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The Different Phytoplankton Found in Freshwater

Freshwater phytoplankton are organisms who absorb carbon dioxide and release oxygen through the process of photosynthesis. They float or swim, and are found in lakes, rivers, ponds and streams. The phytoplankton that can swim are very poor swimmers, and are thus subject to water currents. Though several types are unicellular, they often form colonies or filaments. There are about seven major phyla of phytoplankton commonly found in freshwater.

Green Algae
- These members of the phylum Chlorophyta are very common. These include the orders Volvocales and Chlorococcales. The most often studied green alga in the lab is Volvox. Volvox forms a colony of 500 to 5,000 cells, forming a mucilaginous sphere. Many types of green algae have flagella, small whiplike structures that aid in movement. Volvox is commonly found in freshwater lakes and ponds, particularly during warm weather when blooms occur.
Cyanobacteria
- Cyanobacteria are also known as blue-green algae. These are slow moving phytoplankton that can be found in unicellular, filamentous or colony forms. Cyanobacteria used to be in kingdom Plantae, but have been reclassified in kingdom Archaebacteria. Unlike other photosynthetic bacteria, cyanobacteria produce oxygen. The blue-green algae Nostoc is most commonly found at the edges of shallow lakes.
Yellow Green Algae
- These members of phylum Xanthophyceae have carotenoids that give them their yellowish color. Compared to other freshwater algae, these are fairly rare. They can be epiphytic, growing on plants, or free swimming with two flagella. Members include Chlorobotrys, Gloeobotrys, Botrydium and Gloeochloris. The yellow green algae Botrydium is found at the bottoms and banks of rivers and creeks.
Golden Brown Algae
- Golden Brown Algae are usually unicellular, most with a single flagellum. The group includes Ochromonas, Dinobryon and Cynura. Dinobryon in particular is widely distributed. Golden Brown algae are all members of phylum Chrysophyceae. Carotene and xanthophylls give them their color. Ochromonas is found in oligotrophic, low nutrient, freshwater.
Diatoms
- There are two major groups of diatoms, classified by shape: the centrales have radial symmetry and pennales have bilateral symmetry. The pennales are further divided into four groups: Araphidineae, Raphidioidineae, Monoraphidineae and Biraphidineae. Most diatoms are found in shallow waters. They are nonmotile. The diatom Cyclotella is found in the deep part of oligotrophic lakes.
Dinoflagellates
- Dinoflagellates are unicellular flagellated algae with a conspicuous cell wall, though a few species of order Gymnodiniales lack a cell wall. The dinoflagellate Ceratium is unique in that it changes shape and size seasonally. The dinoflagellate Peridinium is found in waters rich in calcium and low in nutrients.
Euglenoids
- The most "famous" euglenoid is the one found in high school biology class: Euglena. Euglenoids are unicellular, lack a cell wall and have between 1 and 3 flagella. They are most often found where concentrations of ammonia and organic detritus are high.

Nature