Although the stable nitrogen isotope ratio (δ15N value) of macroalgae is used to indicate sources of dissolved inorganic nitrogen in coastal marine environments, little is known about the effects of isotope fractionation on the δ15N value. We compared the δ15N values of Undaria pinnatifida cultivated at an inner bay and an exposed site (sites A and B, respectively) in Shizugawa Bay on the northeastern Pacific coast of Japan. Values for algal growth indicators, including thallus length, area, and weight, were higher at site B than at site A. The δ15N value of U. pinnatifida was significantly lower at site B (4.7 ± 1.0‰; mean ± standard deviation) than at site A (6.7 ± 0.4‰). This difference in the δ15N value of U. pinnatifida could not be explained by the δ15N value of seawater NO3 (source isotopic signature), which was similar at the two sites (7.5 ± 0.3‰). The pooled data from the two sites indicated that the δ15N value of U. pinnatifida decreased with increasing thallus size. The results suggest that the δ15N value of U. pinnatifida is influenced by isotope fractionation.
ASJC Scopus subject areas
- Aquatic Science
- Agricultural and Biological Sciences (miscellaneous)
- Plant Science