The occurrence of ectocarpene, which is the attractant of male-gamete excreted by the female gametese of the brown maring alga Ectocarpus siliculosus, was first confirmed by the odoriferous essential oils of Dictyopteris prolifera and Dictyopteris undulata. The “ ocean smell ” of the essential oils from both species of Japanse Dictyopteris, consisted of mainly non-isoprenoids C11-hydrocarbons [dictyopterenes (A.B and C') and ectocarpene]. In striking contrast to D. prolifera, the constituents of “ beach odor ” from Dictyopteris divaricata were sesquiterpenes (hydrocarbons) insteda of the non-isoprenoids (hydrocarbons).