A field experiment testing for correspondence between trace elements in otoliths and the environment and for evidence of adaptation to prior habitats

Abstract

Site-specific variation in the trace element composition of fish otoliths can be used to identify fish to source, but the mechanisms controlling elemental composition are poorly understood. Environmental influences on the deposition of barium (Ba), copper (Cu), manganese (Mn), and strontium (Sr) in the otoliths of mudsuckers (Gillichthys mirabilis) were tested using a reciprocal field transplant experiment, in which fish from 3 estuaries were transplanted to each of the 3 estuaries. Fish originating from the 3 estuaries showed no differences in otolith chemistry that might reflect acclimation to past conditions in their home estuary or genetic differences among populations, which simplifies the interpretation of otolith chemistry. Cu and Mn concentrations in otoliths differed according to the site of transplant. Cu in otoliths showed the same pattern of difference among estuaries as did Cu in sediments, but there was no correspondence between Cu in otoliths and dissolved Cu. Ranked differences among estuaries in otolith Mn matched the ranking of estuary-specific differences in dissolved Mn, and there was no correspondence between the concentration of Mn in otoliths and sediments. Fish transplanted to different estuaries showed no differences in otolith concentrations of Ba or Sr, and the concentrations of Ba and Sr in the water column showed a similar lack of difference among estuaries. This study provides field evidence supporting the conclusion that the elemental composition of otoliths reflects environmental conditions to which fish have been recently exposed, but whether that correlation is with trace elements in the sediment or water column can vary.