Does otolith geochemistry record ambient environmental conditions in a temperate tidal estuary?

The use of otolith geochemistry to track fish migration patterns and establish past habitat use in estuarine environments relies on the presence of significant correlations between the physicochemical properties of ambient water and otolith composition. To test this assumption, juvenile Solea solea and ambient waters were sampled at fortnightly and monthly intervals in six sites within the Tejo estuary (Portugal) from May to October 2009. A number of element:Ca ratios (Li:Ca, Mg:Ca, Mn:Ca, Cu:Ca, Sr:Ca, Ba:Ca) along with delta C-13 and delta O-18 values were measured in otoliths and water samples. The distributions of some element:Ca ratios (Mg:Ca, Cu:Ca and Ba:Ca) and both delta C-13 of dissolved inorganic carbon (DIC) and delta O-18(water) values were correlated with salinity in the estuarine waters. Otolith Ba:Ca, delta C-13 and delta O-18 ratios were significantly correlated with their respective ambient water values. Each of these variables showed distinctive mixing patterns along the salinity gradient of the estuary and therefore may be valuable tracers of habitat use in euryhaline environments. Surprisingly, only the partition coefficient of Li (D-Li) was significantly negatively correlated with ambient temperature. While more work is obviously needed, Li:Ca may be a useful, but currently overlooked, temperature proxy in fish otoliths. Our results highlight the difficulties of linking measurements of otolith geochemistry to individual water masses or habitats in estuarine systems with large physicochemical gradients over relatively small spatial and temporal scales. (c) 2013 Elsevier B.V. All rights reserved.