Preliminary molecular examination of zooxanthellate zoanthid (Hexacorallia, Zoantharia) and associated zooxanthellae (Symbiodinium spp.) diversity in Singapore

Singapore is located at the southern tip of the Malaysian peninsula between the Indian and Pacific Oceans. Despite being in Such an important biogeographical location, many groups of marine invertebrates from this area remain poorly understood. One such group is the zoanthids (Order Zoantharia, = Zoanthidea, Zoanthiniaria), hexacorallians known from almost all marine environments but historically taxonomically neglected. In this study we examined the species diversity of zoanthids from the genera Zoanthus and Palythoa, as well as their associated symbiotic dinoflagellates (Symbiodinium spp.), for the first time in Singapore. After specimen collection (n = 44) and preliminary identification using traditional morphological characters (oral disk color and polyp shape, etc.) we used two host DNA markers, mitochondrial 16S ribosomal DNA (mt 16S rDNA) and cytochrome oxidase Subunit I (COI), to confirm all collected specimen identities (to species or species group level). Results show the presence Of five putative species of zoanthids [Z. sansibaricus (n=11), Z vietnamensis (n = 17), P. tuberculosa (n = 13), P. mutuki or closely related (11 = 2), and a potential new species designated P. sp. "singapura" (n = 1)] in Singapore. Symbiodinium from these zoanthids generally followed patterns previously seen in Japan, Z. sansibaricus and P. sp. "singapura" possessing C1/C3-derived Symbiodinium, Z. vietnamensis with C15/C91-derived Symbiodinium, and P. mutuki with generalist C1/C3 Symbiodinium. However, nine of 12 P. tuberculosa examined, as well as one P. mutuki possessed clade D Symbiodinium, were previously hypothesized to be tolerant to extreme hot or cold temperatures. Our results demonstrate the necessity of further worldwide zoanthid sampling in order to property understand the distribution and diversity of zooxanthellate zoanthids and their Symbiodinium.