Algicidal activity of polyunsaturated fatty acids derived from Ulva fasciata and U-pertusa (Ulvaceae, Chlorophyta) on phytoplankton

Isolation of algicidal compounds from Ulva fasciata revealed that the algicidal substances were the polyunsaturated fatty acids (PUFAs) as hexadeca-4,7,10,13-tetraenoic acid (HDTA) C16:4 n-3, octadeca-6,9,12,15-tetraenoic acid (ODTA) C18:4 n-3, alpha-linolenic acid (ALA) C18:3 n-3 and linoleic acid (LA) C18:2 n-6. The fatty acid composition of four species of Ulvaceae (U. fasciata, U. pertusa, U. arasakii and U. conglobota) was analyzed by capillary gas chromatography to investigate the relationship with the algicidal activity. The results indicate that highly algicidal species, U. fasciata and U. pertusa, showed higher contents of C16:4 n-3, C18:3 n-3, and C18:4 n-3. Concentrations of these PUFAs released from the seaweed in the culture medium were also analyzed. These PUFAs were found to be significantly active against Chattonella antiqua, C. marina, Fibrocapsa japonica, Heterosigma akashiwo, Karenia mikimotoi, moderately effective against Heterocapsa circularisquama, Prorocentrum minimum, P. sigmoides, Scrippsiella trochoidea, whereas low effective against Alexandrium catenella and Cochlodinium polykrikoides. It is suggested that the PUFAs are useful mitigation agents to remove several harmful effects without causing detrimental effects on surrounding marine living organisms.