Molecular Phylogeny Demonstrates the Need for Taxonomic Reconsideration of Species Diversity of the Hydrocoral Genus Millepora (Cnidaria: Hydrozoa) in the Pacific.

Millepora (Cnidaria: Hydrozoa: Milleporidae) spp. are distributed throughout shallow subtropical and tropical marine environments in the Indo-Pacific and Caribbean-Atlantic, and have traditionally been identified using pore characteristics and colony form. Until now, representatives of Millepora spp. on the island of Okinawa-jima, Japan, have been divided into five species; three branching species (Millepora intricata, M. tenera, M. dichotoma), one species with plate-like morphology (M. platyphylla), and one encrusting species (M. exaesa). There have been only a few reports from the Indo-Pacific that have studied the genetic diversity within Millepora spp., although phylogenetic analyses in the Caribbean-Atlantic have proven useful in delimiting closely-related species, while demonstrating that morphologically-based identification systems may have problems. In the present study, we sought to clarify taxonomic confusion of Millepora spp. in the Pacific by using sequence data of the ribosomal internal transcribed spacer (ITS-rDNA) of specimens from Okinawa, Japan and other localities (Johnston Atoll, Great Barrier Reef). Four separate clades were recovered from the ITS-rDNA analyses. Although we examined specimens of all three branching Millepora spp. previously reported from Okinawa-jima Island, in our phylogenetic analyses they were concentrated within a single clade, with only three specimens in other clades. Encrusting Millepora specimens were found within all clades, although it should be noted all species initially start as encrusting forms, and plate-like specimens were found within three clades. Our data also point to the existence of a previously unknown lineage within Millepora characterized by its ability to overgrow live scleractinian corals.

Extremely low genetic variability within and among locations of the greenfish holothurian Stichopus chloronotus Brandt, 1835 in Okinawa, Japan.

The greenfish sea cucumber Stichopus chloronotus is an economically and ecologically important sea cucumber species throughout its range. This species is widely distributed, inhabiting coral reefs of the Indo-Pacific Ocean. Our study evaluated population genetic structure and levels of genetic diversity in southern Japan. A total of 180 individuals were collected from eight locations from Okinawa and Okinoerabu Islands and sequenced using mitochondrial 16S ribosomal DNA (16S) and nuclear histone H3 (H3) gene. Only three 16S haplotypes were detected (518 bp) with haplotype diversity ranging from 0 to 0.56 and nucleotide diversity from 0 to 0.1%. H3 showed no variation among the studied locations. It is plausible that such results could be due to a shift to asexual reproduction. Additionally, the presence of the species on the east coast of Okinawa could only be detected in one location and all individuals consisted of a single haplotype. Genetic differences between the east and west coasts of Okinawa have been noticed in other coral reef organisms, and attributed to either ecological or biogeographical historical differences between the coasts due to differing levels of isolation during Pleistocene ice ages. Results from the present study should inform management and conservation policies of S. chloronotus in southern Japan.