Relative Impact of Environmental (Temperature and pH) and Biological Factors (Size and Growth) on Otolith Trace Elemental Composition

Using of calcium carbonate (CaCO ₃ ) structures as an ecological tool relies on the assumption that, for some elements, their composition is influenced by the water in which an organism lives. However biological processes including, growth rates, diet, ontogeny, reproductive state, or genetics can also influence their composition. It is essential we understand how intrinsic biological factors, external environmental conditions, and interactions impact the composition of CaCO ₃ structures to make ecological inferences. We examined how temperature, pH, growth, and body size influenced elemental composition of staghorn sculpin ( Leptocottus armatus ) otoliths. We held animals (108–183 mm length) under three pH (7.60, 7.75, and 7.96) and two temperature (11.5°C and 14.0°C) treatments and examined relationships of three trace element:calcium ratios (Sr:Ca, Ba:Ca, B:Ca) to experimental conditions and body size. Sr:Ca ratios showed a temperature × size interaction, with smaller fish at 11.5°C having higher values than those at 14.0°C, while differences between temperatures diminished at larger sizes. Ba:Ca ratios were lower at 14.0°C across sizes, indicating consistent temperature effects. B:Ca ratios showed weak but statistically significant negative relationships with size. No consistent effects of pH or growth rate were observed. Results highlight that trace element:calcium ratios vary in sensitivity to intrinsic and extrinsic factors, with Sr:Ca influenced by both temperature and body size, Ba:Ca reflecting moderate environmental effects, and B:Ca responding primarily to biological variation. Findings reinforce the value of otolith chemistry as an ecological tool, while emphasising the importance of considering individual-level variation when interpreting elemental signatures.