1992 年 58 巻 3 号 p. 571-575
Although the brown alga Eisenia bicyclis is regarded as a suitable food for abalones and sea urchins, fresh alga appears to devoid of predation by these marine herbivores, while fallen thalli are actively eaten. The feeding-deterrent activities of fractions prepared from the methanol extracts were examined against the abalone Haliotis discus hannai. The water-soluble fraction prepared from a fresh algal sample showed a marked feeding-deterrent activity, while that from the dried algal sample was inactive. On the other hand, the water-soluble fraction of the brown exudates obtained during air-drying in the shade revealed more potent activity than the water-soluble fraction of fresh alga. The active compounds were found to be phlorotannins which were previously obtained from the brown alga Ecklonia stolonifera. It may be suggested that the living E. bicyclis excretes phlorotannins into sea water to avoid predation by marine herbivores.