Japanese Journal of Benthology
Online ISSN : 1883-891X
Print ISSN : 1345-112X
ISSN-L : 1345-112X
Volume 54
Displaying 1-8 of 8 articles from this issue
  • [in Japanese]
    1999 Volume 54 Pages 1-3
    Published: August 25, 1999
    Released on J-STAGE: August 07, 2009
    JOURNAL FREE ACCESS
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  • Naoko UEDA, Hiroaki TSUTSUMI, Kumi AKASHI, Chiemi HAYASHIDA, Machiko Y ...
    1999 Volume 54 Pages 4-13
    Published: August 25, 1999
    Released on J-STAGE: August 07, 2009
    JOURNAL FREE ACCESS
    In an estuary there is a clear gradient of water salinity from the seaward to the upstream area due to river water inflow. However, the salinity profile of the water changes over time as the result of tidal action, meteorological influences and wind, etc. Estuarine organisms must tolerate such strong and variable environmental stresses. In general, the diversity of aquatic organisms tends to be limited in estuaries due to the relatively severe environmental conditions. However, information concerning the distribution of aquatic organisms in estuaries is limited. To this date, few estuaries have been intensively researched in this regard in Japan. In 1993, we carried out benthic sampling to describe seasonal changes in the distribution of macrobenthic animals and physicochemical conditions of the water and sediments in the tidal areas of the Murasaki River, Kitakyushu, Japan. A clear faunal replacement was observed in the dominant species of macrobenthic animals along the gradient of salinity of the bottom water. At the most seaward end of the river mouth, the polychaetes Cossura coasta and Lumbrineris longiforia and a bivalve, Theora fragilis, occurred densely. Upstream, a polychaete, Capitella sp., an amphipod, Grandidierella japonica, and the bivalves Musculista senhousia and Ruditapes philippinarum were the dominant macrobenthic animals. Furthest upstream, in the brackish areas of the tidal river, two brackish-water organisms occurred, a gastropod, Clithon retropictus, and a polychaete, Neanthes japonica. The distribution patterns and abundance of these dominant species changed markedly with the seasons, particularly around the midpoint of the tidal river, due to the flooding of the river in the summer. However, the total number of species and mean biomass of the macrobenthic animals in the tidal river as a whole were very stable, 39 to 43 species and 51.8 to 68.9gWW/m2, respectively, throughout the year.
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  • Masayuki SAWAMURA
    1999 Volume 54 Pages 14-23
    Published: August 25, 1999
    Released on J-STAGE: August 07, 2009
    JOURNAL FREE ACCESS
    From August 1993 to June 1994, the feeding habits of fishes and distribution of benthos were investigated off the coast of Usujiri, Hokkaido. Most of the 30 fish species sampled fed on benthic crustaceans: cumaceans, isopods, caprellideans, macrurans, and especially gammarideans and mysidaceans. The population of some dominant crustaceans dramatically varied depending on season and water depth; in shallow sea-grass beds in summer, their population exploded. Additionally if life-form categories are considered free-living surface dwellers comprised the principal diet for most fish species. Phytal animals, nest builders and epifaunal tube dwellers, infaunal dwellers, and nekton were also well represented in the stomach contents of fishes. Whittaker's percentage similarity (PS2) of stomach contents was relatively high on average among feeders on mysids or free-living surface-dwelling gammarideans, which appeared in shallow areas in summer. In contrast, the PS2 of stomach contents was consistently low between polycheate feeders and other fish species.
