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[APD] algae population dynamics


Recently while perusing the web for who-knows-what I came across an article 
on phytoplankton population dynamics.  That article is by Roelke, Augustine 
and Buyukates and may be downloaded as a pdf file from:


The twri article builds in part on work from a few years earlier by Huisman 
and Weissing.  One of their articles can be found on line at:


These articles seem to me to have quite a bit of relevance to algae problems 
in aquaria.  Algae problems in planted tanks only occasionally deal with 
phytoplankton (green water).  More often the problems are with attached 
algae.  Those "algae" are actually communities of algae rather than 
individual species.

Both of the studies above address the makeup of algae communities and 
transitions between one community and another.  It is that similarity that 
piqued my interest.  In a nutshell, what these and other studies have found 
is that under conditions of competition for a limiting resource (nutrient, 
normally) the succession of algae communities can be chaotic.  Any of a 
number of possible dominant communities may arise under very similar 
conditions.  The dominant community can switch between two or more different 
combinations of species without a clearly determinstic reason for the changes.

Oddly, if a system is regularly perturbed (as with periodic water changes or 
nutrient dosing) then the resulting populations may become strictly 
determined by initial conditions rather than chaotic.

I haven't thought through the articles in a lot of details right now, but 
three things came to mind.

1)  For the sake of stability it's probably a good idea to avoid any kind of 
nutrient limitation as the dynamics of a nutrient-limited population may be 

2)  Regular system perturbations like periodic cleaning, water changes and 
nutrient dosing may promote stability.

3)  Anectdotal evidence along the lines of "I changed X and algae problem Y 
disappeared" may be unreproducable and largely useless because the result of 
the change was the response of a chaotic system.  Similarly for observations 
like "I added X and it caused algae problem Y."

It might be interesting to apply one of these competition models to aquarium 
conditions.  Even more interesting if the model could be modified to include 
competition with a macrophyte community.

Roger Miller

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