The role of extrinsic variation—cohabiting juvenile fish species exhibit similar otolith elemental signatures

Abstract

The effect of extrinsic (environmentally based) and intrinsic (physiologically based) controls on otolith elemental signatures remains poorly understood. We evaluated the relative importance of both extrinsic and intrinsic factors using juvenile fish in Eastern Tropical Pacific (ETP) mangroves. To assess extrinsic influences, we compared the cohabiting yellow snapper Lutjanus argentiventris and sailfin grouper Mycteroperca olfax from the Galápagos Archipelago. To evaluate intrinsic influences, we compared yellow snapper from the Gulf of California (Mexico) and the Galápagos Archipelago (Ecuador). The 2 cohabiting species in the Galápagos exhibited very similar otolith elemental signatures, with no significant differences observed for Li, Cu, Mg, Mn, Rb, and Sr (univariate ANOVAs, p > 0.05), and a small separation achieved between these species (ANOSIM test, R = 0.01, p = 0.038). The yellow snappers from Galápagos and the Gulf of California exhibited distinct elemental signatures increasing from Rb, Cu, Mn, Sr, Li to Ba (univariate ANOVAs, p < 0.05), with a large separation between them (ANOSIM test, R = 0.55, p = 0.001). The present study suggests that extrinsic factors (e.g. water chemistry, temperature, salinity) can be more important than intrinsic factors (e.g. physiology, growth rates, genetics) for influencing elemental uptake in the otoliths of juveniles from mangrove waters. However, improved understanding of factors influencing elemental incorporation is still needed to ensure accurate interpretation of field data, especially in dynamic oceanographic systems, which is the case for both the Gulf of California and the Galápagos Archipelago.