Kenzi Takamura

Runoff properties and change in concentrations of agricultural pesticides in a river system during a rice cultivation period

Abstract Residues of 12 pesticides in water and sediment were surveyed in a river system during a rice cultivation period. The highest concentrations of pesticides were 36 μg l−1 for fenobucarb (carbamate insecticide), 11.3 μg l−1 for simetryn (herbicide) and 17.5 μg l−1 for iprobenfos (fungicide). The downstream flux was largest for iprobenfos, which showed a broader peak than the other pesticides. The runoff rates estimated from the ratio of the downstream flux of a pesticide to its retail amount was highest for fenobucarb and lowest for an organochlorine herbicide, chlornitrofen. These rates ranged over two orders according to the difference in the octanol-water partition coefficients or water solubility of the pesticides. Chlornitrofen was persistent in the stream sediment judging from the regression coefficient between concentrations in water and sediment.

Effects of permethrin on phytoplankton and zooplankton in an enclosure ecosystem in a pond

The insecticide permethrin (a synthetic pyrethroid) was applied into enclosures (1 m diameter and 3.5 m deep) placed in a pond. The chemical was rapidly removed from the water to the sediments. Daphnia rosea and its predator, Chaoborus flavicans were seriously affected by this application and disappeared from the enclosure. Acanthodiaptomus pacificus increased as Chaoborus decreased. Two species of Cladocera which had not been observed before the treatment, established their populations after 10 days, when Chaoborus had not recovered. Whereas Tropocyclops pracinus declined when permethrin was applied at 10 µg 1−1, the number of rotifer Keratella valga increased, suggesting a close relationship between these two species.Photosynthesis and phytoplankton were not significantly affected by permethrin, except for Ceratium hirundinella. The dominance of Dinobryon divergens continued in the treated enclosures, whereas other flagellate species, Scenedesmus and Nitzschia occurred during the second half of the experiments in the control enclosure and pond.

Performance as a fish predator of largemouth bass [Micropterus salmoides (Lacepède)] invading Japanese freshwaters: a review.

This review focuses on how predator performance of the invasive largemouth bass [Micropterus salmoides (Lacepède)] has been, or will be, formed in Japanese freshwaters. Predation impacts of largemouth bass on fish communities appear pervasive in both Japanese as well as North American freshwaters. Factors affecting performance as a piscivorous predator are (1) light intensity and water clarity, (2) oxygen depletion, (3) prey size and gape size, (4) behavioral refuge of prey, (5) weed beds as refuge for prey fish, (6) interaction with bluegill. Size and behavioral refuges requirements are so rigorous that they may have evolved only in some North American prey fish species like bluegill; therefore, most Japanese native fish species are unlikely to be equipped with such refuges. However, refuge habitats like aquatic weed beds could develop in Japanese freshwaters, allowing prey fish species to survive under predation pressure. The density, architecture, and species composition of aquatic plants may affect their suitability as refuges. Studies in Japanese waters have suggested that the presence of rich aquatic vegetation or invasive bluegill in bass-introduced waters have suppressed the predation impact of largemouth bass on fish communities. In addition to these environmental factors, original genotypic and phenotypic traits of the introduced largemouth bass, and hybridization between different lineages of largemouth bass or with Florida bass [Micropterus floridanus (Lesueur)] may be involved in further adaptation of invasive largemouth bass to Japanese freshwaters.

Life cycle of the damselfly Calopteryx atrata in relation to pesticide contamination

The life cycle of the damselfly Calopteryx atrata was investigated in relation to pesticide contamination occurring in its aquatic habitat. Calopteryx atrata emerged from the River Onogawa around May and stayed as immature adults in forests away from the stream. From late June to mid-August, mature adults were engaged in reproduction at the stream. On the other hand, pesticide contamination occurred from April to August with its peak in May and June, following transplantation of young rice plants. Mature nymphs of C. atrata experienced pesticide contamination, but may have tolerated it. Hatched nymphs had high susceptibility to two of the commonly used insecticides, fenitrothion (mortality occurred at >4.0 μg l-1 in 24 h and at >2.0 μg l-1 in 48 h) and fenthion (>2.0 μg l-1 in 24 h and >1.0 μg l-1 in 48 h). Hatching was estimated to occur mainly in August, when pesticide contamination was not as high as the susceptibility level. However, the level of pesticide contamination in August is variable due to its origin from aerial spraying, so hatched nymphs may experience a hazardous amount of pesticides depending on the year or place. The population of C. atrata does not escape the risk of pesticide contamination completely and may be affected by it.

Effects of termite exclusion on decay of heavy and light hardwood in a tropical rain forest of Peninsular Malaysia

Wood pieces of a heavy hardwood Neobalanocarpus heimii (King) P. S. Ashton and a light hardwood Shorea macroptera Dyer were used in decomposition experiments with termite-exclusion and control trays on the forest floor of the Pasoh Forest Reserve, West Malaysia to determine effects of wood quality on ter- mite-mediated wood decay. Shorea macroptera had a significant loss of C in the presence of termites while Neobalanocarpus heimii showed no significant termite effect. Neobalanocarpus heimii and S. macroptera both accumulated N in the absence of termites, but S. macroptera lost it when termites were present. The C/N ratio decreased with and without termites as decay proceeded in both species. Neobalano- carpus heimii accumulated P, but S. macroptera lost it with and without termites. The C/P ratio decreased in N. heimii, but did not change in S. macroptera. Decomposition was considerably enhanced by termites in S. macroptera, but not in N. heimii, indicat- ing that termite foraging activity was affected by the different wood qualities of the two trees. The qualities responsible for the differences and how different wood qualities affect nutrient cycling in the tropical rain forest ecosystem are discussed.