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  • Satoshi KOBAYASHI
    1999 Volume 54 Pages 24-35
    Published: August 25, 1999
    Released on J-STAGE: August 07, 2009
    JOURNAL FREE ACCESS
    Reproductive ecology of the Japanese mitten crab Eriocheir japonica (de Haan) is reviewed mainly based on information collected over the last ten years. This crab is a catadromous species which grows to maturity in freshwater and reproduces in brackish waters and the sea. Adult crabs migrate downstream from fully freshwater areas to marine tidal areas for the purpose of copulation, oviposition, and hatching of eggs. Megalopa larvae settle and metamorphose to the crab stage in upper brackish areas after planktonic zoea larva stage in the sea. Juvenile crabs migrate upstream to freshwater and disperse widely along the river. Larger crabs are distributed in the upper reaches. In both sexes, in the upstream direction the population density tends to decrease, and size at maturity tends to be larger, and the sex ratio becomes female-biased. Details of the process and timetable of maturation (puberty moult and gonad maturation), downstream migration, mating behaviour, oviposition and hatching, the planktonic life of the zoea larvae, and the settlement of the megalopa larvae are noted and their ecological significance is discussed. Ovarian maturation occurs after the puberty moult (terminal moult), taking approximately 4 months. Adult crabs in a hard-shell condition migrate downstream to the tidal area and participate in reproduction, but females migrate downstream even if they have not completed maturation. There are two groups of females that differ in the timing of reproduction. The early-maturing group, which is small in number, develops ovaries in September or October and oviposits in October. In the late-maturing group, which is larger in number, the puberty moult occurs in August, maturation is generally complete by December, and oviposition occurs after December. Mating is initiated without any precopulatory behaviour. Females do not use a sex pheromone to attract mates and males approach without determining the receptivity of the females. Females can copulate only after their ovaries have matured, and they lay eggs within a day after copulation. However, females are not necessarily in a receptive condition in the tidal area, and approaching males are often rejected by females with not fully matured ovaries. The duration of copulation is from 13 to 43 minutes and is negatively correlated with water temperature. Postcopulatory guarding by males continues for several hours, and females may be released by males when oviposition occurs. Females often reject guarding by small males. Females oviposit and hatch eggs up to a maximum of three times. The number of eggs tends to decrease in later clutches. Most crabs seem to die after reproduction without further moulting. Size at maturity varies from approximately 35mm to 75mm in carapace width, but each crab can participate in reproduction only in one season and cannot thereafter grow larger. Thus, there is a wide variation of reproductive success in E, japonica. In the females, fecundity is higher in larger crabs. As for the males, larger ones with larger chelipeds can most effectively guard females after copulation. The duration of embryonic development varies from 2 weeks to 3 months, and that of the planktonic life of zoea larvae in the sea is estimated to vary with water temperature. Settlement of megalopa larvae in the upper tidal reaches occurs from 2 weeks to 4 months after hatching, depending on the river, and it takes place mainly in mid-autumn (October) and early summer (May to June). The young crabs that metamorphose in autumn and winter neither migrate nor grow during the winter. Upstream migration of the autumn settlers and the summer settlers to freshwater occurs from March to June and from July to August, respectively. This mode of settlement with two peaks reflects the temporal pattern of reproduction. Autumn settlers are derived from the eggs produced by the early-maturing females, and summer settlers from the latematuring ones. The reproductive strategy of this crab
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  • Toshio FUROTA, Kahei SUZUKI
    1999 Volume 54 Pages 36-43
    Published: August 25, 1999
    Released on J-STAGE: August 07, 2009
    JOURNAL FREE ACCESS
    The Yatsu Tidal Flat is a small tidal wetland of approximately 40 ha, located in the middle of landfill along the northern shore of Tokyo Bay. The flat is connected to the bay through two narrow tidal waterways. Originally, extensive tidal flats rimmed the entire coast of Tokyo Bay. Almost all of these, however, have been landfilled, and the Yatsu Tidal Flat was left stranded in the center of the landfill. This small flat is now the most important feeding habitat for shorebirds along the northern bay. The flat was registered under the Ramsar Convention in 1983. Macrobenthic animals are vital prey for shorebirds, and they are also important elements in the tidal flat ecosystem. Observations of the macrobenthic fauna at the Yatsu Tidal Flat were conducted in 1974-75, one year after the flat was enclosed by the surrounding landfill, by a team of researchers. A similar survey was later implemented in 1994-95 by the Japanese Environmental Agency and local governments. Environmental conditions of the flat, such as particle size distribution of the sediment and nutrient load, changed greatly between these surveys. The authors also conducted observations at the Yatsu Tidal Flat during the winter of 1986-87. Both the horizontal distribution of macrobenthic animals and their vertical distribution in the sediment column were observed. The results were correlated with sediment conditions (redox potential and particle size). The macrobenthic fauna was dominated by the polychaetes Tylorrhynchus heterochaetus and Neanthes succinea. Tylorrhynchus heterochaetus was restricted to the margin of the flat, which consisted of fine-sandy aerobic sediments; N. succinea was found in the central part of the flat, which consisted of reduced muddy sediments. In general, the number of species tended to decrease in more reduced sediments, but the largest number of species was found in an area where the sediment was heavily reduced in its deeper layers but aerobic near the surface. In addition, oligochaetes and several species of small polychaetes, such as Sigambra sp. and Capitella sp., occurred in very reduced sediment (Eh less than-200mV). The results of our observations indicate that aerobic conditions near the surface are important in maintaining the macrobenthic population in an organically polluted tidal wetland. A comparison of the results of the three surveys that have been conducted during the 20 years since the flat was enclosed shows that the diversity of the macrobenthos increased gradually, but that the size of the nereidid polychaete population, which provides the most important food source for shorebirds, has decreased in recent years. This decrease may be due to a reduction in the loads of organic matter and inorganic nutrients entering the flat.
