Central Ryukyu Islands Research Articles

Biogeographical patterns of the porcelaneous larger foraminifer Alveolinella quoyi through the integration of fossil data

In the present-day Indo-Pacific coral-reef settings two genera of alveolinoidean porcelaneous larger benthic foraminifera (LBF) occur, namely Alveolinella and Borelis. Alveolinella is represented by a single species, A. quoyi, whose northernmost record is in Okinawa-jima (central Ryukyu Islands, Japan). Although the Indo-Pacific area, and especially the Coral Triangle, is a biodiversity hotspot since the Early Miocene, in-depth investigation on fossil representatives of present-day LBF is limited to a few taxa. To help bridge this knowledge gap, the palaeobiogeographical dynamics of A. quoyi is assessed. Analysis of data from the palaeontological literature shows that its first appearance datum is from the Tortonian (Late Miocene) of East Kalimantan and Papua New Guinea. In the Pliocene–Pleistocene the Indonesian Throughflow constrained the species within the Central Indo-Pacific. Finally, during the Late Pliocene the northward migrants arrived in the shallow-water carbonate settings of Okinawa-jima where the species is still thriving.

Paleoenvironmental significance of growth story of long-living deep-water acervulinid macroids from Kikai-jima shelf, Central Ryukyu Islands, Japan

Macroids are unattached centimetre-sized nodules built by encrusting invertebrates. Encrusting foraminifera (Acervulina inhaerens) and subordinate thin coralline algae form extensive macroid beds on sandy and gravelly bioclastic carbonates off Kikai-jima, on a coral-reef-related island shelf, in the Central Ryukyu Islands, Japan. At water depths from 75 to 100 m, the beds consist of spheroidal and sub-spheroidal macroids, c. 6 cm in mean diameter, with asymmetric concentric inner arrangement. The macroids are bioeroded by Entobia, Maeandropolydora, Trypanites, Gastrochaenolites, and microborings. They generally show two distinct growth stages separated by an abraded rugged surface deeply colonized by borers, mainly Entobia. Radiocarbon dating yielded an oldest age of c. 4400 cal yr BP for the earliest acervulinid growth, whereas the second stages were much younger, ranging in age from c. 1500 cal yr BP to present day. Datings of the two growth stages in five specimens indicate that active growth and growth interruption were not synchronous in the different nodules. For c. 4400 years the macroids grew within an estimated maximum range of palaeotemperature changes of c. 4.7 °C, under chronic oligotrophic to mesotrophic conditions, low-level hydrodynamism and low sedimentation rates. The lack of synchroneity among individual macroids rules out catastrophic events and ecosystem-wide environmental changes as possible causes of growth interruption. Random biogenic mobilization and temporal occupation of the macroid surface by organisms with no rigid skeleton and/or biofilms likely interrupted acervulinid growth at individual macroid scale. The environmental conditions in which Kikai-jima macroid beds develop do not support interpretations of acervulinid macroid accumulations during Paleocene−Eocene Thermal Maximum (PETM) and Middle Eocene Climatic Optimum (MECO) events in the Western Tethys as indicators of eutrophic conditions.

Intraspecific divergence in a coastal plant, Euphorbia jolkinii, at a major biogeographic boundary in East Asia.

Quaternary climatic fluctuations and long-distance seed dispersal across the sea are critical factors affecting the distribution of coastal plants, but the spatiotemporal nature of population expansion and distribution change of East Asian coastal plants during this period are rarely examined. To explore this process, we investigated the genome-wide phylogenetic patterns of Euphorbia jolkinii Boiss. (Euphorbiaceae), which grows widely on littoral areas of Japan, Korea, and Taiwan. We used plastome sequences and genome-wide single nucleotide polymorphisms in samples across the species range to reveal phylogeographic patterns and spatiotemporal distributional changes. We conducted ecological niche modeling for the present and the last glacial maximum (LGM). Genetic differentiation was observed between the northern and southern populations of E. jolkinii, separated by the major biogeographic boundary, the Tokara Gap. These two groups of populations differentiated during the glacial period and subsequently intermingled in the intermorainic areas of the central Ryukyu Islands after the LGM. Ecological niche models suggested that the potential range of E. jolkinii was restricted to southern Kyushu; however, it was widespread in the southern Ryukyu Islands and Taiwan during the LGM. This study provides evidence of genetic differentiation among coastal plant populations separated by the prominent biogeographical boundary. Although coastal plants are typically expected to maintain population connectivity through sea-drifted seed dispersal, our findings suggest that genetic differences may arise because of a combination of limited gene flow and changes in climate during the glacial period.

