海藻という植物

摘要

A green alga growing in the Lake Akan is a special natural monument of Japan. This alga Aegagropila linnaei, called `marimo' in Japanese, grows into a ball as large as 20 cm or more in diameter. The balls of this alga larger than 20 cm in diameter were also found in the Lake Zeller in Australia but disappeared. Recently the algal balls were found in a Lake in Iceland, but they are smaller than 10 cm in diameter and looser than those in the Lake Akan. Therefore, the algal balls lager 20 cm are known only in the Lake Akan in the world. On 1991 Dr. Wakana of the Lake Akan Eco-Museum Center commenced to work on the preservation of `marimo' from the physiological and ecological viewpoints. The studies on photosynthetic characteristics of the algal balls of different sizes clarified that the transparency in the Lake Akan is severe for large ones since an enough quantity of light is hardly supplied to the depth giving an adequate water movement necessary for large balls to grow. The growth rate and the photosynthetic activity of A. linnaei are promoted with adding sea water in the culture medium. These results support the view that the ancestor of `marimo' was an alga which inhabited in an arm of the sea about 6,000 years ago. The photosynthetic and respiratory characteristics of the algal balls suggest that the cells in the inner part of the balls are dormant. The cells are awakened with the light irradiation on the part exposed by cutting the ball. The ultrastructure of chloro-plasts of the cells in the inner part can be changed from an abnormal state into the normal with the light irradiation.