Random dispersal of Bursaphelenchus xylophilus (Nematoda: Aphelenchoididae) in Pinus densiflora branches

Bursaphelenchus xylophilus is the causative agent of pine wilt disease. These nematodes disperse in the cortical and wood resin canals of host tree branches in the early stage of infection. To determine whether the dispersal can be regarded as diffusion, we inoculated B. xylophilus into living or boiled Pinus densiflora branch sections and investigated the spatial distribution 24 hr later. Assuming that some nematodes disperse randomly in the axial direction of branch sections and the rest remain at the inoculation site, the coefficient of diffusion (D) by dispersers was estimated to be 23.7–40.7 and 109.4 cm²/day for the living and boiled branches, respectively. The proportion of nondispersers was estimated to be 0.46–0.79 and 0.52 for the living and boiled branches, respectively. When the nematodes were inoculated at the centre of upright living branch sections, they dispersed up and down at similar D values of 7.4 and 7.9 cm²/day, respectively.     

Single spaghetti tagging as a high-retention marking method for Japanese common sea cucumber <Emphasis Type="Italic">Apostichopus japonicus</Emphasis>

Populations of sea cucumbers, including the Japanese common sea cucumber Apostichopus japonicus, have been seriously depleted worldwide due to overfishing. Mark–recapture study is an efficient means of collecting ecological data. However, the use of such a method in sea cucumbers is difficult because they lack hard tissues in the body wall. Here we tested the viability of various tagging methods on A. japonicus. First, we applied conventional tags using four different methods [single spaghetti (T-bar) tagging, double spaghetti tagging, ribbon tagging, and Atkins tagging] to ten individuals per method in aquaria for 14 days. Of the methods used, single spaghetti tagging had the highest retention rate. Then we examined the retention rate of single spaghetti tags on ten individual sea cucumbers for up to approximately 6 months in rearing conditions. The single spaghetti tagging method showed a retention rate of 100% over at least 7 days, and 50% of the tags remained embedded after 56 days. The longest duration of tag retention was 174 days, at which time the experiment was terminated. These results indicate that single spaghetti tagging is reliable for both short- and longer-term studies, making it a useful tool for ecological and conservation studies in sea cucumbers.     

Ontogeny of tolerance to and avoidance of ultraviolet radiation in red sea bream Pagrus major and black sea bream Acanthopagrus schlegeli

ABSTRACT:   Ontogenetic changes of tolerance to, and avoidance of, ultraviolet-B radiation (UV-B) were examined in red sea bream Pagrus major and black sea bream Acanthopagrus schlegeli . In the tolerance experiment, larvae and juveniles (age 13–46 days) were put in beakers, and were exposed to one of five different levels of UV-B radiation (1.8, 1.1, 0.2, 0.1, and 0 W/m²) for one hour. Their survival rates were calculated either 12 or 24 h later. In the avoidance experiment, fish (age 3–49 days) were put in a long experimental tank, half of which was covered with UV-blocking film and placed under two levels of UV-B radiation (1.1 and 0.2 W/m²), and their avoidance indices were calculated. Black sea bream had significantly better survival compared to red sea bream for most ages. Only black sea bream of ages 37 and 49 days showed significant avoidance of UV radiation under the higher level of UV-B, whereas both species did not show avoidance on any days at the lower level. The present results suggest that black sea bream are significantly better adapted to habitats with high UV-B radiation, than red sea bream, reflecting that back sea bream live in shallower waters through their early life stages.     

Ontogenetic habitat shift of age-0 Japanese flounder <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis> on the Pacific coast of northeastern Japan: differences in timing of the shift among areas and potential effects on recruitment success

Ontogenetic habitat shift and feeding habits in the shallow (< 15 m) and deep (30–80 m) habitats of age-0 Japanese flounder Paralichthys olivaceus in Sendai Bay, the Pacific coast of northeastern Japan, were examined to understand the mechanisms that potentially enable area-specific high recruitment success. The flounder was able to use the shallow nursery habitat for about 1 year, until the next summer of their settlement (June–August) when they had reached 250 mm total length (TL). In addition, age-0 flounder between 150 and 250 mm TL used both shallow and deep habitats from winter to the next summer of their settlement, where species, size, and availability of potential food and susceptibility to predators are considerably different. These area-specific characteristics in Sendai Bay are clearly different from other areas around Japan that have been described in the literature: shorter residence in the shallow habitat and smaller size at emigration to the deep habitat. The characteristics in Sendai Bay seem to be enabled by prolonged good feeding conditions in the shallow habitat, which result from an abundant food supply and relatively lower temperature that does not exceed the uppermost temperature (25 °C) for maximum growth of the age-0 flounder. We consider that the prolonged better feeding conditions in the shallow habitat in the study area for ca. 1 year after settlement contribute to higher recruitment success.     

