Impact of metabolism on biocalcification processes: new tools to reconstruct environmental conditions and individual life histories from biogenic carbonates. Keynote speaker

International audienceCalcified structures of aquatic species, such as fish otoliths and bivalves shells, are remarkable archives of individual life histories and environmental conditions of past and present species. Based on increments that are periodically formed, individual age and growth can be successfully reconstructed. Chemical composition of these structures can also yield information regarding temperature conditions, upwelling events, and productivity, as well as fish migration patterns. How metabolism and environmental conditions control biomineralization processes and growth, optical properties and chemical composition of these structures in particular, is, however, poorly understood. Thus, full and reliable exploitation of the information extracted from these calcified structures is often limited and striking examples of misinterpretations and subsequent erroneous conclusions regarding the dynamics of some exploited fish populations have been documented.Here, to better understand the complex interplay between metabolism and environmental conditions on biomineralization, a new modelling framework that couples both the growth of a biogenic carbonate and its optical properties with the metabolism of the organism is explored. This new approach greatly benefits from the conceptual and quantitative framework of Dynamic Energy Budget (DEB) theory for metabolic organization. Applied to fish otoliths, this model resolves controversial issues and explains poorly understood observations of otolith formation. It can also be used to extract new information from these structures: the temporal variations in the food assimilated by individual fish in their natural environment, which is key ecological information to better understand population dynamics.Comparing fish otoliths and bivalve shells within this new framework for biogenic carbonate formation was then key to better understand mechanisms underlying their carbon isotopic composition. Two carbon sources participate in their formation: ambient dissolved inorganic carbon (DIC) and respired CO2 derived from food. Disentangling the contribution from these two carbon sources remains challenging, which prevents a routine use of otolith and shell 13C proxies. Taking into account the fact that that the respired CO2 flux scales similarly with body size both in fish and bivalves, but hypothesizing that the input flux of DIC scales differently with body size in fish and bivalves, resolves discrepancies among the mechanisms suggested in the literature for fish and bivalves. These assumptions could be tested experimentally and the new framework could be used to further improve our understanding of biomineralization processes and the proxies we can extract from calcified structures such as fish otoliths, bivalves shells and coral skeletons. Further extensions of this unique simulation tool could also help us to address the effects of ocean acidification on calcifying organisms