OOS 21-5 - Understanding mercury accumulation in pelagic and benthic fish species using compound-specific stable isotope analysis

The global fishery industry is facing the issue of mercury accumulation in aquatic resources, which poses a health risk to humans who consume them. This issue is compounded by the decline of fish populations and alteration of the food web structure. Although the strong bioaccumulation of mercury and its subsequent trophic transfer can result in magnification at higher trophic levels, the degree mercury accumulate through food chains remains unclear due to the lack of a scientific tool to reliably estimate the trophic position. To address this, we investigated trophic dynamics in winter (February 2020) for 4 commercial seafood fish (1 pelagic species: Scomber japonicas; 3 benthic species: Stephanolepis cirrhifer, Conger myriaster, and Lophiomus setigerus) in different regions (the East/ Japan, Yellow, South, and East China Sea) in Korea using C and N stable isotope analysis (SIA) of bulk tissue, individual amino acids (AA), along with measuring mercury concentrations [Log10Hg(ug/kg)] in the target fish.
Our findings indicate that the AA-based trophic position (TPAA) of S. japonicus had a significant correlation with Hg concentration (P <0.05). Furthermore, the TPAA and Hg concentration of pelagic S. japonicus were significantly different, respectively, by 0.7 and 2.1 times higher in the East Sea than the South Sea (P <0.01). However, there were no significant regional differences in TPAA and Hg concentration for most of fish species. These results indicate that the Hg concentration might be closely associated with TPAA particularly for the pelagic fish in the East Sea. This could be caused by characteristics of local habitats, such as basal diet sources, from dominant phytoplanktons (from micro-sized to pico, nano–sized phytoplankton) and their trophic transfer through the pelagic food web. Thus, as significant changes of dominant phytoplankton cells size are expected with recent climate change, it might elongate the pelagic plankton food chain length and subsequently induce mercury bioaccumulation in pelagic fish.