Bacterial Secondary Production

Abstract

During the past decade ecologists have become more aware of the significant role that heterotrophic bacteria play in aquatic ecosystems. In both the water column and sediments of freshwater and marine systems, bacteria are thought to be the major decomposers of organic matter (Point and Morris 1982, Azam and Cho 1987, Münster and Chróst 1990, Chróst 1990; Chapter 6, this volume). Nowadays we accept that the production of bacterial biomass represents an important link among detritus, dissolved organic matter (DOM), and higher trophic levels in aquatic ecosystems. Important recent findings demonstrate that DOM → heterotrophic bacteria → protozoa → metazoa process as much energy as the classical grazing food chains. By virtue of their abundance, low substrate affinities, and potentially rapid growth rates, bacteria are capable of rapidly converting energetically low labile DOM into their biomass, i.e., high-quality bacterial particulate organic matter that can be utilized by bacterivorous protozoans and zooplankton (Pedrós-Alió and Brock 1983, Hessen and Andersen 1990, Pace et al. 1990). Moreover, bacterivores feeding on bacteria liberate a substantial amount of macromolecular DOM that is enzymatically degradable and utilizable by bacteria (Jumars et al. 1989, Nagata and Kirchman 1991, 1992; Chapter 6, this volume).