Japanese Journal of Benthology
Online ISSN : 1883-891X
Print ISSN : 1345-112X
ISSN-L : 1345-112X
Volume 72, Issue 1
Displaying 1-9 of 9 articles from this issue
Original Articles
  • 2017 Volume 72 Issue 1 Pages 1-11
    Published: August 31, 2017
    Released on J-STAGE: April 18, 2018
    JOURNAL FREE ACCESS

    The distribution and size composition of free-living marine nematodes were investigated in relation to the sediment condition at 55 stations on the Mae tidal flat, Hiroshima Bay. The relationship between environmental factors, frequency of human maintenance of Manila clam beds, and the horizontal and vertical distribution and size composition of nematodes were studied. The density of nematodes showed a significant correlation with viable numbers of bacteria and the frequency of clam bed maintenance. The maintenance of clam beds, which includes the installation of anti-predator nets and removal of Musculista senhousia mats, may reduce ignition loss, thereby promoting an increase in the percentage of small nematodes (63–125 μm in mesh size). The present results indicate that the size composition of nematodes and their distribution within the sediment are affected by differences in sediment organic content and redox potential.

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  • Yukiko NAKAOKA, Keiji WADA
    2017 Volume 72 Issue 1 Pages 12-15
    Published: August 31, 2017
    Released on J-STAGE: April 18, 2018
    JOURNAL FREE ACCESS

    For the varunid crab Cyclograpsus pumilio Hangai & Fukui, 2009, that inhabits the upper intertidal limit of pebble shores, habitat preference for tidal height and pebble size was investigated using field and laboratory experiments. Crabs transplanted to a level lower than the distribution range survived less than those within the distribution range. Crabs placed in cages containing differently sized pebbles showed no difference in their survival with respect to the pebble size. An experiment to determine the pebble size preference showed that the males preferred the smaller pebbles, whereas the females preferred the larger pebbles.

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  • Susumu OHTSUKA, Naohisa NISHIHARA, Ryota HIRAYAMA, Hayato TANAKA, Yusu ...
    2017 Volume 72 Issue 1 Pages 16-26
    Published: August 31, 2017
    Released on J-STAGE: April 18, 2018
    JOURNAL FREE ACCESS

    The tri-spine horseshoe crab Tachypleus tridentatus is considered at risk and has been granted protection in Japan at least since the 1990s. The breeding areas in Okayama, Ehime and Saga prefectures, Japan, are protected by national and local laws, while in Hiroshima Prefecture the species has not been officially conserved by local administrations. However, its breeding has long been noticed at two sites there: Etajima and Takehara cities. We compiled data on the habitat of these two populations, using published literature, inquiries to the public, and our own research from 1999 to 2016. During the period of our investigation, breeding at Etajima City was observed only once, in July 2000. In Takehara City, a distinct recruitment of juveniles has been observed since 2015. The compiled data on this horseshoe crab in Hiroshima Prefecture confirms that juveniles up to the tenth-instar stage inhabit the mud flats and that adults appear in the habitat only during the summer, as similarly observed for populations in other regions of Japan. The Takehara population was genetically characterized with the AT-rich region of mitochondrial DNA by only one haplotype, inferring that the Seto Inland Sea populations exhibit the founder effect.

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  • Shiho OGATA, Rocille PALLA, Ryoko UENO, Masanori SATO, Hiroshi SUZUKI, ...
    2017 Volume 72 Issue 1 Pages 27-38
    Published: August 31, 2017
    Released on J-STAGE: April 18, 2018
    JOURNAL FREE ACCESS

    The Amami Islands are located south of Japan's main islands and their inherent fauna and flora have high species diversity. In order to augment our limited knowledge on the coastal benthic fauna of these islands, we investigated the macrobenthic fauna in four tidal flats on Amami-Oshima Island. A total of 123 species or taxa ware sampled at the four study sites, with the number of species at each site varying from 39 to 89. Species richness was highest at Tekebu-higata tidal flat (the northernmost study site) and lowest at Ichi-higata tidal flat (central Amami). Yanyu-higata in the northern part of the island, and Kunetsu-higata, the southernmost study site, had intermediate species richness. The density of benthic animals was lowest at Yanyu-higata and highest at Kunetsu-higata. The local diversity, the mean number of species at a station, did not vary markedly among the study sites (ranging from 3.35 to 4.79), whereas the species richness of tidal flats tended to differ among the study sites. This indicates that the species diversity of the tidal flats can be attributed to the diversity among stations (β diversity). The heterogeneity of benthic community is discussed in relation to tidal flat sediment condition.

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  • Shohei UMEMOTO, Taeko KIMURA
    2017 Volume 72 Issue 1 Pages 39-47
    Published: August 31, 2017
    Released on J-STAGE: April 18, 2018
    JOURNAL FREE ACCESS

    The free-living marine nematode Terschellingia longicaudata is a cosmopolitan species inhabiting muddy tidal flats, which has tolerance to pollution and low oxygen concentration in sediments. Although T. longicaudata is known to be a useful indicator of tidal flat environments, we currently have little ecological information on this nematode. In this study, we examined the distribution and population dynamics of T. longicaudata on a small tidal flat at the mouth of a short river (the Tanakagawa River) along the western coast of Ise Bay, central Japan. Sampling was undertaken at 13 sites on the flat once in June 2013, and also every 3 months from July 2013 to April 2014. T. longicaudata was found to be highly abundant at two sites, St.1 and St.13, which were characterized by reductive sediment with a high organic matter content. The density of T. longicaudata was in the range of 1.7−2.3×103 ind./10 cm2 at St.1 and 0.5−1.7×103 ind./10 cm2 at St.13. From August 2013 to July 2014, sampling was also undertaken every month at these two sites dominated by T. longicaudata. Juveniles and adults, including gravid females, occurred throughout the year at both sites. On the basis of monthly data for environmental conditions and T. longicaudata density, the density showed negative correlations with the ORP and salinity of the interstitial water. In contrast, the rate of gravid females showed a positive correlation with sediment temperature. In this study, we observed that T. longicaudata reproduced throughout the year. Further, the density of this species in the high-density distribution regions suggested that it is more sensitive to variations in the salinity and redox potential of interstitial water than to seasonal environmental variations.

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