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The tropical catadromous eel, Anguilla bicolor pacifica, an important fishery resource in Southeast Asia, is under threat due to overexploitation (especially of its glass eel phase) and the limited information on their current genetic status which is necessary for resource management. Mitochondrial DNA (mtDNA) control region sequences, a useful marker for population genetic studies in many aquatic organisms, were used to investigate the genetic diversity, population structure and demographic history of A. bicolor pacifica in the region. A total of 151 specimens were collected from three sites in Southeast Asia, namely: Phu Yen, Vietnam (n = 48); General Santos, Philippines (n = 52); and, Palu, Indonesia (n = 51). A total of 138 haplotypes were identified using the mtDNA control region sequences. In spite of the lack of shared haplotypes, low and non-significant FST values, high haplotype diversity in concurrence with relatively low nucleotide diversity, a haplotype network with no phylogeographic structuring indicate no significant genetic population structuring among the eel samples from Vietnam, Philippines and Indonesia. Population expansion of A. bicolor pacifica was also suggested based on the results of the neutrality tests, mismatch distribution analysis and Bayesian skyline plot. Taken together, a joint management strategy for A. bicolor pacifica must involve countries in Southeast Asia particularly Vietnam, Philippines and Indonesia for its sustainable use.

Because fish have a high dispersal ability, an understanding coral reef fish metacommunity structure is vital for effective conservation. Coral reefs provide patchy habitat of various sizes and scales. We examined the species–area relationship (SAR) of damselfish (Pomacentridae) assemblages over 81 environmentally homogenous patch reefs ranging 0.07–45.4 m2 with low coral cover. Patch reefs were located in the shallow back reef ( 1/2500) color aerial photograph used as a fine-scale seascape map. To assess the effects of three-dimensional meso-scale rugosity on species richness, we assumed that all reefs had a cylindrical shape and examined species by volume (area × height) relationships (SVR). Patch reef volume was a better determinant of species richness than area, and the regression functions of SVR provided better estimates of patch reef species richness. Neither the observed SVRs nor SARs, however, could be explained by a random placement model alone. Our results suggest that several small reefs are likely to have higher species richness than a single large reef of equivalent area in the shallow back reef where large patch reefs are flat. Thus, total patch reef volume (area × height) better reflects meso-scale rugosity and is a useful indicator of total species richness relative to the total amount of essential habitat in shallow back reefs.

Small cryptic animals utilize the interstices of coral rubble as a refuge from predators and form a significant part of the diversity and productivity of coral reef ecosystems. In the present study, we examined the composition of cryptic mobile animals along an estuarine gradient within a mangrove-seagrass-coral reef seascape off Ishigaki Island, southwest Japan. We used mesh traps with defaunated coral rubble to sample cryptic mobile animals quantitatively at four sites: upper-estuary mangrove, lower-estuary mangrove, seagrass bed, and coral lagoon. Sixty-five species of decapod crustaceans, gastropods, fishes, and other mobile animals were identified. The assemblage composition of these identified species was significantly different among the four sites. Low-resolution taxa including copepods, gammarids, and other taxa also showed significant differences in composition among the four sites. Two types of rubble (branch and lump) were used to examine the possible effects of microhabitat structure, but no significant effect on assemblage composition was detected. Results indicate that, despite the close proximity and high degree of water mass mixing among the sites, cryptic animals colonized the trays from the surrounding habitats, and that the assemblage of cryptic animals varied considerably along the estuarine gradient.

