As you can see the classification is quite complex and numerous orders (families) exist and within each of them I have only listed a few representative ones.Note that not all of the ones mentioned occur in saltwater and that some are free floating and non benthic. The free floating ones are removed by skimming mostly. The benthic ones are the ones that attach to rock, glass, acrylic, sand and anything else in the aquarium, including other types of algae.
The simplest forms of cyanobacteria are the unicellular ones (Chroococcales). They reproduce by binary fission (splitting in two, then again in two, and this process is repeated over and over. Some split and do not remain together and become free floating. Others, as in Microcystis agglomerate and make up a large colony held together by a slimy mass (Fay calls it a matrix). What you see, in essence, is not an alga but literally thousands upon thousands of them, all bound by the slime - the latter being what you see, not the individual algae. Remember they are so small that even normal strong microscopes cannot detect them.
Many blue-greens are characterized a filamentous appearance. This results from binary splitting where the split cells string themselves together, one attaching itself to the other and so on, until what appears like a filament is present (e.g. the types that may grow on your glass and seem not to go away even when phosphate levels are real low. The reason for this will become clear later. Indeed their main food source is not PO4 but nitrogen, which they uptake directly from the water.
Filaments can be straight as in Oscillatoria, or appear like a coil as in Spirulina. Of course variations occur that result from the shape of the actual cell (round, plate-lie, cylindrical, ovoid, rod-like, etc.). All these affect what you see. Again a slimy mass may hold the cells together, giving the algae the appearance of strings of slime rather than patches of slime. The strings can be straight or curled or even branched. Often the visible eye cannot detect the exact shape of the filaments even though they are made up of thousands and thousands of individual cells. There are so many cells though, that we see a filament or a patch or something similar.
The shape of what you see can also be affected by whether or not the cells are all identical in shape or not. Indeed some of these algae cells' shape will change depending on what type of nutrients are available at the time the splitting occurs (Cole and Sheath). Nitrogen availability levels and types appear to be the determining factor in the shape and size the cell takes on when division occurs (Carr and Whitton). By type of nitrogen source is meant: nitrogen, nitrogenous compounds, nitrogen nitrate, and so on. Fay also points out that genetics appears to determine the positioning of the cells but not necessarily their size. The postulate is that the food source at the time of splitting has lot to do with size.
The peripheral (outer) region of the cell contain the photosynthetic algal mechanism and the ensuing pigments.
Depending on what pigments are present in that region and in what Carr calls supramolecular complexes, various color forms appear. It should be obvious that the type of lighting used may influence the growth of these algae. Indeed pigments absorb certain wavelengths of light. The one that we are probably most concerned with, the red slime algae, have a great deal (relatively speaking) of phycoerythrins. The latter's absorption level is optimized at 555-564 nm (manometer) wavelength.
Aquariums where a high amount of this light wavelength is present are, therefore, much more likely to see the appearance of red slimy algae, given that nutrients will be present (any nitrogen based food source - or in other words breakdown from protein or stated differently yet, dissolved organic matter or dissolved organic carbon).
Red phycoerythrin is not the only pigment that is present in these algae of course and is what differentiates (amongst other characteristics) the blue greens. Blue phycocyanin and allophycocyanin are present in some as well. These have different wavelength uptake patterns and result in some blue greens taking on other colors. In addition, some blue greens have a mix of these pigments and the eventual color they take on depends on the spectrum of the light over them aquarium, as this will favor one pigment over another, meaning one color versus another one.
For the sake of completeness let me point out that the pigments just mentioned are Phycobiliproteins. This is in contrast to other pigments such as Chlorophyll and Carotenoids. All pigments in blue greens are incorporated in the lipid outer layer, referred to earlier (lipid=fat and fat-like esters). After being harvested by phycobiliproteins in the PS II (photosythesis II) cycle, light wavelength energy now trapped is transmitted to the PS I system and its Chlorophyll (mostly of type a). This appears to be a very efficient process (Zhevner and Shestakov). Clearly light is a major player in the type of blue-green algae that will appear.
Whe we talk about light in the context of photosynthesis we always need to take into account that wath we are really talking about is two distinct aspects of light: its intensity and its spectrum. Intensity can be viewed as its amount, spectrum can be seen as its quality. Both play a role in how much and what type of blue-green algae (and for that manner any photosynthesizing algae) will appear.
It is also known that other nutrients play a role in the growth of blue-greens: iron, phosphorurs, magnesium and so on. We will see more about this later in this article. Although the main nutrient appears to be nitrogen in many forms, this is not the only nutrient source these algae rely on and which makes them appear in an aquarium or aquatic environment.
End of Part 1. ©, Albert Thiel, December 1996
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