Ishigaki Island Research Articles

Characteristics of Residential Locations and Demographic Structural Trends of the Shiraho Rural Settlement on Ishigaki Island

This study clarifies three things about the housing environment that should be considered when planning future community vitalizations through collaborations among people on remote island regions with different origins and immigration motives. First, it identifies the factors that influenced the residential composition of Shiraho. Second, it classifies residents by origin. Third, it identifies the characteristics of residential locations according to the residents′ origins and immigration timing. The results show that the residential composition of Shiraho changed in four stages. Regarding the spatial distribution of households in the residential areas of Shiraho, similar Shuriners and similar Taramanians resided in respective clusters, which were spatially separate from Shirahonians. Recent immigration of outsiders changed the distribution of the old residential area, but in some cases they came to reside in newly opened areas that other residents avoided for various reasons.

Using molluscan assemblages from paleotsunami deposits to evaluate the influence of topography on the magnitude of late Holocene mega-tsunamis on Ishigaki Island, Japan

Four ancient tsunami deposits were identified in a trench excavated on Ishigaki Island, Okinawa, Japan. Three of the tsunami deposits (T-I, T-II, and T-IV) consist of calcareous sand beds, whereas the other (T-III, located stratigraphically between T-II and T-IV) consists of boulders. Deposit T-I was caused by a tsunami in 1771. 14C dating, together with the elevations of the landward margins of these sandy tsunami deposits, suggests that tsunamis II and IV were similar in size to the 1771 tsunami, although the influence of local topographic features on the magnitudes of tsunamis has not yet been examined. This study reconstructs the local topographic features by comparing the molluscan assemblages incorporated within the tsunami deposits with those in recent beach deposits. The presence of species that inhabit the intertidal zone in lagoonal settings in all the assemblages indicates that the present-day shallow lagoon has been present off the study area since the occurrence of tsunami T-IV, which supports the previous hypothesis that the magnitudes of the 1771 tsunami and tsunamis II and IV were similar. These molluscan assemblages also suggest that a high relative abundance of large, heavy mollusc shells is a feature of the paleotsunami deposits in the coastal lowlands found along the shallow coral lagoons.

Micro-distribution of Four Species of Neritid Gastropods in an Upper Mangrove Area, Ishigaki Island, Japan

Micro-distribution of Four Species of Neritid Gastropods in an Upper Mangrove Area, Ishigaki Island, Japan

Assessment of Machine Learning Algorithms for Automatic Benthic Cover Monitoring and Mapping Using Towed Underwater Video Camera and High-Resolution Satellite Images

Benthic habitat monitoring is essential for many applications involving biodiversity, marine resource management, and the estimation of variations over temporal and spatial scales. Nevertheless, both automatic and semi-automatic analytical methods for deriving ecologically significant information from towed camera images are still limited. This study proposes a methodology that enables a high-resolution towed camera with a Global Navigation Satellite System (GNSS) to adaptively monitor and map benthic habitats. First, the towed camera finishes a pre-programmed initial survey to collect benthic habitat videos, which can then be converted to geo-located benthic habitat images. Second, an expert labels a number of benthic habitat images to class habitats manually. Third, attributes for categorizing these images are extracted automatically using the Bag of Features (BOF) algorithm. Fourth, benthic cover categories are detected automatically using Weighted Majority Voting (WMV) ensembles for Support Vector Machines (SVM), K-Nearest Neighbor (K-NN), and Bagging (BAG) classifiers. Fifth, WMV-trained ensembles can be used for categorizing more benthic cover images automatically. Finally, correctly categorized geo-located images can provide ground truth samples for benthic cover mapping using high-resolution satellite imagery. The proposed methodology was tested over Shiraho, Ishigaki Island, Japan, a heterogeneous coastal area. The WMV ensemble exhibited 89% overall accuracy for categorizing corals, sediments, seagrass, and algae species. Furthermore, the same WMV ensemble produced a benthic cover map using a Quickbird satellite image with 92.7% overall accuracy.

