriptors used in WFD and MSFD. • Maps showing the areas not in Good Environmental Status for the descriptors are provided. • A running operational application of this model provides N-tracking from 3 rivers. Abstract European directives (Water Framework Directive - WFD and Marine Strategy Framework Directive - MSFD) require a regular survey of several descriptors of the Environmental Status of coastal waters of the North-east Atlantic Ocean. Especially for the MSFD, which may concern large continental shelf areas where measurements are scarce, realistic ecological models can help assessing the Environmental Status. The ECO-MARS3D model of the pelagic ecosystem of the Bay of Biscay and English Channel continental shelf (NE Atlantic) has been developed for these applied purposes and validated against various types of historic data. This first paper deals with the basic biogeochemical version, which contains inorganic nutrients (NH 4 , NO 3 , PO 4 , Si(OH) 4), three phytoplankton bulk types (diatoms, nanoflagellates and dinoflagellates), two zooplankton bulk types, particulate detrital forms and dissolved oxygen. A second paper presents a version of this model including 3 harmful phytoplanktonic groups. A simulation covering the 2000–2010 decade is compared to satellite sea surface data for temperature and surface chlorophyll, to the Southampton-Bilbao and Ouistreham-Portsmouth ferrybox surface data for temperature, salinity, chlorophyll and nutrients, to point samples provided by the French network of phytoplankton monitoring (REPHY) for inorganic nutrients and chlorophyll, and to high frequency time series of dissolved oxygen measured by a moored automatic buoy. From a spatial point of view, the model provides realistic fields of annual means of surface temperature (but with a systematic bias of about + 1.0°C) and phytoplanktonic biomass. From a seasonal point of view, the temperature and salinity follow correctly the observed variations. For nutrient and total chlorophyll, the model succeeds in reproducing the difference amounting to one order of magnitude between the North Sea coastal zones and the oligotrophic oceanic zone above the abyssal plain of the bay of Biscay. It also reproduces the spring-neap tide oscillation visible in satellite observations of surface chlorophyll. Simulated seasonal cycles are realistic in the coastal stations, but the French Atlantic coast seems slightly too nutrient-rich. In coastal eutrophicated areas, the model does not produce chlorophyll peaks as high as measured. In the Vilaine bay (France), the summer hypoxic conditions (down to 4 mg/L O 2 or less) are correctly reproduced. This ecological model has been used off-line to map some classical eutrophication descriptors (winter DIN and DIP, March-October 90th percentile of chlorophyll) used by the WFD and MSFD European directives. It has also been turned into an operational real-time mode, as part of the French Previmer project (now: http://marc.ifremer.fr/resultats/production_primaire). [ABSTRACT FROM AUTHOR]

In the frame of a national, joint scientific appraisal, 45 scientific French-speaking experts have been mandated in 2015–2016 by the French ministries of Environment and Agriculture to perform a global review of scientific literature dealing with the eutrophication phenomenon, in freshwater as well as in marine waters. This paper summarizes the main results of this review restricted to a sub-domain, the modelling approach of the marine eutrophication. After recalling the different aims pursued, an overview is given on the historical time course of this modelling effort, its world distribution and the various tools used. Then, the main results obtained are examined, highlighting the specific strengths and weaknesses of the present models. Needs for future improvement are then listed. [ABSTRACT FROM AUTHOR]

