phytoplankton

Phytoplankton are the photosynthetic components of the plankton community in aquatic environments. They are microscopic to millimeter-sized organisms that float or drift in the upper sunlit layer of oceans, seas, and freshwater bodies. The term encompasses a diverse range of organisms, including cyanobacteria (often called blue-green algae), diatoms, dinoflagellates, coccolithophores, green algae, and other microalgae.

They require light and inorganic nutrients such as nitrate, phosphate, and trace elements to photosynthesize and grow. Through photosynthesis they convert carbon dioxide into organic matter, forming the base of most aquatic food webs. Population dynamics are influenced by light, nutrients, temperature, and water column mixing. Some phytoplankton form resting stages or have silica (diatoms), carbonate (coccolithophores), or cellulose-based cell coverings that influence their ecological role and sinking rates.

Phytoplankton are the primary producers in nearly all aquatic ecosystems. In marine environments they contribute a substantial share of global photosynthesis and play a key role in the carbon cycle, including the biological carbon pump that transports carbon to deeper waters. They also generate a large proportion of atmospheric oxygen.

Phytoplankton communities exhibit seasonal and geographic variability, with blooms of species such as diatoms, coccolithophores, and dinoflagellates under favorable conditions. Some dinoflagellates and cyanobacteria can produce toxins or form harmful algal blooms, which can affect marine life and human health.