Abstract
A size-based ecosystem model has been developed to understand a detailed food web system
such as a micro-bial loop occurred in a coastal bay (estuary).The model is applied to TokyoBay
by coulpling with a 3-D hydrodynamical model. In this application, picoplankton, nano-diatom,
nano-flagellate, net-diatom and net flagellate are considered as compartments of autotrophic level.
Bacteria, heterotrophic flagellate, micro-zooplankton and meso-zooplankton are considered as
compartments of heterotrophic level.
According to the sensitivity tests of the model, it is found that the most sensitiveparameterin
themodel is the meso-zooplankton grazing rate. Thechange of 0.1 day1 in the meso-zooplankton
grazing rate leads to the change of 90 mgCnr3 diatom biomass. The results of the sensitivity
analysis show thatthe value of 0.8day1 forthemeso-zooplankton grazing rateis appropriate. The
simulated phytoplankton is well reproduced for the present situation inTokyo Bay.
The time variations of the simulated biomass of autotrophic components show that diurnal
variations caused byphotosynthesis arepredominant. In the heterotrohphic compartments, mesozooplankton
biomass also shows typical diurmal variations as a resultof prey-predator interac
tion. The net-diatom and net flagellate vary within the period of 10 days in the simulation, and
meso-zooplankton also varies with thesame time period but with lags lOdays behind net-phytoplankton,
which reflects on the prey-predator interaction.
In thesimulation, net-phytoplankton is dominant in the upper bay, whereas nano- and pico
plankton becomedominantnear the entranceof the bay.
This study demonstrates that the developed model can clarify the temporal and spatial varia
tions of each size category and of each trophic level.
