1 The Defense Mechanisms and Reproductive Barriers of Spirobranchus giganteus

Spirobranchus giganteus is a species or species complex of serapulid polychaetes that lives on hermatypic coral. Its defense mechanisms and reproductive barriers were studied in Opunohu Bay, Moorea, French Polynesia, November 2004. The removal of opercular spines, which have been considered a defense mechanism, was observed to have no effect on Christmas tree worm (CTW) fitness. Interestingly, however, spine regrowth was observed, and more CTW’s exhibited this behavior over time. We estimate that full spine regrowth will take 182 days. In the part of this experiment devoted to reproductive barriers, three surveys were conducted. S. giganteus was found to aggregate by color within, but not between, coral heads and there was no association found between cohort age and CTW color. These patterns are consistent with the hypothesis that CTW color morphs represent different species, assuming CTW’s reproduce at the same time and are small-scale broadcast spawners. Color morph reproductive compatibility was examined directly by crossing three color morphs, where the larvae produced were observed for 24 hours. The development of these larvae suggests that the Y and RW color morphs are the same species, the RW and WPT color morphs are different species, and the Y and WPT color morphs are different species that don’t exhibit complete reproductive incompatibility. Spirobranchus giganteus is a species or species complex of serapulid polychaetes that exist in