A new species of the larger porcelaneous foraminifer Borelis provides novel insights into Neogene to Recent western Pacific palaeobiogeographical dispersal patterns

Only three species of alveolinoidean larger foraminifera occur in present-day tropical shallow-water marine settings. Alveolinella quoyi thrives in the Central Indo-Pacific and Eastern Indo-Pacific, Borelis pulchra in the Central and Eastern Indo-Pacific and in the central Atlantic, whereas Borelis schlumbergeri inhabits the Indo-Pacific Ocean. The northernmost record is that of Alveolinella quoyi from the shallow-water settings in Okinawa (central Ryukyu Islands, Japan). A new porcelaneous larger foraminiferal species, Borelis matsudai sp. nov. (Alveolinoidea, Borelinae), is established herein, based on specimens discovered in present-day shallow-water sediments from Sekisei Lagoon, southern Ryukyu Islands (Japan). This is the northernmost record of the genus in the western Indo-Pacific Warm Pool. The architectural characters of this species suggest its phylogenetic relationship with the Borelis pulchra group. A comprehensive literature survey of fossil and modern records of Borelis pulchra over the past 30 million years shows that the Middle Miocene constriction of the Indonesian Seaway and the Late Miocene–Early Pliocene restriction of the Indonesian Throughflow impacted the species-level dispersal of this species in the Indo-Australian Archipelago. Driven by the Kuroshio dispersal route Borelis matsudai sp. nov. likely appeared in the southern and central Ryukyu Islands at least from the Chibanian (Middle Pleistocene). This species represents a marginal part of a population in significant contact with its ancestor (B. pulchra), which is widespread southward since the Oligocene (Philippines). With ongoing global warming possible occurrences of Borelis matsudai sp. nov. in the northern Ryukyu Islands, where it has not yet been found, are expected. The Sekisei Lagoon represents, therefore, a biogeographical stepping stone relay station in northward migration of the shallow-water benthic organisms along the Kuroshio dispersal route.

Geographic Distribution and Genetic Structures of the Tideland Snails Pirenella nipponica and P.asiatica in Taiwan and Japan.

The tideland snails Pirenellanipponica and Pirenellaasiatica are distributed north of the central Ryukyu Islands and in South Ryukyu, respectively, in Japan. To reveal their distribution and genetic characteristics in Taiwan, we sampled Pirenella snails along the western coast of Taiwan Island and analyzed the nucleotide sequences of their mitochondrial DNAs. Pirenella nipponica and P. asiatica inhabit the northern and southern parts of the western coast of Taiwan, respectively, and coexist only in the central part. Taiwanese and Japanese populations of P. asiatica showed significant genetic differentiation. The former showed higher genetic diversity and a larger effective population size than the latter. However, the Taiwanese population of P. nipponica was not genetically deviated from the local Japanese population on Kyushu Island. Both the Taiwan and Kyushu populations of P. nipponica showed significant genetic differences from local populations in other regions of Japan, namely, Honshu Island (the Japanese mainland) and Central Ryukyu. They also showed higher genetic diversity and a larger effective population size than the others. The Taiwanese populations of both species might be part of a large panmictic population with individuals from the Asian continent and Kyushu Island.

