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Kitade Y.,Tokyo University of Marine Science and Technology | Igeta Y.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Fujii R.,Canon Inc. | Ishii M.,Chiba Prefectural Fisheries Research Center
Journal of Oceanography | Year: 2011

Monitoring using a thermistor array and an acoustic Doppler current profiler was carried out in the outer part of Tokyo Bay from May 20 to November 30, 2006. Current fluctuations with tidal periods were amplified during the maximum temperature period in early September. The strong current interfered with fishing operations using set nets. Although the current fluctuation was speculated to be baroclinic motion from a phase relationship among fluctuations of temperature, current and sea level, empirical orthogonal function analysis showed the dominance of a barotropic structure. Such a discrepancy in the current structure was explained by an internal tide propagating along a deep canyon in the outer part of Tokyo Bay. Furthermore, amplification of the semidiurnal internal tide and the warming of the temperature field were found to be induced by the intrusion of Kuroshio warm water. The amplification mechanism was examined using a two-dimensional model with idealized topography. It was concluded that the large amplitude of the semidiurnal internal tide is resonantly generated in the deep canyon in the outer Tokyo Bay when stratification becomes strong and the period of the internal seiche approaches the semidiurnal period. © 2011 The Oceanographic Society of Japan and Springer. Source


Fukui Y.,Japan National Research Institute of Fisheries Science | Abe M.,National Fisheries University | Kobayashi M.,Seikai National Fisheries Research Institute | Shimada Y.,Chiba Prefectural Fisheries Research Center | And 4 more authors.
International Journal of Systematic and Evolutionary Microbiology | Year: 2014

Gram-stain-negative, aerobic, halophilic bacteria, designated SCM-1T, LCM10-1 and CTBL-B-147, were isolated from modified half-strength SWM-III medium, PES medium and thalli after laboratory cultivation of a red alga, Porphyra yezoensis. Phylogenetic analysis of 16S rRNA gene sequences indicated that the new isolates were affiliated to the genus Sulfitobacter of the class Alphaproteobacteria, and the 16S rRNA gene sequence similarity of the new isolates with the closest related species, Sulfitobacter mediterraneus CH-B427T, was 98.8 %. The DNA G+C contents of the new isolates were in the range of 61.4-62.3 mol%. DNA-DNA relatedness values of strain SCM-1T with other type strains of the genus Sulfitobacter were less than 15.9 %. The new isolates contained Q-10 as the predominant ubiquinone, phosphatidylcholine, phosphatidylglycerol, an unidentified amino lipid and an unidentified lipid as the main polar lipids, and C18: 1ω7c, C19: 1ω7c and C16: 0 as the major fatty acids (>10 % of the total). Strain SCM-1T could be differentiated from Sulfitobacter mediterraneus JCM 21792T by 35 morphological and phenotypic characteristics. On the basis of the phylogenetic, genetic and phenotypic properties of the new isolates, the name Sulfitobacter porphyrae sp. nov. is proposed, with strain SCM-1T (= LMG 27110T = NBRC 109054T) as the type strain. © 2014 IUMS. Source


Kodama K.,Japan National Institute of Environmental Studies | Tajima Y.,Kanagawa Prefectural Fisheries Technology Center | Shimizu T.,Kanagawa Prefectural Fisheries Technology Center | Ohata S.,Chiba Prefectural Fisheries Research Center | And 2 more authors.
Marine Pollution Bulletin | Year: 2014

We investigated effects of severe hypoxia (dissolved oxygen <1 mll-1) on recruitment of mantis shrimp Oratosquilla oratoria in Tokyo Bay. Ten-year field surveys were conducted to examine quantitative relationships in annual mean densities of larvae and juveniles, and spatial distribution of juveniles and severe hypoxia. There was no significant correlation between annual mean densities of larvae and juveniles, suggesting that mortality during larval or juvenile stages varies among years, which might have regulated abundance of young-of-the-year juveniles. Juvenile density was low in the severely hypoxic area, implying that hypoxia could affect survivals and spatial distribution of juveniles. Meanwhile, there are yearly fluctuations in juvenile density in normoxic areas of both northern and southern part of the bay. This evidence suggests that abundance of post-settled juveniles might have been determined by not only effects of hypoxia, but also other factors influencing mortality during the early life stages. © 2014 Elsevier Ltd. Source


