Decreasing mercury concentrations in beaks of the giant warty squid Moroteuthopsis longimana in the Scotia Sea (Southern Ocean) since the 1970s

The giant warty squid Moroteuthopsis longimana is an important prey of top predators in the Southern Ocean. It is therefore a major link in the pathway of contaminants like mercury (Hg) to higher levels in food webs. In this study, we evaluated changes in Hg concentrations in beaks of adult M. longimana collected from the boluses (pellets) of wandering albatross Diomedea exulans chicks at Bird Island (South Georgia) over five decades (1976, 1984, 1995, 2006 and 2016). A steep decrease in Hg concentrations was observed in M. longimana from 1984 to 1995 (0.086 ± 0.021 μg.g^-1 to 0.017 ± 0.013 μg.g^-1), with concentrations remaining low thereafter, likely reflecting the effects of international regulations and the global reductions in Hg emissions and usage initiated in the 1970s. Hg concentrations were not related to the squid size, δ¹⁵N nor δ¹³C values (proxies for trophic position and habitat, respectively), providing no evidence of bioaccumulation nor biomagnification in this squid species. Our results suggest that Hg concentrations in the beaks may be related to Hg bioavailability in the ecosystem, which makes M. longimana a potential biomonitor of Hg concentrations in pelagic environments of the Southern Ocean. However, further investigations are needed to confirm this finding.