Simulating On The Seasonal Variation Of The Microbial Food Loop And Its Role In The Main Food Chain In The Yellow Sea With An Ecosystem Model

The microbial food loop（MFL）is one of the central topics of recent studies onmarine ecosystem. The study on the MFL helps the re-assessment of the importanceof micro-biological ecosystem processes，and is an essential step for more in-depthstudy on the structure and function of the marine ecosystem. The MFL plays anessential role in the energy flow and mass cycle. Through the development ofnumerical models for the dynamics of the MFL，quantitative estimates can beobtained for the contribution of the MFL on the main marine food chain and theacceleration of nutrient cycling. Eventually，this helps to build the basis for theprediction of the dynamics of the marine ecosystem.As a typical continental sea, the Yellow Sea（YS）is one of the most importantfishery grounds in China, and one of50large marine ecosystems in the world ocean.Research on seasonal variation of microbial food loop and its role in the main foodchain in the Yellow Sea is key to the assessment of potential resources andmanagement of a large marine ecosystem.In this study，a two-dimensional model for the MFL is developed and is applied tosimulated the seasonal variations of various parameters of the ecosystem in the YS.Model results show that the contributions of the MFL to the main food chain differ indifferent seasons and geographic locations. Analyses reach the following majorconclusions:(1) During the spring bloom of phytoplankton，nutrients are compensatedby de-composition of detritus by the bacteria; and the dissolved organic material is theprimary nutrition source of the bacteria;(2) Compared to the oligotrophic regions of the deep and open oceans，the continental shelf seas have more abundant nutrients andhigher new primary productions. Phytoplankton carbon fixing is a major way of thetransfer of organic material to higher trophic level. The hyterotrophic bacteria canassimilate the DOM or POM，be predated by microzooplankton to enter the main foodchain as a supply of energy. During winter，the phytoplankton biomass is low and theMFL plays a more prominent role in the energy supply for the main food web（ca.30%）.(3) The contribution of the MFL to the main food web differs in differentregions of the YS. The contributions in the spring， summer and winter seasons aresimilar in terms of the spatial distribution. In the fall season， however， thecontribution to the total main food chain amounts to9%in the central YS，and18%in the coastal waters.Further studies are needed to refine the MFL model by including the autotrophicbacteria， flagellate and ciliophora. Through coupling to the physical processes， onecan explore the response of the MFL to climate change， for example， the influenceof global warming and the weakening/strengthening of the currents on changes inthe structure of the ecosystem and the role played by bacteria and MFL. The modeldeveloped in this study could be an effective tool for the marine ecosystem basedmanagement.