Models of the microbial food web have their origin in the debate over
the importance of bacteria as an energetic subsidy for higher trophic
levels leading to harvestable fisheries. Conceptualization of the micr
obial food web preceded numerical models by 10-15 years. Pomeroy's wor
k was central to both efforts. Elements necessary for informative and
comprehensive models of microbial loops in plankton communities includ
e coupled carbon and nitrogen flows utilizing a size-based approach to
structuring and parameterizing the food web. Realistic formulation of
nitrogen flows requires recognition that both nitrogenous and nonnitr
ogenous organic matter are important substrates for bacteria. Nitrogen
regeneration driven by simple mass-specific excretion constants seems
to overestimate the role of bacteria in the regeneration process. Qua
ntitative assessment of the link-sink question, in which the original
loop models are grounded, requires sophisticated analysis of size-base
d trophic structures. The effects of recycling complicate calculation
of the link between bacteria or dissolved organic matter and mesozoopl
ankton, and indirect effects show that the link might be much stronger
than simple analyses have suggested. Examples drawn from a series of
oceanic mixed layer plankton models are used to illustrate some of the
se points. Single-size class models related to traditional P-Z-N appro
aches are incapable of simulating bacterial biomass cycles in some loc
ations (e.g., Bermuda) but appear to be adequate for more strongly sea
sonal regimes at higher latitudes.