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A bay's capacity to buffer fluvial fluxes between the land and sea is sensitive to hydrological changes that can affect its water renewal rates. In Cartagena Bay, Colombia, pollution issues have been associated with freshwater fluxes which are projected to increase in future years. This has led to plans to reduce freshwater flows by constructing upstream hydraulic doors. Given the influence of freshwater discharge on coastal water renewal, it is important to assess how these upstream changes will affect the bay's hydrodynamic processes. This study calibrated the 3D MOHID Water model, configured with a high-resolution mixed vertical discretization to capture the bay's characteristic processes of vertical stratification and mixing. A Lagrangian transport model was used to analyze the flow of passive particle tracers and calculate water renewal time scales. Mean residence times of 3–6 days and flushing times of 10–20 days for canal water were found, while mean residence times of 23–33 days and flushing times of 70–99 days were calculated for the bay's complete water volume. An assessment of future scenarios showed that increases in freshwater runoff would result in faster water renewal in the bay, while plans to decrease freshwater discharge would result in slower water renewal in the bay. It is therefore imperative that any plans for reducing fluvial fluxes into the bay be accompanied by the control of local pollution sources, which are abundant and could worsen the bay's water quality issues should water renewal times become longer. © 2019 Elsevier Ltd

The number, size, and shape of lakes are key determinants of the ecological functionality of a lake district. The lake area scaling relationships with lake number and volume enable upscaling biogeochemical processes and spatially considering organisms’ metapopulation dynamics. These relationships vary regionally depending on the geomorphological context, particularly in the range of lake area <1 km2 and mountainous regions. The Cajas Massif (Southern Ecuador) holds a tropical mountain lake district with 5955 water bodies. The number of lakes deviates from a power law relationship with the lake area at both ends of the size range; similarly to the distributions found in temperate mountain ranges. The deviation of each distribution tail does not respond to the same cause. The marked relief limits the size of the largest lakes at high altitudes, whereas ponds are prompt to a complete infilling. A bathymetry survey of 202 lakes, selected across the full-size range, revealed a volume-area scaling coefficient larger than those found for other lake areas of glacial origin but softer relief. Water renewal time is not consistently proportional to the lake area due to the volume-area variation in midsize lakes. The 85% of the water surface is in lakes >104 m2 and 50% of the water resources are held in a few ones ( 10) deeper than 18 m. Therefore, midlakes and large lakes are by far more biogeochemically relevant than ponds and shallow lakes in this tropical mountain lake district.

The Mediterranean Sea, which has a rapid water masses’ renewal time, undergoes numerous upheavals in response to the current climate change induced by anthropic activities. As a consequence, the oceanic pH decrease, the temperature increase, and the modification of air-sea CO2 exchanges are already visible. In this context, the study of the oceanic carbonate system and its short- and long-term variability in this basin is essential to estimate the impact of current and future changes on the oceanic carbon cycle. This thesis, carried out in the framework of the PERLE project and the National Observation Services MOOSE and SOMLIT, aims to describe the variability of the oceanic carbonate system in the surface waters of three distinct regions of the Mediterranean basin. With the complementary use of high-resolution data acquisition tools (Argo floats, underwater gliders, instrumented mooring lines), this work has contributed to better understand and quantify the processes responsible for the short (seasonal) and long (multiannual) term variability. Although thermal processes and variations in total inorganic carbon (CT ) concentrations are generally accepted as the factors governing seasonal variability, this work has highlighted the impact of total alkalinity (AT ) variations on seasonal oceanic pCO2 changes in the Eastern Mediterranean Sea. Thus, the estimated ratio of annual variations in AT to CT in the Eastern sub-basin shows the interest of this metric to estimate the sensitivity of the system to changes in AT , and highlights the uniqueness of this sub-basin compared to other oceanic regions, including the Western Mediterranean Sea. In the coastal environment, freshwater intrusion events and CO2 plumes emitted by urban areas have been identified as significant contributors to seasonal variability. Windy events and water renewal time also impact these dynamic environments. The long-term evolution of the mediterranean carbonate system parameters is firstly control, La mer Méditerranée, qui présente un temps de renouvellement de ses eaux rapide, subit de nombreuses perturbations en réponse au changement climatique actuel induit par les activités anthropiques. En conséquence, la baisse du pH des eaux, l’augmentation de la température et la modification des échanges air-mer de CO2 y sont observables. Dans ce contexte, l’étude du système des carbonates océanique et de sa variabilité à court et long termes dans ce bassin est essentielle pour estimer l’impact des changements actuels et à venir sur le cycle du carbone océanique. Ces travaux de thèse, réalisés dans le cadre du projet PERLE et des Services Nationaux d’Observation MOOSE et SOMLIT, visent à décrire la variabilité du système des carbonates océanique dans les eaux de surface de trois régions distinctes du bassin méditerranéen. Avec l’utilisation complémentaire d’outils d’acquisition de données à haute résolution (flotteurs Argo, planeurs sous-marins, lignes de mouillage instrumentées), ces travaux ont contribué à mieux comprendre et quantifier les processus responsables de la variabilité à court (saison) et long (pluriannuelle) termes. Bien que les processus thermiques et les variations des concentrations en carbone inorganique total (CT ) soient généralement admis comme étant les facteurs régissant la variabilité saisonnière, ces travaux ont mis en lumière l’impact des variations de l’alcalinité totale (AT ) sur les changements saisonniers de la pCO2 océanique en Méditerranée orientale. Ainsi, le rapport des variations annuelles de l’AT par rapport au CT estimé dans le sous-bassin oriental montre l’intérêt de cette métrique pour estimer la sensibilité du système aux changements de l’AT , et souligne la singularité de ce sous-bassin par rapport aux autres régions océaniques, y compris la Méditerranée occidentale. En milieu côtier, les événements d’intrusion d’eaux douces et les panaches de CO2 émis par les agglomérations urbaines ont été mis en évidence comme des contribut

