The rich diversity of animal life in estuaries represents a complex food web. A food web is a set of interconnected food chains by which energy and materials circulate within an ecosystem. The foundation of the estuarine food web is plankton. These microscopic animals are more diverse and essential to food webs and community structure than are vertebrates. Zooplankton feed on phytoplankton and are, in turn, eaten by fish and other animals.
Dead plankton make up an important element of the organic bottom layer of estuaries.
Fish, crabs, and shrimp take advantage of the large numbers of invertebrates found in estuaries. This extremely high productivity makes the estuary an attractive nursery habitat for many crustacean and fish species, and as such, an attractive fishing ground for humans.