1Okayama Prefectural Technology Center for Agriculture, Forestry and Fisheries, Research Institute for Fisheries Science, Setouchi, Okayama 701-4303, 2Kagawa Prefectural Fisheries Experimental Station, Takamatsu, Kagawa 761-0111, 3Hokkaido National Fisheries Research Institute, Kushiro, Hokkaido 085-0802, 4Graduate School of Agriculture, Kyoto University, Sakyo, Kyoto 620-0861, Japan
To elucidate the threshold amount of DIN value for keeping the nori color, nori color (a* value) and variability of fluval DIN concentration were investigated in the Bisan Strait. The results show that even if oceanic DIN is less than 1 μM, nori can keep its color (a* value>6) by taking up the DIN supplied intermittently from rivers. In that time, the standard deviation of DIN was larger than 2 μM. At this farm, the total period when DIN>7 μM was 1.6 hour day-1; this condition coincides with an incubation experiment conducted in a laboratory. The discolored nori transplanted to this place recovered its a* value within 14 days to the same level as that of the nori originally growing at this place.