Otolith microchemistry: The geochemical link between environment and biomineralization in fish

Abstract Assessing environmental change relies on monitoring physical, chemical, and biological parameters over extended periods of time. However, detecting change is difficult in areas where base-line data is sparse or non-existent. Biominerals, which may archive chemical information, are becoming important tools for monitoring environmental change. In particular, otoliths have been referred to as continuous recorders of exposure to the environment. Otoliths are calcified structures in the inner ear of teleost fish that are composed of alternating layers of calcium carbonate (typically aragonite), separated by thin bands of protein. They are metabolically inert, unlikely to be resorbed, and grow throughout the life of the fish, and their annular structure produces a time scale that may be added to the record. However, previous studies indicate that only selected trace elements in otoliths are influenced by water composition, a relationship that is complicated by fish physiology and habitat of the fish.;This study examines if the geochemistry of a habitat has an affect on otolith microchemistry, specifically, if otoliths retain a chemical signature that may be related to the geology of the watershed. Otoliths were taken from four geologically distinct areas in Manitoba that have been influenced by mining activity. In each case, a suite of elements indicative of the surrounding geology was chosen for LA-ICP-MS analyses across the annuli. Otoliths from fish captured near and downstream from a rare element pegmatite mine contain signatures of Li, Cs, and elevated Rb, whereas those from lakes distant to or upstream from the pegmatite do not have such concentrations of those elements. Otoliths taken from lakes adjacent to Cu, Pb, and Zn mining contain coincident peaks of the three metals that are interpreted to indicate when the fish came into contact with the tailings. Constant levels of Ni detected in otoliths from lakes near Ni mining operations suggest that the fish are exposed to consistent levels of the metal. Fish stocked in a closed open-pit Ni-Cu mine contain constant levels of these base metals throughout their life history. These cases indicate the affect habitat has otolith microchemistry and highlight the possibility of using otolith microchemistry to develop base-line chemical signatures for environmental assessments.