Molecular analyses of shallow-water zooxanthellate zoanthids (Cnidaria: Hexacorallia) from Taiwan and their Symbiodinium spp

Background: Although we previously reported on surveys of shallow-water zoanthid (Anthozoa: Hexacorallia: Zoantharia) species diversity from localities in Taiwan, no study has yet examined the molecular phylogeny of the majority of specimens, nor has any study examined zoanthid zooxanthellae (Symbiodinium spp.) diversity in Taiwan. As many phylogenetic results have been reported from Japan, a critical step in testing DNA identification of zoanthids and their symbionts is the application of these techniques to specimens from neighboring regions such as Taiwan. We utilized three DNA markers (mitochondrial cytochrome oxidase subunit I (COI), mitochondrial 16S ribosomal DNA (mt 16S rDNA), and the nuclear internal transcribed spacer region of ribosomal DNA (ITS-rDNA)) to examine the molecular phylogeny of 110 zooxanthellate specimens collected from 10 localities in Keelung, Kenting, and Green Island. Additionally, we report on the types of Symbiodinium spp. (zooxanthellae) from the three regions above plus the Penghu Islands, utilizing sequences of ITS2-rDNA. Results: Most specimens in the suborder Brachycnemina belonged to previously reported species. However, it appears that there are still some undescribed Palythoa species groups in the northwestern Pacific that are cryptic in having small colony sizes (<5 polyps) and occurring in low numbers. With regards to Symbiodinium spp. diversity, Palythoa tuberculosa and Palythoa mutuki associated with subclade C1 and related types, Zoanthus sansibaricus associated with subclade C3-derived types, and Zoanthus kuroshio that harbored C15/C91-related Symbiodinium. Notably, 1/2 of the P. tuberculosa specimens from the Penghu Islands harbored a previously unreported clade C symbiont, and two Zoanthus. vietnamensis specimens from Keelung also had a unique symbiont type within clade C. Conclusions: It appears that undescribed Palythoa species in the northwestern Pacific may be widely distributed yet low in numbers, often cryptic in their habitat, and with a small colony size. As well, it is clear that much work remains to understand zoanthid-symbiont associations in Taiwan.