Boring bivalve traces in modern reef and deeper-water macroid and rhodolith beds

Macroids and rhodoliths, made by encrusting acervulinid foraminifera and coralline algae, are widely recognized as bioengineers providing relatively stable microhabitats and increasing biodiversity for other species. Macroid and rhodolith beds occur in different depositional settings at various localities and bathymetries worldwide. Six case studies of macroid/rhodolith beds from 0 to 117 m water depth in the Pacific Ocean (northern Central Ryukyu Islands, French Polynesia), eastern Australia (Fraser Island, One Tree Reef, Lizard Island), and the Mediterranean Sea (southeastern Spain) show that nodules in the beds are perforated by small-sized boring bivalve traces (Gastrochaenolites). On average, boring bivalve shells (gastrochaenids and mytilids) are more slender and smaller than those living inside shallow-water rocky substrates. In the Pacific, Gastrochaena cuneiformis, Gastrochaena sp., Leiosolenus malaccanus, L. mucronatus, L. spp., and Lithophaga/Leiosolenus sp., for the first time identified below 20 m water depth, occur as juvenile forms along with rare small-sized adults. In deep-water macroids and rhodoliths the boring bivalves are larger than the shallower counterparts in which growth of juveniles is probably restrained by higher overturn rates of host nodules. In general, most boring bivalves are juveniles that grew faster than the acervulinid foraminiferal and coralline red algal hosts and rarely reached the adult stage. As a consequence of phenotypic plasticity, small-sized adults with slow growth rates coexist with juveniles. Below wave base macroids and rhodoliths had the highest amounts of bioerosion, mainly produced by sponges and polychaete worms. These modern observations provide bases for paleobiological inferences in fossil occurrences.

First record of Propagurus haigae (McLaughlin, 1997) (Decapoda, Anomura, Paguridae) from Japan

Abstract Propagurus haigae (McLaughlin, 1997), a relatively large-sized species of Paguridae, is reported for the first time from Japanese waters based on a single specimen collected from a depth of 620 m off Ie Island, central Ryukyu Islands, southwestern Japan. It is the third species of the genus Propagurus McLaughlin & de Saint Laurent, 1998 known from Japanese waters. The present specimen greatly extends the distribution range of P. haigae, because the previous northernmost record was the Molucca Sea in Indonesia.

Deep-Water Macroid Beds of the Ryukyu Islands, Japan: Encrusting Acervulinids as Ecosystem Engineers

Bassi, D.; Iryu, Y.; Humblet, M.; Matsuda, H.; Machiyama, H.; Sasaki, K.; Matsuda, S.; Arai, K., and Inoue, T., 2019. Deep-water macroid beds of the Ryukyu Islands, Japan: Encrusting acervulinids as ecosystem engineers. Journal of Coastal Research, 35(2), 463–466. Coconut Creek (Florida), ISSN 0749-0208.Encrusting acervulinid foraminifera can produce centimeter-sized, free-living coated grains named macroids. Macroid beds are an interesting feature of subtidal environments and have been recognized as important carbonate producers, habitat-forming structures, and paleoenvironmental indicators. Macroids provide a hard, three-dimensional substrate serving as microhabitat for a wide range of diverse organisms. As yet, the most extensive known occurrence of macroid beds in the western Pacific Ocean is found on the insular shelf of Kikai-jima, a coral reef–related island in the central Ryukyu Islands. The surveyed beds occur at water depth of 61–105 m arrayed on a ca. 6-km2 area. Despite their importance for the benthic communities of the Ryukyu Islands, only in the last decade have sampling efforts led to a more comprehensive understanding of the beds' distribution, their structure and associated communities, and the data concerning the influence of environmental factors on macroid beds and their ecological dynamics. In this study, the available information on the biodiversity associated with the recently described Ryukyu macroid beds are reviewed. This review is intended to inform and influence future research and policy planning on this largely unexplored, highly diverse marine ecosystem.

Intraspecific Variation of Eysarcoris guttigerus (Hemiptera: Pentatomidae) in Japanese Southwest Population Based on Mitochondrial DNA.

