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The recruitment patterns of black-spot tuskfish Choerodon schoenleinii were compared with those of orange-dotted tuskfish (OT) C. ancholago. Individuals at the settlement and juvenile stages were collected using a push net in the intertidal zone and a seine net in seagrass beds. Relative values of standard length to total length (TL) for the two Choerodon species indicated an inflection point at approximately 10-20 mm TL, suggesting that both species complete metamorphosis at a similar size. However, their temporal and spatial occurrence patterns were distinct. Newly settled individuals (postflexion stage) of black-spot tuskfish were collected mainly within foliage of Sargassum plants of the intertidal zone around March-April, while those of OT occurred in both the intertidal zone and seagrass beds mainly in May and June. In seagrass beds, the abundances of both species increased from May or June; however, the TL of black-spot tuskfish was bigger than that of OT. Therefore, black-spot tuskfish progressively migrate to seagrass beds after settling and completing metamorphosis in the intertidal zone, indicating that they utilize two different habitats as nursery grounds. Early spawning and migration from the intertidal zone by this species contributed to the occurrence of relatively large individuals in seagrass beds. [ABSTRACT FROM AUTHOR]

The interstices of coral rubble provide a good refuge for cryptic small crustaceans and molluscs, which are important prey items for reef fishes. In this study, we focused on the assemblage composition of cryptic mobile species along the depth gradient at an outer reef slope. Traps with coral rubble (22 × 18 × 6 cm) were set at three sites at different depths, and mobile animals that colonized the traps were sorted. In total, 117 species of larger animals (mainly Decapoda and Gastropoda) were recorded: 71 species at the 3 m point, 53 species at the 11 m point, and 37 species at the 22 m point. On average, 260.3 individuals were captured in the traps at 3 m, while 95.3 and 57.8 individuals were captured at 11 and 22 m, respectively. MDS ordination showed that assemblage composition differed among the three sites. The most abundant species at the 3 m was the galathean crab Galathea mauritiana, followed by the gastropod Diala albugo. At 11 and 22 m, the galathean crab Sadayoshia edwardsii was most abundant. Thus, at the reef slope, the benthic assemblage was most diverse at the shallow site, and specific communities occurred at the three sites. [ABSTRACT FROM AUTHOR]

A new method for assessing coastal environments using the reproduction potential of corals has been developed and examined in situ. Six assessment racks were deployed before the full moon of May 2006 at three sites located around a river outlet in Nagura Bay, Ishigaki Is. and at one control location in Sekisei Lagoon. Each rack was equipped with two marine blocks (MB) containing 378 holes, two cases of coral settlement devices (CSDs), each containing 120 CSDs, and a water temperature logger. Assessment was based on recruitment of Acropora due to mass spawning. After 4 months of deployment, the surface of assessment racks showed apparent biofouling depending on sites mainly by algal settlement on the surfaces. Almost all the holes of the MBs were partly occupied, mainly by turf algae. Nagura Bay was thought likely to be an “unhealthy” coral reef due to runoff from land. However, our assessment showed that there were 0.85 corals per CSD in the Bay, compared with 0.51 in Sekisei Lagoon, indicating that coral larvae supply is not the cause of the unhealthy condition of corals in the Nagura Bay. [ABSTRACT FROM AUTHOR]