Determination of the growth pattern of a harvested species is an important step toward a proper assessment and suitable management of the stock. Although coconut crab Birgus latro populations in most regions have been severely depleted, few reliable biological data are available. We assessed the growth of B. latro using a mark-recapture method based on the use of passive integrated transponder (PIT) tags on Hatoma Island, located southwest of Okinawa, Japan. Of 781 crabs tagged (337 males, 444 females; 14.89 to 58.03 mm thoracic length (ThL)), 17 males and 20 females were recaptured. The application of PIT tags provided field data for growth of individuals for up to 2326 d and confirmed that coconut crabs molt during the winter dry season on Hatoma Island. The curves relating ThL with age, estimated from data of 29 crabs that had spent one or multiple winter dry seasons at liberty, showed that the coconut crab is an extremely slow growing species, with males showing much higher mean asymptotic ThL (69.87 mm) than females (42.79 mm). The Brody growth coefficient (K)was 0.061 yr �1 for males and 0.091 yr �1 for females. This study is the first to provide growth estimates of wild coconut crabs based on mark- recapture over multiple years. Potentially long-lived, slow growing species such as coconut crabs may be susceptible to overharvesting, and a cautious approach is recommended to the determina- tion of resource management regimes for B. latro.

Successful settlement of pelagic fish larvae into benthic juvenile habitats may be enhanced by a shortened settlement period, since it limits larval exposure to predation in the new habitat. Because the spatial distribution of marine fish larvae immediately prior to settlement versus during settlement was unknown, field experiments were conducted at Ishigaki Island (Japan) using light trap sampling and underwater visual belt transect surveys to investigate the spatial distribution patterns of selected pre- and post-settlement fishes (Acanthuridae, Pomacentridae, Chaetodonidae and Lethrinidae) among four habitats (seagrass bed, coral rubble, branching coral and tabular coral). The results highlighted two patterns: patterns 1, pre- and post-settlement individuals showing a ubiquitous distribution among the four habitats (Acanthuridae) and pattern 2, pre-settlement individuals distributed in all habitats, but post-settlement individuals restricted to coral (most species of Pomacentridae and Chaetodontidae) or seagrass habitats (Lethrinidae). The first pattern minimizes the transition time between the larval pelagic stage and acquisition of a benthic reef habitat, the latter leading immediately to a juvenile lifestyle. In contrast, the second pattern is characterized by high settlement habitat selectivity by larvae and/or differential mortality immediately after settlement.

Mangroves are often considered to be important nurseries for coral reef fishes, yet this assumption has rarely been tested. At Ishigaki Island, southern Japan, black-tail snapper Lutjanus fulvus juveniles often occur in mangroves, whereas subadults and adults are usually found on coral reefs. To test the hypothesis that L. fulvus uses mangroves as a nursery, we conducted stomach content and stable isotope analyses of L. fulvus collected from mangroves and an adjacent coral reef. Stomach content analysis showed that specimens from mangroves fed on mangrove-associated prey, whereas those from the coral reef took coral reef-associated prey, indicating that the species undergoes ontogenetic changes in resource use from the mangroves to the coral reef, i.e. coral reef individuals did not migrate to the mangroves to feed. Stable isotope analysis showed that potential prey and mangrove red snapper L. argentimaculatus (control fish for mangroves) collected from the mangroves had 13 C-depleted values of -23 to -17‰, distinct from the -16 to -8‰ values of potential prey and humpback red snapper L. gibbus (control fish for coral reef) collected from the coral reef. δ 13 C values of L. fulvus in the mangroves had a mangrove signature, whereas individuals on the coral reef gradually shifted from a mangrove signature to a coral reef signature with growth, indicating that small individuals on the coral reef were recent migrants from the mangroves. Based on the δ 13 C values of the subadult population of L. fulvus on the coral reef, 36 of 41 individuals were estimated to have inhabited the mangroves during their juvenile stage, demonstrating that L. fulvus used the mangroves as a nursery.