Since 1950, increase in nitrogen (N) and phosphorus (P) river loadings in the North-East Atlantic (NEA) continental seas has induced a deep change in the marine coastal ecosystems, leading to eutrophication symptoms in some areas. In order to recover a Good Ecological Status (GES) in the NEA, as required by European Water Framework Directive (WFD) and Marine Strategy Framework Directive (MSFD), reductions in N- and P-river loadings are necessary but they need to be minimal due to their economic impact on the farming industry. In the frame of the “EMoSEM” European project, we used two marine 3D ecological models (ECO-MARS3D, MIRO&CO) covering the Bay of Biscay, the English Channel and the southern North Sea to estimate the contributions of various sources (riverine, oceanic and atmospheric) to the winter nitrate and phosphate marine concentrations. The various distributed descriptors provided by the simulations allowed also to find a log-linear relationship between the 90th percentile of satellite-derived chlorophyll concentrations and the “fully bioavailable” nutrients, i.e. simulated nutrient concentrations weighted by light and stoichiometric limitation factors. Any GES threshold on the 90th percentile of marine chlorophyll concentration can then be translated in maximum admissible ‘fully bioavailable’ DIN and DIP concentrations, from which an iterative linear optimization method can compute river-specific minimal abatements of N and P loadings. The method has been applied to four major river groups, assuming either a conservative (8 μg Chl L −1 ) or a more socially acceptable (15 μg Chl L −1 ) GES chlorophyll concentration threshold. In the conservative case, maximum admissible winter concentrations for nutrients correspond to marine background values, whereas in the lenient case, they are close to values recommended by the WFD/MSFD. Both models suggest that to reach chlorophyll GES, strong reductions of DIN and DIP are required in the Eastern French and Belgian-Dutch river groups. [ABSTRACT FROM AUTHOR]

The anthropogenic introduction in U.K. waters of the north-American marine gastropod Crepidula fornicata (Linné, 1758), commonly called slipper limpet, and its consecutive spreading has led in less than a century to the invasion of a part of benthic grounds along the North-European coasts. Competition for space has hampered the maintenance of the native scallop Pecten maximus , whereas dredge clogging has drastically limited scallop fishing, especially in the Western English Channel. In order to assess the possible future distribution and abundance of both species ( Crepidula and Pecten ), an original model of slipper limpet chains joined to a simple year-class model of the scallop (Ménesguen and Grégoris, 2017) has been coupled to a connectivity matrix summarizing the annual dispersion of emitted larvae in a realistic marine domain. This distributed model can explore the dynamics of both populations at the century scale and has been applied at two different geographical scales: a local one (the bays of Brest and Douarnenez, Western Brittany, France) and a regional one (Bay of Biscay and English Channel). First eigenvectors of the connectivity matrix are used to delineate the main retention areas. For each species taken alone, simulations starting with a few animals in different spots do converge in less than a century towards the same geographic distribution, compatible with the actual field distribution. This suggests that hydrodynamic patterns of larval drift create a strong attractor for these populations; it is reached by different routes of colonization, depending on the initial inoculation. The non-linear interaction created by the lack of space when the populations have filled the benthic area seems to be stronger for scallop populations than for slipper limpets, because of the permanent capacity of Crepidula beds to fix some larvae on the top of existing colonies. Whereas the scallop abundance experiences a rather large limit-cycle, with a dominant 11 years period and a lot of harmonics, the slipper limpet has commonly a stable steady state abundance. Competition between both populations tends to lower the mean scallop abundance and to lengthen and damp its fundamental period of oscillations. Simulated distributions can be locally improved by linking the larval survival to a distributed environmental stressor, as the salinity for scallop or a metallic contamination for the slipper limpet in the case of the bay of Brest. [ABSTRACT FROM AUTHOR]

The north-American marine gastropod Crepidula fornicata (Linné 1758), commonly called slipper limpet, has been introduced accidentally in Great Britain, along with American oysters ( Crassostrea virginica ) at the end of the 19th century. Its spreading, enhanced by oyster transport and international shipping, turned into invasion of a lot of benthic grounds along the North-European coasts. When local conditions are favorable to larval confinement and adult growth, the invasion by very dense populations may deeply change initially sandy or muddy benthic communities into similar “slipper limpet communities”. Competition for space eliminates several species of native infauna, and hampers the survival of some epibenthic bivalves such as the scallop Pecten maximus . As the clogging of dredges by superabundant slipper limpets drastically limits scallop fishing, some insight in the future distribution and abundance of both species ( Crepidula and Pecten ) seems necessary, especially in the English Channel where the scallop is intensively harvested. An original model, storing in a “intraspecific matching matrix” the numbers of pairs of aged animals present in the slipper limpet chains, has been developed to take into account the year-class association and stack formation specific to Crepidula fornicata. Then, an “interspecific matching matrix” component has been added to that “intraspecific matching matrix” in order to describe the simple year-class structure of the scallop along with the age distribution of slipper limpets stuck on scallop shells and forming the base of chains. Such a model can explore the dynamics of both populations at a secular time scale. This first part of work details the 0D-behavior of the populations, alone or together, on 1 m 2 benthic area. As far as the scallop is concerned, the fact that class 1 cannot recruit in dense populations until the death of old animals has freed some place induces a limit-cycle, with a 11 years period, and a large amplitude. On the contrary, in the case of the slipper limpet, because of the constant possibility for class 1 to recruit on the top of existing colonies, even if the bottom coverage is total, the population reaches a stable steady state abundance, without significant oscillations. Competition for space between the two species does not alter significantly the slipper limpet, whereas it lowers the mean abundance and alters (by damping and slowing down) the limit cycle of the scallop. [ABSTRACT FROM AUTHOR]

