Isolation of halimedatrial: chemical defense adaptation in the calcareous reef-building alga halimeda.

Halimedatrial, a structurally unprecedented diterpenoid trialdehyde, has been identified as the major secondary metabolite in six species of the calcareous reef-building alga Halimeda. In laboratory bioassays, halimedatrial is toxic toward reef fishes, significantly reduces feeding in herbivorous fishes, and has cytotoxic and antimicrobial activities. The widespread occurrence of halimedatrial and its potent biological activities suggest that this metabolite represents a chemical defense adaptation in this pantropical marine alga.