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

Leticia Maria Cavole*, Jessica A. Miller, Pelayo Salinas-de-León, Octavio Aburto-Oropeza, Jose R. Marin Jarrin, Andrew Frederick Johnson

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ABSTRACT: The role 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 the 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 between the Gulf of California (México) and the Galápagos Archipelago (Ecuador). The two 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). These contrasting results suggest that environmental factors could be greater than physiological factors (i.e. growth rates or genetics). These results indicate that ecological inference based on geographic variation in otolith chemistry is not necessarily confounded by physiology, at least for some trace elements, during early life stages inside mangroves. 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.