Recruitment and movement of the hard clam Meretrix lusoria in a tidal river of northern Kyushu,Japan

Size-frequency distributions of Meretrix lusoria, a commercially important bivalve in Japan, were compared among 6 sites in tidal flats of a small river in Kafuri Bay, northern Kyushu, Japan during 2006–2008. In Kafuri Bay, the hard clam resource is strictly managed and mean biomass of this species on the fishing ground (about 1.5 km²) exceeded 1.5 kg m^?2 in 2008. Small clams (<5 mm in shell length, SL) were most abundant in the border area between the river and the sea, while large clams (>40 mm SL) were rare there. In contrast, in the lower site of the marine area (site L), most clams were >30 mm SL. These results indicate that small clams move from riverine to marine areas with growth (post-settlement movement). Year-round, very small clams (<1 mm SL) were present and clams that were 2–5 mm SL were very rare, although the spawning season is thought to occur in summer. Probably, the early growth of many new recruits is very slow and most may even be <1 mm SL in the next spring, although some clams grow to >5 mm SL in a short period of time.     

Differential growth rates related to initiation of piscivory by hatchery-reared larval Pacific bluefin tuna Thunnus orientalis

Fast growth plays an important role in survival processes during the early life stages of both field-captured and hatchery-reared Pacific bluefin tuna Thunnus orientalis. Marked growth variations in hatchery-reared tuna larvae are frequently observed even for the same age and within the same rearing tank after the onset of the piscivory. We hypothesized that these small growth variations in the growth of tuna larvae at the onset of piscivory lead subsequently to large growth variations and tested the hypothesis using three size groups (large, intermediate and small) of hatchery-reared fish by nitrogen stable isotope and otolith analyses. Stable isotope analysis revealed that the large group rapidly utilized prey fish larvae, but the smaller groups depended more on rotifers as the main prey item relative to the large group. The otolith radius from the core to the increment corresponding to the first feeding on yolk-sac larvae was compared among the three size groups. The results revealed that the large group had larger otolith radii than the small and intermediate groups. Our findings suggest that small growth variations apparent during the early larval stage of tuna could induce further large growth variations in the late-larval and juvenile stages through differences in the initial ability to utilize piscivory.     

Kazusa Marker DataBase: a database for genomics,genetics, and molecular breeding in plants

In order to provide useful genomic information for agronomical plants, we have established a database, the Kazusa Marker DataBase (http://marker.kazusa.or.jp). This database includes information on DNA markers, e.g., SSR and SNP markers, genetic linkage maps, and physical maps, that were developed at the Kazusa DNA Research Institute. Keyword searches for the markers, sequence data used for marker development, and experimental conditions are also available through this database. Currently, 10 plant species have been targeted: tomato (Solanum lycopersicum), pepper (Capsicum annuum), strawberry (Fragaria × ananassa), radish (Raphanus sativus), Lotus japonicus, soybean (Glycine max), peanut (Arachis hypogaea), red clover (Trifolium pratense), white clover (Trifolium repens), and eucalyptus (Eucalyptus camaldulensis). In addition, the number of plant species registered in this database will be increased as our research progresses. The Kazusa Marker DataBase will be a useful tool for both basic and applied sciences, such as genomics, genetics, and molecular breeding in crops.     

Abnormal morphology in megalopae of the swimming crab,Portunus trituberculatus during seed production: causes and prevention

The occurrence of morphologically immature megalopae, which retain zoeal features such as dorsal spines and furcae of telson, is closely correlated with larval mass mortality during seed production of the swimming crab Portunus trituberculatus in Japanese hatcheries. To determine the cause of immature megalopal morphology, zoeae were reared with various supplementary schedules and density of diets (rotifer, Artemia and phytoplanktons including Chlorella vulgaris and Nannochloropsis oculata). In addition, to assess the relationship between immature morphology and endocrine control, the effect of causative dietary factor was compared with the effect of eyestalk ablation at various timing during zoeal development. Megalopal immature morphology was more distinct in Chlorella‐supplemented groups than in Nannochloropsis‐supplemented groups. High density Chlorella supplementation was associated with the highest incidence of immaturity and resulted in larval mass mortality. The premoult of the third zoeal stage was identified as a critical period at which Chlorella supplementation led to the highest incidence of immaturity. This critical period coincided with the critical period at which larval metamorphosis was regulated by the eyestalk neurosecretory system. Our results suggested that the occurrence of immature megalopal morphology under culture conditions is most likely caused by phytoplankton (especially, Chlorella) supplementation, which disrupts the endocrine regulation. On the basis of our results, we successfully prevented the occurrence of immature megalopal morphology in 500 L tanks by excluding the influence of phytoplankton before the critical period (i.e. discontinuing phytoplankton supplementation and supplying rotifer cultured with non‐phytoplankton materials).     

Predicting the spatial distribution of major species composition in secondary hardwood forests on Mt. Gozu,central Japan,based on environmental factors

Our goal was to predict the spatial distribution of canopy species composition in secondary deciduous hardwood forests at a fine spatial resolution, based on climatic and topographical factors using a geographic information system. We studied secondary forests on Mt. Gozu, Niigata Prefecture, central Japan. Canopy species composition was investigated in 100 sample plots within the study area. A digital elevation model (DEM) was created, and topographical, hydrological, and light factors were calculated using the DEM. Climatic factors were interpolated by kriging. The five major species used as response variables were Fagus crenata, Quercus serrata, Quercus crispula, Magnolia obovata, and Castanea crenata. We prepared three possible explanatory variable sets: climatic variables only, both climatic and topographic variables, and topographic variables only. Multivariate regression trees were derived, and the accuracy of predicting the major species composition was tested. The multivariate regression trees derived from the climatic variable set and from the climatic and topographic variable set had better accuracy than the regression tree derived from the topographic variable set. In the regression tree generated by the climatic and topographic variable set, the warmth index was the principal explanatory variable in classifying forest types, followed by topographic factors. This regression tree would be preferable to the other two regression trees for the prediction of canopy species composition.     

Mechanisms of perception of laid lines in Japanese paper

Laid lines are observed frequently in Japanese paper. For restoration of historic document paper, the laid line intervals should be consistent between the restoration paper and the original paper for harmonized appearance. Considering this prerequisite, the perception mechanisms of the laid lines are discussed. Laid lines can be easily observed against backlight. However, there are several cases where laid lines are not visible against backlight, but are clearly visible with diffuse reflected light. With paper sheets formed on screens with short bamboo splint pitches, laid lines were observed only with diffuse reflected light. Within these sheets, there was no fiber mass distribution or surface roughness that correlated with the periodicity of the laid lines. On the other hand, paper sheets produced using long splint pitches exhibited light transmission unevenness, fiber mass unevenness, and surface roughness. Microscopic observations using two-way low-angle illumination revealed the following mechanism. In the flow sheet-forming method, fibers are oriented strongly in the cross-splint direction in the first layer while some fibers rotate and become aligned along the interspaces between the splints in the second layer during dehydration. Bidirectionally oriented fibers perpendicular to each other result in a contrasting reflectivity perceived as laid lines.