Application of a lower trophic level model to a coastal sea ecosystem

Two years of environmental and plankton monitoring data observed at a station located in the coastal zone of Peter the Great Bay (Japan Sea) are used to study the seasonal development of a pelagic ecosystem. The functioning of the lower trophic levels was approximated with a semi-empirical ecosystem model based on the set of differential equations of NEMURO LTL model including nutrients, phytoplankton, and zooplankton. Advective fluxes were parameterised because of the strong cross-shelf circulation in the area driven by monsoon winds. Realistic results were obtained with variable coefficients of growth, grazing and mortality instead of constant coefficients. The coefficients’ variability takes into account seasonal fluctuations of species composition and plankton ontogenic changes. Lack of a bacterial component in the NEMURO-based model was compensated by very high production of phytoplankton. Horizontal advection was important for nutrients export from the coastal zone in summer, for herbivorous zooplankton transport into the area in spring and autumn, and controlled predatory zooplankton abundance throughout the period of investigation.