Martin Gretchen Bath

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Gretchen Bath

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  • Article
    Temperature and salinity effects on strontium incorporation in otoliths of larval spot (Leiostomus xanthurus)
    (National Research Council Canada, 2004-02-03) Martin, Gretchen Bath ; Thorrold, Simon R. ; Jones, Cynthia M.
    Temperature dependence of strontium/calcium (Sr/Ca) ratios in foraminiferal calcite and coral aragonite is well established; however, factors controlling Sr/Ca ratios in fish otoliths remain obscure. To assess temperature dependence of Sr/Ca in marine fish otoliths, we reared spot (Leiostomus xanthurus) larvae under controlled temperature (17–26 °C) and salinity (15‰ and 25‰). We found a significant linear relationship between temperature and Sr/Ca ratios, with a sensitivity of approximately 5%·°C–1. Otolith Sr/Ca values were also significantly higher at a salinity of 25‰ vs. 15‰, after accounting for differences in dissolved Sr/Ca ratios in the ambient water, with a sensitivity of approximately 1%/salinity (‰). These observations complicate the use of Sr/Ca ratios to determine temperature histories of spot larvae, because accurate temperature reconstructions are possible only with a priori knowledge of both ambient salinity and dissolved Sr/Ca ratios. Fully marine species residing in oceanic waters will not experience significant salinity variations; therefore, otolith Sr/Ca ratios may be useful recorders of temperature exposure. Otolith Sr/Ca thermometry in coastal fish species that make regular excursions into estuarine waters will be more problematic. Multiple geochemical tracers, including oxygen stable isotopes and other trace elements, may be necessary to accurately reconstruct temperature and salinity histories in these species.
  • Article
    Temperature and salinity effects on magnesium, manganese, and barium incorporation in otoliths of larval and early juvenile spot Leiostomus xanthurus
    (Inter-Research, 2005-06-02) Martin, Gretchen Bath ; Thorrold, Simon R.
    The use of otolith chemistry to delineate fish populations and trace migration pathways is premised on a significant correlation between the elemental composition of otoliths and physicochemical properties of the ambient environment. However, few experiments have been rigorously designed to address the effects of temperature and salinity on the elemental composition of otoliths. We examined the effects of temperature and salinity on the incorporation of magnesium (Mg), manganese (Mn), and barium (Ba) in the otoliths of larval and early juvenile spot Leiostomus xanthurus by rearing fish in the laboratory under controlled environmental conditions. L. xanthurus are an estuarine dependent species that traverse varying temperature and salinity regimes throughout their life histories. It is important, therefore, to understand the influence of physicochemical properties of different water masses before attempting to reconstruct important life history transitions based on variations in otolith chemistry. Both [Mg/Ca]otolith and the Mg partition coefficient, DMg, were not significantly affected by either temperature or salinity, but were correlated with otolith precipitation and somatic growth rates. Temperature and salinity had significant interaction effects on DMn, but not on [Mn/Ca]otolith. Finally, DBa was influenced by salinity but not temperature. These results highlight the complex nature of elemental deposition in otoliths, and suggest that both environmental and physiological effects likely influence elemental ratios in fish otoliths.