Proposal of a Culture Method for Maintaining High Growth of Sterile Ulva spp./species (Chlorophyta)

To determine height growth conditions of sterile Ulva lactuca, green algae collected from Tokyo Bay, Japan, were evaluated for efficient culture. A culture tank simulating the sea surface was prepared, and the maximum condition of specific growth rate was verified. This was achieved using the Photosynthetic Photon Flux Density (PPFD) of the bottom of the culture tank as an index-an alternative to leaf area index. In the results, the specific growth rate showed the highest value at the average PPFD of 20.6 μmol m-2 s -1 for one week on the bottom of the culture tank. The specific growth rate decreased significantly at 4.0 μmol m-2 s -1. From these data, the method of controlling the density of sterile Ulva using the PPFD of the bottom surface as an index will lead to a culture control method. Consequently, it is possible to maintain a high growth rate of sterile Ulva without the complicated leaf area index measurement. Based on these data, we propose a new type of efficient, sterile Ulva production system instead of our model that has been advocated using enriched seawater.