Validation of species specific otolith chemistry and salinity relationships

Abstract

Strontium (Sr), barium (Ba), and their ratios to calcium (Ca) may be used as indirect proxies of salinity in otoliths, given that generally Sr:Ca is positively and Ba:Ca is negatively related to salinity. However, these relationships are non-linear, dependent on water chemistry, and vary among species. To determine if salinity reconstructions in northern Gulf of Mexico estuaries (nGOM) are possible for Red Drum (Sciaenops ocellatus) and Gulf Killifish (Fundulus grandis), and if ratios were similar between species, the relationships of Sr:Ca and Ba:Ca with salinity in water and otoliths were examined. Fishes were held at low (<1 psu), mid (10 psu), and high (30 psu) salinities established and maintained with water collected from local estuaries. Sr:Ca differed among all treatments for water and Gulf Killifish otoliths, increasing with salinity increases. Sr:Ca was lowest at the <1 psu treatment in Red Drum otoliths, remaining treatments did not differ, and was lower than Gulf Killifish at all treatments. Red Drum otolith and water Ba:Ca differed among all treatments, decreasing with increasing salinity, while Gulf Killifish otolith Ba:Ca was higher at the <1 psu than other treatments. Partition coefficients also differed among species and salinities. These results demonstrate that it should be possible to reconstruct salinities of Red Drum using otolith chemistry in nGOM estuaries. However, Gulf Killifish is not a good proxy species and species-specific validation, across a wide range of salinities, in the estuary of interest, should be conducted before salinity exposure is inferred from otolith elemental ratios.