[APD] Re: nutrient limitation vs. competition: algae control

["Steve Pushak" <teban at powersonic_bc.ca>]

Roger wrote:
>
> "Pollute" and "excess" are such loaded terms.

You can create a problem with algae if you put in too much fish food
without exchanging sufficient water. Are you truly disputing this? You
cannot mean that unlimited amounts of organic materials may be added to
an aquarium without consequences.

> > If you don't dump in more nutrients than the system can properly
> > metabolize at a certain rate, then you would not experience the
> > explosion; can't we then say we are controlling or managing
> the algae?
>
> I could be wrong about this, but *not* doing something isn't usually
> considered to be management.

Oh, I think you can consider proper water changes, correct fish load,
correct fish feeding to be positive actions or management. These affect
the amount of various nutrients and pollutants in the aquarium. This has
everything to do with preventing problems with algae. You may consider
food to be a pollutant when it is added in quantity sufficient to create
an undesirable outcome. The definition is circular.

I'm trying to point out the confusion that you guys create by saying (or
seeming to say) that nutrient control is not important to algae
management. I totally agree that you cannot eradicate algae by limiting
nutrients & I think this is the point that you guys really want to make.
I also want to point out the problems with your terminology for
"limiting" algae growth. There is a point where algae ceases to grow in
isolation from competitors when a given nutrient is reduced. Long before
the algae can no longer grow, its rate of growth has declined in direct
proportion to the concentration of the growth limiting nutrient.

To say that phosphate cannot limit growth is extremely misleading; it
can indeed be the growth rate dominant factor (AKA growth limiting
factor) at many different concentrations, depending whether other
nutrients are available above the molar ratios required. Experimental
data describing algae blooms above given N & P concentrations are
plentiful.

I have also pointed out how nutrient & food management may allow
competitors to successfully reduce populations of certain kinds of
algae. Why not comment upon this?

Tom has said that epiphytic algae in the motile reproductive stage have
trouble attaching to healthy leaves. What is the mechanism? We need to
advance a theory rather than to leave it as an anthropomorphic
implication about "troubled" algae. Perhaps the algae are in their
teens? ;-)

Steve P

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