Expanding the horizons of sclerochronology: New perspectives for life history and environmental monitoring

Sclerochronology is the study of physical, chemical and structural variations in the accretionary hard parts of organisms and the temporal context in which they formed (Buddemeier et al. 1974; Oschmann 2009; Trofimova et al. 2020). Among others, these biomineralized materials include mollusk shells, coral skeletons, fish otoliths, as well as statoliths and cuttlebones of cephalopods. Drawing on the growth patterns of biomineralized hard parts, sclerochronology seeks to deduce organismal life history traits as well as to reconstruct records of environmental, ecological and climatic change at temporal scales ranging from days to centuries. Effective management of natural environments and sustainable ecosystem use requires a thorough understanding of environmental fluctuations and their interactions with organisms, with sclerochronology serving as a crucial tool in this effort. The International Sclerochronology Conferences have been held every 3 years since 2007, contributing to community interaction and the advancement of sclerochronology (St Petersburg, Florida, USA 2007; Mainz, Germany 2010; Caernarfon, North Wales, UK 2013; Portland, Maine, USA 2016; and Split, Croatia 2019). Due to the global challenges posed by COVID-19, the 6th International Sclerochronology Conference (ISC), originally scheduled for 2022, was postponed by 1 year. To support early-career researchers during the delay, a virtual International Sclerochronology Conference (vISC) was organized in 2022 by an Organizing Committee comprising early-career researchers. This initiative provided an accessible platform for presenting their work, engaging with attendees, and receiving valuable feedback. The main ISC2023 conference was held in Tokyo, Japan, from 22 to 25 May 2023. It brought together scientists from diverse backgrounds across the globe to share advancements in the field of sclerochronology. To ensure accessibility for all participants, the conference adopted a hybrid format, featuring both on-site and remote participation options. The ISC2023 conference was attended by a total of 129 participants. The program included 62 oral presentations, 51 poster sessions and 7 keynote presentations, offering a diverse platform for scientific exchange and discussion. To date, eight special issues on sclerochronology have been published in the last two decades (Schöne and Surge 2005; Gröcke and Gillikin 2008; Oschmann 2009; Schöne and Gillikin 2013; Butler and Schöne 2017; Gillikin et al. 2019; Peharda et al. 2020; Peharda et al. 2021), including five linked to ISC conferences (Oschmann 2009; Schöne and Gillikin 2013; Gillikin et al. 2019; Peharda et al. 2020; Peharda et al. 2021). These publications showcase remarkable advances in sclerochronology made over two decades. In 2025, two new special issues linked to 6th ISC conference have been published, further advancing the dynamic field of sclerochronology: in Palaeogeography, Palaeoclimatology, Palaeoecology (Prendergast et al. 2025) and Limnology and Oceanography Letters (this volume). The former addressed paleontology, paleoceanography and archeology, with a particular emphasis on paleoenvironmental reconstructions. The latter highlights topics related to aquatic sciences, including environmental monitoring, proxy development and biomineralization. It is with great excitement that we present this special issue, which showcases groundbreaking studies presented at the 6th International Sclerochronology Conference and supplemented by remarkable contributions from researchers around the world. The articles in this special issue reflect a rich diversity of topics, methodologies and scales of analysis, uncovering insights into life history traits and environmental patterns in aquatic ecosystems. Notably, this issue highlights the expanding interdisciplinarity of sclerochronology, as the field increasingly intersects with disciplines such as aquatic sciences, evolutionary biology, organismal physiology and metabolism, biomineralization and ecosystem management. These contributions exemplify the discipline's potential to transcend traditional scientific boundaries and drive innovative approaches. Through advanced analytical techniques and multidisciplinary perspectives, the studies in this issue delve deeply into ecological and environmental histories, offering insights that are critical for addressing challenges such as climate change, biodiversity loss, and ecosystem conservation. The authors of this special issue have explored diverse biological hard parts and organic materials, employing a range of analytical approaches and methodologies. The studies include brachiopod shells (Crippa et al. 2025), fish otoliths (Ando et al. 2025; Brennan et al. 2025; Leonhard et al. 2025; Makhlouf et al. 2025; Mnich et al. 2025; Sakamoto 2025; Yokouchi et al. 2025), organic materials in otoliths (Li et al. 2025), structural carbonate in fish vertebrae (Hsieh et al. 2025), fish muscle tissues (Stanek et al. 2024), mollusk shells (Gey et al. 2024; Zemunik Selak et al. 2024; Arellano-Nava et al. 2025; Mouchi et al. 2025; Xu et al. 2025), hormones in octopus beaks (Durante et al. 2025), molecular analysis of bivalves (Xu et al. 2025; Setiamarga et al. 2025) and the review of accretionary structures of diverse aquatic species (Doubleday et al. 2025). Topics span growth line analysis and geochemical studies of biogenic carbonates, structural carbonate and organic substrate analyses in fish hard