日本ベントス学会誌
Online ISSN : 1883-891X
Print ISSN : 1345-112X
ISSN-L : 1345-112X
55 巻
選択された号の論文の8件中1~8を表示しています
  • 堤 裕昭, 竹口 知江, 丸山 渉, 中原 康智
    2000 年 55 巻 p. 1-8
    発行日: 2000/07/25
    公開日: 2009/08/07
    ジャーナル フリー
    There are sandy tidal flats along the Ariake Sea coast in Kumamoto Prefecture, where 40 to 65 thousand tons of clams, Ruditapes philippinarum, were harvested until the mid-1980s. However, the clam population has collapsed over the past two decades. In the past few years, less than five thousand tons of the clams have been harvested per year. We have studied the population dynamics of several dominant species of bivalves and the benthic community dynamics of the Midori River tidal flats in Kumamoto. The results of population studies of two bivalves, Ruditapes philippinarum and Musculista senhousia, revealed one of the reasons why these populations collapsed on the tidal flats. They suffered high mortality after settling on the substrate. In experimental studies to recover the clam population, sand was brought from the sea floor offshore to the tidal flats, covering an area of 6, 750m2 with a 50cm in depth. Abundant benthic communities over 370gWW/m2 were formed only in areas where new sand had been placed. Several species of bivalves, including Ruditapes philippinarum and Musculista senhousia, polychaetes and other animals occurred densely one year after the treatment. These benthic animals had low mortality after settling on the new substrate.
  • 大隅 大, 弥益 輝文
    2000 年 55 巻 p. 9-14
    発行日: 2000/07/25
    公開日: 2009/08/07
    ジャーナル フリー
    Specimens of the nudibranch Gymnodoris nigricolor were found on the fins of three gobiid fish species, Amblyeleotris ogasawarensis, Ctenogobiops pomastictus, and C, feroculus, near Oujima and Sesoko Islands, Okinawa, in February and May, 1994. These gobiids inhabit the burrows of snapping shrimps. The nudibranchs could be found attached to any fin (caudal, dorsal, pectoral, anal, and pelvic fins) of these fish, and they appeared to feed on a portion of the fin membrane together with one or two of the adjacent fin rays. In the laboratory, G. nigricolor also attached to a free-living gobiid fish, Bathygobius cocosensis. Nudibranchs gathered in glass tubes that had been used as refuges by A. ogasawarensis and C. pomastictus. This suggests that the nudibranchs were attracted to substances that had originated from the fish and remained in the tubes. The nudibranchs did not always attach to the fins of test fish, and individuals that did so detached themselves 1-2 days later. Their association with the fish thus appears to be a predator-prey interaction. Spawning of Gymnodoris nigricolor was observed in a rearing tank. About 200-700 eggs of 0.15 mm in diameter were found in each egg mass. Embryos hatched 10-11 days after oviposition at 24°C.
  • 前田 耕作, 清野 聡子, 西原 繁朝, 日野 明日香
    2000 年 55 巻 p. 15-24
    発行日: 2000/07/25
    公開日: 2009/08/07
    ジャーナル フリー
    The horseshoe crab Tachypleus tridentatus is known to lay its eggs on beaches in the upper intertidal zone in summer, and the embryos develop and hatch in the sand. The hatched larvae emerge from the sand surface and move into the sea on the night of the high tide in spring tide. Up to now, however, larval emergence, seasonal change, and their relationship to the physical environment at spawning sites have not been fully studied. The duration and frequency pattern of emergence and peculiarities of the physical environment were investigated at two spawning sites (A: Kubihineri; B: Eitaibashi) in Moriye Bay, Oita Prefecture. The number of emerged hatched larvae was investigated using a fish-luring light around high tide during the spring tide. Furthermore, the spawning period was identified to analyze its effect on the emergence period. The temperature and salinity of the interstitial water were measured at the spawning sites, and pH, turbidity and dissolved oxygen in the surface water were measured around the high tide in the spring tide. The relationships with lunar phase and tidal height were investigated. More larvae emerged in autumn (from mid-September to mid-November) than in spring-summer (from late April to late June). At site B, the beginnings of both larval emergence and spawning were delayed by about half a month in comparison with site A. The beginning of emergence in autumn thus appeared to be influenced by the timing of the spawning season. The majority of hatched larvae emerged during the period between one hour before and two hours after the high tide. Most of the larvae emerged after seawatel had flooded the spawning site. Therefore, hatched larvae appeared to be stimulated to move by seawater flooding into the sand, and began moving within the sand. The larvae emerged when the temperature was higher than 16°C, salinity was higher than 19 psu, and the dissolved oxygen was higher than 6 mg/l. Hatched larvae did not emerge at neap tide when the tidal height was less than 190 cm. There was no significant difference between the number of larvae that emerged during spring tides at full moon and at new moon.
