Phytoplankton (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, and other zooplankton.

Phytoplankton plays an important ecological role in food webs. These organisms are the main producers in aquatic ecosystems. All other organisms in the food web are directly or indirectly dependent upon them. Organisms, such as zooplankton, that consume phytoplankton, are directly dependent upon them. Organisms that consume the organisms that eat phytoplankton are indirectly dependent upon them.