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Auteur Malauene, B.S.; Moloney, C.L.; Lett, C.; Roberts, M.J.; Marsac, F.; Penven, P.
Titre Impact of offshore eddies on shelf circulation and river plumes of the Sofala Bank, Mozambique Channel Type Article scientifique
Année 2018 Publication (up) Revue Abrégée Journal of Marine Systems
Volume 185 Numéro Pages 1-12
Mots-Clés Mesoscale eddies; River plume; Roms; Shelf processes; SOMs
Résumé A high-resolution, two-way nested Regional Ocean Modeling System, forced with monthly climatologies, has been set up for the Sofala Bank and adjacent deeper ocean of the Mozambique Channel to investigate the role of offshore mesoscale eddies on the shelf circulation, hydrographic structures and river plumes. The model is shown in comparison with available observations and published studies. Most known oceanographic features are reproduced by our model. We applied Self-Organizing Maps and showed that offshore passing eddies, depending on their strength and proximity to the shelf, modulate the shelf circulation and river plume direction and spread. The presence of a strong cyclonic eddy close to the shelf induces northward surface shelf currents. In contrast, the presence of a strong anticyclonic eddy close to the shelf induces a strong southward current over most of the shelf, except off Beira. Our analyses confirm that the plume of the Zambezi River is bi-directional. The southward-directed plume patterns, opposite to the dominant northwards, occur in response to nearby offshore anticyclonic eddies (26% of occurrence). This behavior could have an influence on water dispersal, shelf ecosystems and important fisheries. Therefore, offshore mesoscale eddies should be taken into account when studying the ocean dynamics of the Sofala Bank.
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ISSN 0924-7963 ISBN Médium
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Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 2358
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Auteur Halouani, G.; Gascuel, D.; Hattab, T.; Lasram, F.B.R.; Coll, M.; Tsagarakis, K.; Piroddi, C.; Romdhane, M.S.; Le Loc'h, F.
Titre Fishing impact in Mediterranean ecosystems: an EcoTroph modeling approach Type Article scientifique
Année 2015 Publication (up) Revue Abrégée Journal of Marine Systems
Volume 150 Numéro Pages 22-33
Mots-Clés Ecosystem modeling; EcoTroph; Fishing impact; food web; Mediterranean Sea; Trophic levels; Trophic spectrum
Résumé The EcoTroph modeling approach was applied to five Mediterranean marine ecosystems to characterize their food webs and investigate their responses to several simulated fishing scenarios. First, EcoTroph was used to synthesize the outputs of five pre-existing heterogeneous Ecopath models in a common framework, and thus to compare different ecosystems through their trophic spectra of biomass, catch, and fishing mortalities. This approach contributes to our understanding of ecosystem functioning, from both ecological and fisheries perspectives. Then, we assessed the sensitivity of each ecosystem to fishery, using EcoTroph simulations. For the five ecosystems considered, we simulated the effects of increasing or decreasing fishing mortalities on both the biomass and the catch per trophic class. Our results emphasize that the Mediterranean Sea is strongly affected by the depletion of high trophic level organisms. Results also show that fisheries impacts, at the trophic level scale, differ between ecosystems according to their trophic structure and exploitation patterns. A top-down compensation effect is observed in some simulations where a fishing-induced decrease in the biomass of predators impacts their prey, leading to an increase in the biomass at lower trophic levels. The results of this comparative analysis highlight that ecosystems where top-down controls are observed are less sensitive to variations in fishing mortality in terms of total ecosystem biomass. This suggests that the magnitude of top-down control present in a system can affect its stability.
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Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 1345
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Auteur Colléter, M.; Gascuel, D.; Albouy, C.; Francour, P.; Tito de Morais, L.; Valls, A.; Le Loc'h, F.
Titre Fishing inside or outside? A case studies analysis of potential spillover effect from marine protected areas, using food web models Type Article scientifique
Année 2014 Publication (up) Revue Abrégée Journal of Marine Systems
Volume 139 Numéro Pages 383-395
Mots-Clés Biomass exports; Ecopath; EcoTroph; Fishing impact; food web model; Marine protected area (MPA)
Résumé Marine protected areas (MPAs) are implemented worldwide as an efficient tool to preserve biodiversity and protect ecosystems. We used food web models (Ecopath and EcoTroph) to assess the ability of MPAs to reduce fishing impacts on targeted resources and to provide biomass exports for adjacent fisheries. Three coastal MPAs: Bonifacio and Port-Cros (Mediterranean Sea), and Bamboung (Senegalese coast), were used as case studies. Pre-existing related Ecopath models were homogenized and ecosystem characteristics were compared based on network indices and trophic spectra analyses. Using the EcoTroph model, we simulated different fishing mortality scenarios and assessed fishing impacts on the three ecosystems. Lastly, the potential biomass that could be exported from each MPA was estimated. Despite structural and functional trophic differences, the three MPAs showed similar patterns of resistance to simulated fishing mortalities, with the Bonifacio case study exhibiting the highest potential catches and a slightly inferior resistance to fishing. We also show that the potential exports from our small size MPAs are limited and thus may only benefit local fishing activities. Based on simulations, their potential exports were estimated to be at the same order of magnitude as the amount of catch that could have been obtained inside the reserve. In Port Cros, the ban of fishing inside MPA could actually allow for improved catch yields outside the MPA due to biomass exports. This was not the case for the Bonifacio site, as its potential exports were too low to offset catch losses. This insight suggests the need for MPA networks and/or sufficiently large MPAs to effectively protect juveniles and adults and provide important exports. Finally, we discuss the effects of MPAs on fisheries that were not considered in food web models, and conclude by suggesting possible improvements in the analysis of MPA efficiency.