The Mediterranean Sea, which has a rapid water masses’ renewal time, undergoes numerous upheavals in response to the current climate change induced by anthropic activities. As a consequence, the oceanic pH decrease, the temperature increase, and the modification of air-sea CO2 exchanges are already visible. In this context, the study of the oceanic carbonate system and its short- and long-term variability in this basin is essential to estimate the impact of current and future changes on the oceanic carbon cycle. This thesis, carried out in the framework of the PERLE project and the National Observation Services MOOSE and SOMLIT, aims to describe the variability of the oceanic carbonate system in the surface waters of three distinct regions of the Mediterranean basin. With the complementary use of high-resolution data acquisition tools (Argo floats, underwater gliders, instrumented mooring lines), this work has contributed to better understand and quantify the processes responsible for the short (seasonal) and long (multiannual) term variability. Although thermal processes and variations in total inorganic carbon (CT ) concentrations are generally accepted as the factors governing seasonal variability, this work has highlighted the impact of total alkalinity (AT ) variations on seasonal oceanic pCO2 changes in the Eastern Mediterranean Sea. Thus, the estimated ratio of annual variations in AT to CT in the Eastern sub-basin shows the interest of this metric to estimate the sensitivity of the system to changes in AT , and highlights the uniqueness of this sub-basin compared to other oceanic regions, including the Western Mediterranean Sea. In the coastal environment, freshwater intrusion events and CO2 plumes emitted by urban areas have been identified as significant contributors to seasonal variability. Windy events and water renewal time also impact these dynamic environments. The long-term evolution of the mediterranean carbonate system parameters is firstly control, La mer Méditerranée, qui présente un temps de renouvellement de ses eaux rapide, subit de nombreuses perturbations en réponse au changement climatique actuel induit par les activités anthropiques. En conséquence, la baisse du pH des eaux, l’augmentation de la température et la modification des échanges air-mer de CO2 y sont observables. Dans ce contexte, l’étude du système des carbonates océanique et de sa variabilité à court et long termes dans ce bassin est essentielle pour estimer l’impact des changements actuels et à venir sur le cycle du carbone océanique. Ces travaux de thèse, réalisés dans le cadre du projet PERLE et des Services Nationaux d’Observation MOOSE et SOMLIT, visent à décrire la variabilité du système des carbonates océanique dans les eaux de surface de trois régions distinctes du bassin méditerranéen. Avec l’utilisation complémentaire d’outils d’acquisition de données à haute résolution (flotteurs Argo, planeurs sous-marins, lignes de mouillage instrumentées), ces travaux ont contribué à mieux comprendre et quantifier les processus responsables de la variabilité à court (saison) et long (pluriannuelle) termes. Bien que les processus thermiques et les variations des concentrations en carbone inorganique total (CT ) soient généralement admis comme étant les facteurs régissant la variabilité saisonnière, ces travaux ont mis en lumière l’impact des variations de l’alcalinité totale (AT ) sur les changements saisonniers de la pCO2 océanique en Méditerranée orientale. Ainsi, le rapport des variations annuelles de l’AT par rapport au CT estimé dans le sous-bassin oriental montre l’intérêt de cette métrique pour estimer la sensibilité du système aux changements de l’AT , et souligne la singularité de ce sous-bassin par rapport aux autres régions océaniques, y compris la Méditerranée occidentale. En milieu côtier, les événements d’intrusion d’eaux douces et les panaches de CO2 émis par les agglomérations urbaines ont été mis en évidence comme des contribut

