Inferring the distribution of octocorals Nanipora and Heliopora along the coast of the Kerama Islands, Okinawa, Japan, by eDNA metabarcoding

Two zooxanthellate octocorals, Heliopora coerulea and Nanipora kamurai (family Helioporidae, order Scleralcyonacea, class Octocorallia), produce aragonite calcium carbonate skeletons similar to those of scleractinian hexacorals and contribute to the formation of complex coral reef ecosystems. H. coerulea is known to occur along the coasts of the Kerama Islands, Okinawa, Japan and N. kamurai was originally described from the Kerama Islands. An environmental DNA metabarcoding (eDNA-M) method has recently been introduced for comprehensive surveys of zooxanthellate scleractinian corals, supplementing conventional visual census by SCUBA diving or snorkeling. In particular, the Scl-eDNA-M system, which targets mitochondrial 12S rDNA for eDNA amplification, has proven to be an efficient tool for taxonomically identifying nearly all scleractinian genera reported in Japan. Moreover, our recent study showed that Heliopora can also be detected using the Scl-eDNA-M system. This study is the first to examine whether the Scl-eDNA-M is also applicable for the eDNA-based identification of Nanipora . Analyses of primer composition for PCR amplification and metabarcoding of eDNAs sampled from the Kerama Islands confirmed that Nanipora can be detected by this method. Importantly, the results of this study demonstrated that the overall distribution of Nanipora differs from that of Heliopora . Whereas Nanipora was distributed along the coasts of the inland sea of the Keramas, Heliopora occurred mainly along the exposed outer coasts, with only one site hosting both species. Although such differential distributions need to be confirmed by further visual census survey, this study highlights the efficiency of eDNA-M system for broad surveys of zooxanthellate octocorals.