Effects of water temperature and prey density on recent growth of chub mackerel Scomber japonicus larvae and juveniles along the Pacific coast of Boso–Kashimanada

Fisheries Science - The effects of temperature and prey density on the recent growth rate (RGR) of chub mackerel, Scomber japonicus, were examined. Scomber spp. larvae and juveniles were collected...     

Effects of wood species on degradation rates and bacterial communities in a small-scale biodegradation system for garbage using wood matrices

Simulated organic waste was biodegraded in a laboratory-scale machine using matrices prepared from four wood species to investigate the effects of wood species on the degradation rate and the bacterial community. The degradation rate, estimated by measuring weight loss and CO₂ evolution, was found to be equal among the four wood species. Changes in viable cell counts and microbial communities over time were examined. Viable cell counts were also similar among the wood species, but initial bacterial communities differed owing to differences in wood species, although these communities became similar with time. The sensitivity of isolates to wood extractives was examined using paper discs. The extractive-insensitive bacteria species were dominant at the initial stage of biodegradation. However, occupancy of sensitive bacteria increased with time. It was thought that antibacterial extractives were degraded or inactivated after some time.Part of this report was presented at the 50th annual meeting of the Japan Wood Research Society, Kyoto. Japan, April 2000     

Isolation and characterization of a novel anionic peroxidase cDNA found in poplar (Populus nigra) suspension cultured cells

A cDNA clone fromPopulus nigra L. var.italica Koehne, denoted PCY2-6, coding for an anionic peroxidase has been isolated, cloned, and characterized. PCY2-6 is 1160 bp long; and its deduced product, PnC26, contains 343 amino acid residues. The mature protein has a calculated isoelectric point of 4.09. The protein contains two motifs typical of peroxidase and 10 potentialN-glycosylation sites. PnC26 is therefore classified as an anionic peroxidase. The mRNA of the PCY2-6 gene family was detected in immature and mature leaves and in two parts of current-year stems: the shoot tip and the older stem. The mRNA of PCY2-6 gene family was found to localize in the phloem and cortex of the current-year stems. We therefore conclude that expression of the PCY2-6 gene family is related to bark development.     

Bioaccumulation of PCDD/Fs and Co-PCBs in Lower-Trophic-Level Organisms in Sendai Bay,Japan

In Sendai Bay, Japan, the total PCDD, PCDF, and Co-PCB (dioxins) concentrations in phytoplankton were equivalent to 150, 12, and 51 pg/g wet weight (ww), respectively. The average concentrations in seaweed were 3, 0.095, and 2.1 pg/g ww, respectively. The total concentrations in phytoplankton were much higher than those in seaweed, even though both groups are algae. The concentrations in zooplankton were 11, 1.1, and 110 pg/g ww, respectively. The total PCDD/F concentrations in zooplankton (primary consumers and lower-trophic-level invertebrates) were lower than in phytoplankton (primary producers), but the total Co-PCB concentration in zooplankton was higher than that in phytoplankton. The concentrations in mysids (secondary consumers and higher-trophic-level invertebrates) were 190, 18, and 290 pg/g ww, respectively. The average concentrations in shrimp (secondary consumers and higher-trophic-level invertebrates) were 120, 17, and 410 pg/g ww, respectively. The concentrations in higher-tropic-level invertebrates were higher than those in lower-trophic-level invertebrates. The average concentrations in sand lance were 4.5, 1.7, and 550 pg/g ww, respectively. The total PCDD concentration in sand lance was lower than that in zooplankton (prey of sand lance), but the total Co-PCB concentration in sand lance was higher than that in zooplankton. The bioaccumulation of PCDD congeners in sand lance differed from that of Co-PCB congeners. The bioaccumulation of PCDD/Fs from lower- to higher-trophic-level invertebrates through the food web differed from that from lower-trophic-level invertebrates to fish.     

Effects of Riparian Denitrification on Stream Nitrate-Evidence from Isotope Analysis and Extreme Nitrate Leaching during Rainfall-

The effects of riparian denitrification on stream nitrate were investigated by detailed soil water observations and isotope analysis at a small headwater catchment in an urban area near Tokyo, central Japan. In the base flow period, stream nitrate concentration (<100 µM) was comparable with that of riparian ground water which had less nitrate than unsaturated soil water. Nitrogen isotope analysis showed that the consumption of nitrate by denitrification took place in riparian ground water, suggesting that denitrification is an important process to control nitrate leaching to streams. During rainfall, the concentration of stream nitrate increased up to 400 µM, which was comparable with that of pre-event soil water. The fact that soil water nitrate directly leached to streams indicated that the riparian denitrification process did not work during rainfall because of the rapid discharge of water. A decrease of denitrification effects is a possible reason for high stream nitrate concentration during rainfall.