Abstract: It is well known that temporal changes in bivalve body mass are strongly correlated with temporal variations in water temperature and food supply. In order to study the influence of the year-to-year variability of environmental factors on oyster growth, we coupled a biogeochemical sub-model, which simulates trophic resources of oysters (i.e. phytoplankton biomass via chlorophyll a), and an ecophysiological sub-model, which simulates growth and reproduction (i.e. gametogenesis and spawning), using mechanistic bases. The biogeochemical sub-model successfully simulated phytoplankton dynamics using river nutrient inputs and meteorological factors as forcing functions. Adequate simulation of oyster growth dynamics requires a relevant food quantifier compatible with outputs of the biogeochemical sub-model (i.e. chlorophyll a concentration). We decided to use the phytoplankton carbon concentration as quantifier for food, as it is a better estimator of the energy really available to oysters. The transformation of chlorophyll a concentration into carbon concentration using a variable chlorophyll a to carbon ratio enabled us to improve the simulation of oyster growth especially during the starvation period (i.e. autumn and winter). Once validated, the coupled model was a suitable tool to study the influence of the year-to-year variability of phytoplankton dynamics and water temperature on the gonado-somatic growth of the Pacific oyster. Four years with highly contrasted meteorological conditions (river inputs, water temperature and light) 2000, 2001, 2002 and 2003, were simulated. The years were split into two groups, wet years (2000 and 2001) and dry years (2002 and 2003). Significant variability of the response of oysters to environmental conditions was highlighted between the four scenarios. In the wet years, an increase in loadings of river nutrients and suspended particulate matter led to a shift in the initiation and the magnitude of the phytoplanktonic spring bloom, and consequently to a shift in oyster growth patterns. In contrast, in the dry years, an increase in water temperature—especially during summer—resulted in early spawning. Thus, the gonado-somatic growth pattern of oysters was shown to be sensitive to variations in river loadings and water temperature. In this context, the physiological status of oysters is discussed using a relevant indicator of energy needs. [Copyright &y& Elsevier]

Abstract: This paper describes the development of a modelling framework to study the distribution in the English Channel of a benthic bivalve with planktonic larvae, Paphia rhomboïdes. Age-structured population dynamics and growth models are linked together to a compartmental transport and NPZ (Nutrients–Phytoplankton–Zooplankton) model. Used in a spin-up mode, i.e. with identical environmental forcing from a year to the next, this deterministic model converges to the same steady state whatever the initial conditions, after 15–30 years of simulation. Important features of the P. rhomboïdes distribution are reproduced, particularly its high abundance in the GNB (Golfe Normand-Breton) and its almost complete absence in the Western Channel. The results are discussed in relation with the modelling strategies, especially with regard to the advantages and drawbacks which could result from changing the box-model approach into a fine 3D hydrodynamic approach. [Copyright &y& Elsevier]

