Feeding-Deterrents from the Brown Alga Dictyopteris undulata against the Abalone Haliotis discus hannai.

The feeding-deterrent activity of methanol extract from the brown alga Dictyopteris undulata that grows densely in the nursery grounds of the abalone Haliotis discus was tested on the abalone H. discus hannai by the cellulose plate bioassay method. Bioassay-guided isolation afforded five active sesquiterpene derivatives (zonarol, isozonarol, chromazonarol, zonarone, and isozonarone) from the neutral and acidic fractions of the methanol extract. It seems that D. undulata adopts to sublittoral zones where abalone are abundant by virtue of having feeding-deterrent sesquiterpenes.