1Okayama Prefectural Technology Center for Agriculture, Forestry and Fisheries, Research Institute for Fisheries Science, Setouchi, Okayama 701-4303, 2Graduate School of Agriculture, Kyoto University, Kyoto 620-0861, Japan
To clarify the influence of nutrient supply from rivers on nori (Pyropia), we investigated the distributions and variance of nitrogen stable isotope (δ15N) in nori thalli in the Bisan Strait in the eastern part of the Seto Inland Sea. The δ15N value of nori cultured in low salinity areas was 7.7±0.1‰. On the other hand, the δ15N value of discolored nori collected in high salinity areas was 11.1±0.1‰. Using these results, the contribution ratios of riverine nitrogen to nori were estimated. The δ15N value in nori transplanted to an estuarine zone far from the river mouth decreased to the same level as the nori originally growing until 7 days. δ15N reflected the influence of nitrogen supply from rivers more quickly than the change of color.