The effect of coring and pulverizing juvenile red snapper, Lutjanus campechanus, otoliths on their chemical signatures

Experiments were conducted to test whether coring and pulverizing juvenile red snapper otoliths affected their chemical signatures, which consisted of element:Ca ratios (Ba:Ca, Li:Ca, Mg:Ca, Mn:Ca, and Sr:Ca) and stable isotope delta values (δ13C and δ18O). Analysis of otolith pairs revealed no significant difference in elemental (Hotelling’s paired T2, p = 0.954) or stable isotope signatures (Hotelling’s paired T2, p = 0.991) between whole right versus whole left otoliths. Pulverizing otoliths did not contaminate elemental signatures (Hotelling’s paired T2, p = 0.726), but elemental signatures were significantly different in otolith cores versus whole otoliths (Hotelling’s paired T2, p = 0.015). Specifically, significant differences were detected in Ba:Ca, Mn:Ca, and Li:Ca between whole right versus cored left otoliths (paired t-test, p ≤ 0.012 for each), which resulted from systematic differences of slightly higher Ba:Ca and Mn:Ca in cored versus whole otoliths, while the opposite was true for Li:Ca. Stable isotope signatures also were significantly different between pulverized whole right versus cored and pulverized left otolith cores (Hotelling’s paired T2, p = 0.007), which was driven by slightly lower δ13C and δ18O values in otolith cores versus whole otoliths (paired t-test, p ≤ 0.007 for each). However, no significant differences were found in either elemental or stable isotope signatures between whole right and cored left otoliths when residuals of right versus residuals of left signatures were analyzed (Hotelling’s paired T2, p ≥ 0.992). Overall, study results indicate extracted otolith cores reflect the chemistry of whole age-0 red snapper otoliths, but residuals should be modeled to account for systematic ontogenetic shifts observed in some constituents. Alternatively, cores of age-0 otoliths, instead of whole otoliths, could be analyzed initially to derive nursery-specific chemical signatures such that material later extracted from adult cores would correspond to the same dimensions as the otolith material originally assayed in age-0 otoliths.