The Red Sea is a deep marine basin often considered as small‐scale version of the global ocean. Hydrographic observations and ocean‐atmosphere modeling indicate Red Sea deep water was episodically renewed by wintertime open‐ocean deep convections during 1982–2001, suggesting a renewal time on the order of a decade. However, the long‐term pacing of Red Sea deep water renewals is largely uncertain. We use an annually resolved coral oxygen isotope record of winter surface water conditions to show that the late twentieth century deep water renewals were probably unusual in the context of the preceding ~100 years. More frequent major events are detected during the late Little Ice Age, particularly during the early nineteenth century characterized by large tropical volcanic eruptions. We conclude that Red Sea deep water renewal time is on the order of a decade up to a century, depending on the mean climatic conditions and large‐scale interannual climate forcing.

The Red Sea is a deep marine basin often considered as small‐scale version of the global ocean. Hydrographic observations and ocean‐atmosphere modeling indicate Red Sea deep water was episodically renewed by wintertime open‐ocean deep convections during 1982–2001, suggesting a renewal time on the order of a decade. However, the long‐term pacing of Red Sea deep water renewals is largely uncertain. We use an annually resolved coral oxygen isotope record of winter surface water conditions to show that the late twentieth century deep water renewals were probably unusual in the context of the preceding ~100 years. More frequent major events are detected during the late Little Ice Age, particularly during the early nineteenth century characterized by large tropical volcanic eruptions. We conclude that Red Sea deep water renewal time is on the order of a decade up to a century, depending on the mean climatic conditions and large‐scale interannual climate forcing.

This paper examines the on-shelf circulation of the eastern Australian continental shelf for a region off southeast Queensland. We identify a characteristic seasonally reoccurring wind-driven cyclonic flow. It influences the cross-shelf exchange with the East Australian Current (EAC), which is the western boundary current of the South Pacific Ocean. We refer to this cyclonic circulation as the Fraser Gyre. It is located south of Fraser Island between about 25 °S and 27 °S. The region is adjacent to the intensification zone of the EAC where the current accelerates and establishes a swift, albeit seasonally variable southward boundary flow. Through the analysis of several data sets including remotely sensed sea surface temperature and sea surface height anomaly, satellite tracked surface drifters, ocean and atmospheric reanalysis data as well as geostrophic currents from altimetry, we find that the on-shelf Fraser Gyre develops during the southern hemisphere autumn and winter months. The gyre is associated with a longshore near-coast northward flow. Maximum northward on-shelf depth averaged velocities are estimated with about 0.15–0.26 ms-1. The flow turns eastward just to the south of Fraser Island and joins the persistent southward EAC flow along the shelf break. The annual mean net cross-shelf outward and inward flow associated with the gyre is about -1.17 ± 0.23 Sv in the north and 0.23 ± 0.13 Sv (1 Sv = 106 m3s−1) in the south. Mean seasonal water renewal time scales of the continental shelf are longest during austral winter with an average of about 3.3 days due to the Fraser Gyre retaining water over the shelf, however, monthly estimates range from 2 to 8 days with the longer timescale during the austral autumn and winter. The southerly wind during austral autumn and winter is identified as controlling the on shelf circulation and is the principal driver of the seasonally appearing Fraser Gyre. The conceptual model of the Fraser Gyre is consistent with general p

