Lower Food Web

Sometimes it is the tiniest things that have the biggest impact. Such is the case in the Chesapeake Bay.

Microscopic algae and bacteria form the foundation of the entire ecosystem. Together they make energy available to all Bay creatures as carbon — the building block of life. When it comes to the food web, everything starts at the bottom.

From minnows to jellyfish to striped bass, all life in the Bay owes its existence to plant life at the base of the food chain — and plants depend on the remarkable process we call photosynthesis. Fueled by nutrients from land and water, phytoplankton (primarily dinoflagellates and diatoms) use photosynthesis to capture energy from sunlight. The light energy sets off a multi-step chemical reaction that converts carbon dioxide from the air and water into oxygen and glucose (a six carbon sugar). This process sustains the entire food web — glucose provides energy for phytoplankton; phytoplankton feed grazing zooplankton; and zooplankton become food for small fish, which are in turn food for bigger fish.

Uneaten phytoplankton die and become detritus, sinking to the bottom where they are consumed by benthic (bottom) feeders of the middle food web. Detritus may also stay suspended in the water column (pelagic zone).

Bacteria attached to the large carbon-based molecules of this plant and animal waste (particulate organic carbon or POC) break the large molecules down into smaller molecules (dissolved organic carbon or DOC). Most marine animals cannot easily use DOC as an energy source, but free bacteria of the middle food web can. Tiny creatures eat these free bacteria, and are in turn eaten by small zooplankton. In this way energy from organic carbon, whether dissolved or particulate, re-enters the marine food web.