parts, molecular biology and population dynamics. Below, we present the 19 articles in this special issue categorized into three primary topics to reflect the interdisciplinary scope and scientific contributions of sclerochronological research: (1) Environmental monitoring and environmental impact assessment, which highlights the utility of sclerochronological proxies in reconstructing past environments and monitoring ongoing changes, including those driven by human activities; (2) Ecology, fisheries and aquaculture, which emphasizes the role of sclerochronology in understanding species life histories, population dynamics, and sustainable resource management; and (3) Biomineralization and evolution, which offers fundamental insights into the biological and evolutionary mechanisms underlying shell formation and structural diversity. Notably, several articles span more than one category due to their methodological and thematic overlap. This topic encompasses studies that utilize sclerochronological approaches to investigate how aquatic environments have changed over time and how these changes affect biological systems. The studies grouped under this category applied sclerochronology to assess environmental impacts on aquatic organisms and to estimate environmental variability, offering actionable insights to address challenges such as climate change, sustainable resource management and ecosystem resilience. Doubleday et al. (2025) provided an exceptionally thorough and systematic review that highlights the underutilized potential of diverse aquatic species and biomineralized hard parts beyond conventional groups like corals and bivalves. By exploring accretionary structures in species such as gorgonians, turtles and coralline algae, the study identifies key gaps, advocates for procedural standardization and highlights new opportunities for paleoclimate reconstructions and biophysical modeling. This comprehensive review underscores the interdisciplinary value of chemical sclerochronology in addressing ecological and environmental challenges. Crippa et al. (2025) explored the use of brachiopods as archives for environmental and climatic reconstructions. By applying the Brody–Bertalanffy growth model, they transformed shell distances into age profiles and this approach enabled them to identify periodic δ18O and δ13C and Element/Ca variations across temperate and polar species. Faster-growing temperate species captured annual and intra-annual environmental changes, while slower-growing Antarctic species recorded inter-annual variability and endogenous cycles. This novel sclerochronological approach demonstrates how brachiopod shells can reflect past oceanic conditions with high temporal resolution, offering insights into paleoclimate history. Turning to freshwater systems, Gey et al. (2024) demonstrated the potential of freshwater pearl mussel (Margaritifera margaritifera) shells as natural archives for reconstructing streamwater δ18O values, offering valuable insights into watershed dynamics. By analyzing over 2500 isotope values from the prismatic and nacreous sublayers of mussel shells collected from the Our River (Luxembourg) and grown in laboratory tanks, they determined that the prismatic layer closely reflected monitored water δ18O values, while the nacreous layer exhibited a systematic offset from thermodynamic equilibrium. These differences likely stem from variations in biomineralization processes, such as the carbonic anhydrase activity. Therefore, the findings improve the reliability of streamwater δ18O reconstructions based on bivalve shell δ18O, advancing the understandings of watershed dynamics over time. Accretionary hard parts serve as vital archives for recording ambient environments and organism's growth and physiology, making them crucial for assessing the impacts of climate change on aquatic ecosystems. Xu et al. (2025) employed an interdisciplinary methodology, combining molecular biology and shell geochemistry, to assess the effects of ocean acidification on Manila clam (Ruditapes philippinarum). Their findings revealed significant changes in shell geochemistry and transcriptomic responses under acidification conditions. Moreover, they suggested that early-life stressors could leave lasting imprints on subsequent shell growth and geochemical composition, emphasizing the importance of understanding long-term impacts of environmental stressors on marine organisms. Zemunik Selak et al. (2024) investigated the impact of climate warming on bivalve growth phenology along the eastern Adriatic coast using shell δ18O data and a novel kilometer-scale atmosphere–ocean climate model. It forecasted longer winter growth periods for all species by 2070–2100, while summer growth may decline by up to 3 months for some species. Southern populations could experience up to four additional months of annual growth compared to northern ones. By integrating sclerochronology with climate projections, their study provided valuable insights for adaptation strategies in fisheries and aquaculture, presenting a framework for marine species under changing environmental conditions. Addressing ecosystem-level dynamics, Arellano-Nava et al. (2025) explored the use of bivalve shells as natural archives to assess marine ecosystem resilience and provide early warnings for environmental tipping points. By examining resilience indicators such as autocorrelation and variance in growth curves of bivalve shells, they identified reliable methods to track resilience loss over time. The findings highlight the potential of