Reference DNA barcodes and other mitochondrial markers for identifying Caribbean Octocorals

DNA barcoding is a useful tool for documenting the diversity of metazoans. The most commonly used barcode markers, 16S and COI, are not considered suitable for species identification within some "basal" phyla of metazoans. Nevertheless metabarcoding studies of bulk mixed samples commonly use these markers and may obtain sequences for "basal" phyla. We sequenced mitochondrial DNA fragments of cytochrome oxidase c subunit I (COI), 16S ribosomal RNA (16S), NADH dehydrogenase subunits 2 (16S-ND2), 6 (ND6-ND3) and 4L (ND4L-MSH) for 27 species of Caribbean octocorals to create a reference barcode dataset and to compare the utility of COI and 16S to other markers more typically used for octocorals. The most common genera (Erythropodium, Ellisella, Briareum, Plexaurella, Muriceopsis and Pterogorgia) were effectively distinguished by small differences (5 or more substitutions or indels) in COI and 16S sequences. Gorgonia and Antillogorgia were effectively distinguished from each other by unique haplotypes, but the small genetic differences make distance approaches ineffective for these taxa. Plexaura, Pseudoplexaura and Eunicea were indistinguishable from each other but were generally effectively distinguished from other genera, further supporting the idea that these genera have undergone a rapid endemic radiation in the Caribbean.