  • 村田 優子, 和田 恵次
    2000 年 55 巻 p. 25-33
    発行日: 2000/07/25
    公開日: 2009/08/07
    ジャーナル フリー
    The spatial distribution patterns of two species of intertidal boring isopods, Sphaeroma wadai Nunomura and S. sieboldii Dollfus, on the coast of Tanabe Bay, central Japan, were described, and the factors affecting their distributions were investigated. Sphaeroma wadai was distributed mainly in the inner parts of the bay, being found in sandstone and decaying wood. On the contrary, the main distribution areas of S. sieboldii were near the mouth of the bay, and they inhabited sandstone. The hardness of the inhabited sandstone was similar between these two species. Salinity and wave strength (as wave amplitude) at selected stations were measured, and both gradually declined toward the inner parts of the bay. Salinity tolerance tests in the laboratory indicated that S. wadai can better tolerate low salinity than S. sieboldii. Field experiments involving the transplantation of sandstone inhabited by S. wadai to various sites in the bay resulted in the observation that this species had a lower tendency to abandon the transplanted substratum when moved inward in the bay than outward, but the reverse was true in S. sieboldii. Preference tests for wood and sandstone were conducted in the laboratory. Blocks of wood and sandstone were put into aquaria, into which isopods were then released. Both S. wadai and S. sieboldii preferred wood when the wood was soft (hardness=15.45±10.22 kg/cm2), but they chose stone when the wood was hard (20.45±3.84 or 32.94±3.15 kg/cm2). During these experiments, individuals of S. wadai very frequently occurred on the blocks of wood and stone, while more than half the individuals of S. sieboldii were not attracted to any blocks. Observations in tide-simulation tanks revealed that some individuals of S. wadai were active outside of their burrows during nighttime in submerged conditions, while no S. sieboldii were ever active outside of their burrows. This suggests a difference in the intensity of dependence on burrows between the two species. In summary, salinity and wave strength are regarded as the main factors causing differences in the spatial distributions of these two isopod species, although the presence or absence of the substrata they bore into is also considered a primary factor.
  • 古谷 純一
    2000 年 55 巻 p. 34-42
    発行日: 2000/07/25
    公開日: 2009/08/07
    ジャーナル フリー
    “Environmental Impact Assessment Law” was enforced in June 1999, which introduced some new principles into the assessment procedures. “Screening” in small-scale projects (Class-II Projects): to evaluate whether the Environmental Impact Assessments (EIAs) should be conducted or not before conducting assessment, the determination should be made on an individual project basis; Preparation of a “scoping” document which compiles the items to be assessed and techniques used for conducting the surveys relevant to a given assessment, the items should be contained in the EIAs, and the document should be adviced by the prefectural governors, mayors and the public during the course of the preparation; The concept of the “environmental preservation measures” (mitigation and follow-up) is newly introduced; The item “ecosystem” is newly included into the items of environmental factors to be assessed.
  • 風呂田 利夫
    2000 年 55 巻 p. 43-44
    発行日: 2000/07/25
    公開日: 2009/08/07
    ジャーナル フリー
  • 2000 年 55 巻 p. 47-49
    発行日: 2000/07/25
    公開日: 2009/08/07
    ジャーナル フリー
  • 2000 年 55 巻 p. 53-54
    発行日: 2000/07/25
    公開日: 2009/08/07
    ジャーナル フリー
feedback
Top