The white-spotted globular bug Eysarcoris guttigerus (Thunberg) (Hemiptera: Pentatomidae) is widely distributed in East Asia and the Pacific region. In Japan, the species is found in grassy or composite weeds in the western area of the main islands and Ryukyu Islands of Japan. One notable characteristic of the Eysarcoris genus is the two white spots on the scutellum. This is not the case with the Ishigaki Island population, however, which sports red spots instead of white, suggesting that intraspecific variation exists in the species. Therefore, we investigated intraspecific variation in E. guttigerus using mitochondrial NADH dehydrogenase subunit 2 (ND2), cytochrome oxidase subunit 1 (CO1), cytochrome b (Cytb), tRNA-Serine (tRNAser), NADH dehydrogenase subunit 1 (ND1), and 16S ribosomal RNA (16SrRNA) genes from 13 populations of Japan. The obtained maximum likelihood phylogenetic tree was divided into three groups—Group 1: Mainland, Group 2: Central Ryukyu Islands (Okinawa-Amamioshima Islands), and Group 3: South Ryukyu Islands (Ishigaki Island). The Ishigaki population was significantly separated from the other populations with consistent differences in spot color. The estimated period of divergence between the Ishigaki population and the other populations was consistent with the period of formation of the Kerama Gap in the Ryukyu arc. Thus, the process of formation of the Kerama Gap may have influenced the intraspecific variation of E. guttigerus.

An extraordinary case in human history: Prehistoric hunter-gatherer adaptation to the islands of the Central Ryukyus (Amami and Okinawa archipelagos), Japan

The islands of the Central Ryukyus (Amami and Okinawa archipelagos), Japan, were continuously occupied by hunter-gatherers for several thousand years during the Holocene. This occupation would seem to represent a unique example of island settlement by hunter-gatherers. Homo sapiens had expanded into all continents except Antarctica by 10,000 BP, demonstrating high adaptability to various environments, but few islands had been settled by that time. Most islands appear to have been too small to support hunter-gatherer subsistence. Many islands were indeed first colonized by agriculturalists. Some islands located close to large landmasses, having a large surface area, or with reliable sea mammal populations or translocated plants and animals were successfully colonized by hunter-gatherers, but none of these features characterize the prehistoric Central Ryukyu Islands, which were successfully colonized by hunter-gatherers by at least the early–middle Holocene. Furthermore, this colonization was likely accomplished with smaller populations and foraging territories than previously documented for hunter-gatherers. Coral reef resources with nuts (and possibly yams) appear to have played a crucial role in this island colonization. The only similar case to prehistoric Okinawa comes from the Andaman Islands, where hunter-gatherers have occupied small tropical islands for thousands of years. The final part of this paper provides a brief comparison of the Andaman data in light of the results from the Central Ryukyus described here.

An Attempt at Captive Breeding of the Endangered Newt Echinotriton andersoni, from the Central Ryukyus in Japan.

Simple SummaryWe naturally bred the endangered Anderson’s crocodile newt (Echinotriton andersoni) and tested a laboratory farming technique using near-biotopic breeding cages with several male and female pairs collected from Okinawa, Amami, and Tokunoshima Islands. This is the first published report of successfully propagating an endangered species by using breeding cages in a laboratory setting for captive breeding. Our findings on the natural breeding and raising of larvae and adults are useful in breeding this endangered species, and can be applied to the preservation of other similarly wild and endangered species.Anderson’s crocodile newt (Echinotriton andersoni) is distributed in the Central Ryukyu Islands of southern Japan, but environmental degradation and illegal collection over the last several decades have devastated the local populations. It has therefore been listed as a class B1 endangered species in the IUCN Red List, indicating that it is at high risk of extinction in the wild. The species is also protected by law in both Okinawa and Kagoshima prefectures. An artificial insemination technique using hormonal injections could not be applied to the breeding of this species in the laboratory. In this study we naturally bred the species, and tested a laboratory farming technique using several male and female E. andersoni pairs collected from Okinawa, Amami, and Tokunoshima Islands and subsequently maintained in near-biotopic breeding cages. Among 378 eggs derived from 17 females, 319 (84.4%) became normal tailbud embryos, 274 (72.5%) hatched normally, 213 (56.3%) metamorphosed normally, and 141 (37.3%) became normal two-month-old newts; in addition, 77 one- to three-year-old Tokunoshima newts and 32 Amami larvae are currently still growing normally. Over the last five breeding seasons, eggs were laid in-cage on slopes near the waterfront. Larvae were raised in nets maintained in a temperature-controlled water bath at 20 °C and fed live Tubifex. Metamorphosed newts were transferred to plastic containers containing wet sponges kept in a temperature-controlled incubator at 22.5 °C and fed a cricket diet to promote healthy growth. This is the first published report of successfully propagating an endangered species by using breeding cages in a laboratory setting for captive breeding. Our findings on the natural breeding and raising of larvae and adults are useful in breeding this endangered species and can be applied to the preservation of other similarly wild and endangered species such as E. chinhaiensis.

