Temporal variability in strontium, calcium, barium, and manganese in estuaries: Implications for reconstructing environmental histories of fish from chemicals in calcified structures

Estuaries are dynamic environments in which chemical properties can vary over small time-scales. Chemical properties of water are reflected in calcified structures of organisms, such as fish otoliths (ear bones). Interpretations of otolith chemistry can be enhanced using information on the temporal stability of ambient chemistry. We assessed temporal variation in temperature, salinity (environmental variables), and elemental concentrations of strontium (Sr), calcium (Ca), barium (Ba), and manganese (Mn), within three estuarine or coastal locations. Temporal variation was assessed over a series of nested temporal scales: seasons, months, weeks, days, and tidal cycles. Variation in elemental concentration was found between seasons, weeks, and days for the majority of elements, but not between months. Differences in Sr, Ca, Ba, and Mn were found over tidal cycles (low versus high tide) in one estuary. The results provide a clear demonstration that samples collected over a range of temporal scales can detect small-scale variability in water chemistry, the magnitude of which can equal or exceed variability over larger temporal scales. Thus, we stress caution in inferring environmental histories from chemicals in calcified structures within dynamic estuarine environments, when small-scale temporal variability is large.