This paper examines the on-shelf circulation of the eastern Australian continental shelf for a region off southeast Queensland. We identify a characteristic seasonally reoccurring wind-driven cyclonic flow. It influences the cross-shelf exchange with the East Australian Current (EAC), which is the western boundary current of the South Pacific Ocean. We refer to this cyclonic circulation as the Fraser Gyre. It is located south of Fraser Island between about 25 °S and 27 °S. The region is adjacent to the intensification zone of the EAC where the current accelerates and establishes a swift, albeit seasonally variable southward boundary flow. Through the analysis of several data sets including remotely sensed sea surface temperature and sea surface height anomaly, satellite tracked surface drifters, ocean and atmospheric reanalysis data as well as geostrophic currents from altimetry, we find that the on-shelf Fraser Gyre develops during the southern hemisphere autumn and winter months. The gyre is associated with a longshore near-coast northward flow. Maximum northward on-shelf depth averaged velocities are estimated with about 0.15–0.26 ms-1. The flow turns eastward just to the south of Fraser Island and joins the persistent southward EAC flow along the shelf break. The annual mean net cross-shelf outward and inward flow associated with the gyre is about -1.17 ± 0.23 Sv in the north and 0.23 ± 0.13 Sv (1 Sv = 106 m3s−1) in the south. Mean seasonal water renewal time scales of the continental shelf are longest during austral winter with an average of about 3.3 days due to the Fraser Gyre retaining water over the shelf, however, monthly estimates range from 2 to 8 days with the longer timescale during the austral autumn and winter. The southerly wind during austral autumn and winter is identified as controlling the on shelf circulation and is the principal driver of the seasonally appearing Fraser Gyre. The conceptual model of the Fraser Gyre is consistent with general p

The number, size, and shape of lakes are key determinants of the ecological functionality of a lake district. The lake area scaling relationships with lake number and volume enable upscaling biogeochemical processes and spatially considering organisms' metapopulation dynamics. These relationships vary regionally depending on the geomorphological context, particularly in the range of lake area <1 km2 and mountainous regions. The Cajas Massif (Southern Ecuador) holds a tropical mountain lake district with 5955 water bodies. The number of lakes deviates from a power law relationship with the lake area at both ends of the size range; similarly to the distributions found in temperate mountain ranges. The deviation of each distribution tail does not respond to the same cause. The marked relief limits the size of the largest lakes at high altitudes, whereas ponds are prompt to a complete infilling. A bathymetry survey of 202 lakes, selected across the full-size range, revealed a volume-area scaling coefficient larger than those found for other lake areas of glacial origin but softer relief. Water renewal time is not consistently proportional to the lake area due to the volume-area variation in midsize lakes. The 85% of the water surface is in lakes >104 m2 and 50% of the water resources are held in a few ones (?10) deeper than 18 m. Therefore, midlakes and large lakes are by far more biogeochemically relevant than ponds and shallow lakes in this tropical mountain lake district.

Author Posting. © American Meteorological Society, 2005. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 35 (2005): 1489–1493, doi:10.1175/JPO2765.1., The Arctic Ocean likely impacts global climate through its effect on the rate of deep-water formation and the subsequent influence on global thermohaline circulation. Here, the renewal of the deep waters in the isolated Canadian Basin is quanitified. Using hydraulic theory and hydrographic observations, the authors calculate the magnitude of this renewal where circumstances have thus far prevented direct measurements. A volume flow rate of Q = 0.25 ± 0.15 Sv (Sv ≡ 106 m3s−1) from the Eurasian Basin to the Canadian Basin via a deep gap in the dividing Lomonosov Ridge is estimated. Deep-water renewal time estimates based on this flow are consistent with 14C isolation ages. The flow is sufficiently large that it has a greater impact on the Canadian Basin deep water than either the geothermal heat flux or diffusive fluxes at the deep-water boundaries., Financial support was provided to P. Winsor from NSF OPP- 0352628.

Author Posting. © American Meteorological Society, 2005. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 35 (2005): 1489–1493, doi:10.1175/JPO2765.1., The Arctic Ocean likely impacts global climate through its effect on the rate of deep-water formation and the subsequent influence on global thermohaline circulation. Here, the renewal of the deep waters in the isolated Canadian Basin is quanitified. Using hydraulic theory and hydrographic observations, the authors calculate the magnitude of this renewal where circumstances have thus far prevented direct measurements. A volume flow rate of Q = 0.25 ± 0.15 Sv (Sv ≡ 106 m3s−1) from the Eurasian Basin to the Canadian Basin via a deep gap in the dividing Lomonosov Ridge is estimated. Deep-water renewal time estimates based on this flow are consistent with 14C isolation ages. The flow is sufficiently large that it has a greater impact on the Canadian Basin deep water than either the geothermal heat flux or diffusive fluxes at the deep-water boundaries., Financial support was provided to P. Winsor from NSF OPP- 0352628.

