Red Slime Algae and Cyanobacteria in general

An Introduction

Blue green algae, or Cyanobacteria, are remarkable in as much as they are somewhat of a hybrid between algae and bacteria. In some ways they resemble green plants and algae, and in others they are much closer to bacteria. The latter explains why antibiotics are sometimes used to rid the tank blue-greens.

Although this method results in their disappearance, at least for a while, the dangers associated with using them in an aquarium need to be stressed here.

Biological filters contain many bacteria themselves. These, too, can be affected and more than likely will be. This can lead to ammonia spikes in the tank due to the loss of the bacterial bed (partially or completely). Note that since live rock and live sand contains bacteria as well, the use of antibiotics will affect them as well.

Cyanobacteria are photosynthetic. They release oxygen and uptake carbon dioxide, depending on the photoperiod and lighting conditions. Cyanobacteria contain pigments. The prevalence of one particular pigment ultimately determines the color of the algae.

It should be noted that they are among the oldest form of organisms found on earth. Traces of cyanobacteria have been found in fossils dating from the early Precambrian period, some 3 billion years ago. They are extremely common, even today, and are found in fresh, brackish and salt water. They are present even on land in moist environments. Cyanobacteria, referred to as blue-green algae, come in various colors.

Do not let the name confuse you. They are not necessarily blue-green but can be blackish, greenish, blue greenish, yellowish, brownish and reddish. The latter color is perhaps the one most saltwater hobbyists are familiar with.

Note that your aquarium doubtlessly contains many more cyanobacteria than you are aware of. The main reason being that many of the various forms of cyanobacteria are present in any environment where photosynthesis takes place. Their numbers may be small and their size certainly is. You do, therefore, not notice them.

At times though they become really conspicuous because they agglomerate and form masses and patches. By themselves they are extremely small and are generally studied under an electron microscope, lest they would not be visible. Regular microscopes are not powerful enough to allow scientists to study them in detail.

The appearance of blue-green algae is always a disappointment to the hobbyist. Regardless of the type though their presence indicates a disturbance of the biological equilibrium in the tank (Fay, 1983). More on this later.

Note that blue greens are neither algae nor bacteria. They exhibit characteristics of both and can thus be considered an evolutionary link between the two. From the standpoint of cell structure they are clearly bacteria. From the perspective of their photosynthetic ability and the presence of pigments, they are algae. Confusing? Probably so, but of no real importance since we are not trying to come up with the ultimately correct nomenclature.

Various classification models have been put forth. Ongoing studies of Cyanobacteria result in frequent changes. A recent one I came across (Rippla et al.) and Fritsch (an older one) proposes the following principal groups (principal being the key word here):

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.