Heterozygosity and phylogenetic relationship of Japanese threespinestickleback (Gasterosteus aculeatus) populations revealed bymicrosatellite analysis

Heterozygosity and phylogenetic relationships were analyzed using eight microsatellite loci for nine freshwater and one anadromous populations of threespine stickleback Gasterosteus aculeatus from northern Japan. Fis values and Hardy–Weinberg tests indicated that nine of the populations were in heterozygote deficit. Furthermore, on-going isolation of most of the populations by artificial destruction of population connection and habitat deterioration suggested that nearly all of the populations are likely to be in a threatened condition. Phylogenetic analysis revealed that there were two distinctive phylogenetic groups, each of which was composed of two and three freshwater populations. These populations included in the groups except ones recently established were located in inland waters and isolated from anadromous populations, so that they may have been able to keep unique genetic features. Therefore, it is necessary to protect as many populations as possible within the local population network including these inland populations. On the other hand, for freshwater populations located near the river mouth but recently isolated from anadromous populations by weir construction, it is important to remove or ameliorate the barrier and recover the gene flow. Microsatellite markers are important tools to monitor the population network and gene flow.

Chironomids fail to emerge from LAS-contaminated water.

The effect of the surfactant LAS was investigated on chironomid emergence using six outdoor artificial channels. The concentrations of LAS were mostly between 1 and 2 mgl-1 in the three treated channels. Chironomus yoshimatsui, Cricotopus tamapullus, Eukiefferiella coerescens, Eukiefferiella sp. and Thienemanniella majuscula were the major chironomids obtained with emergence traps. The number of midges trapped did not differ significantly between the treatment and the control for either of the species. On the other hand, the ratios of midges failing to emerge to the total midges trapped was significantly higher in the treatment than in the control for all of the species. The results show that chironomids emergence is difficult as a result of LAS treatment probably due to the lowered surface tension.

Primary production of phytoplankton and standing crops of zooplankton and zoobenthos in hypertrophic Lake Teganuma

Primary production of phytoplankton and standing crops of zooplankton and zoobenthos were intensively surveyed in Lake Teganuma during May 1983–April 1984. The annual mean chlorophyll a concentrations were as high as 304 µg · l−1–383 µg · l−1. The daily gross primary production of phytoplankton was high throughout the year. The peak production rate was recorded in August and September, when blue-green algae bloomed. The annual gross primary production was estimated as 1450 g C · m−2 · y−1, extremely high as compared with other temperate eutrophic lakes. Zooplankton was predominantly composed of rotifers. The annual mean standing crop of zooplankton was 0.182 g C · m−2 around the middle between the inlets and the outlet and was lower than in most other temperate eutrophic lakes. Zoobenthos was mostly composed of Oligochaeta and chironomids. The annual mean standing crop of zoobenthos ranged from 0.052 g C · m−2 to 0.265 g C · m−2, the lowest values among temperate eutrophic lakes, which is in contrast to the high primary production.

Phylogeographic insights into the invasion history and secondary spread of the signal crayfish in Japan.

Abstract Successful invasion by nonindigenous species is often attributed to high propagule pressure, yet some foreign species become widespread despite showing reduced genetic variation due to founder effects. The signal crayfish (Pacifastacus leniusculus) is one such example, where rapid spread across Japan in recent decades is believed to be the result of only three founding populations. To infer the history and explore the success of this remarkable crayfish invasion, we combined detailed phylogeographical and morphological analyses conducted in both the introduced and native ranges. We sequenced 16S mitochondrial DNA of signal crayfish from across the introduced range in Japan (537 samples, 20 sites) and the native range in western North America (700 samples, 50 sites). Because chela size is often related to aggressive behavior in crayfish, and hence, their invasion success, we also measured chela size of a subset of specimens in both introduced and native ranges. Genetic diversity of introduced signal crayfish populations was as high as that of the dominant phylogeographic group in the native range, suggesting high propagule pressure during invasion. More recently established crayfish populations in Japan that originated through secondary spread from one of the founding populations exhibit reduced genetic diversity relative to older populations, probably as a result of founder effects. However, these newer populations also show larger chela size, consistent with expectations of rapid adaptations or phenotypic responses during the invasion process. Introduced signal crayfish populations in Japan originate from multiple source populations from a wide geographic range in the native range of western North America. A combination of high genetic diversity, especially for older populations in the invasive range, and rapid adaptation to colonization, manifested as larger chela in recent invasions, likely contribute to invasion success of signal crayfish in Japan.

Intraspecific invasion occurring in geographically isolated populations of the Japanese cyprinid fish Zacco platypus.

Geographically isolated populations of freshwater fish have been introduced into conspecific native populations. One of the most representative cases is the pale chub Zaccoplatypus. The pale chub of Lake Biwa in western Japan has been inadvertently introduced to other waters with the release of game fish. Because they are not clearly discriminated from other populations by their morphological characteristics, the morphological detection of the colonization is not possible. Hence, a genetic analysis of fish collected from rivers of the Kanto Plain in eastern Japan, where the introduction was made, was conducted. The haplotype variety of the mitochondrial gene cytochrome b of the fish revealed the presence of two major groups of haplotypes. We concluded that one of the groups was introduced from western Japan, especially Lake Biwa, and the other was native to the Kanto Plain. The haplotypes from western Japan were established in all of the rivers studied and occurred together with the native haplotypes in the rivers within the original distribution range of the species. The allelic composition of microsatellite loci indicated that fish from the two different sources were well admixed through hybridization in the populations of the rivers of the Kanto Plain.