We calculated average aquatic dissolved organic carbon (DOC) age (the time span from soil discharge to observation) in water from the inlets and outlets of two unproductive Swedish lakes at different times during an annual cycle. Bacterial production (BP) and bacterial growth efficiency (BGE) determined during 7-d bioassays decreased with increasing average aquatic DOC age. Parallel to the declines in BP and BGE there was a rise in specific ultraviolet absorbance at the wavelength of 254 nm (SUVA254), which indicates that decreasing BP and BGE were connected to a shift to a more aromatic and recalcitrant DOC pool. The relationships between bacterial metabolism and DOC age were stronger after a Q10 correction of the DOC age, showing that temperature affected rates of DOC quality changes over time and should be taken into account when relating lake bacterial growth to substrate aging in natural environments. We propose that hydrological variability in combination with lake size (water renewal time) have a large influence on pelagic BP in lakes with high input of terrigenous DOC.

The oyster growth has been studied for a 10 year period, from 1986 to 1995, in four locations of the bay of Bourgneuf (French Atlantic Coast). The relations between oysters growth and the main molluscs stocks (cultivated oysters and wild mussels) or environmental factors (hydrobiology, currents, climatology) are analysed to understand the functioning of this shellfish ecosystem. As the water renewal time is about two months, primary production is essentially autochtonal. Phytoplankton development is controlled by the nutrients brought by the river Loire. An important part of the microalgac is composed by the microphytobenthos resuspended by west wind. High seston concentrations, measured on the North of the bay (150 mg/1 as an average), have a negative influence on the feeding physiology of die oyster. The important food development of this area (20 ug/1 of chlorophyll a) cannot be fully exploited. The decrease of the oyster growth rate,observed since 1980, on the whole bay, is due to an overexpioitation induce by a too large cultivated oyster stock (45 to 50 000 tonnes). The cultural practices (concentration of oysters parks, double row of oysters tables, use of collector support for oyster growth) increase the oyster density and the overexpioitation. The oyster meat, produced during spring and summer, is lost during spawning. As fall blooms are exceptional, the oyster quality at the end of the year is not satisfactory. There is no recruitment in Bourgneuf bay, and more than 99 % of the spat come from Fouras in the bay of Marennes-Oléron. The oyster production seems to be independent from the oyster stock. New research and management axes arc proposed in order to improve the oyster quality in the bay of Bourgneuf., La croissance des huîtres de la baie de Bourgncuf est étudiée sur 10 ans, de 1986 à 1995, en quatre points de la baie. Ces croissances sont mises en relation avec les stocks des principaux mollusques de la baie (huîtres cultivées et moules sauvages) ainsi qu'avec les facteurs environnementaux (hydrobiologie, courantologie et climatologie) afin de comprendre le fonctionnement de cet écosystème conchylicole. Le temps de renouvellement des masses d'eau étant d'environ deux mois, la production primaire est essentiellement autochtone. La croissance phyloplanctonique est contrôlée par les sels nutritifs apportés par la Loire. Une part importante des microalgues est constituée par le microphytobenthos remis en suspension par les vents d'ouest. Les fortes charges sestoniques, mesurées au nord de la baie (150 mg/1 en moyenne) ne permet pas aux huîtres d'utiliser l'important potentiel nutritif qui s'y développe (20 ug/1 de chlorophylle a). La diminution des performances de croissance des huîtres, observée, depuis le début des années 19S0 sur l'ensemble de la baie, résulte d'une surexploitation engendrée par un stock Irop important d'huîtres en culture (45 à 50 000 tonnes). La pratique culturale (concentration des parcs ostréicoles, doubles rangées de tables ostréicoles et utilisation de collecteurs comme support de croissance) entraîne des densités supérieures à celles des autres bassins ostréicoles français aggravant le phénomène de surexploitation. Les gains de chair, accumules pendant les périodes printanière et estivale sont perdus lors de la ponte ce qui explique la qualité variable des huîtres en lin d'année car les blooms automnaux sont exceptionnels en baie de Bourgneuf. Faute de recrutement local plus de 99% du naissain provient de Fouras dans le bassin de Marennes-Oléron. La production ostréicole commercialisée de la baie de Bourgneuf semble indépendante du stock d'huîtres en culture. Des mesures de gestion et de nouveaux axes de recherche sont proposés pour tenter

