However, this type of cultivation is restricted to the inside of bays with shallow, sandy bottoms. Another method of nori cultivation is also in use, in Japan, where it was devised. The nets are attached to buoys floating on the surface of the sea, so the nori thalli would be soaked in the sea water constantly. With this method it is possible to cultivate the thalli even areas outside of shallow bays in depths of 10-20m. The growth of nori thalli is mostly inhibited by high temperature.
Temperatures are higher in the dark, than in the light.
To overcome this problem, nets with young thalli can be preserved in a deep-freeze. They are the put into vinyl bags and stored in a freezer at -20 degrees celcius. Cultivation in the nori season does not have to be interrupted, as the nets can be brought back to the nori fields whenever they are required. Porphyra has a vitamin C content very similar to lemons, is rich in vitamin B, and proves an excellent source of iodine and other trace elements. Nori is also a source of vitamin E used in facial creams, and contains antioxidants which are substances that slow food spoilage and eliminate free radicals from the body.