What are
Algae & Cyanobacteria?

What are algae?

The term algae is used to describe a diverse collection of aquatic organisms that, in general, have the ability to produce their own food through the process of photosynthesis (though there are exceptions). Algae have fairly simple vegetative and reproductive structures lacking the complex tissues found in higher plants. They are found in a wide variety of habitats including ponds, lakes, rivers, estuaries, oceans, soils, snow, and in symbiotic relationships with other organisms such as fungi (lichens). They can be free-floating in the water (planktonic) or attached to some substrate (periphytic). Many can only be seen under a microscope, although some are large enough to be seen with the naked eye. 

What are cyanobacteria?

Cyanobacteria are sometimes considered algae, but they are actually bacteria (prokaryotic), where the term “algae” is now reserved for eukaryotic organisms. They also derive their energy through photosynthesis, but lack a nucleus or membrane bound organelles, like chloroplasts. Actually, cyanobacteria may have evolved into the first chloroplasts, as evidenced by similar structural and genetic traits. Cyanobacteria have a unique set of pigments used in photosynthesis, called the phycobiliproteins (phycobilins), which can give some of them a blue-green color. Cyanobacteria are also responsible for many of the Harmful Algal Blooms (HABs) that cause ecological, economical and public health concerns in waterways, many times through the production of cyanotoxins.

To view various cyanobacteria photos, please see the Harmful Algal Bloom (HAB) Events Gallery or the Cyanobacteria Gallery.

Why are algae and cyanobacteria important?

Algae (including cyanobacteria) are important members of aquatic communities. They provide oxygen as a by-product of photosynthesis, a food source for other organisms such as zooplankton, insects and snails, and in the case of larger filamentous algae, a habitat for small animals. Algae can supply useful information about the productivity and health of aquatic ecosystems. For example, some forms of algae are indicative of low nutrient conditions while others indicate high nutrient levels and some species favor acidic conditions while others more basic. Some species, under optimal conditions, can grow to such high densities that they form algal blooms. Such blooms can adversely affect recreation, water treatment plant operation and ecosystem health.


Is it important to tell one alga or cyanobacterium from another?

Yes, it is important to tell one alga from another because some groups of algae or algal species are more beneficial in a water body than others. Some provide a better food source for zooplankton while others can cause unsightly blooms. Many of the bloom-forming algae are cyanobacteria (blue-green algae), some of which can potentially produce toxins that may have harmful effects on aquatic and terrestrial life. Some species of cyanobacteria, as well as some diatoms, chrysophytes and other types of algae, can produce taste and odor compounds, which can impart off-flavor to fish or make drinking water taste unpleasant. It is critical to be able to differentiate between species that can potentially produce toxins, taste and odor compounds from more benign species.