Precise estimation of concentration is required for suspended organic matters (phytoplankton. zooplankton. and detritus) to perform the improvement in calculations of chemicals in sea area. The seasonal variations of plankton concentration in Tokyo Bay were simulated using a size-based ecosystem model. Concentration of marine microorganism was simulated for three species of phytoplankton. two species of zooplankton. and the marine bacteria with the considerations of the dominant species in zoo- and phyto-plankton. their size, and the prey-predator relationships based on the plankton data obtained from June 1995 to April 1996 in Tokyo Bay. The calculation results of zooplankton concentration are higher than the observation data. For the improvement of the model, a juvenile and medusae were added this model as zooplankton feeder. The calculation results of zooplankton concentration agreed fairly well with observed data. The predation rate for juvenile and medusae were estimated with approximately 0.31 mgOday^-1・m^-3 and 6.99 mgC・day^-1・m^-3 respectively. The present study showed that zooplankton concentration depends on predation of medusa above juvenile in Tokyo Bay.

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We examined a risk assessment method of lead solder in Tokyo Bay using a numerical model. Three kinds of metal (Pb. Ag and Cu) contained in solders were evaluated. The ambient concentration of the metals was estimated by the model AIST-RAMTB (Aist - The Risk Assessment Model for Tokyo Bay) considering the atmosphere and seven major rivers as the supplying sources of metals. The Giant Pacific Oyster {Crassostrea gigas) was selected to evaluate the extinction risk. The growth inhibition concentration for 50% (EC50) was used for Pb as 380 μg・L^-1. Ag and Cu were evaluated based on the lethal concentration for 50% (LQ50); 100 μg・L^-1 for Agand 560 μg • L^-1 for Cu. Uncertainty factor (UF) was defined as 10. The result shows the maximum risk values of 5.57 x 10^-6 for Pb, 1.40 x 10^-6 for Ag and 4.09x 10^-8 for Cu. It suggested that the risk of solder lead was reduced by changing the lead solder to lead-free solder in Tokyo Bay.

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The current system east of the Ryukyu Islands has been called the Ryukyu Current System (RCS) to express its possibly different origins and features. In this paper, we presented a new feature on the vertical structure of the current system by using lowered acoustic Doppler current profiler (LADCP) data in early October 2005: a southwestward countercurrent was demonstrated to flow near the eastern slope of the Nansei-Shoto (Ryukyu Islands) Ridge in a layer deeper than the northeastward current core of the RCS. This supports the existence of the countercurrent suggested by Nagano et al. (2009). The maximum speed of the countercurrent was measured to be 25 cm s^-1 at a depth of approximately 600 m.

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We improved a bioaccumulation model for a Windows® PC operating system. This software can predict the concentration of chemical substances and heavy metals in marine fishes. We have called this version the AIST-CBAM (National Institute of Advanced Industrial Science and Technology-Chemical Bioaccumulation Model) ver. 2.0. In previous version (1.0). the target substance was persistent organic pollutants, such as coplanar polychlorinated biphenyl. AIST-CBAM ver. 2.0 enables the prediction of the concentration of heavy metals (e.g.. Pb. Cu. Ag). Both versions can operate easily by using a graphical user interface. With the upgrade, the following functions were added: choice of the target substance (chemicals or heavy metals), setting of the parameters required for the prediction of heavy metal concentrations, and image output in EMF (Enhanced Metafile) format.

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