Seasonally resolved environmental reconstructions using fish otoliths

Abstract

Exploiting the chemical and growth properties of otoliths, this study demonstrates how environmental archives with high temporal resolution can be developed. Elemental profiles (Ba:Ca and Sr:Ca) of fish otoliths (ear bones) from the estuarine species Acanthopagrus butcheri (black bream) were related to growth increments on a seasonal time scale. A series of mixed effects models were used to investigate biological, temporal, and environmental factors influencing seasonal otolith elemental profiles. Resultant seasonally resolved chemical chronologies were correlated with environmental data (i.e., salinity) to develop an element–salinity regression function, which when fit to an independently derived chemical chronology showed strong agreement between reconstructed and recorded salinities. Support for the element–salinity regression function through independent verification provided confidence in environmental reconstructions derived from an archaeological otolith. This suggests otoliths can be used to reconstruct past environmental conditions over decadal and centennial time scales. Moreover, the application of mixed effect models to develop chemical chronologies also provides information on drivers of elemental profiles and allows a range of ecological questions to be addressed. This approach may be further adapted and employed across a broader range of taxonomic groups and environments.