Japanese Journal of Benthology
Online ISSN : 1883-891X
Print ISSN : 1345-112X
ISSN-L : 1345-112X
Volume 74, Issue 1
Displaying 1-11 of 11 articles from this issue
Original Articles
  • Hiroaki TSUTSUMI, Misato TSUJI, Tomo TATEISHI, Tomohiro KOMORITA
    2019 Volume 74 Issue 1 Pages 1-15
    Published: August 31, 2019
    Released on J-STAGE: September 09, 2019
    JOURNAL FREE ACCESS

    Corbicula japonica is one of the most dominant bivalves in macro-benthic communities in brackish lakes and estuaries throughout Japan. The population of this species in the Kikuchi River estuary, which is located in Kumamoto Prefecture, western Japan, exhibited unique mechanisms for persisting in the estuary with variable salinity of the water (0 and 30 within a day) caused by tidal activity. The planktonic larvae settled on the substrate at the upper part of the estuary, the juveniles grew up to adults, while being carried downward, and the adults occurred mainly at the lower part of the estuary. There, 2-year old adults started breeding at exceptionally small shell sizes (about 6 to 9 mm in length). However, this early reproduction seemed to give an advantage for Corbicula population to persist in the estuary. During the neap tide in autumn, reproducible adults suffer a high mortality event at the lower part of the estuary caused when high salinity water (>30) is formed on the floor of the estuary. Therefore, early reproduction enabled most adult clams to contribute to reproduction at least once in their lifetimes before they are exposed to high salinity conditions, although the number of gametes they released tended to be restricted due to their small sizes.

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  • Hiroshi HIRAKIUCHI, Tadashi SASAKI, Hitoshi SEMURA, Tetsuya MUKAI, Kaz ...
    2019 Volume 74 Issue 1 Pages 16-24
    Published: August 31, 2019
    Released on J-STAGE: September 09, 2019
    JOURNAL FREE ACCESS

    This study was conducted to clarify the effect of summer hypoxic water on the spatial distribution of ark shells (Anadara Kagoshimensis) in Lake Nakaumi, a brackish lake in the Japan Sea coast in Western Japan. From July to September in 2011 and 2012, dissolved oxygen (DO) concentration was monitored monthly at 29 sites in the lake, along with weekly/hourly DO measurements at a site in the center of the lake. Sixteen sites were sampled for ark shells using towed dredge in March and November 2012. In the July–September both in 2011 and 2012, hypoxic and/or anoxic water extensively covered the bottom surface of the lake excluding the northern part near Nakaura Channel, which is a major supplier of sea water from Japan Sea to the lake. Among the sampled sites, ark shells were collected from 8 and 5 sites in March and November, respectively. The collection sites were located near the southern end of Nakaura Channel. No ark shells were collected in the rest of the sites that were away from the channel. In March, collected ark shells were larger (shell length >40 mm) and had higher density (>11 ind./230 m2) in the sites near the channel than those in the other sites (<32 mm, <5 ind./230 m2). The relation between density of ark shells that survived >1 yr after settlement and collection site distance to the inlet of Nakaura Channel strongly suggested that high-DO water that flowed through the channel into the lake may have contributed toward the adult ark shells colonization in Lake Nakaumi.

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  • Mutsumi TSUJINO, Toshihiro SHIGETA
    2019 Volume 74 Issue 1 Pages 25-34
    Published: August 31, 2019
    Released on J-STAGE: September 09, 2019
    JOURNAL FREE ACCESS

    Macrobenthos including Asari clam (Ruditapes philippinarum) and meiobenthos inside and outside of cover-nets on the Minami tidal flat, Yamaguchi Bay were examined to study the effect of the nets on the benthos. Cover-net (5×7 m, 9 mm mesh size) have remained for five–seven years to protect from predation by fishes. The density of R. philippinarum and gastropods in the cover-net area were higher than those outside of the cover-net area. The density of nematodes in the cover-net was higher than outside area. Considering three sizes of nematodes (63–125, 125–250, and ≧250 μm), the percentage of the smaller size increased in the cover-net area, and the percentage of the large size tended to be low. The nematode family composition in the cover-net area differed from that in the outside area. The nematode density of Xyalidae, Comesomatidae and Oncholaimidae in the cover-net increased. The percentage of 1B nematode feeding type (non-selective deposit feeder) in the cover-net area was higher than outside area. This suggests that the cover-net not only affects the density of R. philippinarum and nematodes but also changes the nematode family composition.

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Note
  • Yumi HENMI, Yuto SHIOZAKI, Luna YAMAMORI, Gyo ITANI
    2019 Volume 74 Issue 1 Pages 35-40
    Published: August 31, 2019
    Released on J-STAGE: September 09, 2019
    JOURNAL FREE ACCESS

    Pseudopinnixa carinata (Crustacea: Decapoda: Varunidae) is a monotypic rare brachyuran endemic to the Japanese coast. Seventeen specimens of the crab were collected from tidal flats in Yamaguchi and Kochi Prefectures, Japan. The collection from Kochi Prefecture sets a new record from the Pacific coast of Shikoku. A review of P. carinata collection sites and the habitat information revealed that the species is widely distributed in Honshu, Shikoku, and Kyushu, but has never been collected in the Ryukyu Islands and southern Kyushu. This crab inhabits intertidal to subtidal sandy sediments with its deepest record being at 55 m depth. Several studies have shown that the crab was collected from sediments where burrowing invertebrates were abundant. Crabs have been found inside burrows of the echiuran Urechis unicinctus, the gebiidean shrimp Upogebia sakaii, and the axiidean shrimp Nihonotrypaea japonica by digging sediments. In this study, some specimens were pulled out from the burrows of N. japonica and other callianassid shrimp species as well as those of the polychaete Arenicola brasiliensis by yabby pumps.

