Response of otolith microchemistry to environmental variations experienced by larval and juvenile Atlantic croaker (Micropogonias undulatus)

Minor and trace elements incorporated into otoliths during growth may permanently record environmental conditions experienced by fishes. To determine the validity of this approach, we used laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) to assay sectioned otoliths from juvenile Atlantic croaker (Micropogonias undulatus) collected from each of three sites in the Neuse River, North Carolina, and the Elizabeth River, Virginia. Elemental concentrations at the center of the otoliths did not differ between locations, although both Mg : Ca and Ba : Ca were significantly higher at the edge of otoliths from the Neuse River than from the Elizabeth River. Three of the elements (Mg : Ca, Sr : Ca, and Ba : Ca) showed significant variation across otoliths. Sr : Ca, and to a lesser extent Mg : Ca, showed progressive decreases as the fish moved from offshore spawning sites to estuarine nursery areas. The opposite pattern was shown by Ba : Ca. We hypothesize that these patterns were related to the elemental concentrations within oceanic and estuarine water masses. Although both Sr : Ca and Ba : Ca seem to be useful tracers of offshore-inshore migration of estuarine-dependent species, the sensitivity of the technique to more subtle changes in water chemistry remains to be determined.