The oyster growth has been studied for a 10 year period, from 1986 to 1995, in four locations of the bay of Bourgneuf (French Atlantic Coast). The relations between oysters growth and the main molluscs stocks (cultivated oysters and wild mussels) or environmental factors (hydrobiology, currents, climatology) are analysed to understand the functioning of this shellfish ecosystem. As the water renewal time is about two months, primary production is essentially autochtonal. Phytoplankton development is controlled by the nutrients brought by the river Loire. An important part of the microalgac is composed by the microphytobenthos resuspended by west wind. High seston concentrations, measured on the North of the bay (150 mg/1 as an average), have a negative influence on the feeding physiology of die oyster. The important food development of this area (20 ug/1 of chlorophyll a) cannot be fully exploited. The decrease of the oyster growth rate,observed since 1980, on the whole bay, is due to an overexpioitation induce by a too large cultivated oyster stock (45 to 50 000 tonnes). The cultural practices (concentration of oysters parks, double row of oysters tables, use of collector support for oyster growth) increase the oyster density and the overexpioitation. The oyster meat, produced during spring and summer, is lost during spawning. As fall blooms are exceptional, the oyster quality at the end of the year is not satisfactory. There is no recruitment in Bourgneuf bay, and more than 99 % of the spat come from Fouras in the bay of Marennes-Oléron. The oyster production seems to be independent from the oyster stock. New research and management axes arc proposed in order to improve the oyster quality in the bay of Bourgneuf., La croissance des huîtres de la baie de Bourgncuf est étudiée sur 10 ans, de 1986 à 1995, en quatre points de la baie. Ces croissances sont mises en relation avec les stocks des principaux mollusques de la baie (huîtres cultivées et moules sauvages) ainsi qu'avec les facteurs environnementaux (hydrobiologie, courantologie et climatologie) afin de comprendre le fonctionnement de cet écosystème conchylicole. Le temps de renouvellement des masses d'eau étant d'environ deux mois, la production primaire est essentiellement autochtone. La croissance phyloplanctonique est contrôlée par les sels nutritifs apportés par la Loire. Une part importante des microalgues est constituée par le microphytobenthos remis en suspension par les vents d'ouest. Les fortes charges sestoniques, mesurées au nord de la baie (150 mg/1 en moyenne) ne permet pas aux huîtres d'utiliser l'important potentiel nutritif qui s'y développe (20 ug/1 de chlorophylle a). La diminution des performances de croissance des huîtres, observée, depuis le début des années 19S0 sur l'ensemble de la baie, résulte d'une surexploitation engendrée par un stock Irop important d'huîtres en culture (45 à 50 000 tonnes). La pratique culturale (concentration des parcs ostréicoles, doubles rangées de tables ostréicoles et utilisation de collecteurs comme support de croissance) entraîne des densités supérieures à celles des autres bassins ostréicoles français aggravant le phénomène de surexploitation. Les gains de chair, accumules pendant les périodes printanière et estivale sont perdus lors de la ponte ce qui explique la qualité variable des huîtres en lin d'année car les blooms automnaux sont exceptionnels en baie de Bourgneuf. Faute de recrutement local plus de 99% du naissain provient de Fouras dans le bassin de Marennes-Oléron. La production ostréicole commercialisée de la baie de Bourgneuf semble indépendante du stock d'huîtres en culture. Des mesures de gestion et de nouveaux axes de recherche sont proposés pour tenter

The role of oceanic tide, wind stress, hoa inflow and stratification in the long-term circulation in Mururoa lagoon is investigated using a sensitivity analysis carried out by means of a three-dimensional model. Water renewal time scales are estimated. Wind stress is shown to be the dominant forcing. The hoa inflow slightly increases the turnover time, while stratification enhances the impact of motion in vertical planes parallel to the wind stress. The modelled turnover time is approximately 100 days, and becomes much larger than one year whenever the wind stress is disregarded.

