Feeding-Deterrent Activity of Diterpenes from the Brown Alga Dilophus okamurai against the Abalone Haliotis discus hannai.

Feeding-deterrent activity of the methanol extract from the brown alga Dilophus okamurai was tested on the abalone Haliotis discus hannai by the cellulose plate bioassay method. From the neutral fraction of methanol extract which showed feeding-deterrent activity, the following active compounds have been obtained: three spatane-type diterpenes, two of which have also inhibited the settlement and the metamorphosis of the abalone veliger, two secospatane-type, and two cubebane-type diterpenes. It may be suggested that D. okamurai chemically deters predation of marine herbivores by the production of these diterpenes. Consequently, the laminariaceous brown algae, such as Eisenia bicyclis, whose sporelings are eaten by marine herbivores, can germinate in communities of D. okamurai to form their own large communities in place of D. okamurai