Thioguanine

Antarctic krill (Euphausia superba) is a key species in the Antarctic marine ecosystem and also the largest fishery in terms of catch in the Southern Ocean. Bransfield Strait on the northern Antarctic Peninsula is a key fishing ground. Mercury is a globally recognized toxic element that can affect pelagic organisms through bioaccumulation and biomagnification. Understanding mercury dynamics in krill is crucial for understanding its impacts on Antarctic food webs and potential impacts on the uses of krill in the human food chain. However, the factors influencing Hg accumulation in krill remain unclear, especially in the autumn when there is a transition from an environment of abundant food to a period of lower abundance in winter. We therefore investigated the total mercury (THg) accumulation in krill using randomly collected samples (n = 60) from the krill fishery in the Bransfield Strait from 14 May to June 15, 2023. We further explored the potential drivers influencing THg accumulation in krill. The results indicated that THg levels in male krill (46.7 ± 10.8 ng g^-1) are comparable to those in females (40.0 ± 7.8 ng g^-1), and that krill THg levels in May (47.1 ± 11.5 ng g^-1) are significantly higher than in June (41.3 ± 8.2 ng g^-1), indicating seasonal variation in krill THg levels. Moreover, the THg concentration of krill showed a significant positive correlation with krill size, regardless of sex or month. Krill size and sex, slope, water mass at 100 m, and sea ice dynamics all affected THg accumulation. Briefly, the THg level decreased with the increases in seafloor slope, and krill accumulated higher level of THg in the open water compared to ice-covered regions, highlighting the importance of seafloor slope and sea ice dynamics in THg dynamics in krill.

Mercury (Hg) accumulation and biomagnification in the barn owl (Tyto alba) food chain were investigated using bioindicator samples from three trophic levels: (1) soil and moss (atmospheric deposition indicators), (2) small mammal fur from regurgitated pellets (herbivores and omnivores), and (3) barn owl down feathers (apex predators). Spatial analysis identified regional Hg variation in soil, fur and feathers. Statistical models explored the effects of proximity to water bodies, wetlands and nearby pollution sources. The highest total Hg (THg) concentrations were found in feathers (170 ± 160 µg kg^-1, n = 246) and fur in regurgitated pellets (150 ± 200 µg kg^-1, n = 150), followed by soil (63 ± 17 µg kg^-1, n = 63). Bioaccumulation factors were 2.3 (soil to fur) and 2.7 (soil to feather). Biomagnification factor from fur to feathers was 1.8. Methyl Hg (MeHg), measured in a subset of samples, was 120 ± 130 µg kg^-1 in fur (n = 29) and 150 ± 98 µg kg^-1 in feathers (n = 42), with 75-97 % of THg in feathers as MeHg. Prey composition significantly influenced fur THg levels, with higher concentrations in diets with omnivorous prey (Apodemus flavicollis) compared to herbivorous prey (Microtus arvalis). These findings highlight the importance of diet in Hg monitoring and biomagnification studies.