The University of Tokyo · Earth and Planetary Sciences
Professor Kazutaka Takahashi's research lab specializes in marine ecology and oceanography, focusing on predator-prey interactions, plankton dynamics, and the influence of physical oceanographic processes on marine organism distributions. The lab investigates submesoscale physical-biological interactions, particularly how environmental factors such as temperature, salinity, and water density affect the vertical and horizontal distribution of key species like doliolids and copepods. A central theme is the role of behavioral adaptations—such as diel vertical migration and feeding rhythms—in shaping the ecology of sandy beach and pelagic ecosystems in the North Pacific. The lab employs advanced observational tools, including video plankton recorders and in situ monitoring, to study ecological processes at fine spatial and temporal scales.
Figures are computed from collected data and may differ slightly.
Abstract We investigated distribution patterns of a doliolid ( Dolioletta gegenbauri ) bloom in relation to the physical environment using a video plankton recorder in the Oyashio–Kuroshio mixed water region. Using 12 km transects, doliolid blooms were encountered at a horizontal scale of about 2–3 km, which corresponds to submesoscale physical events. Doliolids were also consistently encountered in the subsurface layer above the pycnocline in warmer (> 14ºC) and higher‐salinity (> 34) wat
Predation on intertidal sand-burrowing peracarid crustaceans by fish was investigated in a diel regime in the spring and summer of 1994 and 1995 in the surf-zone of a sandy beach in Otsuchi Bay, northeastern Japan. The mysid Archaeomysis kokuboi, the amphipod Haustorioides japonicus, and the isopod Excirolana chiltoni were the main peracarids preyed on by the surf-zone fish. The importance of each prey species was evaluated using indices of stomach fullness and the relative importance of each fo
We investigated predatory behavior of sapphirinid copepods on doliolids around the Kuroshio Extension at stations experiencing blooms of Dolioletta gegenbauri . Onboard observations showed that adult Sapphirina nigromaculata was an active predator of doliolids, with a preference for internal tissues. When entering a doliolid body cavity, sapphirinids left a characteristic bite mark around the fringe of oral and atrial aperture or hole on the tunic of the doliolid. In situ observations with a vid
Diel and tidal changes in distributions of the 3 species of sand-burrowing mysids, .Archaeomysis kokuboi Ii, A. japonica Hanamura, Jo & Murano and Iiella ohshimai (Ii), were studied during summer on a sandy beach in Otsuchi Bay, on the P a c ~f ~c coast of northeastern Honshu, mainland Japan. During the day A. kokubol, the closest dweller to the shoreline, showed remarkable tidal migratlons that differed among the developmental stages and sexes. D u r ~n g the daytime, intraspecific zonatlon of
Mechanisms of interactions among different scale phenomena play important roles for forecasting of weather and climate. Multi-scale Simulator for the Geoenvironment (MSSG), which deals with multi-scale multi-physics phenomena, is a coupled non-hydrostatic atmosphere-ocean model designed to be run efficiently on the Earth Simulator. We present simulation results with the world-highest 1.9km horizontal resolution for the entire globe and regional heavy rain with 1km horizontal resolution and 5m ho
Feeding rhythm, in terms of die1 change in frequency of occurrence of empty stomachs and in gut pigment content, and composition of diets were investigated for the sand-burrowing mysids Archaeomysis kokubo! and A japonica during the summer season on a sandy beach at Otsuchi Bay, northeastern Japan A kokuboi exhibits pronounced nocturnal feeding regardless of sex or developmental stage A laponica also shows nocturnal feeding, although the nocturnal feeding rhythm of the mature mysids is less clea
Seasonal abundance and distribution patterns of the 3 species of sand-burrowing mysids, Archaeomysis kokuboi Ii, A. grebnitzkii Czerniavsky and Iiella ohshimai (Ii), were studied on a sandy beach at Otsuchi Bay, northeastern Honshu, Japan. Clear interspecific bathymetric zonation was recognized among the 3 species. Their habitats shifted seasonally and according to development in species-specific ways. A. kokuboi was the shallowest dweller and was distributed from the swash zone to the step area
Antioxidants found in microalgae play an essential role in both animals and humans, against various diseases and aging processes by protecting cells from oxidative damage. In this study, 26 indigenous tropical marine microalgae were screened. Out of the 26 screened strains, 10 were selected and were further investigated for their natural antioxidant compounds which include carotenoids, phenolics, and fatty acids collected in their exponential and stationary phases. The antioxidant capacity was a
The distribution of floating plastic debris around the Kuroshio Current which transports plastics from the coastal waters of Asian countries to North Pacific subtropical gyre, was investigated in 2014. The mean abundance and weight of plastic debris on the sea surface were 100,376 counts/km<sup>2</sup> and 446.16 g/km<sup>2</sup>, respectively. Intensive plastic accumulation was observed in the frontal area between the northern edge of the Kuroshio and coastal waters off Shikoku, while a relativ
Abstract Nitrogen‐fixing microorganisms (diazotrophs) significantly influence marine productivity by converting N 2 gas into bioavailable nitrogen. Recent studies revealed that nitrogen fixation occurs in both warm oligotroph and colder and/or N‐rich water; however, little is known about the spatial variability of nitrogen fixation activity and diazotroph diversity in cold waters. In this study, we examined the nitrogen fixation activity and diazotroph community structure in the subarctic waters
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