Spatial and Developmental Effects on the Accumulation of Mercury in Antarctic Krill (E. superba) Along the West Antarctic Peninsula (WAP)

Philip T. Sontag¹, Deborah K. Steinberg², and John R. Reinfelder¹

¹Rutgers University, Department of Environmental Sciences, New Brunswick, New Jersey, USA

²College of William and Mary, Virginia Institute of Marine Science, Gloucester Point, Virginia, USA

The Antarctic krill Euphausia superba is a critical component of the WAP food web and is therefore a potentially important link in the transfer of mercury (Hg) to higher trophic levels including penguins, seals, and whales. In order to examine ontogenetic (juvenile, adult), spatial (north-south, onshore-offshore) and annual differences in Hg accumulation by E. superba, we measured concentrations of total Hg (THg) and monomethylmercury (MMHg) in krill collected at northern (~64.5°S) and southern (67.4-69°S) stations during the summers of 2013-2015 along the WAP. Total mercury in krill (4.6 ± 1.1 to 20 ± 13 ng g^-1), which includes both inorganic Hg and organic MMHg (0.3 ± 0.2 to 3.2 ± 0.8 ng g^-1) was higher in offshore than nearshore adults in 2014, but north-south differences in krill THg were not observed. THg concentrations were positively correlated with trophic level (derived from δ¹⁵N) for both juvenile (R²=0.86) and adult (R²=0.45) krill at northern and southern stations. However, higher concentrations of MMHg, the form of Hg that biomagnifies in marine food webs, were observed in juvenile than adult E. superba collected at the same latitude and longitude (p<0.005). In addition, both juvenile and adult krill collected at northern latitudes contained higher MMHg concentrations than krill collected farther south near the summer sea ice edge (p<0.005). Differences in MMHg accumulation in krill were not explained by δ¹⁵N-based trophic levels indicating that spatial and developmental factors were most important.