Modelling The Microbial Loop In The Yellow Sea

Yellow Sea is a typical shelf sea adjacent to the west Pacific with complex ecosystem.It is recognized that small size organism in the sea plays an important role in matter and energy flow of an ecosystem. Organic matter in the sea is consumed by bacteria. The later are grazed by small zooplanktons and thus the waste energy flow back to the main food chain form the microbial loop. This loop is regarded as an important factor of ecosystem stability and a necessary supplement to the main food chain. The ecological role of microbial loop is particularly significant in tropics and oligotrophic area, and the temporal and spatial variation of the role is needed to be further researched and analyzed by a model in the eutrophicated shelf sea. This paper intends to establish a two-dimension microbila loop ecosystem model in the Yellow Sea and analyze the role quantificationally.A new microbial ecosystem model was established on the base of the existed plankton ecosystem model in the Yellow Sea, i.e. modified NEMURO, to quantify the role of the microbial loop in such a shelf sea. The biological compartment of this new model included11state variables, bacteria biomass, phytoplankton biomass (small and large), zooplankton biomass (small, large and predacious), phosphorus nutrients concentration (phosphate, dissolved organic phosphorus and particulate organic phosphorus) and silicon nutrients concentration (silicate and biogenic silica). The microbial loop ecosystem model was driven by the two-dimensional climatologically averaged daily temperature and circulation output from Princeton Ocean Model. The annual cycle and horizontal distribution of biomass of each trophic level in the ecosystem and nutrients concentration were simulated. The energy flow was in agreement with the ecosystem evolution in the Yellow Sea learned from other literatures. This model was proved to be credible and could be used to quantify the role of microbial loop in this shelf sea.The results shows that the nutrients concentration is higher and bacteria biomass is almost the same in the west coast of Yellow Sea, but in the middle the concentration is lower which reaches the lowest value in spring and summer and the biomass is higher in winter. The phytoplanktons reach the biomass peak in spring, especially the large phytoplankton in the middle. In autumn and winter, the value B:P of the middle is higher than the west. In the section of budgets of endogenous and exogenous nutrients, the consumption of phytoplankton is high, especially in spring, and the bottom supplying nutrients to the upper layer is the mainly way to exogenous supplement. The contribution role is mainly played in summer by primary production, but the energy from microbial loop to the main food chain is more in winter. Compared with the primary production, the contribution ratio of the west is28.4%, but the ratio is45.1%in the middle. The energy transmission ratio of microbial loop is higher in winter than in summer, and the ratios are26.3%and57.1%in the west and middle of the Yellow Sea respectively. We suppose the resean is the different planktonic communities of two areas in the Yellow Sea.