Gomi Y.,Mie University | Gomi Y.,Chiba Prefectural Fisheries Research Center | Miyazaki T.,Mie University
Fisheries Science | Year: 2015

In teleosts, the area of peak ganglion cell density in the retina (area centralis, AC) is thought to reflect the primary visual axis for feeding. The bluegill Lepomis macrochirus are known to undergo ontogenetic shifts in diet preference, but because their diet is affected by population density, interspecific competition, and seasonal changes in prey availability, they are considered generalist predators. We investigated whether the diet shifts of the bluegill were associated with a change in the location of the AC (total length of fish specimens, range 44–243 mm). The AC was located temporally in the retina of smaller fish (40–100 mm), and the area of increased density included the ventral and central regions of the retina. Conversely, the AC was located in the dorso-temporal region of the retina in larger (100–200 mm) fish. Lastly, in the largest bluegill (> 200 mm), the AC was located in the temporal region of the retina. In all cases, the orientation of the visual axis was consistent with the known diet preferences of the different size classes. © 2015, Japanese Society of Fisheries Science. Source


Toba M.,Chiba Prefectural Fisheries Research Center | Ito M.,Tokyo University of Marine Science and Technology | Kobayashi Y.,Chiba Prefectural Fisheries Research Center
Journal of Shellfish Research | Year: 2011

There have been numerous attempts to create and/or develop harvestable tidal areas where juveniles of the natural Manila clam Ruditapes philippinarum may be abundantly stocked. To prevent erosion and/or promote the colonization of natural juveniles through improving the physical stability of bottom sediment, it is important to understand the mechanisms that regulate dispersal and recolonization of benthic juveniles. The physical transport of bottom sediment is known to have a substantial effect on the spatial distribution patterns of infaunal bivalves in intertidal soft-bottom habitats. During the summers of 2004 and 2005, we conducted field experiments to identify the physical transport mechanisms for newly-settled postlarval Manila clams until growth to a size of 1 mm shell length at the Banzu tidal flat of Tokyo Bay in Japan. We used sediment traps to collect natural and released hatchery-reared juveniles, in parallel to acquiring measurements of seawater flow and observations of the spatial distribution of newly-settled natural juveniles. There was a sharp increase in the number of clams that were collected in the traps placed on the soft-bottom surface when τ w (wave shear stress) exceeded 0.3 N m -2. Because the τ c (advection shear stress) was far lower than τ w (τ c/τ w =1/601/130), the initiation of juvenile transport appeared to depend primarily on wave-generated oscillatory flow. The number of trapped juveniles regressed linearly to the weight of the sediment that was simultaneously collected in the trap (R 2 = 0.99, 0.81), which indicated that clams were transported in a similar way to that of sediment grains, despite juveniles and sand particles exhibiting different physical properties (size and specific gravity). Hence bedload transport may have resulted from the biologically induced adhesion of juvenile clams to sediment grains and/or their burrowing behavior. In the release-recovery experiment of marked juveniles, a larger number of clams were recovered from traps that had been placed downstream of the water current from the release point. A denser distribution of the natural Manila clam population settled in mid-July 2004, and subsequently moved several hundreds of meters inshore within a one month period. The concurrent monitoring of bottom flow during a total 4 wk period in the summer of 2004 indicated that τ w frequently exceeded the incipient threshold of bedload transport (assumed to be 0.3 N m -2). Consequently, the bedload movement of Manila clam juveniles in the study area was expected to be initiated at a wave shear stress that was greater than the incipient threshold, and in a downstream direction of the advection current. Because juvenile clams in the summer population appeared to be frequently subjected to hydrodynamic stress, which forces juveniles to move and halt incidentally in the early benthic stages, physical transport is likely to contribute to the changing pattern of juvenile distribution at the Banzu tidal flat of Tokyo Bay in Japan. Source

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