What Are Algae?

You have probably heard of the term algae but you might not know exactly what makes up this group. The term algae is used to refer to a very diverse group of photosynthetic organisms. The most common place to find algae is in any aquatic habitat, whether it be the ocean, a lake, a pond, or a river. But you can also find algae in the soil, in the air, on the bark of trees, and on rocky cliff faces. You can find algae almost anywhere!

Algae play many important roles in our environment. As photosynthesizers, algae convert energy from the sun to a form that can be utilized by other non-photosynthetic organisms. This puts algae as the first step in every aquatic food chain as all other aquatic organisms rely either directly or indirectly on algae as their food source. Also, as photosynthesizers, algae produce oxygen as a by-product of this energy conversion. As we know, oxygen is a requirement for the life we see on Earth, and at least half of the oxygen in the atmosphere is produced by algae. Algae are also a very useful tool for monitoring the health of aquatic systems. Algae have much shorter life cycles than other aquatic organisms, and so they respond more rapidly to changes in the environment.

Algae are comprised of many different types of organisms. One way these groups are differentiated is by the photosynthetic pigments they possess. These pigments influence the color of these organisms, and gave rise to the common names for these groups. So, now let's take a brief look at some of the major groups of algae.

 

The Green Algae: As the name implies, species in this group are green in color. Members of this group range from single-celled species to filamentous species. There are motile and non-motile species within the green algae. There are close to 20,000 known species of freshwater green algae, making this group alone extremely diverse.

 

The Euglenoids: This group is considerably smaller than the Green Algae with approximately 200 known species. The Euglenoids are Green in color, single-celled, and all species move with use of flagella.

 

The Diatoms: This is another extremely diverse group of organisms, with approximately 24,000 known species. Diatoms are single-celled and golden-brown in color with motile and non-motile species. The cell walls of diatoms are made of silica, or glass, and can be extremely ornate. Their beauty can really be appreciated when observed under the scanning electron microscope, or SEM, which provides high resolution images of the diatom structure.

 

The Synurophytes: This is a relatively small group with approximately 160 known species. Species in this group are single-celled, golden-brown in color, and move with the use of flagella. These organisms are covered with scales made of silica. As with the diatoms, the elaborate patterns in the external structure of the Synurophytes are visible through the SEM.

 

The Dinoflagellates: Species within this group are golden-brown in color, use flagella to move, and are all single-celled.You may have heard the term "red tide."Red tides are blooms, or large populations, of certain species of marine dinoflagellates.

 

The Brown Algae: The brown algae are non-motile, multicellular organisms. While there are freshwater species of brown algae, the majority of species are found in marine habitats, most notable of which are the giant kelp.

 

The Red Algae: Species in this group are typically red in color, but they can look green to gray to black. Species in this group are non-motile and can range from single-celled organisms to multicelled organisms. As with the brown algae, the majority of the red algal species are marine. An interesting note about the red algae is that they are used as two common food additives, carrageenan and agar.

 

The Cyanobacteria: This is a group of photosynthetic bacteria that are typically bluegreen color, but can also be purple, red, yellow, brown, blackish. Species within this group are non-motile and range from single-celled, to colonial, or filamentous. Species of cyanobacteria are responsible for the outbreak of freshwater toxic algal blooms which are currently plaguing lakes within the United States.