Évaluation comparative des traits d'histoire de vie dans les communautés de petits poissons pélagiques des systèmes côtiers à haute productivité

International audienceSmall pelagic fish (SPF) communities are a central link in marine food webs. Moreover, they account for 20% of the global catch. These populations are abundant in the boundary upwelling systems (Humboldt, California, Canary, Benguela Currents) where they are subject to strong variations in abundance. These changes are strongly linked to recruitment variations and environmental “bottom-up” forcing, which makes their dynamics difficult to predict. To better understand the mechanisms underlying these fluctuations, we propose to compare the life history traits of the most abundant species in these systems as well as the characteristics of their habitat that may underlie the observed dynamics. In this framework, the Ph.D. thesis I recently started proposes the development of a generic model of the life cycle of SPF based on DEB theory. Comparison of the same species in different habitats or close species in the same system is an approach that appears promising to limit the uncertainty around the estimated parameter sets. We also aim, in a second objective, to better reconstruct the inter-individual variability in these populations by linking otolith (fish ear bones) formation, to our SPF-DEB model. In this context, the mineral and organic fractions of the otolith are considered as metabolic products linked to the growth and dissipation transformations. This otolith growth module will be coupled with Lagrangian simulations to compare the observed and simulated variability of otolith patterns (size, opacity, and shape). This study will contribute to a better understanding of the variability of individual responses to environmental factors

Évaluation comparative des traits d'histoire de vie dans les communautés de petits poissons pélagiques des systèmes côtiers à haute productivité

Small pelagic fish (SPF) communities are a central link in marine food webs. Moreover, they account for 20% of the global catch. These populations are abundant in the boundary upwelling systems (Humboldt, California, Canary, Benguela Currents) where they are subject to strong variations in abundance. These changes are strongly linked to recruitment variations and environmental “bottom-up” forcing, which makes their dynamics difficult to predict. To better understand the mechanisms underlying these fluctuations, we propose to compare the life history traits of the most abundant species in these systems as well as the characteristics of their habitat that may underlie the observed dynamics. In this framework, the Ph.D. thesis I recently started proposes the development of a generic model of the life cycle of SPF based on DEB theory. Comparison of the same species in different habitats or close species in the same system is an approach that appears promising to limit the uncertainty around the estimated parameter sets. We also aim, in a second objective, to better reconstruct the inter-individual variability in these populations by linking otolith (fish ear bones) formation, to our SPF-DEB model. In this context, the mineral and organic fractions of the otolith are considered as metabolic products linked to the growth and dissipation transformations. This otolith growth module will be coupled with Lagrangian simulations to compare the observed and simulated variability of otolith patterns (size, opacity, and shape). This study will contribute to a better understanding of the variability of individual responses to environmental factors

Évaluation comparative des traits d'histoire de vie dans les communautés de petits poissons pélagiques des systèmes côtiers à haute productivité

Small pelagic fish (SPF) communities are a central link in marine food webs. Moreover, they account for 20% of the global catch. These populations are abundant in the boundary upwelling systems (Humboldt, California, Canary, Benguela Currents) where they are subject to strong variations in abundance. These changes are strongly linked to recruitment variations and environmental “bottom-up” forcing, which makes their dynamics difficult to predict. To better understand the mechanisms underlying these fluctuations, we propose to compare the life history traits of the most abundant species in these systems as well as the characteristics of their habitat that may underlie the observed dynamics. In this framework, the Ph.D. thesis I recently started proposes the development of a generic model of the life cycle of SPF based on DEB theory. Comparison of the same species in different habitats or close species in the same system is an approach that appears promising to limit the uncertainty around the estimated parameter sets. We also aim, in a second objective, to better reconstruct the inter-individual variability in these populations by linking otolith (fish ear bones) formation, to our SPF-DEB model. In this context, the mineral and organic fractions of the otolith are considered as metabolic products linked to the growth and dissipation transformations. This otolith growth module will be coupled with Lagrangian simulations to compare the observed and simulated variability of otolith patterns (size, opacity, and shape). This study will contribute to a better understanding of the variability of individual responses to environmental factors

Classic or hybrid? The performance of next generation ecological models to study the response of Southern Ocean species to changing environmental conditions.