The oyster growth has been studied for a 10 year period, from 1986 to 1995, in four locations of the bay of Bourgneuf (French Atlantic Coast). The relations between oysters growth and the main molluscs stocks (cultivated oysters and wild mussels) or environmental factors (hydrobiology, currents, climatology) are analysed to understand the functioning of this shellfish ecosystem. As the water renewal time is about two months, primary production is essentially autochtonal. Phytoplankton development is controlled by the nutrients brought by the river Loire. An important part of the microalgac is composed by the microphytobenthos resuspended by west wind. High seston concentrations, measured on the North of the bay (150 mg/1 as an average), have a negative influence on the feeding physiology of die oyster. The important food development of this area (20 ug/1 of chlorophyll a) cannot be fully exploited. The decrease of the oyster growth rate,observed since 1980, on the whole bay, is due to an overexpioitation induce by a too large cultivated oyster stock (45 to 50 000 tonnes). The cultural practices (concentration of oysters parks, double row of oysters tables, use of collector support for oyster growth) increase the oyster density and the overexpioitation. The oyster meat, produced during spring and summer, is lost during spawning. As fall blooms are exceptional, the oyster quality at the end of the year is not satisfactory. There is no recruitment in Bourgneuf bay, and more than 99 % of the spat come from Fouras in the bay of Marennes-Oléron. The oyster production seems to be independent from the oyster stock. New research and management axes arc proposed in order to improve the oyster quality in the bay of Bourgneuf., La croissance des huîtres de la baie de Bourgncuf est étudiée sur 10 ans, de 1986 à 1995, en quatre points de la baie. Ces croissances sont mises en relation avec les stocks des principaux mollusques de la baie (huîtres cultivées et moules sauvages) ainsi qu'avec les facteurs environnementaux (hydrobiologie, courantologie et climatologie) afin de comprendre le fonctionnement de cet écosystème conchylicole. Le temps de renouvellement des masses d'eau étant d'environ deux mois, la production primaire est essentiellement autochtone. La croissance phyloplanctonique est contrôlée par les sels nutritifs apportés par la Loire. Une part importante des microalgues est constituée par le microphytobenthos remis en suspension par les vents d'ouest. Les fortes charges sestoniques, mesurées au nord de la baie (150 mg/1 en moyenne) ne permet pas aux huîtres d'utiliser l'important potentiel nutritif qui s'y développe (20 ug/1 de chlorophylle a). La diminution des performances de croissance des huîtres, observée, depuis le début des années 19S0 sur l'ensemble de la baie, résulte d'une surexploitation engendrée par un stock Irop important d'huîtres en culture (45 à 50 000 tonnes). La pratique culturale (concentration des parcs ostréicoles, doubles rangées de tables ostréicoles et utilisation de collecteurs comme support de croissance) entraîne des densités supérieures à celles des autres bassins ostréicoles français aggravant le phénomène de surexploitation. Les gains de chair, accumules pendant les périodes printanière et estivale sont perdus lors de la ponte ce qui explique la qualité variable des huîtres en lin d'année car les blooms automnaux sont exceptionnels en baie de Bourgneuf. Faute de recrutement local plus de 99% du naissain provient de Fouras dans le bassin de Marennes-Oléron. La production ostréicole commercialisée de la baie de Bourgneuf semble indépendante du stock d'huîtres en culture. Des mesures de gestion et de nouveaux axes de recherche sont proposés pour tenter

The oyster growth has been studied for a 10 year period, from 1986 to 1995, in four locations of the bay of Bourgneuf (French Atlantic Coast). The relations between oysters growth and the main molluscs stocks (cultivated oysters and wild mussels) or environmental factors (hydrobiology, currents, climatology) are analysed to understand the functioning of this shellfish ecosystem. As the water renewal time is about two months, primary production is essentially autochtonal. Phytoplankton development is controlled by the nutrients brought by the river Loire. An important part of the microalgac is composed by the microphytobenthos resuspended by west wind. High seston concentrations, measured on the North of the bay (150 mg/1 as an average), have a negative influence on the feeding physiology of die oyster. The important food development of this area (20 ug/1 of chlorophyll a) cannot be fully exploited. The decrease of the oyster growth rate,observed since 1980, on the whole bay, is due to an overexpioitation induce by a too large cultivated oyster stock (45 to 50 000 tonnes). The cultural practices (concentration of oysters parks, double row of oysters tables, use of collector support for oyster growth) increase the oyster density and the overexpioitation. The oyster meat, produced during spring and summer, is lost during spawning. As fall blooms are exceptional, the oyster quality at the end of the year is not satisfactory. There is no recruitment in Bourgneuf bay, and more than 99 % of the spat come from Fouras in the bay of Marennes-Oléron. The oyster production seems to be independent from the oyster stock. New research and management axes arc proposed in order to improve the oyster quality in the bay of Bourgneuf., La croissance des huîtres de la baie de Bourgncuf est étudiée sur 10 ans, de 1986 à 1995, en quatre points de la baie. Ces croissances sont mises en relation avec les stocks des principaux mollusques de la baie (huîtres cultivées et moules sauvages) ainsi qu'avec les facteurs environnementaux (hydrobiologie, courantologie et climatologie) afin de comprendre le fonctionnement de cet écosystème conchylicole. Le temps de renouvellement des masses d'eau étant d'environ deux mois, la production primaire est essentiellement autochtone. La croissance phyloplanctonique est contrôlée par les sels nutritifs apportés par la Loire. Une part importante des microalgues est constituée par le microphytobenthos remis en suspension par les vents d'ouest. Les fortes charges sestoniques, mesurées au nord de la baie (150 mg/1 en moyenne) ne permet pas aux huîtres d'utiliser l'important potentiel nutritif qui s'y développe (20 ug/1 de chlorophylle a). La diminution des performances de croissance des huîtres, observée, depuis le début des années 19S0 sur l'ensemble de la baie, résulte d'une surexploitation engendrée par un stock Irop important d'huîtres en culture (45 à 50 000 tonnes). La pratique culturale (concentration des parcs ostréicoles, doubles rangées de tables ostréicoles et utilisation de collecteurs comme support de croissance) entraîne des densités supérieures à celles des autres bassins ostréicoles français aggravant le phénomène de surexploitation. Les gains de chair, accumules pendant les périodes printanière et estivale sont perdus lors de la ponte ce qui explique la qualité variable des huîtres en lin d'année car les blooms automnaux sont exceptionnels en baie de Bourgneuf. Faute de recrutement local plus de 99% du naissain provient de Fouras dans le bassin de Marennes-Oléron. La production ostréicole commercialisée de la baie de Bourgneuf semble indépendante du stock d'huîtres en culture. Des mesures de gestion et de nouveaux axes de recherche sont proposés pour tenter