Paphia rhomboïdes is an infaunal filter-feeding bivalve, particularly widespread and abundant in the English Channel. In order to investigate the influence of the growth-related post-settlement processes on its distribution, a spatial growth model was developed and linked to an existing ecological model of the English Channel. This model was partially parameterized on the basis of a specific ecophysiological experimental study, and calibrated with growth data collected in the “Golfe Normand-Breton” (GNB), a region of the English Channel. Compared to the actual distribution of P. rhomboïdes, the results suggest a strong influence of the growth-related processes on the distribution of the species: particularly, the extremely low growth obtained with the model in the Western Channel can explain the almost complete absence of the species in this area. [Copyright &y& Elsevier]

Abstract: The general trend in ecosystem modelling is to improve the spatial resolution by shifting from rough box-models to fine 3D models. Despite the continuous speeding-up of computing, 3D models involving numerous state variables may remain intractable, especially for parameter calibration, when processes with long half-life periods (i.e, from years to decades) are introduced, such as the behaviour of organic matter in sediment and population dynamics of benthic species. In these cases, a first approach can be provided by fast-running box-models, if they take into account the most crucial hydrodynamic properties of the system. In a macrotidal shelf sea such as the English Channel, the long-term horizontal transport can be summarized by the tidal residual circulation, and the vertical stratification can be sketched by a two- or three-layered integral model. This paper compares the results obtained in the English Channel area by the same biogeochemical equations of pelagic primary production, coupled to 1) a two-layered box-model 2) a three-layered box-model (i.e., with an intermediate cline layer between surface and bottom ones) and 3) a fine-gridded 3D model. Comparison is focused firstly on thermal stratification and summer dinoflagellate blooms in the north-western Channel and secondly on the haline stratification and the sequence of blooms obtained in the eutrophicated Seine river plume. Comparison shows that box-models act as low-pass filters which reproduce correctly the weekly mean time-course, but greatly reduce the variance locally observed in a tide-oscillating plume region. As far as global characteristics are concerned, such as the annual primary production, or the percentage of variation in annual production after reducing the nutrient loadings, the box and 3D models gave very similar results. This conclusion reinforces the usefulness of using box-models as a first approach in long-term processes, for which a long transient phase is expected before reaching the annual periodic solution. [Copyright &y& Elsevier]

Abstract: Accumulation of heat, or dissolved substances (nutrients, pollutants, etc.), or fine suspended particles in a water body is a key process in the functioning of aquatic ecosystems and their resistance to perturbations. In complex and wide open environments such as marine ecosystems, net accumulation is not only linked to the local renewal capacity of the water body, but also to the partial recirculation of water due to convective cells of various sizes. The English Channel, which can be considered as mainly dominated by tidal movements, exhibits such a complex quasi-permanent long-term circulation, made of a central “river” bordered with a lot of nested gyres. Here, we show that structures visible on satellite images of SST (Sea Surface Temperature), chlorophyll and SPIM (Suspended Particulate Inorganic Matter) can be explained by steady state distributions of tracers having various half-life durations, which can be computed using a simple technique of regularly distributed micro-injection in the permanent flow field. Gyres induced by capes in open water appear to be retention areas, whereas gyres around islands (Channel Isles) appear to be strong disseminating areas, acting as slings. Moreover, SST satellite maps can be explained by a short-lived tracer during the “transitory” seasons (spring and autumn), and by a long-lived one during the “stable” seasons (summer and winter): long-term accumulation structures become apparent only in August and March. SPIM can be considered as a tracer injected only in muddy areas by the bottom friction caused by the swell, and having a half-life duration linked to the turbulent energy dissipation, which controls the settling rate; this succeeds to explain the observed turbidity in the central Channel essentially, as well as the striking asymmetry visible on images between the large turbid coastal band along the English coasts (materializing a natural long-term retention area), and the rather clear waters along the French coasts. The annual mean chlorophyll distribution in the Channel, as derived from satellite reflectance, can be simulated by a short-lived tracer injected proportionally to the mean light availability along the water column. Computing steady state distributions of various substances or particles in permanent circulation gives a simple and quick tool for understanding their mean stable distribution patterns in the oceans. [Copyright &y& Elsevier]

