Primary productivity

In the ocean the total plant biomass (as phytoplankton) is estimated to be 4 * 10⁹ tonnes (dry weight). Annual net primary production is around 50 * 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 heterotro- phic 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. The cells (both alive and as dead particulates), DOM, and prokaryotic populations form the base of the aquatic food chain.