The oyster growth has been studied for a 10 year period, from 1986 to 1995, in four locations of the bay of Bourgneuf (French Atlantic Coast). The relations between oysters growth and the main molluscs stocks (cultivated oysters and wild mussels) or environmental factors (hydrobiology, currents, climatology) are analysed to understand the functioning of this shellfish ecosystem. As the water renewal time is about two months, primary production is essentially autochtonal. Phytoplankton development is controlled by the nutrients brought by the river Loire. An important part of the microalgac is composed by the microphytobenthos resuspended by west wind. High seston concentrations, measured on the North of the bay (150 mg/1 as an average), have a negative influence on the feeding physiology of die oyster. The important food development of this area (20 ug/1 of chlorophyll a) cannot be fully exploited. The decrease of the oyster growth rate,observed since 1980, on the whole bay, is due to an overexpioitation induce by a too large cultivated oyster stock (45 to 50 000 tonnes). The cultural practices (concentration of oysters parks, double row of oysters tables, use of collector support for oyster growth) increase the oyster density and the overexpioitation. The oyster meat, produced during spring and summer, is lost during spawning. As fall blooms are exceptional, the oyster quality at the end of the year is not satisfactory. There is no recruitment in Bourgneuf bay, and more than 99 % of the spat come from Fouras in the bay of Marennes-Oléron. The oyster production seems to be independent from the oyster stock. New research and management axes arc proposed in order to improve the oyster quality in the bay of Bourgneuf., La croissance des huîtres de la baie de Bourgncuf est étudiée sur 10 ans, de 1986 à 1995, en quatre points de la baie. Ces croissances sont mises en relation avec les stocks des principaux mollusques de la baie (huîtres cultivées et moules sauvages) ainsi qu'avec les facteurs environnementaux (hydrobiologie, courantologie et climatologie) afin de comprendre le fonctionnement de cet écosystème conchylicole. Le temps de renouvellement des masses d'eau étant d'environ deux mois, la production primaire est essentiellement autochtone. La croissance phyloplanctonique est contrôlée par les sels nutritifs apportés par la Loire. Une part importante des microalgues est constituée par le microphytobenthos remis en suspension par les vents d'ouest. Les fortes charges sestoniques, mesurées au nord de la baie (150 mg/1 en moyenne) ne permet pas aux huîtres d'utiliser l'important potentiel nutritif qui s'y développe (20 ug/1 de chlorophylle a). La diminution des performances de croissance des huîtres, observée, depuis le début des années 19S0 sur l'ensemble de la baie, résulte d'une surexploitation engendrée par un stock Irop important d'huîtres en culture (45 à 50 000 tonnes). La pratique culturale (concentration des parcs ostréicoles, doubles rangées de tables ostréicoles et utilisation de collecteurs comme support de croissance) entraîne des densités supérieures à celles des autres bassins ostréicoles français aggravant le phénomène de surexploitation. Les gains de chair, accumules pendant les périodes printanière et estivale sont perdus lors de la ponte ce qui explique la qualité variable des huîtres en lin d'année car les blooms automnaux sont exceptionnels en baie de Bourgneuf. Faute de recrutement local plus de 99% du naissain provient de Fouras dans le bassin de Marennes-Oléron. La production ostréicole commercialisée de la baie de Bourgneuf semble indépendante du stock d'huîtres en culture. Des mesures de gestion et de nouveaux axes de recherche sont proposés pour tenter