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Shiba, Japan

Sakurai I.,Tokai University | Nakayama T.,Hokkaido Government Kushiro General Subprefectural Bureau | Hada Y.,Hokkaido Research Organization Central Fisheries Institute | Maekawa K.,Lake Saroma Fisheries and Aquaculture Co operation Organization | And 3 more authors.
Nippon Suisan Gakkaishi (Japanese Edition)

We examined a suitable site for the growth and survival of juvenile Japanese littleneck clam Ruditapes philippinarum. The survey was conducted in three artificial clam nurseries constructed along the intertidal coastline of Lake Saroma, Hokkaido. Cages accommodating the juveniles were embedded in the offshore side of nurseries 1, 2, and 4 in April; then, juvenile growth was investigated after 6 months. The proportion of the juveniles that would be dislodged from the sand by bottom disturbance due to wave action was calculated using a simulation model. Caging experiments revealed that the offshore side of nursery 1 was suitable for achieving high shell growth. The simulation suggested that the survival rate of the juveniles was higher towards the offshore side of the nurseries. On the basis of the results, we hypothesized that the offshore side of nursery 1 would be suitable for the growth and survival of the juveniles. Around 18,000 juveniles were released in the offshore and land sides of nurseries 1 and 4. Mean shell length and survival rate of the juveniles in nursery 1 was 1.7 and 4.4 times as high as that in nursery 4 after 12 months of releasing; this result supported our hypothesis. Source

Sato C.,Tokyo Kyuei Co. | Nakayama K.,Kitami Institute of Technology | Furukawa K.,Japan National Institute for Land and Infrastructure Management
Estuarine, Coastal and Shelf Science

This paper proposes a method of evaluating the occurrence of hypoxia or anoxia in bottom water of Tokyo Bay, which is typical of enclosed bays in Japan. In Tokyo Bay, the exchange of seawater with the ocean has previously been found to be dominantly controlled by estuarine circulation. Thus, one would expect the concentrations of dissolved oxygen (DO) in the bay head to be influenced mainly by estuarine circulation, which changes according to wind strength and river discharges. We investigated the effects of wind and river discharge on DO concentration around the bay head using a three-dimensional ecological model. To evaluate the occurrence of hypoxic or anoxic water, we developed a conceptual DO model, which was verified through the good agreement with the results from a three-dimensional ecological model. We conclude that the conceptual DO model has good potential for evaluating the factors leading to hypoxic or anoxic water around the bay head. Modeling suggested that, on average, wind effects were the dominant factor in the variation of bottom DO concentrations. However, we found that the contribution of extreme events, such as floods and strong winds exceeding 10 m s -1, was 50% or more. This suggests that extreme events play an important role in controlling the variation in DO concentration at the bottom of Tokyo Bay. © 2012 Elsevier Ltd. Source

Asano T.,Kagoshima University | Yamashiro T.,Kagoshima University | Nishimura N.,Tokyo Kyuei Co.
Natural Hazards

A seasonal scale field observation extending over a period of 82 days was conducted in Urauchi Bay on Kami-Koshiki Island, to record meteotsunami events, disastrous secondary oscillations locally known as "abiki." The bay has an elongated T-shape topography with a narrow mouth opening westward to the East China Sea. The area has suffered the effects of meteotsunami causing flooding in residential area and damage to fishing fleets and facilities. A comprehensive observation system for sea level, ocean currents and barometric pressure was deployed to cover the regions within and offshore from Urauchi Bay and the open sea near the island of Mejima in the East China Sea. Vigorous meteotsunami events, where the total height exceeded 150 cm, were observed over five-day periods during the observation period. One or two hours prior to the arrival of meteotsunami events at Kami-Koshiki Island, abrupt 1-2 hPa pressure changes were observed at the Mejima observation site. Pressure disturbances were found to travel eastward or northeastward. The propagation speed was found to nearly coincide with that of ocean long waves over the East China Sea, and as a result, resonant coupling should be anticipated. The incoming long waves were also amplified by geometric resonance with eigen oscillations inherent in the T-shape topography of Urauchi Bay. © 2012 Springer Science+Business Media B.V. Source

Nambu R.,Japan National Research Institute of Fisheries Engineering | Saito H.,Japan National Research Institute of Fisheries Engineering | Tanaka Y.,Tokyo Kyuei Co. | Higano J.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Kuwahara H.,Japan National Research Institute of Fisheries Engineering
Estuarine, Coastal and Shelf Science

There are many studies on spatial distributions of Asari clam Ruditapes philippinarum adults on tidal flats but few have dealt with spatial distributions of newly settled Asari clam (<0.3 mm shell length, indicative of settlement patterns) in relation to physical/topographical conditions on tidal flats. We examined small-scale spatial distributions of newly settled individuals on the Matsunase tidal flat, central Japan, during the low spring tides on two days 29th-30th June 2007, together with the shear stress from waves and currents on the flat. The characteristics of spatial distribution of newly settled Asari clam markedly varied depending on both of hydrodynamic and topographical conditions on the tidal flat. Using generalized linear models (GLMs), factors responsible for affecting newly settled Asari clam density and its spatial distribution were distinguished between sampling days, with " crest" sites always having a negative influence each on the density and the distribution on both sampling days. The continuously recorded data for the wave-current flows at the " crest" site on the tidal flat showed that newly settled Asari clam, as well as bottom sediment particles, at the " crest" site to be easily displaced. Small-scale spatial distributions of newly settled Asari clam changed with more advanced benthic stages in relation to the wave shear stress. © 2011 Elsevier Ltd. Source

Li Z.,Hanyang University | Li Z.,Korea Advanced Institute of Science and Technology | Matsuoka K.,Nagasaki University | Shin H.H.,Korea Advanced Institute of Science and Technology | And 4 more authors.

Two morphologically distinct species, Brigantedinium majusculum and Trinovantedinium applanatum, have been suggested as a cyst stage of Protoperidinium pentagonum; however, the cyst-theca relationships are still virtually undefined. In this study, we re-examined the motile stage of B. majusculum via thecal plate analysis together with a molecular phylogenetic analysis based on partial large-subunit ribosomal DNA gene sequences. The morphological features of motile cells germinated from B. majusculum were identical to those of Pr. sinuosum, and the molecular phylogenetic analysis showed that the germinated cells and B. majusculum are closely related to Pr. pentagonum and Pr. latissimum as a sister group. Additionally, high sequence divergences were observed between the germinated cells and B. majusculum as well as Pr. pentagonum and Pr. latissimum (18.0-19.5% according to P-values and 20.7-22.9% according to Kimura two-parameter values). On the basis of these results, our study indicates that B. majusculum should be accepted as the cyst of Pr. sinuosum. Copyright © 2015 International Phycological Society. Source

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