Mercury concentrations and stable isotope ratios (δ13C and δ15N) in pelagic nekton assemblages of the south-western Indian Ocean

Mercury (Hg) concentrations and stable isotope values (delta C-13 and delta N-15) were investigated in micronekton collected from La Pe ' rouse and MAD-Ridge seamounts, Reunion Island and the southern Mozambique Channel. Organisms occupying epipelagic habitats showed lower Hg concentrations relative to deeper dwelling bentho-pelagic ones. Increasing Hg concentrations with increasing body size were recorded in the Mozambique Channel and Reunion Island. Positive relationships were observed between Hg levels and delta N-15 values in pelagic nekton assemblages collected at MAD-Ridge seamount and the southern Mozambique Channel, suggesting bio-magnification of Hg. Concentrations of Hg in organisms across the south-western Indian Ocean were within the same range of values. Total Hg concentrations depend on a range of factors linked to habitat range, body size and trophic position of the individuals. To our knowledge, this is the first study investigating the patterns of Hg concentrations in pelagic nekton assemblages from the south-western Indian Ocean.

Automated summary

The study found variations in mercury concentrations among different organisms and regions in the southwestern Indian Ocean, with increasing Hg concentrations observed with larger body sizes. Bioaccumulation of mercury may occur in marine ecosystems.