Causes of fading in colour of seaweed cultivated in the laboratory?

The culture of marine algae, primarily for human consumption is a large and expanding industry in Japan. At the present time, the growing and harvesting of Porphyra, "nori," is considered to be one of the most profitable fisheries in Japan. In contrast, seaweed culture is still in a research phase in the United States. Our demand for marine algae is much more limited in terms of both total volume and number of species. This is mainly due to the fact that few Americans eat the plants as such. Our use of seaweed is almost entirely in the form of phycolloids extracted from the plants, and to a very limited degree, as fertilizers and food. These uses of several species of marine algae and the recognition that the U.S. possesses a limited supply of the three or four most used species has led to seaweed culture on an experimental basis in this country. However, we have not and, in the foreseeable future, will not place the amount of our coastal waters under "cultivation" as has Japan. Another important difference between the United States and Japan is that the seaweed beds can be harvested only by fishermen's cooperative associations in Japan whereas in this country the harvesting is done by industrial firms either directly or through contractors. The cooperatives are responsible for the management and protection of these resources while in the United States such efforts are rarely required by the government but are usually voluntary.