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Volume 74, Issue 2
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Asako UCHISDA, Maki OYAGI, Motomi GENKAI-KATO, Masami NAKANISHI2013 Volume 74 Issue 2 Pages 63-72
Published: May 10, 2013
Released on J-STAGE: May 15, 2014
JOURNAL FREE ACCESSThe nutritional status of the sessile algal community in the Yahagi River located in central Japan was examined based on the ratios between particulate carbon (PC), nitrogen (PN) and phosphorus (PP) proposed by Hillebrand and Sommer (1999). The survey was conducted at five stations from August 2008 to September 2009. The concentration of Chlorophyll a of the sessile algal community ranged from 5.0 to 193.7 mg m-2. The composition of the community changed seasonally from blue-green algae dominated by Homoeothrix janthina in May-November to diatoms dominated by Cymbella and Gomphonema in December-April. The PC: PN and PN: PP ratios were 7.2 and 22.3, respectively, which were close to the reference ratios. Our results indicate that the sessile algal community in the Yahagi River was not exposed to severe deficiency in nitrogen or phosphorus.View full abstractDownload PDF (704K) -
Kazuki SEKINÉ, Masanao SUEYOSHI, Koji TOJO2013 Volume 74 Issue 2 Pages 73-84
Published: May 10, 2013
Released on J-STAGE: May 15, 2014
JOURNAL FREE ACCESSThe polymitarcyid mayfly Ephoron shigae is widely distributed in Japan, and inhabits burrows in gravel riverbeds in the mid and lower regions of rivers. This mayfly is renowned for synchronized mass emergences at dusk in early autumn, which have been frequently observed in various Japanese rivers since the 1970s. Although much geographic documentation of synchronized mass emergence has accumulated for major populations, there is not much information for smaller populations. There are a number of reasons the full distribution of this mayfly is not well known, including; 1) the comparatively short period of the adult stage (shorter than two hours), 2) the short emergence season (one or several weeks per year), 3) the short nymphal season (E. shigae remains as diapause stage eggs from autumn to spring), and 4) the typical habitats are below deep water riverbeds in the mid to lower reaches of comparatively large rivers. In this study, we investigated the current distribution range (i. e., the geographic distribution range along the river's course) of the mayfly E. shigae in the Chikuma-gawa River (Nagano Prefecture), where it is considered to be one of the largest continuously extant meta-populations of this mayfly. The first record of mass emergence of this mayfly in the Chikuma-gawa River was reported in the novel entitled "Hounen-mushi" written in 1928 by Shiga Naoya, and has since been observed for more than 80 years. In the results of our research, it was revealed that E. shigae inhabits an extended distribution range from the city of Ueda to the town of Obuse. Further, we observed high mayfly density and high biomass in a region around the Heiwa-bashi and Awasa-bashi bridges. From these areas, the density, body size and the biomass of the mayflies decreased gradually in both the upstream and downstream zones. This result is consistent with a previous study investigating the distribution of the adult stage of this species. However, contrary to the previous study, we found many more nymphs at the downstream sites (the Yashima-bashi and Obuse-bashi bridges) than at the Sai-gawa tributary merge point. However, the collected individuals at these two downstream sites were markedly smaller in size. The inflow of Sai-gawa River into the Chikuma-gawa River is comparatively oligotrophic and may provide fewer food resources for the detritus-feeding nymphs.View full abstractDownload PDF (1358K) -
Misuzu AOKI, Kenji HAMASAKI, Makoto YAMADA2013 Volume 74 Issue 2 Pages 85-91
Published: May 10, 2013
Released on J-STAGE: May 15, 2014
JOURNAL FREE ACCESSWe developed a method for discriminating among three Macrobrachium species (M. nipponense, M. formosense and M. japonicum) that inhabit rivers of the Kii Peninsula, Japan. Using the restriction enzyme, Bsp1286I, we performed polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis on the cytochrome oxidase subunit I (CO I) region of the mitochondrial DNA. Our analysis clearly discriminated among the three Macrobrachium species (62 individuals), and was consistent with classification based on morphological characters. There was no intraspecific variation in the specific restriction profiles. In addition, we were able to classify 95 morphologically unidentified individuals, including juvenile or female individuals, based on their specific restriction profiles. Our results suggest that PCR-RFLP may be used to discriminate among these three Macrobrachium species. The method is particularly useful for classifying juvenile or female individuals that cannot be identified morphologically.View full abstractDownload PDF (824K)
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