17 pagesInternational audienceAimIn the context of intensifying threats of climate change on marine communities, ecological models are widely applied for conservation strategies, though polar studies remain scarce given the limited number of datasets available. Correlative (e.g. species distribution models, SDM) and mechanistic (e.g. dynamic energy budget models, DEB) modelling approaches are usually used independently in studies. Using both approaches in integrative, hybrid models could help to better estimate the species potential ecological niche, as mechanistic and correlative models complement each other very well, giving more insights into species potential response to fast-changing environmental conditions.LocationThe study focusses on the Baie du Morbihan, a silled basin located in the east of the Kerguelen Islands (sub-Antarctic).MethodsA hybrid, correlative-mechanistic model was implemented to predict the response of the endemic sea urchin Abatus cordatus (Verrill, 1876). We compared the performances of classic and integrated approaches to predict A. cordatus distribution according to two dates representing seasonal contrasts. Two integrated approaches were studied and performed by either (1) including the spatial projection of the DEB model as an input layer inside the SDM (‘integrated SDM-DEB’) or (2) using a Bayesian procedure to use DEB model outputs as priors of the SDM (‘integrated Bayesian’ approach).ResultsResults show higher performances of ‘integrated Bayesian’ approaches to evaluate A. cordatus potential ecological niche compared with ‘classic’ and ‘integrated SDM-DEB’ methods. The influence of environmental conditions on model predictions is further captured with these Bayesian procedures and better highlights the environmental influence on the species-predicted distribution. Model performance is good for the different simulations, and uncertainty in predictions is well-highlighted.Main conclusionsThe good performances of ‘integrated Bayesian’ approaches to estimate species potential ecological niche opens perspectives for future applications to a broad panel of natural examples, noteworthy for decision-making and conservation management purposes

Comparing two pectinid species as a fast and a slow depurators of amnesic shellfish toxin through a modelling approach

International audienceMicroalgae species of the genus Pseudo-nitzschia (Psn) may produce domoic acid, anamnesic shellfish toxin (AST), and form blooms. Bivalves, filter-feeding animals, can feed on these microalgae species in the water column or sedimented on the bottom. During blooms of domoic acid-producing Psn, bivalves will accumulate the AST in their tissues via nutrition. By being toxic for Humans, domoic acid concentration is monitored in exploited shellfish species such as Pecten maximus, the king scallop. In France, P. maximus is the second most captured species, representing an important part of the economy. Hence, when the sanitary threshold of AST concentration is exceeded, the fishing closure of the king scallop causes significant socio-economic losses. The French MaSCoET project aims to determinate the reasons for Psn blooms and why P. maximus depurates more slowly than other pectinid species such as the variegated scallop, Mimachlamys varia. The objectives of my PhD thesis are (i) to better understand the links between individual bioenergetics and accumulation, storage and depuration of AST, (ii) to determine the impacts of environmental conditions on these relationships and (iii) to explain the mechanisms behind the different depuration capacities of pectinid species. For this, a contamination and decontamination model of domoic acid will be linked to the bioenergetics of the organism, based on the Dynamic Energy Budget (DEB) theory. The calibration and the validation of the model are based on data from the MaSCoET project. The methodology used to compare the two species with their own toxin retention, and how we could tackle the questions of depuration predictions depending on environmental conditions through model scenarios will be presented. The final goal will be to develop a tool to predict decontamination duration depending on environmental conditions and organism physiology, in order to help fishermen managing their fishing activity

Comparing two pectinid species as a fast and a slow depurators of amnesic shellfish toxin through a modelling approach

Microalgae species of the genus Pseudo-nitzschia (Psn) may produce domoic acid, anamnesic shellfish toxin (AST), and form blooms. Bivalves, filter-feeding animals, can feed on these microalgae species in the water column or sedimented on the bottom. During blooms of domoic acid-producing Psn, bivalves will accumulate the AST in their tissues via nutrition. By being toxic for Humans, domoic acid concentration is monitored in exploited shellfish species such as Pecten maximus, the king scallop. In France, P. maximus is the second most captured species, representing an important part of the economy. Hence, when the sanitary threshold of AST concentration is exceeded, the fishing closure of the king scallop causes significant socio-economic losses. The French MaSCoET project aims to determinate the reasons for Psn blooms and why P. maximus depurates more slowly than other pectinid species such as the variegated scallop, Mimachlamys varia. The objectives of my PhD thesis are (i) to better understand the links between individual bioenergetics and accumulation, storage and depuration of AST, (ii) to determine the impacts of environmental conditions on these relationships and (iii) to explain the mechanisms behind the different depuration capacities of pectinid species. For this, a contamination and decontamination model of domoic acid will be linked to the bioenergetics of the organism, based on the Dynamic Energy Budget (DEB) theory. The calibration and the validation of the model are based on data from the MaSCoET project. The methodology used to compare the two species with their own toxin retention, and how we could tackle the questions of depuration predictions depending on environmental conditions through model scenarios will be presented. The final goal will be to develop a tool to predict decontamination duration depending on environmental conditions and organism physiology, in order to help fishermen managing their fishing activity

A generalized Dynamic Energy Budget model including 3D shape changes for modeling small pelagic fish growth

International audienceSmall pelagic fish (SPF) are key components of marine ecosystems, transporting energy from the lower to the upper trophic levels and thereby influencing the dynamics of the entire ecosystem. Understanding their complex growth patterns from early life stages to adulthood is fundamental to accurately predict larval survival and predator-prey dynamics, which are influenced by individual size. However, growth models are generally unable to accurately reproduce the growth acceleration and deceleration phases observed, particularly during early life stages. Here we propose a growth model based on a Dynamic Energy Budget model (modified as in Maury, 2019 to properly account for size-dependence of maintenance) that captures deviations from pure isomorphy. It represents the fish’s body as an ellipsoid and differentially allocates volumetric growth to length, height and width as a function of the distance between the current shape and characteristic stage-dependent shape attractors (expressed as width/length and height/width ratios). The resulting surface-to-volume ratios mechanistically explain the “metabolic acceleration” often invoked to explain early life growth patterns. We estimated model parameters for three important SPF species in the Benguela upwelling system, using data covering growth at all life-stages, transitions between life-stages, and reproduction. The calibrated models reproduced the observed deviations from isomorphy, with exponential length-dominated growth until metamorphosis, then a shift to height- and width-dominated growth (with a corresponding deceleration of length growth) until the adult shape is reached, and finally isomorphic (characteristic von Bertalanffy) length growth. These deviations from the usual von Bertalanffy growth model could profoundly affect our understanding of larval survival, predator-prey and ecosystem-dynamic

