Algicidal effect of phlorotannins from the brown alga Ecklonia kurome on red tide microalgae

Abstract

The algicidal effects of phlorotannins from the brown alga Ecklonia kurome on three species of red tide microalgae ( Karenia mikimotoi, Cochlodinium polykrikoides and Chattonella antiqua) were examined. Swimming cell density of K. mikimotoi and C. polykrikoides decreased to less than 2% of the initial density within 30 min in medium containing 150 mg/l crude phlorotannins. After losing their motility, almost all of the cells became round. They then expanded and burst. Once cells had become round, none of them recovered to normal vegetative cells within 24 h even if they were transplanted to normal medium. On the other hand, no change was observed on C. antiqua in the 500 mg/l medium within 3 h after inoculation. However, by 24 h, over 99% of the cells were destroyed even in the 100 mg/l medium. Among the five phlorotannins isolated from E. kurome, phlorofucofuroeckol A, a pentamer of phloroglucinol, had the strongest algicidal activity, which was comparable to that of epigallocatechin gallate. No mortality was observed among red sea bream Pagrus major, tiger puffer Fugu rubripes rubripes (body weights ca. 13 and 102 g, respectively) or larval blue crab Portunus trituberculatus (total carapace length ca. 2 mm) which were exposed to 200 mg/l phlorotannins for 30 min.