Step intime12/25/2023 ![]() ![]() ![]() Since growth rate of organisms is largely controlled by environmental drivers, changes in skeleton biomineralisation provide a reliable archive of the environmental variations experienced by organisms ( Kennish and Olsson, 1975). The study of growth patterns has long been used as a timescale in calcified tissues ( Réaumur, 1709 Pulteney, 1781 von Hessling, 1859). By introducing a temporal basis in the study of hard tissues of organisms, this newly research field offers a tremendous potential in various disciplinaries such as physiology, ecology, paleoclimatology. Sclerochronology is the study of physical and chemical variation in the accretionary tissues of calcified biomaterials, where the increment is the unit of time ( Schöne et al., 2003b Schöne, 2008 Huyghe et al., 2019). Therefore, various growth patterns can be observed depending on the experienced environmental conditions and serve as the basis of sclerochronological analysis. This is notably the case in many mid-latitude species during winter, when the temperature is cold and the food is sparse ( Schöne, 2008). The growth of shells and skeletons can slow down or even stop, likely related to the dynamics of environmental and physiological conditions. Consequently, biomineralisation is not homogeneous nor continuous with time. This process infers enzymatic regulation and active pumping of elements from the external medium, leading to a strong connection between biomineralisation and the metabolism of the organism. In the animal kingdom, biologically-controlled mineralisation is the rule. Various strategies for mineralisation can be experienced by organisms, through extrinsic biologically-influenced mineralisation (also called organomineralisation) to intrinsic biologically-induced or controlled mineralisation (biomineralisation s.s.) ( Weiner and Dove, 2003 Dupraz et al., 2009). The ecological and economic values associated with biomineralisation include the sink of carbon, the shellfish production, the supply of building materials, the formation of habitats (reefs and mounds) by engineer species used as refuges for biodiversity, and their use as archive of (paleo)environmental and (paleo)climatic conditions ( Moberg and Folke, 1999 Coen et al., 2007). Biomineralised structures are now considered as fundamental constituents of the environment, found from the micrometric scale in the skeleton of phytoplankton (the major primary producers) to kilometric scales, visible from the space, such as the Great Barrier Reef formed by corals. The production of hard structures by organisms (shell, skeleton) allows better conditions for the preservation of traces of life on the earth, conducing to define this period as the “Phanerozoic times”. This process called biomineralisation offers large possibilities for evolution of organisms by its use in the support of the general shape of organisms together with an efficient protection of soft tissues ( Marin et al., 2007 Murdock, 2020). One of the main keys of the last 500 Myrs is the flourishment of hard structures produced by organisms. ![]() Tackling the question of the integration of the environment by the organism is challenging: is there a direct effect of the environmental variability on bivalve shell biomineralisation? Or is biomineralisation controlled by a biological clock? In this review, the different temporal units observed in bivalve shells and the possible regulatory processes are explored and some research trajectories are suggested. However, the environmental drivers leading to the periodic formation of increments are still poorly understood. Therefore, shells are used as biological archives of (paleo)environmental and (paleo)climatic conditions. For bivalves, increments are considered as the unit of time recorded in shells. This is likely due to variations of environmental and/or physiological conditions, leading to the formation of growth increments or rings. Biomineralisation rate is not constant over time.
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