A new numerical technique is presented that allows the tracking of any chemical element from any source in a simulated foodweb, for instance assessing the proportion of these sources (river loadings, sea entrances, point sources) in the algal diet for the limiting nutrient. An application is shown for nitrogen in an Ulva bloom occurring in a shallow embayment connected with a strongly tidally stirred ecosystem with various sources of inorganic nitrogen, the Bay of Brest, Brittany, France. In a first step, a biogeochemical three-dimensional model was developed to simulate growth and erosion-transport-deposition of free-floating ulvae; this model was able to converge on a realistic distribution of Ulva deposits after a few months, even though it was initialized with a strongly unrealistic distribution of settled ulvae. In a second step, and unfortunately for recovery plans, the tracking technique, applied in this model to all the nitrogen sources entering the hay, revealed that the small, nitrate-polluted rivers flowing directly into the eutrophicated area had a negligible effect, whereas more distant but stronger sources, a big river and a big urban sewage plant, even after dilution, accounted for about 50% and 20%, respectively, of the algal nitrogen content during summer. Despite its high N flux, open ocean contributes only 15% to Ulva growth. The suppression of only one of the main nitrogen sources would not significantly decrease the Ulva bloom, because of the high nitrogen surplus present in the site. The remaining sources would still saturate the needs of the maximum Ulva biomass the site is able to produce. The tracking technique, however, shows that the N turnover in Ulva is only 4 months. Thus, improvements would occur within a year following large N reductions. [ABSTRACT FROM AUTHOR]

Because of the first observations in the 1900s of the oligotrophic and eutrophic states of lakes, researchers have been interested in the process that makes lakes become turbid because of high phytoplankton biomass. Definitions of eutrophication have multiplied and diversified since the mid‐20th century, more than for any other ecological process. Reasons for the high number of definitions might be that the former ones did not sufficiently describe their causes and/or consequences. Global change is bringing eutrophication more into the spotlight than ever, highlighting the need to find consensus on a common definition, or at least to explain and clarify why there are different meanings of the term eutrophication. To find common patterns, we analyzed 138 definitions that were classified by a multiple correspondence factor analysis (MCA) into three groups. The first group contains the most generic scientific definitions but many of these limit the causes to increased nutrient availability. A single definition takes into account all causes but would require additional work to clarify the process itself. Nutrient pollution, which is by far the primary cause of eutrophication in the Anthropocene, has generated a second group of environmental definitions that often specify the primary producers involved. Those definitions often mention the iconic consequences of nutrient pollution, such as increased algal biomass, anoxia/hypoxia and reduced biodiversity. The third group contains operational definitions, focusing on the consequences of nutrient pollution, for ecosystem services and therefore associated with ecosystem management issues. This group contains definitions related to regulations, mainly US laws and European directives. These numerous definitions, directly derived from the problem of nutrient pollution, have enlarged the landscape of definitions, and reflect the need to warn, legislate and implement a solution to remedy it. Satisfying this demand should not be confused with scientific research on eutrophication and must be based on communicating knowledge to as many people as possible using the simplest possible vocabulary. We propose that operational definitions (groups 2 and 3) should name the process "nutrient pollution," making it possible to refine (scientific) definitions of eutrophication and to expand on other challenges such as climate warming, overfishing, and other nonnutrient‐related chemical pollutions. [ABSTRACT FROM AUTHOR]

