BACTERIAL INFLUENCE ON THE VARIABILITY IN THE OCEAN'S
BIOGEOCHEMICAL STATE: A MECHANISTIC VIEW
F. Azam and D. C. Smith
Marine Biology Research Division
Scripps Institution of Oceanography
University of California, San Diego
La Jolla, California 92093
USA
INTRODUCTION AND STATEMENT OF THE PROBLEM
Traditionally, the only component of the microbial communities studied seriously by biological
oceanographers was phytoplankton. Bacteria, protozoa, viruses and fungi were relegated to
"specialists" and it was implicitly assumed that, by and large, the ocean's productivity
mechanisms and biogeochemical dynamics could be understood and modelled without taking into
account the activities of these other components of the pelagic microbiota. This view was
challenged by the seminal paper of Pomeroy (1974) and by quantitative studies inspired by it,
leading up to the discovery that the pathway DOM -- > bacteria -- > protozoa -- > metazoa
(microbial loop; Azam et al., 1983) is a major route for the flows of material and energy in
pelagic marine ecosystems. Further, very recently it has been suggested that viruses may also
play important ecological roles (Bergh et af., 1989; Proctor and Fuhrman, 1990; Suttle et al.,
1990), including a role in the mortality of bacteria and phytoplankton.
Since the heterotrophic bacteria process a large fraction of photosynthetically produced organic
matter, it is now widely appreciated that we need to understand the ecosystem-level
consequences of bacterial metabolism and growth. We now know that organic matter metabolism
by bacteria can have substantial bearing on fundamental issues of foodweb organization, nutrient
cycling, primary productivity, and the vertical flux of organic matter. The new challenge is to
NATO AS) Series, Vol. G 27
Particle Analysis in Oceanography
Edited hy S. Demers
© Springer-Verlag Berlin Heidelberg 1991
BIOGEOCHEMICAL STATE: A MECHANISTIC VIEW
F. Azam and D. C. Smith
Marine Biology Research Division
Scripps Institution of Oceanography
University of California, San Diego
La Jolla, California 92093
USA
INTRODUCTION AND STATEMENT OF THE PROBLEM
Traditionally, the only component of the microbial communities studied seriously by biological
oceanographers was phytoplankton. Bacteria, protozoa, viruses and fungi were relegated to
"specialists" and it was implicitly assumed that, by and large, the ocean's productivity
mechanisms and biogeochemical dynamics could be understood and modelled without taking into
account the activities of these other components of the pelagic microbiota. This view was
challenged by the seminal paper of Pomeroy (1974) and by quantitative studies inspired by it,
leading up to the discovery that the pathway DOM -- > bacteria -- > protozoa -- > metazoa
(microbial loop; Azam et al., 1983) is a major route for the flows of material and energy in
pelagic marine ecosystems. Further, very recently it has been suggested that viruses may also
play important ecological roles (Bergh et af., 1989; Proctor and Fuhrman, 1990; Suttle et al.,
1990), including a role in the mortality of bacteria and phytoplankton.
Since the heterotrophic bacteria process a large fraction of photosynthetically produced organic
matter, it is now widely appreciated that we need to understand the ecosystem-level
consequences of bacterial metabolism and growth. We now know that organic matter metabolism
by bacteria can have substantial bearing on fundamental issues of foodweb organization, nutrient
cycling, primary productivity, and the vertical flux of organic matter. The new challenge is to
NATO AS) Series, Vol. G 27
Particle Analysis in Oceanography
Edited hy S. Demers
© Springer-Verlag Berlin Heidelberg 1991