The Microbial Loop

Lawrence R. PomeroyODUM School of Ecology , University of Georgia

The Ocean’s Food Web, A Changing Paradigm1974

Bacterial Concentrations in the ocean based on plate counts and light microscopy

Methodical Limitations

• AODC developed in the mid to late 1970’s

• DAPI 1980’s

• Bacterial production (rudimentary) 1980’s

Bacterialconcentrations

beforeepiflourescent

microscopy

Bacterialconcentrations after

epiflourescentmicroscopy

Late 1970’s early 1980’s View of the Food Chain

Bacteria

Coined the term “Microbial Loop”

Important for the recycling of organic matter and nutrients above the thermocline

Mid 1980’s View of the Microbial Loop

Bacteria Microbial Loop

Something else?1988 Prochlorococcus was discovered

Very small autotroph (Cyanobacteria, uses chlorophyll b)

Present in high abundance in the ocean, especially in oligotrophicareas

Campbell et al 1994

1990’s View of the Microbial Loop

Bacteria

Microbial Loop

Prochlorococcus

Bacteria

Microbial Loop

Prochlorococcus

Filter Feeders

Why is this important

• Base of the food web

Pomeroy et al 2007

21st Century View of the Microbial Loop

Bacteria

Microbial Loop

Prochlorococcus

Filter Feeders

Why is this important• Base of the food web

• Hetertrophic and autotrophic bacteria are asignificant percentage of the total biomass of theocean

Pomeroy et al 2007

Pomeroy et al 2007

Why is this important• Base of the food web• Hetertrophic and autotrophic bacteria are a significant percentage of

the total biomass of the ocean

• Carbon cycling– ½ of global primary production occurs in the

ocean• How is this carbon used and how does it move

through the system?

Pomeroy et al 2007

Azam et al., 2007

Azam et al., 2007

Bacteria

Microbial Loop

Prochlorococcus

Filter Feeders

Questions?

Works Cited• Azam, F. 1993. Bacteria-Organic Matter Coupling and Its Significance for Oceanic Carbon Cycling.

Microbial Ecology. 28: 167-179.• Azam, F. 1998. Microbial Control of Oceanic Carbon Flux: The Plot Thickens. Science, New

Series.280.5364:694-696• Azam, F. 2007. Microbial structuring of marine ecosystems. Nature Reviews.,5:782-793• Azam, F., Fenchel, T., Field, J.G., Gary, J.S., Meyer-Reil, L.A., and Thingstad, F. 1983. The

Ecological Role of Water-Column: Microbes in the Sea. Mar. Ecol. Prog. Ser., 10:257-263.• Caron, D.A. 1994. Inorganic Nutrients, Bacteria, and the Microbial Loop. Microbial Ecology.28:

295-298• Pomeroy, L.R.1974. The Ocean’s Food Web, A Changing Paradigm. BioScience, 24.9:499-504.• Pomeroy, L.R., Williams, Peter J, Azam, Farooq, and Hobbie John E. 2007. Oceanography,

20.2:28-33.

Why is this important• Base of the food web, hetertrophic and autotrophic bacteria are a

significant percentage of the total biomass of the ocean• Carbon cycling

– Eutrophic systems microbial community acts as a sink fororganic C (respired as CO2)

– Oligotrophic system microbial community acts as a direct linkbetween trophic levels

Why is this important• Base of the food web, hetertrophic and autotrophic bacteria are a

significant percentage of the total biomass of the ocean• Carbon cycling

– Eutrophic systems microbial community acts as a sink fororganic C (respired as CO2)

– Oligotrophic system microbial community acts as a direct linkbetween trophic levels