Science Behind the Energy Network

Dr. Robert Ulanowicz, creator of the Energy Network for the mid-Chesapeake Bay

Any science-fiction buff can surely list numerous books, films, and television shows focused on the search for “carbon-based life forms” on other planets. Even many real-world scientists think that the possibility of life on other planets depends on the presence of carbon. Their assumption seems logical, given carbon’s supreme importance to all living creatures on Earth.

All the essential components of life — DNA, proteins, enzymes, fats, and most notably, carbohydrates (sugars) — are built with carbon molecules. Carbon supports every living thing on our planet, beginning with plants, which perform photosynthesis — capturing energy from sunlight to convert water and carbon dioxide into oxygen and glucose (a carbon-based sugar). As plants use glucose, and then as animals eat plants, and as other animals eat those animals, carbon gets passed throughout the food web. Each organism breaks down carbon molecules, releasing energy stored in the chemical bonds. Although most of this energy is lost as heat, the remaining energy provides fuel for activities from swimming to breathing to building new carbon-based molecules, whether proteins, enzymes, DNA, fats, or sugars.

In the late 1970s, when Chesapeake Biological Laboratory scientist Dr. Robert Ulanowicz set out to understand the food web interactions of Bay creatures, he knew where to start — follow the carbon. After years of research Ulanowicz completed an energy network for the mid-Chesapeake Bay — a “who eats whom” diagram showing the cycle of carbon throughout the 36 major players of the middle Bay. Read a Chesapeake Quarterly article on Ulanowicz and the development of the energy network.

Looking exclusively at the middle (or mesohaline) Bay where estuarine waters are generally well mixed — not as salty as in the southern Bay and not as fresh as in the northern Bay — the diagram provides a framework for understanding how the Chesapeake ecosystem functions. It shows how tiny phytoplankton ultimately sustain large carnivorous fish, how dead plant material (detritus) feeds bottom dwellers like worms and crabs, how top predators feast on small fish like menhaden and shad.

This picture of the interactions beneath the surface highlights that the many creatures of the Bay depend on each other — and they all depend on carbon.

Interactive Food Web

Visit Food Web Levels to learn about 36 major species of the mid-Chesapeake Bay. See how they comprise the lower, middle, and top levels of the food web and mouse over their names to learn about their role in the Bay.

Then click on the Energy Network to explore the flow of energy through the mid-Chesapeake’s food web. Roll your mouse over the orange polygons (striped bass, blue crabs, or oysters) to highlight who eats whom. Trace the red lines and arrows connecting other species to see who they eat and who eats them.

Useful Links

Ecosystem Network Analysis

EcoNetwrk software

Network Analysis of the Trophic Dynamics of South Florida Ecosystems