ULTRAVIOLET ABSORBING SUBSTANCES FROM AGARUM FIMBRIATUM (PHAEOPHYCEAE) PROTECT GRIFFITHSIA PACIFICA FROM UV RADIATION

We examined whether naturally occurring polyphenols produced by a brown alga can protect other organisms from ultraviolet radiation. Fragments of Griffithsia pacifica were grown in medium supplemented with a seawater extract of Agarum fimbriatum (3% w/v in seawater for 2 h). Cultures were exposed to cool‐white fluorescent light (7–7.5 μMol photons cm −2 s −1 ) in the presence or absence of 130 to 168 μW cm −2 UV‐A and 85 to 112 μW cm −2 UV‐B. Regenerating fragments were scored for five qualitative or quantitative measures of growth. Rhizoid growth was not inhibited by the polyphenol extract after ten days. UV radiation in the absence of polyphenols caused considerable cell death and slower growth. Thus, the presence of polyphenols provided protection from UV radiation such that in the highest concentration of polyphenols (1:1 medium:extract), rhizoid growth in UV exposed fragments was approximately 60% as great as control plants without both polyphenols and UV radiation. Plants exposed to UV radiation in the absence of polyphenol extract showed poor rhizoid regeneration and extensive cell death. These experiments document the nature of UV‐A and UV‐B damage to growing red algae, and provide strong evidence that polyphenols from brown algae may have a role in protecting subtidal, benthic algal communities from UV radiation.