Taxonomic reexamination of Portulaca okinawensis (Portulacaceae) in<br />the Ryukyu Archipelago of Japan based on molecular and morphological data

We used molecular phylogenetic and morphological data to reexamine the taxonomic status of Portulaca okinawensis (≡ P. pilosa subsp. okinawensis) endemic to the central Ryukyu islands, southwestern Japan. Our molecular analyses showed that P. okinawensis is monophyletic, sister to the clade of P. psammotropha and P. tuberosa and it is not closely related to P. pilosa subsp. pilosa. Two subclades, one comprising plants from the Okinawa Islands and the other from the Amami Islands, were recognized. The plants from the Okinawa Islands had more than 20 stamens, orange-yellow nallowly obovate to oblanceolate petals, and reddish-green stems (as the holotype), while the plants from the Amami Islands had less than 20 stamens, lemon-colored obovate petals, and bright-green stems. The molecular and morphological data support a taxonomic treatment of Walker & Tawada (1951) regarding P. okinawensis as a separate species, also suggesting that the plants from the Amami and Okinawa islands should be treated as different taxa. A new variety Portulaca okinawensis var. amamiensis was here described.

The first zoeal stage morphology of Crossotonotus spinipes (De Man, 1888) and Pseudopalicus serripes (Alcock & Anderson, 1895), with implications for palicoid systematics (Crustacea: Brachyura: Palicoidea)

Traditionally, Crossotonotus spinipes (De Man, 1888) and Pseudopalicus serripes (Alcock & Anderson, 1895) were as-signed to the Crossotonotinae Moosa & Serène, 1981, and Palicinae Bouvier, 1898, respectively. However, Ng et al.(2008: 127) listed a number of major adult characters that suggested both subfamilies should be recognised as distinct fam-ilies within the Palicoidea Bouvier, 1898 (see also Castro 2010, 2011; Guinot et al. in prep.). Recently, ovigerous speci-mens of C. spinipes and P. serripes were collected from Okinawajima and Kumejima, central Ryukyu Islands, Japan. Thefirst zoeal stages of both species were hatched in the laboratory, dissected, examined, and the appendages illustrated anddescribed. Crossotonotus spinipes first stage zoeas were distinguished by three characters: the absence of lateral carapacespines (present in P. serripes), abdominal somite 4 with a pair of dorsolateral processes directed ventrally (absent in P.serripes) and the presence of a small lateral spine on the telson (absent in P. serripes). These distinguishing features appear to support the recent division of the Palicoidea into two families.

Recent macroids on the Kikai‐jima shelf, Central Ryukyu Islands, Japan

ABSTRACTSandy and gravelly carbonate sediments found off Kikai‐jima, southern Japan, a coral reef‐related island shelf, represent the northernmost sub‐tropical, carbonate deposits in the Central Ryukyu Islands (Ryukyus). On the Kikai‐jima shelf, at water depths of 61 to 105 m, these sediments are characterized by macroid pavements. Since the abundance of very small and of exceptionally large macroids may indicate specific hydrodynamic controls regarding constraints on growth and taphonomy, the detailed analysis of recent and fossil macroid pavements is meaningful ecologically and environmentally. Macroids, ranging in size from ca 25 to 130 mm in diameter, are spheroidal and sub‐spheroidal in shape and consist mainly of the encrusting foraminifer Acervulina inhaerens and subordinate thin encrusting and lumpy coralline algae. Accessory components include bryozoans, serpulids and, to a lesser extent, encrusting arborescent foraminifera (Homotrema and Miniacina). Low sedimentation rates and occasional movement due to current action are indicated by sizes, shapes and growth‐forms of the studied macroids, the Entobia–Gastrochaenolites–Trypanites–Maeandropolydora ichnocoenosis and the ‘Bioerosion Index’ for coated grains (introduced herein). The deep‐water tidally induced current energy was sufficient to maintain multi‐directional growth (spheroidal shapes) of the larger macroids and to initiate macroid growth using the diverse biogenic remnants as nuclei. The asymmetrical inner arrangement suggests possible periods of stability for the macroids. The residence time of the coated grain in its original environment determines the size and morphology of the macroid and the selection of coating organisms. The composition of the coating community is mainly a consequence of component growth rates in relation to turnover time and residence time. Long‐term studies are needed to assess the spatial and temporal resolution of present‐day encrusting communities across biogeographic provinces and shelf to slope regions.