Pelagic larval duration, growth rate, and population genetic structure of the tidepool snake moray Uropterygius micropterus around the southern Ryukyu Islands, Taiwan, and the central Philippines.

The relationships between pelagic larval duration (PLD) and geographic distribution patterns or population genetic structures of fishes remain obscure and highly variable among species. To further understand the early life history of the tidepool snake moray Uropterygius micropterus and the potential relationship between PLD and population genetic structure of this species, otolith microstructure and population genetics based on concatenated mtDNA sequence (cytochrome b and cytochrome oxidase subunit I, 1,336 bp) were analyzed for 195 specimens collected from eight locations around the southern Ryukyu Islands, Taiwan, and the central Philippines. Eels with longer PLD and lower otolith growth rates were observed at relatively higher latitudes with lower water temperatures (54.6 ± 7.7 days and 1.28 ± 0.16 µm day−1 on Ishigaki Island, Japan, vs. 43.9 ± 4.9 days and 1.60 ± 0.19 µm day−1 on Badian, the Philippines), suggesting that leptocephali grew faster and had shortened pelagic periods in warmer waters. Meanwhile, the eels along the southwest coast of Taiwan had relatively longer PLD (57.9 ± 10.5 days), which might be associated with the more complex ocean current systems compared to their counterparts collected along the east coast of Taiwan (52.6 ± 8.0 days). However, the southwestern and eastern Taiwan groups had similar otolith growth rates (1.33 ± 0.19 µm day−1 vs. 1.36 ± 0.16 µm day−1). Despite the intergroup variation in PLD, genetic analysis revealed fluent gene flow among the tidepool snake morays in the study regions, implying that intraspecies PLD variation had a weak effect on genetic structure. The leptocephalus stage might have ensured the widespread gene flow among the study areas and leptocephalus growth was likely influenced by regional water temperature.

Dependence of fish on subtropical riverine mangroves as habitat in the Ryukyu Islands, Japan

To examine whether fish were dependent on mangrove habitat in the Ryukyu Islands (southern Japan), fish assemblage structures were compared on the downstream side between mangrove-rich and mangrove-free rivers on Ishigaki and Okinawa Islands in 2014 and 2015. The mean species richness and abundance of fish were significantly higher in mangrove-rich rivers than in mangrove-free rivers. Mangrove-related food feeders (e.g., benthic invertebrate and detritus) were more abundant in mangrove-rich than mangrove-free rivers while mangrove-unrelated food feeders (e.g., zooplankton feeders) showed no difference between river types. Cluster and ordination analyses demonstrated that fish assemblage structures were clearly different between mangrove-rich and mangrove-free rivers. Of all of the fish species collected (88 species), half of the species (45 species, 51%) occurred exclusively in the mangrove-rich rivers, 9 species (10%) in the mangrove-free rivers and 34 species (39%) were common in both types of rivers. Commercially important fish (e.g., Lutjanus fulvus and L. argentimaculatus) showed greater abundance of juveniles in mangrove-rich rivers than in the mangrove-free rivers, indicating that mangrove-rich rivers can provide important habitat for a variety of fish, including those commercially important to fisheries.

Identification of tsunami deposits using a combination of radiometric dating and oxygen-isotope profiles of articulated bivalves

Four tsunami deposits (deposits I–IV) have been identified on Ishigaki Island, southwest Japan. The youngest tsunami deposit (deposit I) was caused by the Meiwa tsunami, which occurred on 24 April 1771 CE, as described in reliable historical documents. Two well-preserved specimens of articulated marine bivalve were collected from the youngest tsunami deposit (deposit I) and an additional two from the second-youngest tsunami deposit (deposit II; 920–620 cal. yr BP). The shells were tightly closed and empty inside. No encrusting epifauna or evidence of erosion was observed on the inner or outer shell surfaces. In each tsunami deposit, the 14C ages of the shells are nearly identical. The mode of occurrence and coincidence of ages mean that these shells were transported and buried alive by tsunamis. We analyzed the oxygen-isotope (δ18O) profiles of these bivalves to determine the seasons of their death, which provides clues to the seasonal timing of tsunamis. Tsunami deposits I and II were formed during spring and fall, respectively. The former supports the proposal that tsunami deposit I was caused by the 1771 Meiwa tsunami and provides regional radiocarbon reservoir age for the late 1700s; the latter provides a chronological constraint on the identification of tsunami deposit II. Thus, a combination of radiometric dating and δ18O profiles of articulated bivalves derived from tsunami deposits provides important chronologic constraints for examining paleo-tsunami events.