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  • Shoichi KIMURA, Taeko KIMURA
    1999 Volume 54 Pages 44-56
    Published: August 25, 1999
    Released on J-STAGE: February 05, 2010
    JOURNAL FREE ACCESS
    Marshes dominanted by reeds (Phragmites australis (Cav.)) are typical of the high intertidal zones of estuaries and seashores in inlets and bays in temperature Japan. However, recent coastal development has resulted in the reclamation of the coastline before thorough studies of these ecosystems could be undertaken in Japan. We conducted a faunal study of molluscan gastropods inhabiting the reed marshes at 20 locations along coast of Mikawa and Ise Bays in central Japan for 16 years (1982 to 1998). The marshes are categorized in terms of their locations and size, i.e., A: river marsh, which is small and occurs along a river (lower reaches to river mouth); B: seashore marsh, which is relatively large and occurs along the seashore; A+B: which occurs along the river and seashore without a break. Further we determine the degree of human disturbance of the marsh ecosystem, i.e., 1. highly disturbed: reeds remain only in the high intertidal zone, but does higher up the shore due to the installation of coastal protective barriers; 2. intermediately disturbed: reeds remain in the high intertidal zone on a small scale, but the marsh subsystems such as tidal creeks and backshore marshes have disappeared; 3. well conserved: human disturbance has scarcely affected the marsh vegetation. In this last case, reeds are broadly distributed from the high intertidal to higher shores, where growth of Erigeron canadernsis L., Solidago altissima L., Miscanthus sinensis Andress., Rosa wichuraiana Crep., and Vitex ratundifolia L. flu. are found; the marsh subsystems are well developed, which provide highly heterogeneous habitats for various biota. Types of marshes of reed are described. using combination of each three types as related with their locations, size (A, B, A+B) and the degree of human disturbance of the marsh ecosystem (1, 2, 3). In the type Al (St. 1, 4, 5, 6, 10, 11), 5 to 12 (average 7.5) species of gastropods were found. In the type A2 (St. 3, 7, 8, 14), 9 to 15 (average 13.0) species were found. In the type A3 (St. 9, 12, 13, 16, 17, 18, 20), 8 to 19 (average 13.9) species were found. In the type A3+B3 (St.2, 15, 19), 18 to 23 (average 21.0) species were found. The spatial distribution patterns of the mollusc species are categorized by micro-habitat as follows, i.e., S1, on stones; S2, under stones on soft sediment; S3, under the stones half buried in soft sediment; W 1, on decayed wood; W2, under decayed wood on soft sediment; W3, under decayed wood half buried in soft sediment; MU, on soft sediment. A total 26 species were collected during the 16 years (2 spp. of Neritidae, 1 sp. of Phenacolepadidae, 2 spp. of Batillariidae, 3 spp. of Cerithideidae, 2 spp. of Iravadiidae, 1 sp. of Stenothyridae, 1 sp. of Truncatellidae, 8 spp. of Assimineidae, 6 spp. of Ellobiidae). Among these were 18 species determined as “endangered” by the Fish-ery Agency and the Japan Fishery Resouce Conservation Association (1994), the Japan Fishery Resource Conservation Association (1995, 1996, 1997), and Wada et al. (1996): Clithon (Clithon) retropictus (Martens, 1879), Neritina (Dostia) violacea (Gmelin, 1791), Phenacolepas sp., Batillaria multiformis (Lischke, 1869), Cerithidea (Cerithidea) rhizophorarum A. Adams, 1855, Cerithidea (Cerithideopsilla) cingulata (Gmelin, 1791), Cerithidea (Cerithideopsilla) djadjariensis (K. Martin, 1899), Iravadia (Fairbankia) sakaguchii (Kuroda et Habe, 1954), Iravadia (Fluviocingula) elegantula (A. Adams, 1863), Stenothyra edogawaensis (Yokoyama, 1927), Angustassiminea yoshidayukioi Kuroda, 1959, Assiminea parasitologica Kuroda, 1958, Assimineidae gen. et sp., Ellobium chinensis (Pfeiffer, 1855), Auriculastra duplicata (Pfeiffer, 1855), Laemodonta siamensis (Morelet, 1875), Laemodonta exaratoides Kawabe, 1992, Melampus (Melampus) sincarporensis Pfeiffer, 1855. Brief diagnoses of Phenacolepadidae, Iravadiidae, Assimineidae, and Ellobiidae are provided.
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  • 1999 Volume 54 Pages 57-58
    Published: August 25, 1999
    Released on J-STAGE: August 07, 2009
    JOURNAL FREE ACCESS
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  • 1999 Volume 54 Pages 61-63
    Published: August 25, 1999
    Released on J-STAGE: August 07, 2009
    JOURNAL FREE ACCESS
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