Researcher Database

Yoshio Masuda
Faculty of Environmental Earth Science Integrated Environmental Science Practical and Earth Sciences for Environment
Postdoctoral Fellow

Researcher Profile and Settings


  • Faculty of Environmental Earth Science Integrated Environmental Science Practical and Earth Sciences for Environment

Job Title

  • Postdoctoral Fellow

J-Global ID

Research Areas

  • Environmental science/Agricultural science / Environmental dynamics

Research Activities

Published Papers

  • Yoshio Masuda, Yasuhiro Yamanaka, Takafumi Hirata, Hideyuki Nakano, Takashi S. Kohyama
    ECOLOGICAL MODELLING 430 0304-3800 2020/08 
    G. E. Hutchinson raised the paradox of how a number of phytoplankton species competing for the same resources are able to coexist in a relatively isotropic environment. As a key for solving the paradox, we focused on the limiting similarity which prohibits the coexistence of similar species. We expected that the limiting similarity will be mitigated by some factors which are not represented in traditional theoretical studies but can be represented if we use a three-dimensional (3D) model. The use of a 3D model enables us to explore the limiting similarity without using the controversial assumption connecting niche overlap with the competitive exclusion in previous theoretical studies. Furthermore, while constant or no dispersion is given in theoretical studies, it is explicitly represented in a 3D model. The coexistence of similar species in 3D environments was explored by dividing a target persistent species in a quasi-equilibrium community into 80 subspecies, which were slightly different from one another at the optimum temperature for population growth. In the experiments, we found cases in which several dozens of species having nearly-overlapping niches coexist stably at a point for over 80 years. The comparison of experiments with and without dispersion by oceanic currents revealed that dispersion negates the progress of competitive exclusion or significantly delays the exclusion. The result that species having nearly-overlapping niches are able to coexist also highlights the crucial role of the specific rate in determining the number of coexisting species. If the number of coexisting species is not determined by the limiting similarity, it will be determined by the frequency of speciation events, as in the neutral theory.
  • Yasuhiro Hoshiba, Takafumi Hirata, Masahito Shigemitsu, Hideyuki Nakano, Taketo Hashioka, Yoshio Masuda, Yasuhiro Yamanaka
    OCEAN SCIENCE 14 (3) 371 - 386 1812-0784 2018/06 
    Ecosystem models are used to understand ecosystem dynamics and ocean biogeochemical cycles and require optimum physiological parameters to best represent biological behaviours. These physiological parameters are often tuned up empirically, while ecosystem models have evolved to increase the number of physiological parameters. We developed a three-dimensional (3-D) lower-trophic-level marine ecosystem model known as the Nitrogen, Silicon and Iron regulated Marine Ecosystem Model (NSI-MEM) and employed biological data assimilation using a micro-genetic algorithm to estimate 23 physiological parameters for two phytoplankton functional types in the western North Pacific. The estimation of the parameters was based on a one-dimensional simulation that referenced satellite data for constraining the physiological parameters. The 3-D NSI-MEM optimized by the data assimilation improved the timing of a modelled plankton bloom in the subarctic and subtropical regions compared to the model without data assimilation. Furthermore, the model was able to improve not only surface concentrations of phytoplankton but also their subsurface maximum concentrations. Our results showed that surface data assimilation of physiological parameters from two contrasting observatory stations benefits the representation of vertical plankton distribution in the western North Pacific.
  • Yoshio Masuda, Yasuhiro Yamanaka, Takafumi Hirata, Hideyuki Nakano
    ECOLOGICAL MODELLING 343 1 - 14 0304-3800 2017/01 
    To advance our understanding of competition and coexistence in phytoplankton species within a functional group, such as a diatom group, we developed a numerical model composed of 240 within tropic-level virtual species that can actually or potentially compete. We then explored how the phytoplankton assembly is structured by deterministic or stochastic processes, where the former process is typically represented using the traditional niche theory and the latter process is highlighted using the neutral theory. Because we used eddy-resolving resolution, phytoplankton dispersion and the resultant dispersal limitation were explicitly represented, where the dispersal limitation prevents the most competitive species from using its appropriate niche and subsequently enhances stochastic effects. In the simulation results, all surviving species have an oceanic volume in which the phytoplankton species has the highest specific growth rate in all the 240 species. The abundance in the most competitive space has a strong, positive correlation with the relative species abundance. Moreover, of the phytoplankton types whose abundances in the most competitive space are nearly equal, the survival of a species is affected by its residence time within its habitat; the surviving phytoplankton species tend to have larger residence times compared to the non-persistent species. These results led us to conclude that deterministic processes had significant contributions to a formation of phytoplankton assembly. This was supported by the result that a structure of phytoplankton assembly represented by species rank in abundance was invariant with time and hardly dependent on initial conditions of phytoplankton composition. (C) 2016 The Author(s). Published by Elsevier B.V.
  • Xuanrui Xiong, Yoshio Masuda, Taketo Hashioka, Tsuneo Ono, Yasuhiro Yamanaka
    JOURNAL OF OCEANOGRAPHY 71 (6) 685 - 701 0916-8370 2015/12 
    We used an eddy-permitting three-dimensional ocean ecosystem model and applied it in the western North Pacific to understand the seasonal variations and horizontal distributions of the air-sea CO2 flux and difference in the partial pressure between sea water and the atmosphere (a dagger pCO(2)). The high-resolution model reproduced the observed zonal belt of strong CO2 uptake in the mid-latitude (30-45A degrees N) western North Pacific including the Kuroshio extension and mixed water regions, which was difficult to show in previous coarse-resolution models. The East Asian winter monsoon, an important phenomenon in the western North Pacific, affects the seasonal CO2 air-sea gas exchange with a high (low) gas transfer coefficient in winter (summer). In the subtropical region, a dagger pCO(2) is negative in winter and positive in summer as a result of the temperature effect. Combination of seasonal change in gas transfer coefficient with a dagger pCO(2) suppresses CO2 release in the subtropical region, and vice versa in the subarctic region (i.e., suppresses CO2 uptake). That is, the East Asian winter monsoon in the western North Pacific contributes to the reduction of the annual CO2 flux through the seasonal change in the gas transfer coefficient, leading to an overall annual CO2 uptake in the subtropical region and CO2 release in the subarctic region.
  • Yoshio Masuda, Yasuhiro Yamanaka, Yoshikazu Sasai
    JOURNAL OF MARINE SCIENCE AND TECHNOLOGY 18 (2) 220 - 228 0948-4280 2013/06 
    In moving-ship type CO2 ocean sequestration, liquid CO2 is discharged into a domain in a water column. Since the maximum CO2 concentration that is reached depends on the horizontal shape of the water column and the depths of release, it is very important to optimize these parameters for each injection site in order to minimize the biological impact. We conducted numerical experiments using an offline Oceanic General Circulation Model with a horizontal resolution of 0.1 degree x 0.1 degree. Experiments using a different horizontal site shape show that a site elongated in the meridional direction is effective to reduce the CO2 concentration. This is because CO2 has a tendency to be transported in a zonal direction. Optimization of the vertical distribution of CO2 injections is inherently determined by the balance of the following two factors; (1) dilution effect by eddy activity which decreases with depth, and the (2) predicted no effect concentration (PNEC), a criterion concentration causing no effect on biota, which increases with depth. Based on superposition of simulated CO2 concentration, we determined the optimized vertical distribution of CO2 injection which keeps the ratio of a simulated maximum CO2 concentration to PNEC constant.

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