Experimental Investigation of Elemental Incorporation in the Otoliths of Larval and Juvenile Fish: Implications for Use as Environmental Recorders

Innovative techniques for discerning fish stocks, identifying nursery habitats, locating spawning sites, tracing larval transport pathways, and quantifying the degree of population connectivity are required to meet the goals of sustainable management of marine capture fisheries. One of the most promising techniques is the use of elemental signatures in fish otoliths (ear stones), which record valuable life history data and serve as the link between fish and their environment. To validate the assumption that otolith elemental composition is a function of water elemental concentrations, and to address the possible effects of external variables such as temperature and salinity, the composition of the ambient water must be known. Thus, three laboratory experiments were conducted using late larval to early juvenile stage spot (Leiostomus xanthurus) and gray snapper (Lutjanus griseus) to quantify the association between fish otoliths and water elemental composition, test the effects of water temperature and salinity on otolith element incorporation, and assess similarities or differences between species. Strontium/calcium (Sr/Ca) ratios in both L. xanthurus and L. griseus were significantly influenced by temperature. Sr/Ca partition coefficients (DSr) were affected by temperature and salinity in L. xanthurus. Magnesium/calcium (Mg/Ca) ratios and DMg were influenced by otolith precipitation rates in L. xanthurus. DMn for L. xanthurus were significantly affected by both temperature and salinity. Although only barium/calcium (Ba/Ca) ratios in L. griseus otoliths were significantly affected by salinity, DBa in both L. griseus and L. xanthurus were affected by salinity, These results are independent of ontogenetic and diet effects, and represent one of the first attempts at validating minor and trace element incorporation in laboratory reared fish. This work also presents the first comparison of otolith element incorporation between fish species. The results prove that otolith element incorporation is not solely a function of water elemental composition because it is affected by both temperature and salinity and those effects varied uniquely among the elements investigated. This comparison between fish species draws attention to the necessity of validation experiments to interpret species-specific elemental signatures in otoliths