Below is a description of some common species of cyanobacteria.
Anabaena are heterocyst-forming, photoautotrophic cyanobacteria that perform oxygenic photosynthesis. Anabaena grow in long filaments of vegetative cells. During times of low environmental nitrogen, about one cell out of every ten will differentiate into a different type of cell (a heterocyst). Heterocysts then supply neighboring cells with fixed nitrogen in return for the products of photosynthesis that they can no longer perform. This separation of functions is essential because the nitrogen fixing enzyme in heterocysts, nitrogenase, is unstable in the presence of oxygen. They are one of four genera of cyanobacteria that produce neurotoxins, which are harmful to local wildlife, as well as animals and pets. Anabaena also produce the odourus compound geosmin (GSM) which causes an "Off-Flavour" problem in catfish aquaculture and also a significant water quality issue.
Figure 1: Presence of Anabaena in a lake looks like a floating green "oil spill"; Anabaena under a microscope
This type of filamentous cyanobacteria may turn a lake into shades of red and brown. In the northern hemisphere blooms of this species can be seen in lakes around April-May and October-November as they prefer lower water temperatures.
Figure 2: Planktothrix rubescens colours the lake red-brownish; detail of the filamentous cells.
Microcystis sp is a colonial cyanobacteria species. This means that single cells can join together in groups as colonies which tend to float near the water surface. Colony sizes will vary from a few to hundreds of cells. It is a common bloom-forming algae found primarily in nutrient enriched fresh waters and lower salinity estuaries. It becomes very noticeable during bloom events, which are most common around July-August in the northern hemisphere. Thick mats of the algae can coat the water so heavily that you cannot see your hand an inch below the surface. In calm freshwater areas, it may look like someone has spilled green paint on the surface. On closer inspection, the mats can be seen to be comprised of small flakes or balls. If the algae is blown by wind or pushed by currents into higher salinity waters where they cannot survive, they generally take on a greenish-yellow color and a chunky appearance as they die. Microcystis produces a toxin called "Microcystins", which is the most common cyanobacterial toxin found in water.
Figure 3: Microcystis clogging together forming a thick mass; detail of a small colony of cells grouping together like a small ball
This species is present throughout the whole year, with a peak around summer. A colony of Aphanizomenon consists of filaments clogging together making it look like clumps of freshly cut grass.
Figure 4: Aphanizomenon gives a blue-green colour to the water; detail of a small colony