Unicellular Algae

Algae are important for the ecological balance of aquatic ecosystems, as they are the main producers of food that nourishes directly or indirectly other aquatic living beings.

In addition, algae are the major suppliers of oxygen gas that fuels aerobic life on the planet. In the atmosphere or dissolved in water, this gas originates mainly from the photosynthesizing activity of algae, especially single-cell marine algae.

They are responsible for 70% of photosynthesis held on the planet. The excessive proliferation of pyrrophyte red algae - also called dinoflagellates - causes the phenomenon called Red tide, which occurs naturally or by sewage discharge into seawater. These algae release toxic substances that can affect living creatures living in the water and even beach bathers.

"Red tide" caused by Noctiluca sp.

In freshwater, if reproduction is intense and in short time, algae can end up becoming a big problem. When chemicals from industries and untreated sewage are discharged, the waste adds an excessive amount of mineral salts to the water, favoring the rapid multiplication of these beings. Algae reproduce in such a way on the surface of the water that they can prevent light from passing into the deepest layers. Thus, the algae that exist there can not photosynthesize, and many of them end up dying, rotting, accumulating in the bottom and releasing toxic substances. The drop in the amount of oxygen dissolved in water also kills animals like fish, whose bodies float on the surface.

Among the unicellular algae, we will highlight three groups: the euglenophytes, the bacillaryophytes and the pyrrophytes.

The euglenophytes

Euglenophytes, also known as euglena, are unicellular algae that move through a flagellum and live mainly in freshwater but also saltwater.

THE Euglena viridis It is an example of this group of algae, predominantly has the green pigment of chlorophyll. It reproduces by cissiparity and, when its reproduction is intense, the water may turn greenish.

THE Euglena viridis viewed under an optical microscope, the green dots are the chloroplasts that can be seen through the membrane that delimits the cell.


Bacillaryophytes live in fresh or salt water. Most are represented by the diatoms, unicellular algae with a protective shell formed from silica and which usually reproduce by cissiparity.

Debris from the dead diatom cell wall can settle to the bottom of the aquatic environment and eventually form a silica-rich material known as diatomite. This material can have various commercial applications, such as: making certain cosmetics and toothpastes; fine abrasive for polishing silver objects, for example; manufacture of bricks used in construction.

Illustrative drawing of the different shapes of diatoms.



Also known as dinoflagellatesBecause they are endowed with two flagella, pyrrophytes are single-seaweed, usually marine. They are greenish or brown in color and mostly reproduce by cissiparity; some have the ability to emit light, a phenomenon known as bioluminescence.

The luminescent seaweed Noctiluca sp responsible for the red tide.

Want to know more about the protists?