Franck Touratier - Academia.edu (original) (raw)
Papers by Franck Touratier
Journal of Plankton Research, 1999
This study describes a model which addresses the processes of ingestion, assimilation, respiratio... more This study describes a model which addresses the processes of ingestion, assimilation, respiration, excretion and growth of copepods as a function of the concentration of food and its elemental composition in terms of carbon (C) and nitrogen (N). Two experimental data sets are used to estimate several parameters of the model concerned with the influence of food quality. The results of the model suggest that the concentration of food and its quality (i.e. the C:N ratio) largely determine copepod growth. Both the experimental data sets and the model output show that low carbon relative to the nitrogen content of food does not limit the production of copepods. Comparing the results of the model to those of a previous model on bacteria suggests large differences between bacterial and copepod physiological responses to a variable quality of the substrate or food. The results of these models suggest that the regeneration of ammonium performed by copepods always favors regenerated primary production, whereas that performed by bacteria, depending on the quality of assimilated substrates, can favor or limit regenerated production.
Journal of Marine Systems, 2000
A multidisciplinary international oceanographic expedition was conducted in the Northeast Water P... more A multidisciplinary international oceanographic expedition was conducted in the Northeast Water Polynya (NEW, northeast of Greenland) from May to August 1993, to understand the formation of the polynya and its influence on the pelagic ecosystem. The residual circulation in the polynya is characterized by an anticyclonic gyre, which follows a system of troughs. The numerous data acquired during the expedition and the resulting publications provide the background for an ecological modelling study. Since the sampling scheme during this expedition was not appropriate for implementing ecological models, the first objective of the present study was to build up a multivariate time series. Stations in the time series were selected by taking into account the residual circulation in the anticyclonic gyre. Model outputs were compared to data along the time series. From the time series alone, it was not possible to fully understand the development of a second phytoplankton bloom, so that we formulated three hypotheses on the functioning of the ecosystem during that period: (H1) horizontal supply of nitrate from waters located to the north; (H2) vertical diffusion of nitrate; (H3) local remineralization processes in the surface layer. H2 and H3 are evaluated using two ecological models, in which the same components are simulated, but the first considers only the nitrogen cycle and the second simulates both the carbon and nitrogen cycles. Comparing the chemical and biological variables simulated by the models to the observed time series data by reference to the three hypotheses lead to the conclusion that H2 is the most likely hypothesis. This also means that the summer pelagic ecosystem in the anticyclonic gyre was perhaps dominated by a short food chain that mostly comprised large phytoplankton, copepods and appendicularians. However, because the parameterization of vertical mixing used to test hypothesis H2 may be an oversimplification of field conditions, the hypothesis cannot be fully tested.
Aquatic Microbial Ecology, 1999
The present study describes and explores a model to determine bacterial growth, respiration and n... more The present study describes and explores a model to determine bacterial growth, respiration and net ammonium remineralization as a function of the average substrate C:N ratios and concentrations of organic substrates. Several experimental data sets were used to estimate critical parameters of the model. These data sets suggest that carbon and nitrogen growth efficiencies play a central role in the computation of bacterial growth, respiration, and net ammonium remineralization. The new parameterization of these processes, which takes into account the variability of carbon and nitrogen growth efficiencies with the C:N ratio of organic substrates, agrees with the observed expermental trends. The structure of the model and the results are compared to those of other models. According to the output of our model and to experimental data, which were used to validate parts of the structure, bacterial growth increases with organic substrate concentration and decreasing C:N ratios. As a consequence, a low carbon content relative to nitrogen in the substrates does not limit bacterial growth. KEY WORDS: Bacterial growth. Excretion. Respiration. Model. Nitrogen. Carbon
Journal of Plankton Research, 1999
This study describes a model which addresses the processes of ingestion, assimilation, respiratio... more This study describes a model which addresses the processes of ingestion, assimilation, respiration, excretion and growth of copepods as a function of the concentration of food and its elemental composition in terms of carbon (C) and nitrogen (N). Two experimental data sets are used to estimate several parameters of the model concerned with the influence of food quality. The results of the model suggest that the concentration of food and its quality (i.e. the C:N ratio) largely determine copepod growth. Both the experimental data sets and the model output show that low carbon relative to the nitrogen content of food does not limit the production of copepods. Comparing the results of the model to those of a previous model on bacteria suggests large differences between bacterial and copepod physiological responses to a variable quality of the substrate or food. The results of these models suggest that the regeneration of ammonium performed by copepods always favors regenerated primary production, whereas that performed by bacteria, depending on the quality of assimilated substrates, can favor or limit regenerated production.
Journal of Marine Systems, 2000
A multidisciplinary international oceanographic expedition was conducted in the Northeast Water P... more A multidisciplinary international oceanographic expedition was conducted in the Northeast Water Polynya (NEW, northeast of Greenland) from May to August 1993, to understand the formation of the polynya and its influence on the pelagic ecosystem. The residual circulation in the polynya is characterized by an anticyclonic gyre, which follows a system of troughs. The numerous data acquired during the expedition and the resulting publications provide the background for an ecological modelling study. Since the sampling scheme during this expedition was not appropriate for implementing ecological models, the first objective of the present study was to build up a multivariate time series. Stations in the time series were selected by taking into account the residual circulation in the anticyclonic gyre. Model outputs were compared to data along the time series. From the time series alone, it was not possible to fully understand the development of a second phytoplankton bloom, so that we formulated three hypotheses on the functioning of the ecosystem during that period: (H1) horizontal supply of nitrate from waters located to the north; (H2) vertical diffusion of nitrate; (H3) local remineralization processes in the surface layer. H2 and H3 are evaluated using two ecological models, in which the same components are simulated, but the first considers only the nitrogen cycle and the second simulates both the carbon and nitrogen cycles. Comparing the chemical and biological variables simulated by the models to the observed time series data by reference to the three hypotheses lead to the conclusion that H2 is the most likely hypothesis. This also means that the summer pelagic ecosystem in the anticyclonic gyre was perhaps dominated by a short food chain that mostly comprised large phytoplankton, copepods and appendicularians. However, because the parameterization of vertical mixing used to test hypothesis H2 may be an oversimplification of field conditions, the hypothesis cannot be fully tested.
Aquatic Microbial Ecology, 1999
The present study describes and explores a model to determine bacterial growth, respiration and n... more The present study describes and explores a model to determine bacterial growth, respiration and net ammonium remineralization as a function of the average substrate C:N ratios and concentrations of organic substrates. Several experimental data sets were used to estimate critical parameters of the model. These data sets suggest that carbon and nitrogen growth efficiencies play a central role in the computation of bacterial growth, respiration, and net ammonium remineralization. The new parameterization of these processes, which takes into account the variability of carbon and nitrogen growth efficiencies with the C:N ratio of organic substrates, agrees with the observed expermental trends. The structure of the model and the results are compared to those of other models. According to the output of our model and to experimental data, which were used to validate parts of the structure, bacterial growth increases with organic substrate concentration and decreasing C:N ratios. As a consequence, a low carbon content relative to nitrogen in the substrates does not limit bacterial growth. KEY WORDS: Bacterial growth. Excretion. Respiration. Model. Nitrogen. Carbon