To consider effective resource management strategies for the coconut crab, Birgus latro, we determined the size of males at sexual maturity by histological methods and investigated an optimal method to estimate the number of sperm in spermatophores. The size of 50% sexual maturity in male coconut crabs was estimated at 22.2 mm thoracic length (TL) on the Hatoma Island, Japan. We established a procedure to soak spermatophores for more than 120 min in a 20% NaOH solution before mixing, and to count the sperm within 24 h after mixing, thereby enabling us to assess the number of sperm per individual and estimate male reproductive potential. Using this method, we investigated the relationship between male size and number of sperm retained by males. Larger male coconut crabs have a higher number of sperm in both the vasa deferentia and testis. The relationships between male size and spermatophore volume also increased with increasing male size, and the sperm quantity packed in a spermatophore increased with increasing spermatophore volume. Thus, male coconut crabs display a size-dependent reproductive output, as is reported for other species of anomurans.

Coral rubble is one of the characteristic bottom habitats in tropical and subtropical coral reefs. Many mobile organisms inhabit the interstices among coral rubble. Because coral rubble habi- tats are frequently subjected to physical disturbances, the process of assemblage recolonization is important for maintaining the diversity and productivity in coral reefs. The present study examined the colonization patterns of these mobile organisms by using experimental traps with defaunated coral rubble at 3 areas (Back reef, Seagrass bed, and Nearshore) in a fringing coral reef on Ishigaki Island, Japan. Sixteen mesh trays filled with coral rubble were set at each of the 3 areas; 4 trays were collected after 1, 2, 4, and 8 wk. The experiment was repeated in winter and spring. The number of species that occurred in the trays generally increased with the time period, but detailed examination was difficult because of significant interaction factors. Higher order interactions (season, area, and time period) were also significant for variations in assemblage composition. Temporal and spatial variations in abundances of 15 numerically dominant species (gastropods and decapods) were analyzed by a general linear model with an Akaike's information criterion model selection. Although the patterns of colonization were species specific, initial (

In order to monitor sea surface current and transportation of heat and material in and around of coral reefs, we conducted field monitoring of wide-ranging (-70km) sea surface current using High-Frequency (HF) ocean radar, and vertical microstructure in the sea surface layer to estimate magnitude of turbulent vertical mixing. We here report time variation of wind-induced mixing in the sea surface layer which was the upper side of a strong near shore current. In our field measurement off Yaeyama Islands on September 15, 2005, the HF ocean radar could captured the presence of strong near-shore current over 50 cms-1, and the vertical microstructure measurement revealed that both elevated water temperature and uniformalization in the sea surface layer corresponding to increase of turbulent energy dissipation (e). Results suggested that energy led to this uniformalization seemed to derive from not the nearshore current but the ocean surface wind.

Sessile organisms on PVC panels suspended inside and outside coral reef at Ishigaki Island, Yaeyama Islands, Japan, was monitored for 20 days just after the wide-spread incident of coral bleaching in September, 1998. The settlement of a total of 16 species of algae and invertebrates was recorded. Generally, Enteromorpha sp. (Chlorophyceae) dominated the panels. The percentage area cover, number of species, biomass and algal growth were significantly greater in waters outside the reef.

One of the great puzzles of coral reef fish ecology is how pelagic larvae locate the habi- tat in which they settle. The present study explored whether offshore emperor fish (Lethrinidae) lar- vae selected a specific reef and/or habitat at settlement. Although older juveniles are known to use back-reef seagrass beds as a potential nursery habitat, information is scarce regarding pre-settle- ment larvae. Using light traps anchored on the reef slopes at seagrass-replete and seagrass-free reefs (Ishigaki Island, Japan), lethrinid larvae were sampled weekly from April to June 2008. Larval abun- dance in light traps was similar on the 2 reef types. This result implies that lethrinid larvae did not or could not differentiate between the presence or absence of seagrass before settlement. However, in the laboratory, larvae collected from both reef types selected seagrass substrate rather than bare sub- strate or coral. In underwater visual censuses, newly settled juveniles were not observed on the sea- grass-free reef, whereas they were abundant on the seagrass-replete reef. Together, these findings suggest that lethrinid larvae did not settle near the seagrass-free reef but rather preferentially settled near the seagrass-replete reef.