No abstract

To clarify seascape-scale habitat use patterns of fishes in the Ryukyu Islands (southern Japan), visual censuses were conducted in the mangrove estuary, sand area, seagrass bed, coral rubble area, branching coral area on the reef flat, and tabular coral area on the outer reef slope at Ishigaki . During the study period a total of 319 species were observed. Species richness and abundance were highest in the branching and tabular coral areas, followed in order by the seagrass bed and mangrove estuary, and coral rubble and sand areas, in each month. Cluster analysis resulted in a clear grouping of assemblage structures by habitat type rather than by census month. SIMPER analysis showed that fish assemblages in the tabular coral area were mainly characterized by Acanthurus nigrofuscus, Pomacentrus lepidogenys, P. philippinus and P. vaiuli, the branching coral area by Chromis viridis and Pomacentrus moluccensis, the coral rubble area by Amblyeleotris steinitzi and Ctenogobiops pomastictus, the seagrass bed by Cheilio inermis, Lethrinus atkinsoni and Stethojulis strigiventer, the sand area by Valenciennea longipinnis, and the mangrove estuary by Gerres oyena, Lutjanus fulvus and Yongeichthys criniger. Moreover, fishes exhibited two habitat use strategies, inhabiting either a single or several specific habitats throughout their benthic life history stages, or having a possible ontogenetic habitat shift from the mangrove estuary or seagrass bed to coraldominated habitats (e.g., Lethrinus atkinsoni, Lethrinus obsoletus, Lutjanus fulviflamma, Lutjanus fulvus, Lutjanus gibbus, Lutjanus monostigma and Parupeneus barberinus), suggesting that the mangrove estuary and seagrass bed have a nursery function.

Small patch reefs can harbor many reef fishes because most fishes have a drifting larval phase to randomly disperse over patchy habitats. We examined the species-area relationship (SAR) of damselfish (Pomacentridae) assemblages over 84 small patch reefs (0.05-45.4 m 2 ) using an enlarged section of a high-resolution color aerial photograph as a field map (1/2500) in a shallow coral reef shore zone (<2 m deep, 3.6 ha, Shiraho Reef, Ishigaki Island, Japan). This study confirmed that the logarithmic function is better than other functions (including the power function) to explain the SAR in this scale. Actual species richness (24) over the entire study site was much higher than the species richness (15.4) extrapolated from the regression line in semi-log space. Better estimates were obtained using random placement models and computer simulations. These results suggest that several small patch reefs are likely to have higher species richness than a single large reef of equivalent area at the study site. The total number of individuals of the four most abundant territorial herbivores increased almost linearly with patch reef area, but that of other species roughly increased with the square root of the area. While no territorial species were found in the smallest reefs, the large territorial herbivore, Hemiglyphidodon plagiometopon, was abundant and had negative effects on species richness in large reefs. Although the well-known single-large-or-several-small (SLOSS) debate has largely been settled, this dichotomy can be important in places where territorial herbivores do not occupy the smallest reefs.

No abstract

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 markrecapture 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 determination of resource management regimes for B. latro.