Dynamics of organic colloidal particles in aquatic microbial food webs

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The aim of this research is the mechanistic understanding of organic detritus dynamics in marine environments through focusing on the characterization of submicron sized detritus and their production and degradation by microbial food webs such as bacterioplankton and microzooplankton. The finding of" submicron particles " as the predominant forms of non-living organic detritus of bacterial size range in 1990 by our group stimulated the studies on the role of those organic detritus, which are in the boundary between dissolved and suspended forms of detritus in the upper ocean. Before this research, however, a few knowledge has been obtained in the open ocean, such as size distribution and some physico-chemical properties, partially because of the limit of available techniques. Through the interdisciplinary approaches of this study, following new findings were obtained. 1. The size distribution of submicron organic detritus varied significantly with the biological productivity of the env … More ironments, and the production of 0.6-0.8 mum sized detritus dominated under the high biological productivity. 2. Estimated carbon contents of organic detritus of submicron size range gave much higher value compared to the carbon contents of living particles of this size, i.e., bacteria, indicating that organic detritus of submicron size are also predominant form of organic carbon stock in the upper ocean. 3. Using a high sensitivity CCD camera system, amorphous and aggregated nature of those organic detrital particles were confirmed, This finding was consistent with the previous physical characterization of the particles. 4. As the major production process of the submicron detritus, fecal pellets formation of microflagellates through the grazing activities were strongly suggested, and also further aggregation of those submicron detritus to larger sized aggregates were indicated, The above findings were the important contribution to mechanistic understanding of complicated dynamics of marine organic detritus, such as marine snow, suspended-, colloidal- and dissolved-organic forms, and their association with marine food webs. Less