2016 Volume 9 Issue 1 Pages 1-13
A possible new indicator of δ15N for detecting nutrient supply effects to Saccharina japonica var. religiosa was investigated. Nutrient supply was examined by adding (NH4)2SO4 fertilizer which shows lower δ15N than δ15N-NO3 of natural seawater on the southwest coast of Hokkaido, Japan, and the fertilizing amounts and periods were adjusted each year (2009-2013). The δ15N in S. japonica var. religiosa and other species of seaweeds before fertilization were close to δ15N-NO3 in Tsushima Warm Current. After fertilization, S. japonica var. religiosa growth promotion and algal biomass enhancement were observed at the fertilizing point compared with the natural site. The δ15N in algal tissue were significantly depleted at the fertilizing point, and approached levels before fertilization with distance from the fertilizing point. The distance from the fertilizing point at which the δ15N in algal tissue were almost the same level as before fertilization differed among years. These results indicate that the nutrient supply was related to fertilizing amounts, periods, and distance from the fertilizing point affected the algal uptake, and were reflected in the δ15N values of algal tissue. We propose the applicability of δ15N signature as a new indicator for detecting nutrient supply effects to S. japonica var. religiosa.