Utilization of ammonium-nitrogen by Porphyra yezoensis and Gracilaria verrucosa

In some coastal regions of northern China, the nitrogen content of the seawater is rather low. The total NH4 +-N and NO3 –-N contents (Tseng et al. 1955) of the surface water sometimes may be as low as 5 µg 1–1. In some bays, although the N- content is slightly higher, usually between 5–20 µg 1–1, it still is far from adequate for the maintenance of normal rapid growth of economic crop algae. In seawater, the uptake rate of NH4 +-N by algae far exceeds that of NO3 –-N. Thus, it is apparent that NH4 +-N is main source of N in the cultivation of seaweeds.