Ontogenetic niche expansion influences mercury exposure in the Antarctic silverfish Pleuragramma antarcticum

摘要

The effects of body size and age class on mercury concentrations were examined in the Antarctic silverfish Pleuragramma antarcticum, an ecologically important prey species in the Antarctic marine food web. Stable isotope analysis was used to investigate variation in mercury concentrations related to ontogenetic changes in diet and/or foraging habitat. Specimens of P. antarcticum were collected along the Ross Sea shelf in February 2008 and mercury concentrations in homogenized whole fish and muscle tissue were analyzed relative to standard length, age class (juvenile vs. adult) and isotopic measures of diet (δ~(15)N) and foraging habitat (δ~((13)C). While mercury concentration in muscle tended to be higher than whole-fish values, concentrations in these 2 matrices were highly correlated. A positive relationship was found between standard length and mercury concentration; further, adult P. antarcticum had significantly higher mercury concentrations than juveniles. Adult mercury concentrations were also more variable: the coefficient of variation in adult muscle (58.3 %) was more than twice that found in juveniles (25.0 %). Though no linear relationships were detected between standard length and δ~(15)N or δ~(13)C values when all individuals were combined, juvenile and adult size classes of fish differed in their isotopic niche position and width. In addition, δ~(13)C values explained the greatest amount of variation in whole-fish mercury across all age classes and for adult fish alone. By expanding both the horizontal and vertical components of their foraging habitat, adult P. antarcticum may have a wider range of exposure to mercury compared with juvenile fish.