First Record of the mycoheterotrophic plant Sciaphila corniculata (Triuridaceae) from Ishigaki Island, Ryukyu Islands, Japan, with updated description of its morphology, in particular on stylar characteristics

We report three new localities of the mycoheterotrphic plant Sciaphila corniculata (Triuridaceae) froM Ishigaki Island, Ryukyu Islands, Japan. Previously, S. corniculata was reported only from Kolomba

Seasonal variations in leaf growth of Cymodocea serrulata in subtropical seagrass meadows

We estimated the leaf growth of the tropical–subtropical seagrass species Cymodocea serrulata using the conventional leaf-marking method in a subtropical seagrass bed on Ishigaki Island, southern Japan, which is near the northern distributional limit of this species. This survey was conducted over an annual cycle at two sites. The deep site was located in a dense meadow in the subtidal zone. The shallow site was located around the lowest part of the intertidal zone, forming a tide pool during ebb tides of the spring tide, which was considered to approximate the upper depth limit of C. serrulata. The relationships between temperature and shoot weight, and the number of leaves per shoot were significantly influenced by site, resulting in a lower biomass in the shallow site. Leaf growth and shoot length increased with temperature without any spatial variation. Leaf growth and the number of leaves per shoot particularly declined during periods of low temperature in both sites. These results suggest that leaf growth and phenology of C. serrulata in this subtropical area are largely regulated by temperature.

Characterization and high-quality draft genome sequence of Herbivorax saccincola A7, an anaerobic, alkaliphilic, thermophilic, cellulolytic, and xylanolytic bacterium

An anaerobic, cellulolytic-xylanolytic bacterium, designated strain A7, was isolated from a cellulose-degrading bacterial community inhabiting bovine manure compost on Ishigaki Island, Japan, by enrichment culture using unpretreated corn stover as the sole carbon source. The strain was Gram-positive, non-endospore forming, non-motile, and formed orange colonies on solid medium. Strain A7 was identified as Herbivorax saccincola by DNA-DNA hybridization, and phylogenetic analysis based on 16S rRNA gene sequences showed that it was closely related to H. saccincola GGR1 (= DSM 101079T). H. saccincola A7 (= JCM 31827=DSM 104321) had quite similar phenotypic characteristics to those of strain GGR1. However, the optimum growth of A7 was at alkaline pH (9.0) and 55°C, compared to pH 7.0 at 60°C for GGR1, and the fatty acid profile of A7 contained 1.7-times more C17:0 iso than GGR1. The draft genome sequence revealed that H. saccincola A7 possessed a cellulosome-like extracellular macromolecular complex, which has also been found for Clostridium thermocellum and C. clariflavum. H. saccincola A7 contained more glycoside hydrolases (GHs) belonging to GH families-11 and -2, and more diversity of xylanolytic enzymes, than C. thermocellum and C. clariflavum. H. saccincola A7 could grow on xylan because it encoded essential genes for xylose metabolism, such as a xylose transporter, xylose isomerase, xylulokinase, and ribulose-phosphate 3-epimerase, which are absent from C. thermocellum. These results indicated that H. saccincola A7 has great potential as a microorganism that can effectively degrade lignocellulosic biomass.