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Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 1197
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Auteur Le Mézo, P.; Lefort, S.; Séférian, R.; Aumont, O.; Maury, O.; Murtugudde, R.; Bopp, L.
Titre Natural variability of marine ecosystems inferred from a coupled climate to ecosystem simulation Type Article scientifique
Année 2016 Publication (up) Revue Abrégée Journal of Marine Systems
Volume 153 Numéro Pages 55-66
Mots-Clés Fourier transform; North Atlantic; North Pacific; Pelagic environment; Size; Trophic levels; Variability
Résumé This modeling study analyzes the simulated natural variability of pelagic ecosystems in the North Atlantic and North Pacific. Our model system includes a global Earth System Model (IPSL-CM5A-LR), the biogeochemical model PISCES and the ecosystem model APECOSM that simulates upper trophic level organisms using a size-based approach and three interactive pelagic communities (epipelagic, migratory and mesopelagic). Analyzing an idealized (e.g., no anthropogenic forcing) 300-yr long pre-industrial simulation, we find that low and high frequency variability is dominant for the large and small organisms, respectively. Our model shows that the size-range exhibiting the largest variability at a given frequency, defined as the resonant range, also depends on the community. At a given frequency, the resonant range of the epipelagic community includes larger organisms than that of the migratory community and similarly, the latter includes larger organisms than the resonant range of the mesopelagic community. This study shows that the simulated temporal variability of marine pelagic organisms' abundance is not only influenced by natural climate fluctuations but also by the structure of the pelagic community. As a consequence, the size- and community-dependent response of marine ecosystems to climate variability could impact the sustainability of fisheries in a warming world.
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Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 1468
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Auteur Grüss, A.; Schirripa, M.J.; Chagaris, D.; Velez, L.; Shin, Y.-J.; Verley, P.; Oliveros-Ramos, R.; Ainsworth, C.H.
Titre Estimating natural mortality rates and simulating fishing scenarios for Gulf of Mexico red grouper (Epinephelus morio) using the ecosystem model OSMOSE-WFS Type Article scientifique
Année 2016 Publication (up) Revue Abrégée Journal of Marine Systems
Volume 154, Part B Numéro Pages 264-279
Mots-Clés Fishing scenarios; Gulf of Mexico; Marine ecosystem modeling; Natural mortality; Red grouper; West Florida Shelf
Résumé The ecosystem model OSMOSE-WFS was employed to evaluate natural mortality rates and fishing scenarios for Gulf of Mexico (GOM) red grouper (Epinephelus morio). OSMOSE-WFS represents major high trophic level (HTL) groups of species of the West Florida Shelf, is forced by the biomass of plankton and benthos groups, and has a monthly time step. The present application of the model uses a recently developed ‘stochastic mortality algorithm’ to resolve the mortality processes of HTL groups. OSMOSE-WFS predictions suggest that the natural mortality rate of juveniles of GOM red grouper is high and essentially due to predation, while the bulk of the natural mortality of adult red grouper results from causes not represented in OSMOSE-WFS such as, presumably, red tides. These results were communicated to GOM red grouper stock assessments. Moreover, OSMOSE-WFS indicate that altering the fishing mortality of GOM red grouper may have no global impact on the biomass of the major prey of red grouper, due to the high complexity and high redundancy of the modeled system. By contrast, altering the fishing mortality of GOM red grouper may have a large impact on the biomass of its major competitors. Increasing the fishing mortality of red grouper would increase the biomass of major competitors, due to reduced competition for food. Conversely, decreasing the fishing mortality of red grouper would diminish the biomass of major competitors, due to increased predation pressure on the juveniles of the major competitors by red grouper. The fishing scenarios that we evaluated may have slightly different impacts in the real world, due to some discrepancies between the diets of red grouper and its major competitors predicted by OSMOSE-WFS and the observed ones. Modifications in OSMOSE-WFS are suggested to reduce these discrepancies.
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Editeur Lieu de Publication Éditeur
Langue Langue du Résumé Titre Original
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ISSN 0924-7963 ISBN Médium
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Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 1500
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