Suspended Marine Bacteria as a Food Source

Abstract

During the last decade, evidence has accumulated which undermine the classical picture of planktonic food chains. The general belief was that phytoplankton is consumed by herbivorous zooplankters with an efficiency approaching 100% (Steele, 1976). It has more recently been found that the largest fraction of heterotrophic metabolic activity can be attributed to bacteria rather than to the herbivorous Zooplankton. Studies based on a variety of methods suggest that bacterial biomass has turnover times ranging from <0.5 to a few days and that this represents a production which amounts to 10–30% of the primary production. The reduced carbon sustaining this productivity derives mainly from exudates of phytoplankton cells, but leachates from dead cells and from herbivores as well as detrital material contribute, so that as much as 20–40% of the primary production turns up as dissolved organic matter to be utilized by bacteria (Azam and Hodson, 1977; Hagström et al., 1979; Larsson and Hagström 1979; Fuhrman et al., 1980; Rheinheimer, 1981; Williams, 1981; Stuart et al., 1982; Wolter, 1982). To this heterotrophic production of bacteria, a photosynthetic production of unicellular cyanobacteria, now known to be an ubiquitous component of plankton, must be added (Sieburth, 1979).