Most Green Water (phytoplankton) is too small to be individually seen with the unaided eye. However, when present in high enough numbers, some varieties may be noticeable as colored patches on the water surface due to the presence of chlorophyll within their cells and accessory pigments (such as phycobiliproteins or xanthophylls) in some species.
Phytoplankton is a key food item in both aquaculture and mariculture. Both utilize phytoplankton as food for the animals being farmed. Phytoplankton is used as food stock for the production of rotifers, which are in turn used to feed other organisms. Phytoplankton is also used to feed many varieties of aquacultured mollusks, including pearl oysters and giant clams.
The production of phytoplankton under artificial conditions is itself a form of aquaculture. Phytoplankton is cultured for a variety of purposes, including food stock for other aquacultured organisms, a nutritional supplement for captive invertebrates in aquaria. Regardless of the size of the culture, certain conditions must be provided for the efficient growth of plankton. Various fertilizers are added to the culture medium to facilitate the growth of plankton. A culture must be aerated or agitated in some way to keep plankton suspended, as well as to provide dissolved carbon dioxide for photosynthesis. In addition to constant aeration, most cultures are manually mixed or stirred on a regular basis. The light must be provided for the growth of phytoplankton. The duration of light exposure should be approximately 16 hours daily; this is the most efficient artificial day length.