First record of the mycoheterotrophic plant Sciaphila corniculata (Triuridaceae) from Ishigaki Island, Ryukyu Islands, Japan, with updated description of its morphology, in particular on stylar characteristics

First record of the mycoheterotrophic plant <i>Sciaphila corniculata</i> (Triuridaceae) from Ishigaki Island, Ryukyu Islands, Japan, with updated description of its morphology, in particular on stylar characteristics

Pilot Test of Automated Driving Bus at Main Land of Okinawa and Ishigaki Island

Pilot Test of Automated Driving Bus at Main Land of Okinawa and Ishigaki Island

The Study of the Process of Community Improvement based on Coral Reef Conservation in Shiraho, Ishigaki Island

The Study of the Process of Community Improvement based on Coral Reef Conservation in Shiraho, Ishigaki Island

Complete mitochondrial DNA sequence of the tropical hornet Vespa affinis (Insecta, Hymenoptera)

We analyzed the complete mitochondrial genome of the Asian tropical hornet Vespa affinis from Ishigaki Island, Japan. It consisted of a circular molecule with 19,109 bp, which is larger to other hornet species e.g. V. velutina. We predicted the genome contained 13 protein-coding, 22 tRNA, and two rRNA genes, along with one A + T-rich control region. The repetitive sequences were confirmed at multiple positions in the non-coding genes. The initiation codons ATA was found in one, ATG in seven, and ATT in five genes, while the termination codons TAA and TAG were observed 11 and two genes, respectively. The average AT content of the genome was 78.4%.

Methods for invasive species control are transferable across invaded areas.

Cane Toads (Rhinella marina) are invasive pests in many parts of the world, including the Japanese island of Ishigaki. Extensive research in Australia has identified promising new methods for control, but also has shown that toads exhibit geographic variation in many traits (suggesting that methods developed in one location may not work in another). Can the approaches developed in Australia play a useful role for controlling this invasive species in Japan? Our experimental trials on Ishigaki Island suggest that these new methods can be successfully applied to Japan. First, Cane Toad embryos exposed to chemical cues of conspecific tadpoles exhibited a reduction in viability (subsequent growth and development). This response appears to be species-specific, with native frog embryos not being affected by exposure to cues from toad tadpoles, and Cane Toad embryos not being affected by exposure to cues from native frog tadpoles. Second, Cane Toad tadpoles were attracted to traps containing water from conspecific eggs, and toxin from adult conspecifics. Third, adult Cane Toads were attracted to acoustic cues of calling males, with sex differences in rates of attraction to specific versions of a synthetic call (males were attracted to choruses whereas females were attracted to low-frequency calls). Our results suggest that the methods developed by Australian researchers are applicable to controlling invasive Cane Toads in Japan.

Reef-scale modeling of coral calcification responses to ocean acidification and sea-level rise

To predict coral responses to future environmental changes at the reef scale, the coral polyp model (Nakamura et al. in Coral Reefs 32:779–794, 2013), which reconstructs coral responses to ocean acidification, flow conditions and other factors, was incorporated into a reef-scale three-dimensional hydrodynamic-biogeochemical model. This coupled reef-scale model was compared to observations from the Shiraho fringing reef, Ishigaki Island, Japan, where the model accurately reconstructed spatiotemporal variation in reef hydrodynamic and geochemical parameters. The simulated coral calcification rate exhibited high spatial variation, with lower calcification rates in the nearshore and stagnant water areas due to isolation of the inner reef at low tide, and higher rates on the offshore side of the inner reef flat. When water is stagnant, bottom shear stress is low at night and thus oxygen diffusion rate from ambient water to the inside of the coral polyp limits respiration rate. Thus, calcification decreases because of the link between respiration and calcification. A scenario analysis was conducted using the reef-scale model with several pCO2 and sea-level conditions based on IPCC (Climate change 2013: the physical science basis. Contribution of working group I to the fifth assessment report of the intergovernmental panel on climate change, Cambridge University Press, Cambridge, 2013) scenarios. The simulation indicated that the coral calcification rate decreases with increasing pCO2. On the other hand, sea-level rise increases the calcification rate, particularly in the nearshore and the areas where water is stagnant at low tide under present conditions, as mass exchange, especially oxygen exchange at night, is enhanced between the corals and their ambient seawater due to the reduced stagnant period. When both pCO2 increase and sea-level rise occur concurrently, the calcification rate generally decreases due to the effects of ocean acidification. However, the calcification rate in some inner-reef areas will increase because the positive effects of sea-level rise offset the negative effects of ocean acidification, and total calcification rate will be positive only under the best-case scenario (RCP 2.6).

