Measurements of primary productivity are crucial inputs for models that describe how ecosystems function.

1. The Trophic-Dynamic Model and Energy Flow

• Concept: Developed by Raymond Lindeman (1942), this model introduced the concept of “energy flow,” tracking the transfer of energy between trophic levels. Measured primary productivity represents the initial energy input into the food chain.
• Challenges in Application:
  • Model Complexity: Modern biochemistry and ecology require models of energy flow so complex they are difficult to relate to the natural world.
  • Extracellular Production: The significant portion of primary production released in soluble form does not follow the linear phytoplankton-to-herbivore energy pathway.
  • External Inputs: Allochthonous material (organic matter from outside the system) and chemosynthesis (a form of primary production) are often unmeasured but can be important energy sources for consumers.

1. Information Theory and Community Maintenance

• Concept: This theory posits that phytoplankton communities must use a portion of their production to maintain their community structure. This energy cost is referred to as “information.”
• Implication: Grazers, and subsequently fish, may only have access to the production that is in excess of this maintenance threshold.