Plankton form the base of the Chesapeake Bay food web. All fish and shellfish depend on plankton for food during the early part of their lives, and some consume plankton their entire lives.

Zooplankton are free-floating animals. They are the most plentiful animals in the Bay and its rivers. Zooplankton are mostly microscopic, but can range in size from single-celled protozoa to large jellyfish. Zooplankton form a link between the phytoplankton community and larger species at higher levels in the food web.

Phytoplankton (or algae) are tiny, single-celled plants. They are the primary producers of food and oxygen in the Chesapeake Bay, forming the base of the food web.