Abstract Eutrophication is one of the most common causes of water quality impairment of inland and marine waters. Its best-known manifestations are toxic cyanobacteria blooms in lakes and waterways and proliferations of green macro algae in coastal areas. The term eutrophication is used by both the scientific community and public policy-makers, and therefore has a myriad of definitions. The introduction by the public authorities of regulations to limit eutrophication is a source of tension and debate on the activities identified as contributing or having contributed decisively to these phenomena. Debates on the identification of the driving factors and risk levels of eutrophication, seeking to guide public policies, have led the ministries in charge of the environment and agriculture to ask for a joint scientific appraisal to be conducted on the subject. Four French research institutes were mandated to produce a critical scientific analysis on the latest knowledge of the causes, mechanisms, consequences and predictability of eutrophication phenomena. This paper provides the methodology and the main findings of this two years exercise involving 40 scientific experts. Graphical abstract Unlabelled Image Highlights • Eutrophication in the 70ies was related to point source pollution, mainly phosphorus. • Eutrophication is pervasive in many lakes, coastal areas and rivers of the world. • Diffuse nitrogen and phosphorus losses are now the main drivers of this new wave of eutrophication. • It is a wicked problem as a consequence of multiple, often cumulative actions other large spatio-temporal scales. • Solutions to tackle eutrophication need to address the entire land-sea continuum. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: In many ecosystem models based on empirical formulations, parameters generally are calibrated in order to achieve the best fit between measured and simulated chlorophyll a standing stocks. An accurate calibration of rate processes as primary production rarely is taken into account. In this paper, we test the usefulness of calibration of phytoplankton photosynthetic processes in an ecosystem model using field primary production data. We used 18months of photosynthetic process data from the Baie des Veys ecosystem (Normandy, France). Five empirical formulations of photosynthesis–irradiance curve models amongst the most widely used were tested. In each formulation, the variability of photosynthetic parameters (i.e. the light-saturated rate of photosynthesis (P max B) and the initial slope of the photosynthesis–light curve (α B)) was considered depending on environmental factors (temperature and nutrient availability). The fit of the five equations as well as the calibration of parameters on field measurements (i.e. the light-saturated rate of photosynthesis (P ref B), the initial slope of the photosynthesis–light curve (α ref B), the half-saturation constant for nitrogen (K N) and silicates uptake (K Si), and the coefficient in the exponential thermal effect (K T)) was performed using the whole available data set of P vs. E curves (n =143, P vs. E curves). Then, the Smith formulation allowing the best simulation of the Baie des Veys primary production and corresponding parameters were introduced in an ecosystem box model. This formulation led directly to a satisfactory representation of the Baie des Veys phytoplankton dynamics without additional calibration. Results obtained were compared with a more classical approach in which ecosystem models were calibrated using published values of parameters. This comparison showed that for the two years studied, annual primary production estimated through the ecosystem model was 13% and 26% higher with our approach than with the more classical approach. This work emphasizes the importance of accurately representing rate processes in ecosystem models in order to adequately simulate production as well as standing stocks. [Copyright &y& Elsevier]

Observations from space and in situ from the R.V. Corystes 8/03 Cruise show that a massive Karenia mikimotoi bloom occured during summer 2003 in the western English Channel. Due to exceptional climatoligical conditions that occured in June 2003, the installation of a very strong thermocline enhanced the development of a massive bloom over 1 millioncellsl−1 in the Central English Channel. This paper presents the application of a mathematical model of this species, previously developed in for the Bay of Biscay, into a general 3D model of the primary production of the English Channel and southern Bight of the North Sea. Allelopathic interactions exerted by K. mikimotoi on other phytoplankton species and the role of agitation in the mortality of this species are taken into account. The model includes the dynamics of the bloom and consequently reproduces with good agreement the geographical distribution of the K. mikimotoi bloom both surface and subsurface. The model suggests that the apparent transport of the bloom towards the French coasts as inferred from the satellite observation was not due to advection but was only caused by the establishment of suitable conditions. The sensivity of the K. mikimotoi distribution to boundary conditions, initialization and the role of turbulence is discussed. [Copyright &y& Elsevier]

A numerical deterministic model for a seagrass ecosystem (Zostera noltii meadows) has been developed for the Thau lagoon. It involves both above- and belowground seagrass biomasses, nitrogen quotas and epiphytes. Driving variables are light intensity, wind speed, rain data and water temperature. This seagrass model has been coupled to another biological model in order to simulate the relative contributions of each primary producer to: (i) the total ecosystem production, (ii) the impact on inorganic nitrogen and (iii) the fluxes towards the detritus compartment. As a first step in the modelling of seagrass beds in the Thau lagoon, the model has a vertical structure based on four boxes (a water box on top of three sediment boxes) and the horizontal variability is neglected until now. This simple box structure is nevertheless representative for the shallow depth Z. noltii meadows, spread over large areas at the lagoon periphery.After calibration, simulation results have been compared with in situ measurements and have shown that the model is able to reproduce the general pattern of biomasses and nitrogen contents seasonal dynamics. Moreover, results show that, in such shallow ecosystems, seagrasses remain the most productive compartment when compared with epiphytes or phytoplankton productions, and that seagrasses, probably due to their ability in taking nutrients in the sediment, have a lower impact on nutrient concentration in the water column than the phytoplankton. Furthermore, in spite of active mechanisms of internal nitrogen redistribution and reclamation, the occurrence of a nitrogen limitation of the seagrass growth during summer, already mentioned in the literature, have also been pointed out by the model. Finally, simulations seems to point out that epiphytes and phytoplankton could compete for nitrogen in the water column, while a competition for light resources seems to be more likely between epiphytes and seagrasses. [Copyright &y& Elsevier]

