Mercury is a toxic element for animals and its increasing concentration in the world’s ocean as been acknowledged as a global issue. Though the Southern Ocean presents overall high mercury levels, very few studies addressed this issue and how it is affecting marine fauna. Nevertheless, the few studies that did, have shown that, for example, the Antarctic seabird wandering albatross (Diomedea exulans) has the highest mercury concentration of any marine bird recorded worldwide. Even more surprising is the absence of studies of mercury content in Antarctic krill Euphausia superba, given that this is a key species [1] in the Southern Ocean ecosystem.
Using males, females, juveniles and eggs from Antarctic krill captured in South Orkneys (an Antarctic Island with winter sea ice), South Georgia (a Subantarctic Island without sea ice) and Antarctic Polar Front (oceanic front that separates the Southern Ocean from the Atlantic Ocean, in the case of the Atlantic Sector) to understand the possible biomagnification [2] of mercury in the Antarctic food webs.
Different mercury concentrations were found in individuals from the three sampling sites, with individuals from South Orkney Islands showing higher values than the other 2 regions. Authors suggest that the habitat and the presence of winter sea ice may influence mercury levels as ice captures contaminants from the atmosphere. More differences were found between the life-stage of individuals, with juveniles showing higher mercury levels that adults, which can be explained by the elimination of mercury through their gonads (reflected in the eggs), with individuals releasing mercury throughout their lives by different processes, such as the moulting.aça.
Results show that Antarctic krill presents levels similar (or higher) that other krill species near industrialized areas, confirming mercury as a global problem, demanding this way a world monitoring program to reveal sources, pathways and effects of this contaminants, especially in the Antarctic.
[1] a key species is a fundamental species in an ecosystem, and if disappears all the system may collapse.
[2] biomagnification refers to the increase of concentrations throughout individuals’ life.
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Source: Seco J, Xavier JC, Coelho JP, Pereira B, Tarling G, Pardal MA, Bustamante P, Stowasser G, Brierley AS, Pereira ME (2019) Spatial variability in total and organic mercury levels in Antarctic krill Euphausia superba across the Scotia Sea. Environ Pollut. doi: 10.1016/j.envpol.2019.01.031
Author: José Queirós
