ABSTRACT
In the ocean the total plant biomass (as phytoplankton) is estimated to be 4 x 109 tonnes (dry weight). Annual net primary production is around 50 x 109 tonnes. Productivity ranges from 25 g carbon m-3 in oligotrophic waters to 350 g carbon m-3 in eutrophic waters. This is released as dissolved organic matter (DOM), which accounts for 80–90% of organic matter present in the sea. The DOM is used as a nutrient source by heterotrophic Bacteria; populations between 104 and 106 ml-1 are commonly found in nutrient-poor (oligotrophic) waters, and much higher populations are found in nutrient-rich (eutrophic) waters (SECTION J5). The cells (both alive and as dead particulates), DOM, and prokaryotic populations form the base of the aquatic food chain.
