Zooplankton (many species)

Plankton consists of tiny organisms that float or swim weakly near the surface of water. Plankton and detritus are very important parts of the food web in estuaries. There are two main categories of plankton: phytoplankton and zooplankton. Phytoplankton is "plant-like" plankton. These organisms get their energy through photosynthesis. Most of the organisms that make up phytoplankton are algae, single-celled plant-like organisms. Zooplankton is "animal-like" plankton. These organisms get their energy by eating other tiny organisms, including phytoplankton, bacteria, detritus, and other zooplankton.

Zooplankton plays an important ecological role in food webs. Zooplankton feeds on phytoplankton, the main producers in aquatic ecosystems. Zooplankton provides energy to many other species. Fish, filter feeders such as clams and mussels, birds, and even whales feed on zooplankton.