The native Hawaiian plant, Scaevola taccada, commonly grows in tropical coastal areas throughout the Pacific and Indian oceans. Oral tradition suggests that the fruit of this species may have been used as a natural sunblock. To examine this, an extract of S. taccada fruit was tested to determine whether it had UV-absorbing properties, and if so, to determine its stability and potential toxicity to coral. Scaevola taccada contained UV-absorbing compound(s) with a sun-protection factor of 20, on average, that absorbed in the UVB and UVA (19.6% and 24.4% absorbance, respectively). The UV stability of the fruit extract over time and to various treatments (fresh, heated, and frozen) did not change (ANOVA, p = .396, F= 1.018). In addition, we examined the toxicity of S. taccada juice by exposing coral fragments of Porites compressa (n = 7) to four treatments (fresh and heated S. taccada extract, cytotoxic Montipora capitata eggs, and filtered seawater control). Changes in color and photosynthetic yield in treated tissue areas were measured after 4 days. Only the concentrated S. taccada fruit extract and M. capitata eggs resulted in significant changes in pigmentation or photosynthetic yield of the coral (p <= .0001). Further investigation is needed to isolate and expand tests on the UV-absorbing component(s) to understand this toxicity more clearly.
