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We quantified the relative contributions of water and food to strontium (Sr) and barium (Ba) Ba ratios in otoliths were quantified using laser ablation ICP-MS. The relative contributions of water and food sources to otolith aragonite were assessed using a simple linear isotope mixing model. Water sources contributed 83% of Sr and 98% of Ba in otoliths formed in spiked seawater. Our results indicate that water chemistry is the dominant factor controlling the uptake of Sr and Ba in the otoliths of marine fishes. Thus, chemical signatures recorded in the otoliths of marine fishes should reflect the ambient water composition of these elements at the time of deposition. KEY WORDS: Otolith · Element uptake · Sr isotope · Ba isotope · Water sources Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 311: [125][126][127][128][129][130] 2006 water and diet is important because we would only expect otolith chemistry to reflect dissolved concentrations in the environment if water were the primary source of ions in the otoliths.Traditionally, water was thought to contribute most to the composition of calcareous structures in teleosts (Schiffman 1961, Berg 1968, Simkiss 1974, Hoff & Fuiman 1995, Farrell & Campana 1996, Gallahar & Kingsford 1996. However, dietary composition may also influence otolith chemistry. The elemental composition of otoliths has been shown to reflect diet in both freshwater (Limburg 1995, Kennedy et al. 2000 and marine (Buckel et al. 2004) fishes. We sought to address these discrepancies by rearing juvenile mummichogs Fundulus heteroclitus in seawater spiked with enriched Sr and Ba isotopes beyond the natural isotope ratios found in food. This experimental approach provided a definitive test of the relative contributions of water and diet to otolith composition. MATERIALS AND METHODSFish-rearing conditions. Mummichogs are estuarine killifish that occupy marsh habitats along the east coast of North America from Florida to Newfoundland (Collette & Klein-MacPhee 2002). Individuals were collected from Eel Pond in Woods Hole, Massachusetts, using baited minnow traps set during spring tides in June 2002. Eggs were manually extracted from gravid females and fertilized in vitro by commingling eggs and diced testes from sacrificed males in Petri dishes containing filtered natural seawater. The pieces of testes were removed after 24 h. Eggs developed in Petri dishes at a room temperature of 19°C and seawater was changed every 3 d. Eggs hatched after approximately 28 d and the larvae were then transferred to experimental tanks.High-density polyethylene tanks were filled with 10 l filtered natural seawater at a salinity of 30 (PSU). Replicate control tanks contained unaltered seawater, while treatment tanks were spiked with 1 mg 86 Sr and 50 μg 137 Ba each. Stable isotopes were purchased from Oak Ridge National Laboratory, Tennessee, USA. After treatment tanks were spiked, 10 fish were added to each tank, except for 1 control tank that contained only 9 fi...

Chemical constituents in otoliths have become a valuable tool for fish ecologists seeking to reconstruct migratory patterns and life-history diversity in a wide range of species worldwide. This approach has proved particularly effective with fishes that move across substantial salinity gradients over the course of their life, including many diadromous species. Freshwater endmembers of several elemental and isotope ratios (e.g. Sr:Ca, Ba:Ca and (87)Sr:(86)Sr) are typically identifiably distinct from marine values, and often differ among freshwater tributaries at fine spatial scales. Because these chemical tags are generally incorporated in proportion to their ambient dissolved concentrations, they can be effective proxies for quantifying the presence, duration and frequency of movements between freshwater and marine habitats. The development of high precision probe-based analytical techniques, such as laser ablation inductively coupled plasma mass spectrometry (ICP-MS) and microbeam methods, has allowed researchers to glean increasingly detailed life-history profiles of these proxies across otoliths. Researchers are also combining multiple chemical proxies in an attempt to refine interpretations of habitat residence patterns. A thorough understanding of the spatial and temporal variation in water chemistry as well as environmental and physiological controls on incorporation of specific elements into otoliths is required for confident estimation of lifetime salinity experience. First some assumptions, methodological considerations and data processing options that are particularly relevant to diadromous otolith chemistry studies are discussed. Insights into diadromous migrations obtained from decades of otolith chemistry research, highlighting the increasingly recognized importance of contingent behaviour and partial migration are then discussed. Finally, areas for future research and the need to integrate otolith chemistry studies into comprehensive assessments of the effects of global environmental change are identified.

The potential for environmental and physiological modification of elemental incorporation in otoliths is significant and must be validated before otoliths can be used reliably to estimate water parameters over the life history of a fish. We experimentally manipulated temperature and diet quantity for juvenile, sub-adult, and adult Acanthochromis polyacanthus, a tropical damselfish of the SW Pacific. Significant interactive effects between life history stage, temperature and food quantity were observed for otolith Ba/Ca, while significant interactions between stage and food were observed for Sr/ Ca. Specific growth rates were negatively correlated with D Ba and D Sr for juveniles and sub-adults. These interactions indicated elemental incorporation dynamics varied depending on the life history stage, suggesting variation in effects of stage-specific metabolism or reproductive status. Our results highlight complex responses of elemental incorporation to both endogenous and exogenous factors. Interpretations of life history transects across otoliths must account for these effects to avoid confounding environmental variability with ontogenetic changes in physiology.