Carbon- and oxygen-isotope compositions of a modern deep-water brachiopod Campagea japonica collected off Aguni-jima, Central Ryukyu Islands, southwestern Japan

We present carbon- and oxygen-isotope compositions in a shell (δ13CS and δ18OS, respectively) of a modern brachiopod Campagea japonica collected at a water depth of 606 m off Aguni-jima, Central Ryukyu Islands, southwestern Japan. The δ13CS and δ18OS profiles of the outermost portions of the secondary shell layer along the axis of shell growth do not display significant seasonal variations. The δ13CS values display a gradual decrease with growth, whereas the δ18OS values are nearly constant. The δ13CS and δ18OS values along a particular growth line and from the inner shell surface are rather constant. The δ13CS values near the posterior shell edge of the ontogenetic series and the δ18OS values near the anterior shell edge of the inner series fall within the ranges of δ13C and δ18O values of calcite in equilibrium with ambient seawater (equilibrium calcite) (δ13CEC and δ18OEC, respectively). Therefore, they are the best portions to use as proxies of δ13C values of dissolved inorganic carbon (δ13ODIC) and temperature and/or δ18O values of seawater (δ18OSW), respectively. The δ13CS values of the ontogenetic series near the anterior shell edge and the entire isochronous and inner series display the smallest decrease (less than ~0.2‰) compared with the δ13CEC values. The δ18OS values of the entire ontogenetic series and an interior part of the inner series are slightly greater (less than ~0.3‰) than the δ18OEC values. Thus, these portions can be used as paleoenvironmental proxies if appropriate corrections are made. A significant positive correlation is recognized between the δ13CS and δ18OS values for the ontogenetic-series samples, which can be ascribed to a kinetic isotope effect. A metabolic isotope effect is not evident for the δ18OS values in these samples. Our study provides useful information for the appropriate selection of brachiopod taxa and shell portions that reflect isotopic composition of ambient seawater for paleoenvironmental studies.

Genetic variation of the white-spotted longicorn beetle Anoplophora spp. (Coleoptera: Cerambycidae) in Japan detected by mitochondrial DNA sequence

Genetic variation of the white-spotted longicorn beetle Anoplophora spp., distributed on the Japanese mainland and the Ryukyu Islands, was examined using nucleotide sequences of mitochondrial DNA. Two fragments, a 1.2-kb-long fragment containing portions of the cytochrome oxidase subunit I and II genes and a 1.4-kb-long fragment containing portions of 16S and 12S rDNAs, were sequenced. In phylogenetic analyses based on the sequences, 294 individuals collected at 75 localities were divided into two major groups (groups A and B) and then split into seven subgroups (A1–A4 and B1–B3). In group A, the closely related subgroups A1, A2, and A3 were mainly distributed on the Japanese mainland and were roughly separated among geographic areas, although the range of A3 spread significantly from Kyushu to the Central Ryukyu Islands. The sequence of A4, detected from one individual collected in eastern Honshu, was almost the same as that reported for A. chinensis (Forster) on the Chinese continent. In group B, subgroups B1 and B2 were restricted to the Central and Southern Ryukyu Islands, respectively, while B3 was distributed widely in both regions. Based on the results, we discuss the geographic origin of the haplotypes and movement of the insects between geographic areas.

