A natural algacide from soft coral Sinularia flexibilis (Coelenterata, Octocorallia, Alcyonacea)

A crude lipophilic extract and specific pure metabolites of the soft coral Sinularia flexibilis have been examined for algacidal properties both in laboratory and field experiments. Laboratory algal bioassays, in which cultures of the common fouling alga Ceramium codii were incubated with six different diterpenes isolated from S. flexibilis, revealed that 11-episinulariolide exhibits strong algacidal properties. Field experiments carried out with treated settlement tiles confirmed the laboratory findings and provided evidence for the algacidal properties of 11-episinulariolide against several other common reef algae. Sinulariolide, which had previously been reported to inhibit the growth of unicellular algae, was approximately one third as effective as its stereoisomer 11-episinulariolide in the laboratory growth inhibition bioassay and showed no significant algacidal properties at the concentrations used in the field experiments.