Compréhension des mécanismes de Biominéralisation de l'otolithe : quantification spatialisée des fractions minérale et organique et influence des facteurs environnementaux

Despite numerous applications on the use of otoliths at both population and individual levels, knowledge regarding the mechanisms of the otolith and their variations with environmental and physiological factors has to be improved. In particular, the characterization of mineral and organic fractions of the otolith structures and the influence of their qualitative and quantitative composition on the opacity remain poorly documented. Yet this information is of key interest for the calibration of the archive "otolith" allowing a robust analysis of information. The first issue of this study focused on the analysis of the opacity and the effects of temperature, growth and metabolism through experiments in controlled conditions. Results led to the modelling of opacity as a function of two energetic contributions: one related to somatic growth and the other independent of somatic growth and associated to maintenance mechanisms. The second issue dealt with the physico-chemical characterization of otolith structures. The development of an approach based on micro-spectrometry Raman, non-destructive, has allowed to quantitatively discriminating organic and mineral signatures at very high resolution. It has led to the characterization of microstructures (L and D zones) and macrostructures (translucent and opaque zones) led to the development of a predictive model of opacity from the signatures of these two fractions. The relationship between the environmental and metabolic factors and the chemical composition of structural features has still to be established but our results promising perspectives for a better understanding of the mechanisms of otolith biomineralisation.