Excretion of dissolved organic carbon by phytoplankton of different sizes and subsequent bacterial uptake

EOC [excreted organic carbon -Ed) may be important as a source of primary growth substrates for free-living bacteria (Larsson & Hagstrom 1982).  The importance of microbial food chains parallel to the conventional grazing ones in aquatic food webs is now recognised (Azam et al. 1983).  The significance of phytoplankton excretion as contributor to the ‘microbial loop’ has been studied (Cole et a.1. 1982, Brock & Clyne 1984).  EOC contributed to about half of the bacterial carbon requirement in some environments (Larsson & Hagstrom 1982).  Some studies suggested that a considerable amount of the annual primary production passed through the bacterial component (Brock & Clyne 1984),and bacterial production averaged 20% of planktonic primary production (Cole et al. 1988).