Fast and slow depurators of amnesic shellfish toxin: a bioenergetic modelling approach to compare twopectinid species

International audienceMicroalgae species of the genus Pseudo-nitzschia may produce toxic domoic acid and form blooms. Domoic acid, the amnesic shellfish toxin, is a threat for Humans, thus its concentration is monitored within exploited shellfish species. Indeed, by their active filtration, bivalves may accumulate toxins in their tissues. When the sanitary threshold is exceeded, fishing is closed until decontamination. In France, the king scallop (Pecten maximus) is thesecond most economically important bivalve species. Over the last decade, fishing closures have led to a decrease in the fishing fleet in the Bay of Brest and a significant economic loss. Not all bivalve species respond in the same way to contamination, there exist "slow" depurators, such as P. maximus, and "rapid" ones like Mimachlamys varia, the variegated scallop. The French MaSCoET project aims to understand the ecology of this microalgae and the contamination and decontamination kinetics of the king scallop compared to other bivalves. The objectives of my PhD thesis are to compare these two pectinid species by developing a contamination/decontamination model of domoic acid, linked to the bioenergetics of the individual. The final goal should be to develop a tool to predict decontamination duration depending on environmental conditions and organism physiology, in order to help fishermen managing their fishing activity in case of a toxic algal bloom. The methodology used to develop the model and compare two pectinids species with their own toxin retention and how we could tackle the questions of depuration predictions will be presented

A generalized Dynamic Energy Budget model including 3D shape changes for modeling small pelagic fish growth

Small pelagic fish (SPF) are key components of marine ecosystems, transporting energy from the lower to the upper trophic levels and thereby influencing the dynamics of the entire ecosystem. Understanding their complex growth patterns from early life stages to adulthood is fundamental to accurately predict larval survival and predator-prey dynamics, which are influenced by individual size. However, growth models are generally unable to accurately reproduce the growth acceleration and deceleration phases observed, particularly during early life stages. Here we propose a growth model based on a Dynamic Energy Budget model (modified as in Maury, 2019 to properly account for size-dependence of maintenance) that captures deviations from pure isomorphy. It represents the fish’s body as an ellipsoid and differentially allocates volumetric growth to length, height and width as a function of the distance between the current shape and characteristic stage-dependent shape attractors (expressed as width/length and height/width ratios). The resulting surface-to-volume ratios mechanistically explain the “metabolic acceleration” often invoked to explain early life growth patterns. We estimated model parameters for three important SPF species in the Benguela upwelling system, using data covering growth at all life-stages, transitions between life-stages, and reproduction. The calibrated models reproduced the observed deviations from isomorphy, with exponential length-dominated growth until metamorphosis, then a shift to height- and width-dominated growth (with a corresponding deceleration of length growth) until the adult shape is reached, and finally isomorphic (characteristic von Bertalanffy) length growth. These deviations from the usual von Bertalanffy growth model could profoundly affect our understanding of larval survival, predator-prey and ecosystem-dynamic

Fast and slow depurators of amnesic shellfish toxin: a bioenergetic modelling approach to compare twopectinid species

Microalgae species of the genus Pseudo-nitzschia may produce toxic domoic acid and form blooms. Domoic acid, the amnesic shellfish toxin, is a threat for Humans, thus its concentration is monitored within exploited shellfish species. Indeed, by their active filtration, bivalves may accumulate toxins in their tissues. When the sanitary threshold is exceeded, fishing is closed until decontamination. In France, the king scallop (Pecten maximus) is thesecond most economically important bivalve species. Over the last decade, fishing closures have led to a decrease in the fishing fleet in the Bay of Brest and a significant economic loss. Not all bivalve species respond in the same way to contamination, there exist "slow" depurators, such as P. maximus, and "rapid" ones like Mimachlamys varia, the variegated scallop. The French MaSCoET project aims to understand the ecology of this microalgae and the contamination and decontamination kinetics of the king scallop compared to other bivalves. The objectives of my PhD thesis are to compare these two pectinid species by developing a contamination/decontamination model of domoic acid, linked to the bioenergetics of the individual. The final goal should be to develop a tool to predict decontamination duration depending on environmental conditions and organism physiology, in order to help fishermen managing their fishing activity in case of a toxic algal bloom. The methodology used to develop the model and compare two pectinids species with their own toxin retention and how we could tackle the questions of depuration predictions will be presented