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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 (down) 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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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 (down) 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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Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 1500
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Auteur Grüss, A.; Schirripa, M.J.; Chagaris, D.; Drexler, M.; Simons, J.; Verley, P.; Shin, Y.-J.; Karnauskas, M.; Oliveros-Ramos, R.; Ainsworth, C.H.
Titre Evaluation of the trophic structure of the West Florida Shelf in the 2000s using the ecosystem model OSMOSE Type Article scientifique
Année 2015 Publication (down) Revue Abrégée Journal of Marine Systems
Volume 144 Numéro Pages 30-47
Mots-Clés Gag grouper; Marine ecosystem modeling; Natural mortality; resource management; trophic structure; West Florida Shelf
Résumé We applied the individual-based, multi-species OSMOSE modeling approach to the West Florida Shelf, with the intent to inform ecosystem-based management (EBM) in this region. Our model, referred to as ‘OSMOSE-WFS’, explicitly considers both pelagic-demersal and benthic high trophic level (HTL) groups of fish and invertebrate species, and is forced by the biomass of low trophic level groups of species (plankton and benthos). We present a steady-state version of the OSMOSE-WFS model describing trophic interactions in the West Florida Shelf in the 2000s. OSMOSE-WFS was calibrated using a recently developed evolutionary algorithm that allowed simulated biomasses of HTL groups to match observed biomasses over the period 2005–2009. The validity of OSMOSE-WFS was then evaluated by comparing simulated diets to observed ones, and the simulated trophic levels to those in an Ecopath model of the West Florida Shelf (WFS Reef fish Ecopath). Finally, OSMOSE-WFS was used to explore the trophic structure of the West Florida Shelf in the 2000s and estimate size-specific natural mortality rates for a socio-economically important species, gag grouper (Mycteroperca microlepis). OSMOSE-WFS outputs were in full agreement with observations as to the body size and ecological niche of prey of the different HTL groups, and to a lesser extent in agreement with the observed species composition of the diet of HTL groups. OSMOSE-WFS and WFS Reef fish Ecopath concurred on the magnitude of the instantaneous natural mortality of the different life stages of gag grouper over the period 2005–2009, but not always on the main causes of natural mortality. The model evaluations conducted here provides a strong basis for ongoing work exploring fishing and environmental scenarios so as to inform EBM. From simple size-based predation rules, we were indeed able to capture the complexity of trophic interactions in the West Florida Shelf, and to identify the predators, prey and competitors of socio-economically important species as well as pivotal prey species of the ecosystem.
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Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 1253
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Auteur Tew-Kai, E.; Marsac, F.
Titre Patterns of variability of sea surface chlorophyll in the Mozambique Channel : a quantitative approach Type Article scientifique
Année 2009 Publication (down) Revue Abrégée Journal of Marine Systems
Volume 77 Numéro 1-2 Pages 77-88
Mots-Clés Climate forcing; Mesoscale; Mozambique Channel; Quantitative approach; Seasonal variability; Sea Surface chlorophyll
Résumé We analyse the coupling between sea surface chlorophyll concentration (CC) and the physical environment in the Mozambique Channel (MZC) using statistical models. Seasonal and interannual patterns are studied along with the role of mesoscale dynamics on enhancement and concentration processes for phytoplankton. We use SeaWifs data for CC and two other remotely sensed data sets, TMMI for sea surface temperature (SST) and merged altimetry products for sea level anomaly and geostrophic current. Empirical Orthogonal Functions (EOF) on SSC and SST show strong seasonality and partition the MZC into three distinct sub-areas. The chlorophyll variability is mostly driven by seasonality, but more in the North (10 degrees S-16 degrees S) and South (24 degrees S-30 degrees S), and explains respectively 64% and 82% of the CC variance. In the Central part (16 degrees S-24 degrees S), the seasonal signal has less influence (60% variance). There, complex EOFs on Sea Level Anomaly (SLA) highlight the role of mesoscale activity (i.e. eddies and filament structures) in the spatial distribution of chlorophyll. Five mesoscale descriptors (shear, stretch, vorticity, deformation and eddy kinetic energy) are derived from the altimetry data to quantify the eddies-related physical patterns in the central region of the MZC. We use generalized Additive Models to explain the effect of those features on phytoplankton enhancement. The best model fit (r(2) = 0.73) includes shear, stretch, vorticity and the latitude-longitude interaction as eddies are well structured in space. Cyclonic eddies associated with negative vorticity are conductive to phytoplankton enhancement by the effect of upwelling in the core notably during the spin-up phase. The interaction between eddies generate strong frontal mixing favourable to the production and aggregation of organic matter. The mesoscale activity is also affected by interannual variability with consequences on CC. We highlight a substantial reduction of the SLA pattern in 2000-2001 when the SOI positive phase is peaking (Nina-type pattern). The strong relationship between mesoscale eddies and SOI suggests that primary productivity in the MZC is also under the influence of distant forcing at a basin scale.
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Numéro d'Appel LL @ pixluser @ collection 13
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Auteur Hattab, T.; Lasram, F.B.R.; Albouy, C.; Romdhane, M.S.; Jarboui, O.; Halouani, G.; Cury, P.; Le Loc'h, F.
Titre An ecosystem model of an exploited southern Mediterranean shelf region (Gulf of Gabes, Tunisia) and a comparison with other Mediterranean ecosystem model properties Type Article scientifique
Année 2013 Publication (down) Revue Abrégée Journal of Marine Systems
Volume 128 Numéro Pages 159-174
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Résumé Abstract In this paper, we describe an exploited continental shelf ecosystem (Gulf of Gabes) in the southern Mediterranean Sea using an Ecopath mass-balance model. This allowed us to determine the structure and functioning of this ecosystem and assess the impacts of fishing upon it. The model represents the average state of the ecosystem between 2000 and 2005. It includes 41 functional groups, which encompass the entire trophic spectrum from phytoplankton to higher trophic levels (e.g., fishes, birds, and mammals), and also considers the fishing activities in the area (five fleets). Model results highlight an important bentho-pelagic coupling in the system due to the links between plankton and benthic invertebrates through detritus. A comparison of this model with those developed for other continental shelf regions in the Mediterranean (i.e., the southern Catalan, the northern-central Adriatic, and the northern Aegean Seas) emphasizes similar patterns in their trophic functioning. Low and medium trophic levels (i.e., zooplankton, benthic molluscs, and polychaetes) and sharks were identified as playing key ecosystem roles and were classified as keystone groups. An analysis of ecosystem attributes indicated that the Gulf of Gabes is the least mature (i.e., in the earliest stages of ecosystem development) of the four ecosystems that were compared and it is suggested that this is due, at least in part, to the impacts of fishing. Bottom trawling was identified as having the widest-ranging impacts across the different functional groups and the largest impacts on some commercially-targeted demersal fish species. Several exploitation indices highlighted that the Gulf of Gabes ecosystem is highly exploited, a finding which is supported by stock assessment outcomes. This suggests that it is unlikely that the gulf can be fished at sustainable levels, a situation which is similar to other marine ecosystems in the Mediterranean Sea.
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Numéro d'Appel LL @ pixluser @ collection 270
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