Aerial images can detect 3D small patch reefs that are potential habitats for anemonefish Amphiprion frenatus

Patchy habitats often enhance species coexistence and, consequently, abundance of each species. The present study examined two indicators of potential habitats for anemonefish Amphiprion frenatus: total area of dark-colored patch reefs that are detectable on an aerial image with image analysis software, and total area of tall patch reefs (>1.5 m in height) that are detectable on stereoscopic aerial images with a stereoscope. Relationships between patch reef area and anemonefish abundance, as estimated by number of host anemone Entacmaea quadricolor, were investigated at Shiraho Reef, Ishigaki Island, Japan. Total number of anemones was not correlated with total area of tall patch reefs but was highly correlated with total area of dark-colored patch reefs. Underwater observations confirmed that upper surface of tall patch reefs often involved bare substratum, whereas dark-colored patch reefs did not include this substratum. Because reef area approximately reflected reef volume within shallow back reefs, total area of dark-colored patch reefs that are detectable by aerial photography will reflect total volume of reef fish habitat. The present study suggests that aerial photography with a drone can provide a useful predictor of reef fish abundance.

Oleanane triterpenes with protein tyrosine phosphatase 1B inhibitory activity from aerial parts of Lantana camara collected in Indonesia and Japan

During the search for new protein tyrosine phosphatase (PTP) 1B inhibitors, EtOH extracts from the aerial parts of Lantana camara L. (lantana) collected at Manado (Indonesia) and two subtropical islands in Japan (Ishigaki and Iriomote Islands, Okinawa) exhibited potent inhibitory activities against PTP1B in an enzyme assay. Four previously undescribed oleanane triterpenes were isolated together with known triterpenes and flavones from the Indonesian lantana. The EtOH extracts of lantana collected in Ishigaki and Iriomote Islands exhibited different phytochemical profiles from each other and the Indonesian lantana. Triterpenes with a 24-OH group were isolated from the Indonesian lantana only. Five known triterpene compounds were detected in the Ishigaki lantana, and two oleanane triterpenes with an ether linkage between 3β and 25 were the main components together with five known triterpenes as minor components in the Iriomote lantana. The structures of previously undescribed compounds were assigned on the basis of their spectroscopic data. Among the compounds obtained in this study, oleanolic acid exhibited the most potent activity against PTP1B, and is used as a positive control in studies on PTP1B.

List of the Butterflies from Ishigaki Island, the Southern Loochoos, collected by Dr. R. KANO, with the Description of a New Subspecies (4)

List of the Butterflies from Ishigaki Island, the Southern Loochoos, collected by Dr. R. KANO, with the Description of a New Subspecies (4)

Stomach Contents of Three Sea Kraits (Hydrophiinae: Laticauda spp.) in the Ryukyu Islands, Japan

Abstract: We collected stomach contents of sea kraits, Laticauda laticaudata, L. colubrina, and L. semifasciata around Ishigaki and Iriomote Islands of the southern Ryukyu Islands, Japan. Twelve species belonging to three families of Anguilliformes (Congridae, Muraenidae, and Ophichthidae) were detected as prey of fifteen individuals of L. laticaudata and seven individuals of L. colubrina. On the other hand, four species of the families Labridae, Opistognathidae, and Ptereleotridae were found in the stomach of three individuals of L. semifasciata. These results indicate that L. laticaudata and L. colubrina around the northern limit of their distribution (Ryukyu Islands, Japan) preyed upon anguilliform fish, as previously found at the southern limit of their distribution (Vanuatu and New Caledonia), whereas L. semifasciata consumed various families of fish other than Anguilliformes, as reported in Taiwan. Thus, it is confirmed that L. laticaudata and L. colubrina are specialist predators on anguilliform fi...