An allelopathic fatty acid from the brown alga Cladosiphon okamuranus

Abstract

An allelopathic substance was isolated from the methanol extract of the brown alga, Cladosiphon okamuranus. Extraction and purification of the active substance was monitored by bioassays against the conchospores of Porphyra yezoensis and Heterosigma akashiwo. The compound was identified as 6 Z,9 Z,12 Z,15 Z-octadecatetraenoic acid and its activity was then tested against 36 species of microalgae. Many of eukaryotes tested were affected at 5 ppm, but prokaryotes were unaffected at 25 ppm. The tetraunsaturated fatty acid exterminated toxic red tide planktons such as Chattonella antiqua at 1 ppm concentration.