Marine organisms are currently experiencing an unprecedented rate of climatic warming, which affects their biogeography and threatens marine ecosystem integrity. To understand how benthic species will respond to ongoing seawater warming, we assessed the relative importance of processes acting at different scales using an individual-based modelling approach. Our model integrates: (1) at the individual scale, interactions between the environment, metabolism and ontogenic transitions; (2) at the habitat scale, competition for space at settlement and mortality; and (3) at the regional scale, larval dispersal and connectivity between habitats. We focused on a coastal area in the North-East Atlantic that has experienced a significant seawater warming trend over recent decades. We built and ran a population dynamics model for the blue mussel (Mytilus edulis) in this area, which is a known biogeographic boundary zone. We then compared the response for a reference scenario and a RCP8.5 temperature projection for 2100. We found that (1) increase in seawater temperature would result in a decrease in average biomass associated with a change in recruitment phenology; (2) response to seawater warming is not spatially homogeneous, showing the importance of processes at the habitat scale; (3) connectivity clearly limits the consequences of warming compared with other regulation processes; and (4) larval supply does not seem to be a limiting factor regulating population biomass. The use of such generic models would therefore be very valuable for guiding and optimizing research efforts and supporting the implementation of management and conservation measures. [ABSTRACT FROM AUTHOR]

Abstract: In this paper the results from a workshop of the OSPAR Intersessional Correspondence Group on Eutrophication Modelling (ICG-EMO) held in Lowestoft in 2007 are presented. The aim of the workshop was to compare the results of a number of North Sea ecosystem models under different reduction scenarios. In order to achieve comparability of model results the participants were requested to use a minimum spin-up time, common boundary conditions which were derived from a wider-domain model, and a set of common forcing data, with special emphasis on a complete coverage of river nutrient loads. Based on the OSPAR requirements river loads were derived, taking into account the reductions already achieved between 1985 and 2002 for each country. First, for the year 2002, for which the Comprehensive Procedure was applied, the different horizontal distributions of net primary production are compared. Furthermore, the differences in the net primary production between the hindcast run and the 50% nutrient reduction runs are displayed. In order to compare local results, the hindcast and reduction runs are presented for selected target areas and scored against the Comprehensive Procedure assessment levels for the parameters DIN, DIP and chlorophyll. Finally, the temporal development of the assessment parameter bottom oxygen concentration from several models is compared with data from the Dutch monitoring station Terschelling 135. The conclusion from the workshop was that models are useful to support the application of the OSPAR Comprehensive Procedure. The comparative exercise formulated specifically for the workshop required models to be evaluated for pre-defined target areas previously classified as problem areas according to the first application of the Comprehensive Procedure. The responsiveness of the modelled assessment parameters varied between different models but in general the parameter showed a larger response in coastal rather than in offshore waters, which in some cases lead to the goal to achieve a non-problem status. Therefore, the application of the Comprehensive Procedure on model results for parameter assessment opens a new potential in testing eutrophication reduction measures within the North Sea catchment. As a result of the workshop further work was proposed to confirm and bolster confidence in the results. One general field of difficulty appeared to be the model forcing with SPM data in order to achieve realistic levels of light attenuation. Finally, effects of the prescribed spin-up procedure are compared against a long-term run over many years and consequences on the resulting initial nutrient concentrations are highlighted. [Copyright &y& Elsevier]