The art of otolith chemistry: interpreting patterns by integrating perspectives

Abstract

The ability to obtain high-resolution chemical profiles across otoliths has expanded with technological advancements that prompted an explosion of data from diverse taxa in coastal, marine and freshwater systems worldwide. The questions pursued by most otolith chemists fall broadly into six categories: identifying origins, tracking migration, reconstructing environments, quantifying growth or physiology, validating ages and assessing diets. Advances in instrumentation have widened the periodic table of otolith elements, and two-dimensional mapping has further illuminated spatial heterogeneity across these complex structures. Although environmental drivers of observed elemental signatures in otoliths are often assumed to be paramount, multiple intrinsic and extrinsic factors can disrupt simple relationships between an element and a single environmental parameter. An otolith chemical profile is not a direct photograph of an environment, but rather an impressionistic image filtered through the multifaceted experiences of the fish itself. A ‘signal-to-noise’ approach that assesses the relative magnitudes of variation from intrinsic and extrinsic factors on chemical profiles may be a promising way to resolve the factor of interest against the ‘noise’ of others. A robust appreciation of environmental drivers, physiological regulation and calcification dynamics that affect the ability to effectively interpret otolith chemical patterns is necessary to drive the field forward.