Multi-tracer evaluation of cesium-137 bioaccumulation and trophic transfer in marine organisms off Jeju Island, Korea

Radionuclides accidentally released from nuclear facilities into the marine environment may affect ecosystems far from their original sources, yet their ecological behavior in such regions remains poorly understood. Using a multi-tracer approach, we evaluated 137 Cs bioaccumulation and trophic transfer at a coastal station (R0) and an offshore station (R1) east of Jeju Island, a region strongly influenced by the Tsushima Warm Current, in 2024 and 2025. Bulk δ 13 C and δ 15 N, amino acid-specific δ 15 N-derived trophic position (TP Glu/Phe ), 137 Cs, 133 Cs, total mercury (THg), and Al were determined across organisms spanning multiple trophic levels. Bulk δ 15 N did not consistently reflect trophic position estimated by TP Glu/Phe in this dataset. The highest 137 Cs concentration factors were observed in the fish Pagrus major at R0 and the sponge Euplectella marshalli at R1. However, Al concentrations in sponges exceeded those in sediments and increased with 133 Cs, suggesting that retained sediment particles may have contributed to apparent Cs enrichment. Excluding samples with potential particle influence further strengthened the relationships of 137 Cs, 133 Cs, and THg concentrations with TP Glu/Phe at R0; the respective trophic magnification factors were 2.95, 3.24, and 6.17. In contrast, no significant trophic relationships were detected at R1. These findings indicate that 137 Cs bioaccumulation and trophic transfer may vary spatially and among taxa, potentially reflecting differences in food-web structure and basal resources. A multi-tracer approach is therefore important for understanding these processes by accurately determining trophic position and identifying apparent enrichment associated with retained sediment particles.