Flora of freely floating, often minute organisms that drift with water currents. Like land vegetation, phytoplankton uses carbon dioxide, releases oxygen, and converts minerals to a form animals can use. In fresh water, large numbers of green algae often colour lakes and ponds, and cyanobacteria may affect the taste of drinking water. Oceanic phytoplankton is the primary food source, directly or indirectly, of all sea organisms. Composed of groups with silica-containing skeletons, such as diatoms and dinoflagellates, phytoplankton varies seasonally in amount, increasing in spring and fall with favourable light, temperature, and minerals.
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