bivalve shell-derived proxy data for generating long-term, high-resolution ecological records, addressing gaps in marine observational datasets. This approach provides critical insights into ecological changes driven by climate shifts, offering valuable tools for proactive environmental management and forecasting tipping point scenarios in marine ecosystems. Papers accepted under this category explored the application of sclerochronology to understand ecological processes, fisheries management and aquaculture methods and practices. Their studies encompassed diverse topics, including the use of hard parts to investigate population structure and dynamics, movement patterns, physiological and trophic ecology, seafood provenance and environmental impact assessments based on field observations or rearing experiments. Estimating fish provenance, habitat and migration patterns is vital for ensuring the sustainable use of aquatic resources. Makhlouf et al. (2025) combined radiogenic strontium isotope analysis (87Sr/86Sr) from water samples collected across the riverine basin and otoliths of Chinook salmon (Oncorhynchus tshawytscha) with genetic data to reconstruct fish provenance across riverscapes. By analyzing fish sampled in 2015 from the Yukon River, they achieved a higher-resolution reconstruction of natal origin than would have been possible using genetic or strontium isotope data alone, showcasing the power of interdisciplinary methods in ecological research. Brennan et al. (2025) applied an innovative approach to delineating population structures of sea/river-type sockeye salmon (Oncorhynchus nerka) by integrating otolith strontium isotope data, genetic analysis and radiotelemetry. Through the probabilistic framework combining environmental isotope variations and Bayesian modeling, four distinct subpopulations were identified, overcoming challenges in genetic differentiation due to high gene flow. This approach enhances resilience-focused fisheries management, offering new insights into population dynamics and environmental adaptability under changing climatic conditions. Yokouchi et al. (2025) conducted a large-scale analysis of otolith Sr/Ca ratios in 600 Japanese eels (Anguilla japonica) (2015–2020) to investigate their shifting life-history patterns amid declining stocks and global changes. Results confirmed a strong preference for marine habitats among high-latitude individuals, with females favoring marine areas and males preferring estuarine habitats. A decline in marine-resident males since the 2000s was observed, potentially linked to density-driven impacts. These findings underscore the critical need for management strategies to address the changing demographic patterns and habitat use of Japanese eel populations in response to environmental challenges. Furthermore, Sakamoto (2025) introduced a novel straightforward method to infer marine fish migrations using high-resolution otolith δ18O chronologies, addressing challenges posed by habitat temperature and ambient water δ18O variability. By utilizing hydrodynamic models to predict δ18O isoscapes from temperature and salinity distributions, and comparing these with observed otolith δ18O values, potential fish locations can be identified. This method successfully tracked seasonal northward migrations of juvenile sardines (Sardinops sagax melanostictus) in the western North Pacific, aligning with sampling surveys and capture points. The findings and methodological insights introduce transformative advancements in sclerochronology research, offering innovative approaches to track organismal movements through carbonate δ18O values. Further advancing analytical techniques, Mnich et al. (2025) presented a novel method for high-resolution δ18O analysis on a microscopic scale using Secondary Ion Mass Spectrometry (SIMS) and identified challenges such as hydrogen content effects and immersion oil influences, providing critical insights for advancing microscope-scale analysis of otoliths. They applied this technique to Atlantic bluefin (Thunnus thynnus) tuna larvae and successfully generated δ18O data in over 90% of otoliths, establishing baseline data for spawning sites, demonstrating the method's potential for advancing ecological and environmental studies. In addition, Leonhard et al. (2025) reported a novel application of backscattered electron (BSE) imaging to examine the microstructure of both modern and fossil otoliths of black gobies (Gobius niger). Traditionally, the identification of growth rings in otoliths relies on the optical contrast between opaque and translucent bands. However, this approach is often limited in fossil otoliths, where microstructural details are less visible due to diagenetic processes. The BSE imaging, with optimized imaging workflows, significantly enhances the resolution of growth increment patterns. Notably, in the test of Holocene otoliths, microincrement visibility was not affected by post-mortem alteration or radiocarbon age, demonstrating the approach's feasibility and its contribution to understanding the paleoecology of fish. This special issue features four papers on reconstruction of fish metabolism, trophic level and food web structure. Estimating the fish metabolic rates is crucial for understanding their response to environmental change, as it provides key information on their energy requirements. Hsieh et al. (2025) extended methods developed on otoliths to show that δ13C values in structural carbonate of bone mineral can also be used to reconstruct metabolic histories. By analyzing structural