Belgium

Intrinsic biogeochemical markers, such as stable isotope ratios of carbon (C), nitrogen (N), sulphur (S) and mercury (Hg) are increasingly used to trace the effects of trophic ecology on Hg accumulation in marine top predators. However, they are often used separately. This leaves the interpretation of the data at times incomplete. Using a multivariate approach could contend with the complexity of the natural world and reveal patterns that would not be detectable by univariate methods. Our main objective was to assess which factor influences the most Hg sourcing in Arctic marine top predators and evaluate the consequences relative to the rates of exposure. We measured THg levels, C, N, S and Hg stable isotopes in three true seal species living in the Greenland Sea: the hooded seal Cystophora cristata, the harp seal Pagophilus groenlandicus and the ringed seal Pusa hispida. They present distinct habitat use, diet and geographical distribution. We integrated all the measured parameters into a multivariate analysis and quantify species multi-isotopic niches (SEAs) with SIBER. The multi-isotopic niches of the three species resulted highly separated. Hooded seals presented the largest multivariate SEA (Mode, 95% CI: 0.93, 0.60 – 1.41), a result of its highly distributed oceanic behaviour. Harp seals presented the second largest SEA (Mode, 95% CI: 0.31, 0.14 – 0.68), while ringed seals presented the smallest niche (Mode, 95% CI: 0.22, 0.14 – 0.37) as a result of its strong territoriality within the Scoresby Sound. Ringed seals presented the highest THg levels (1190±488 ng.g-1 dw), followed by hooded (881±942 ng.g-1 dw) and harp seals (407±289 ng.g-1 dw). Our study showed how habitat use (offshore / bentho-pelagic for Cc vs. offshore / pelagic for Pg vs. coastal / sympagic for Ph) is the most important factor influencing Hg accumulation in Arctic true seals. A species like the ringed seal; which lives in the fjords, on land-fast ice, is more influenced by the enhanced MeHg production typical of these zones and accumulate higher levels of Hg compared to offshore hooded and harp seals.SODYAR