Variations in Pleistocene coral assemblages in space and time in southern and northern Central Ryukyu Islands, Japan

We studied the taxonomic and morphological compositions of Pleistocene coral assemblages in 24 quadrats in Okinawa-jima, southern Central Ryukyus, and in 14 quadrats in Kikai-jima, northern Central Ryukyus. A total of 72 species belonging to 35 genera were identified in Okinawa-jima, whereas 65 species coming under 33 genera were recorded in Kikai-jima. Cluster analysis of the Bray-Curtis (BC) similarity coefficient produced 8 coral associations and 3 ungrouped taxa; they correspond to a wide range of reef environments, from shallow lagoon to lower reef-slope settings. The analysis of taxonomic similarities among quadrats leads to the identification of 7 clusters and 5 isolated quadrats. The segregation of quadrats indicating a same reef zone into distinctive groups or single branches in the cluster diagram reflects the within-reef-slope variability in community structure. Specifically, encrusting Acropora palifera, indicative of the upper reef-slope zone, shows a great variability of associated coral species and morphologies. We also report differences in the geographic distribution of Acropora palifera and Platygyra contorta between present-day and Pleistocene reefs, which may be linked to changes in sea surface temperature. The decrease in the total species and generic richness recorded in modern reefs is not clearly detected in the fossil record. In addition, MDS ordination of the BC similarities highlights patterns of reef zonation and geographic differences in taxonomic composition. One-way tests of similarity (ANOSIM) show that differences in the composition of upper reef-slope coral assemblages between Okinawa-jima and Kikai-jima are not larger than those observed between southern and central Okinawa-jima. Finally, we report various types of coral successions. Sea-level changes resulted in transitions from one reef zone to another, whereas local disturbances are likely to have been responsible for the successions of distinctive coral assemblages with overlapping depth ranges, which reflect the within-reef-zone variability.

Spatial and Temporal Variations in Pleistocene Coral Assemblages in the South and Central Ryukyu Islands

Spatial and Temporal Variations in Pleistocene Coral Assemblages in the South and Central Ryukyu Islands

Genetic variation of the green chafer, Anomala albopilosa (Hope) (Coleoptera: Scarabaeidae), in the Ryukyu Islands of Japan detected by mitochondrial DNA sequences

In the Ryukyu Islands of Japan, larvae of the green chafer Anomala albopilosa (Hope) are known as a serious pest of sugarcane. Based on sequences of mitochondrial ribosomal RNA genes obtained from specimens collected in this and adjacent areas, the phylogenetic relationships among local populations and geographic distribution patterns of haplotypic groups were examined. As a result, individuals were divided into five groups of haplotypes (Groups A–E). The shape of the phylogenetic trees suggested that they have been separated for a long period in their evolutionary history. Among the three groups distributed in the Ryukyu Islands, Groups B and D were restricted to the northern Amami region and Yaeyama region, respectively, while the range of Group C extended from the Amami to Yaeyama regions through the Okinawa and Miyako regions and largely overlapped the other two groups. This result was considered to suggest that the insular populations of this species were genetically muddled by the recent expansion of Group C that probably originated in the Okinawa region in the central Ryukyu Islands. Causes of these phenomena are discussed in relation to the food habits of this species and the paleogeography of this area.

Two new species of freshwater crab (Crustacea: Decapoda: Potamidae) from Tokashiki Island, central Ryukyu Islands, Japan

Two new species of freshwater crabs are described from Tokashiki Island, the central Ryukyu Islands, Japan. Candidiopotamon tokashikense sp. nov. can be distinguished from the closest congener, C. kumejimense, by the shape of the terminal segment of the male first gonopod and the armature of the outer dorsal margin of the second ambulatory propodus. Amamiku occulta, sp. nov. is differentiated from its only congener, A. amamensis, by the shape of the terminal segment of the male first gonopod and the form of the supraorbital margin of the carapace. Candidiopotamon tokashikense and A. occulta are superficially very similar, but they can be differentiated from each other by the relative length of the antenna, the shape of the male first gonopod, and the relative width of female abdominal segments. A key to the species of Candidiopotamon and Amamiku is provided.