Continued from page 2

Cyanobacteria and Blue-Green Algae Part 2

In Part 1 we touched on the reproduction of Cyanobacteria (the table listed various methods of reproduction): binary fission, budding, fragmentation. These forms of reproduction explain to a great extent the various appearances that Cyanobacteria take on in the aquarium: patches, slimy masses, strings, filaments, branched filaments and so on. We have seen that photosynthesis plays a large and important role in the reproduction and growth of such algae. The wavelength of the lighting that you provide determines what form of Cyanobacteria will grow in the tank. Keep the wavelengths that particularly promote blue-green algae growth low and you will have far less problems.

We have also noted that other nutrients play a role in growth and reproduction (dissolved organic carbon or material being an important one). Phosphate and iron are other ones.

Because of the usually high amount of pigments present in Cyanobacteria (as mentioned in Part 1), and because these pigments assist in the photosynthesis process (both PS I and PS II or Photsystem I and II), light does plays a great role in their growth and bears looking at some more. Indeed, slime algae of various colors can appear when the light source has degraded and when the wavelengths mentioned in Part 1 are suddenly becoming stronger (more intense or appear as a greater proportion of the total amount of lighting provided that penetrates the water.

This is often overlooked. Hobbyists are more likely to look for other reasons to explain the blue-green growths, and forget that old bulbs, fluorescents tubes, and other forms of lighting may need to be replaced to eliminate the spectra that are undesirable in terms of their effect on Cyanobacterial growth in general.

Photosynthesis can best and in its easiest form be described as the synthesis of organic compounds through the uptake of carbon dioxide and its fixation, light being used as the energy source. The total process involves several complex enzymatic and energy requiring reactions, all of which follow each other in a very particular order. I will not go into the details and mention the various enzymes involved such as carbonic anhydrase, dark reactions and other terminology that is not necessary to understand what is actually going on. For more information on those processes you can refer to specialized books or articles in the Review of Microbiology.

What is important to note is two-fold at least:

carbon dioxide is required, and it can come from two sources
decay of organic material

bicarbonates in the water

energy from light is required. This light has to be of the right spectrum (Kelvin degrees), as outlined in Part 1 of this article on blue-green algae.

The carbon dioxide can come from the breakdown of organic material but can also come from bicarbonate ions. Note, therefore, that a high dissolved organic load, combined with a high dKH, is practically certain to lead to the appearance of blue-greens.

Note also that higher or greater amounts of photosynthesis, with at the same time the presence of a great deal of organic material in the water, will produce more CO2 on one hand and increase growth on the other. Higher amounts of light combined with more CO2 provide more energy and since the carbon dioxide is present, blue-greens will start to grow.

The ideal combination for blue-greens to grow is: high DOC (dissolved organic carbon = dissolved organic protein = dissolved organic matter and the decay of that organic matter), high dKH levels and over saturation of CO2. The latter can occur if and when the carbon dioxide is not degassed properly from the water through the overflow leading to the sump, or when the water enters the sump by falling down in it in small streams.

If no sump is present at all the likelihood of carbon dioxide being high increases. Add to that lighting ot the type of wavelengths indicated in Part 1 and you are just about sure to get blue-green algae to grow in your aquarium. Add a high dKH and you really have an ideal environment for Blue-Greens to appear and proliferate and be hard to eradicate.

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