carbonate in the vertebrae of reared fish, black porgy, Acanthopagrus schlegelii, Hsieh et al. (2025) was the first to utilize the vertebra as a metabolic recorder, successfully validating that the δ13C metabolic proxy in vertebral structural carbonate can be used to infer oxygen consumption rates. Ando et al. (2025) explored isotopic fractionation effects integral to the carbon isotope metabolic proxy in otoliths using radiocarbon (Δ14C) analysis in experimentally reared Banggai cardinalfish (Pterapogon kauderni). Ando et al. (2025) combined stable and radiocarbon isotope analyses to independently assess fractionation in carbon isotopes associated with biomineral formation and mixing of carbon sources of external and metabolic origin. These findings enhance understanding of the temperature dependence of metabolic rates, offering insights into species resilience to environmental changes. Furthermore, novel analytical methods for examining organic substances and hormones contained within accretionary hard parts have recently garnered significant attention, as they enable the extraction of physiological information from living organisms. Li et al. (2025) focused on the organic matter contained in otoliths as a sclerochronological archive and successfully reconstructed time-series of stable carbon and nitrogen isotope (δ13C and δ15N) histories in five fish species of the family Sciaenidae. While δ13C values revealed habitat shifts, the δ15N values provided information on trophic level changes, which are both associated with the growth of these species. Durante et al. (2025) developed a groundbreaking method for collecting reproductive data by analyzing hormones in the accretionary hard parts of marine invertebrates. Using cephalopod beaks as natural recorders, subsamples (> 2 mg) taken along the growth axis revealed reproductive histories through lifetime. Analyses of samples from two octopus species detected estradiol and progesterone in both sexes but not testosterone, with hormonal peaks suggesting sexual maturity timing. This innovative approach, the first to extract hormones from chitinous tissues, overcame the constraints of gonad analysis requiring deceased specimens and offered critical insights into physiology such as age at maturity for understanding reproductive histories in understudied species. In addition, Stanek et al. (2024) investigated the impact of Arctic warming and permafrost on carbon age and sources within aquatic food through radiocarbon analysis of fish Using fish as natural they freshwater food on carbon to of years while marine food use fish data revealed a role of carbon over time. These findings in carbon dynamics, the ecological of climate change and interactions between food and these studies highlight the potential of sclerochronology in advancing fisheries management and ecological resilience under changing environmental conditions. The articles in this special issue also explored biomineralization mechanisms and using and molecular biological offering insights to evolutionary studies and paleoenvironmental reconstructions. Among these Mouchi et al. (2025) provided a comprehensive and systematic review of methods and in sclerochronology, the diverse of shells as environmental and life-history shells growth patterns and are often in sclerochronological studies. They how and geochemical methods can improve of the shell and identify gaps across including ecology, and paleoclimate reconstructions. sclerochronology could and paleoenvironmental reconstructions. Furthermore, by using molecular genetic it is possible to the history of marine responses to climate change, a crucial of and studies. Setiamarga et al. (2025) revealed genetic diversity of a marine along the of Japan, by shifts, including ocean and by integrating molecular and time genetic analysis of samples from the of were used to identify into and by the and with from to aligning with the last age and by fossil These findings the impact of environmental changes on genetic diversity and provided a for sclerochronological to understand marine biodiversity and climate change that the studies serve as a valuable resource for and new and across this special issue to the power of to ecological interactions and for a sustainable are that it with and to the ongoing advancement of aquatic climate change and biodiversity loss the and methods presented be for and sustainable resource use in aquatic ecosystems. In addition, remarkable to be made in proxy development for sclerochronological research. This special issue highlights significant advancements in the of innovative indicators and the of methodological the potential of these approaches for aquatic and paleoenvironmental research. the in the exchange of sclerochronological brought by COVID-19, we this offered a to innovative and with conference these challenges community to a of and resilience. The their to the and made this May this special issue the for the growth and of sclerochronology and its impact on understanding and aquatic ecosystems. The was by and the review and were by and would like to to the and the of the for their in and this special issue on sclerochronology. Their and have been in together innovative and generating a of studies that understanding of aquatic and also at the of Tokyo, the of the ISC2023 Organizing the Committee and all of this all authors and are for their contributions and time. was by and Peharda was by Schöne support by the under the and program was by support from the and

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