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  • Shin’ichi SATO, Ryo ORITA, Ayako YAMAKAWA, Hirokazu ABE, Masatoshi MAT ...
    2019 Volume 74 Issue 1 Pages 41-42
    Published: August 31, 2019
    Released on J-STAGE: September 09, 2019
    JOURNAL FREE ACCESS
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  • Ryo ORITA, Masanori SATO, Shin’ichi SATO, Hiroshi KONDO, Masatoshi MAT ...
    2019 Volume 74 Issue 1 Pages 43-63
    Published: August 31, 2019
    Released on J-STAGE: September 09, 2019
    JOURNAL FREE ACCESS
    Supplementary material

    Changes during a 10-year period in distributional patterns of 24 polychaete species belonging to eight families [Glyceridae, Sigalionidae (Pisione and Pisionella), Pilargidae, Nereididae, Amphinomidae, Scalibregmatidae, Sternaspidae, and Pectinariidae] were described based on quantitative data by grab-samplings at 92 or 88 fixed subtidal stations in the Ariake Sea, western Kyushu, Japan in June in 1997, 2002, and 2007. The distributional pattern of each species was categorized into the following seven types: I) occurrence in all of six areas of the Ariake Sea (6 spp.), II) occurrence in five areas excluding the mouth part (1 sp.), III) occurrence mostly in four areas from the inner-south to mouth parts (2 spp.), IV) occurrence in three areas of the inner-south, center-east, and center-west parts (1 sp.), V) occurrence mostly in three areas of Isahaya bay, innermost, and center-east parts (1 sp.), VI) occurrence mostly in the mouth part (5 spp.), and VII) few appearances of up to three sites in each year (8 spp.). The mode of the temporal change in the distributional range and density was variable even among species belonging to the same distributional type. The ranges and densities of several species including some rare species extremely decreased from 2002 to 2007.

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  • Takaki YAMANAKA, Shin’ichi SATO, Masatoshi MATSUO, Masanori SATO, Miki ...
    2019 Volume 74 Issue 1 Pages 64-74
    Published: August 31, 2019
    Released on J-STAGE: September 09, 2019
    JOURNAL FREE ACCESS
    Supplementary material

    In the inner part of the Ariake Sea, Kyushu, Japan, several environmental changes caused by hypoxia and red tides have been observed after the dike construction for the reclamation of Isahaya Bay in 1997. We examined the changes in water quality, bottom sediments, and community structures of major benthic macrofauna (bivalves, gammaridean amphipods, and polychaetes) using samples obtained from 88 fixed stations covering the whole area of the Ariake Sea between June 1997(two months after the complete closure of the inner part of the Isahaya Bay by the dike construction) and June 2002(two months after the temporary opening of the water gates in the dike). Our results showed that the distribution of benthic macrofauna was altered by spatial patterns of mud content and median grain size of bottom sediments. Hierarchical cluster analysis identified seven macrobenthic animal assemblages distributed in the innermost and central-east parts (groups I to III), inner-south to central-west parts (groups V to VII), and in the mouth of the Ariake Sea (group IV) in 1997. However, in 2002, group VI (characterized by abundance of Photis reinhardi, Gammaropsis utinomii, Corophium sp. A, and Modiolus comptus), expanded its distribution into the central-west and inner-south parts of the Ariake Sea, where mud content of bottom sediment changed to 0–1% and hypoxia had occurred in the bottom waters from 1997 to 2002. These results suggest that the changes in macrobenthic community structures are altered by changes in bottom sediments and the occurrence of hypoxia in the Ariake Sea.

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  • Akifumi OHTAKA, Shin’ichi SATO, Mikio AZUMA
    2019 Volume 74 Issue 1 Pages 75-80
    Published: August 31, 2019
    Released on J-STAGE: September 09, 2019
    JOURNAL FREE ACCESS

    Species composition of aquatic oligochaetes was studied almost annually in the reservoir pond of Isahaya Bay in the Ariake Sea, Kyushu, Japan, starting after the closing of the floodgate in 1997 until 2018. Ten species all belonging to the family Naididae were recorded in the reservoir pond during the study period. Short after the closing of the floodgate, oligochaete species composition changed drastically from an epibenthos-dominated to a burrowing-dominated community. The change could be partly caused by eutrophication and mud sedimentation in the bottom. The present oligochaete community in the pond is composed of a small number of freshwater thermophile species with salinity and low-oxygen resistance, with Limnodrilus hoffmeisteri surpassing the others. A brackish limnodriloidine Doliodrilus tener, which became abundant soon after opening the floodgate in 2002, is newly recorded in Japan and re-described based on the specimens from the reservoir pond.

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