Otolith Chemistry in Freshwater and Marine Ecosystems

Otoliths are biogenic calcium carbonate structures in the inner ear of teleost fishes that accrete layers of mineral and organic matrix in rhythm with growth. Their chemical composition incorporates trace elements and stable isotopes from ambient waters and metabolic processes, creating a lifelong record of environmental history and physiological status. In freshwater systems, otolith chemistry captures the influence of catchment geology, anthropogenic inputs and seasonal hydrology, yielding highly variable elemental baselines. In contrast, marine otoliths often reflect broader salinity gradients, ocean currents and upwelling dynamics, with Sr:Ca and Ba:Ca ratios serving as robust proxies for transitions between estuarine, coastal and open‐ocean habitats. Isotopic signatures, notably 87Sr/86Sr, trace natal origins to specific river systems or water masses. Advances in laser ablation‐ICP‐MS and high‐resolution mapping now permit microchemical profiling at subdaily scales, enabling precise reconstruction of migration pathways, age validation and life‐history events. By integrating otolith chemistry with genetic, telemetry and physiological data, researchers have developed powerful frameworks for delineating population connectivity, detecting habitat shifts and informing fisheries management, conservation planning and ecosystem restoration across diverse freshwater and marine realms.

Research from Nature Portfolio

Recent studies have employed otolith microchemistry to reveal complex life‐history diversity in an endangered threadfin species over a 1 200 km coastal gradient. High‐resolution Sr:Ca and Ba:Ca profiles from core to edge distinguished individuals rearing in estuarine nurseries from those remaining in marine coastal systems, while multivariate chemical clustering uncovered broad population mixing during feeding and overwintering. Another foundational work integrated near‐core elemental composition with genetic microsatellites to assess demographic and genetic connectivity of flounder across the northeast Atlantic and Baltic Sea. That synergistic approach showed that otolith chemistry delineates natal sources obscured by gene flow, whereas genetic markers reveal latitudinal clines, together offering a comprehensive picture of population exchange and guiding regional management units.

Otolith Chemistry in Freshwater and Marine Ecosystems publication trend

The graph below shows the total number of articles in otolith chemistry in freshwater and marine ecosystems across all publications each year (not limited to Nature Index journals).

Technical terms

Otolith microchemistry: Analysis of elemental and isotopic composition in fish ear stones to infer environmental history and life‐history events.

Sr:Ca and Ba:Ca ratios: Molar ratios of strontium or barium to calcium in otoliths used as proxies for salinity gradients and habitat transitions.

87Sr/86Sr signature: Ratio of strontium isotopes reflecting geological origin of ambient water, enabling natal source identification.

Laser ablation‐ICP‐MS: Analytical technique that uses a focused laser to vaporise otolith material, coupling it to inductively coupled plasma mass spectrometry for high‐resolution chemical profiling.

Population connectivity: Degree of exchange among distinct fish groups inferred from otolith chemistry, genetics and movement data to guide management units.

References

1. Overcoming Shifting Baselines: Paleo‐Behaviour Reveals Industrial Revolution as Tipping Point. Global Change Biology (2025).
2. Delineating population structure of resilient sea/river‐type sockeye salmon. Limnology and Oceanography Letters (2024).
3. Diversity of life history and population connectivity of threadfin fish Eleutheronema tetradactylum along the coastal waters of Southern China. Scientific Reports (2023).
4. Reconciling differences in natural tags to infer demographic and genetic connectivity in marine fish populations. Scientific Reports (2018).
5. Reading the biomineralized book of life: expanding otolith biogeochemical research and applications for fisheries and ecosystem-based management. Reviews in Fish Biology and Fisheries (2022).